MERCURY ANALYSIS MANUALMarch 2004

Ministry of the Environment, Japan

March 2004

Foreword
The February 2003 meeting of the Governing Council of the 22nd UN
Environmental Program (UNEP) reported on the Global Mercury Assessment andadopted a resolution for future international action.
Developed countries are currently addressing the issue of the adverse healtheffects of human exposure to low-level methylmercury. In Japan, fish and shellfish
are a valuable source of protein as well as a mainstay of the nation’s culinary
culture; therefore, a careful, prompt, and science-centered response to the risk ofmercury exposure through the consumption of fish and shellfish is needed.
To study the adverse health effects of low-level methylmercury exposure on
the development of fetuses and infants, Japan initiated a cohort study in 2002
following two preceding cohort studies: one undertaken in the Faroe Islands, theother in the Republic of Seychelles.
Even today, coal-fired thermal power plants in various countries around theworld continue to discharge mercury into the surrounding environment, while
industrial plants producing chlorine and alkali continue to discharge mercury into
water systems. Moreover, developing countries with gold mining operations are
suffering from serious pollution caused by the use of mercury in gold refining.
Clearly, therefore, it is essential that the state of mercury pollution be monitored.
Against this background, technology capable of highly precise analysis of
total mercury and methylmercury must be made available in Japan and elsewhere
so that precise risk assessment can be conducted. In this spirit, the Ministry of theEnvironment has prepared the Mercury Analysis Manual in order to put in place
proven and internationally accepted analytical methods for more widespreadpractical application.
2

As the chairperson of the committee for this manual, I would like to express
my appreciation to all who participated in its preparation. I am confident thismanual will be widely employed worldwide as a practical aid for mercury analysis.
Tsuguyoshi Suzuki
Chairperson
The Committee for the Mercury Analysis Manual3Members of the Committee for the Mercury Analysis Manual
Tsuguyoshi Suzuki ........... Honorary Professor, Tokyo University (Chairperson)
Hirokatsu Akagi.................. Director, International Mercury Laboratory Inc.
(Ex-Director, Department of International Affairs andEnvironmental

Sciences,

National

InstituteforMinamata Disease)
Kimiyoshi Arimura............. Associate Professor, Graduate School of Medicine,Kagoshima University
Tetsuo Ando ....................... Research Assistant, Graduate School of Medicine,Kagoshima University
Mineshi Sakamoto .............. Chief, Survey Section, Department of Epidemiology,
National Institute for Minamata Disease
Hiroshi Satoh ...................... Professor, Graduate School of Medicine, Tohoku
University
Akira Naganuma................ Professor, Graduate School of Pharmaceutical Sciences,
Tohoku University
Makoto Futatsuka ............... Professor, Graduate School of Medicine, Kumamoto
University
Akito Matsuyama……….Chief Researcher, National Institute for Minamata
Disease4

Contents
Foreword..................................................................................................................... 2
1. Introduction ............................................................................................................ 7
2. Sampling................................................................................................................. 9
2-1 Environmental samples .................................................................................... 9
2-1-1 Biological samples (fish and shellfish)..................................................... 9
2-1-2 Water....................................................................................................... 10
2-1-3 Sediment/soil .......................................................................................... 11
2-1-4 Plants....................................................................................................... 13
2-1-5 Atmosphere/air ....................................................................................... 14
2-2 Human samples .............................................................................................. 16
2-2-1 Hair ......................................................................................................... 16
2-2-2 Blood....................................................................................................... 17
2-2-3 Urine ....................................................................................................... 18
2-2-4 Umbilical cord ........................................................................................ 19
3. Analytical Method for Total Mercury .................................................................. 21
3-1 Determination by the wet digestion/reduction/cold vapor atomic absorption
spectrometry (CVAAS) (circulation-open air flow system) ................................ 23
3-1-1 Biological samples (including fish, shellfish, human blood, urine, andtissues such as umbilical cord) ......................................................................... 26
3-1-2 Hair ......................................................................................................... 34
3-1-3 Sediment/soil .......................................................................................... 39
3-1-4 Water....................................................................................................... 44
4. Analytical Method for Methylmercury ................................................................ 52
4-1 Determination by the dithizone extraction/gas-liquid chromatography withelectron capture detection (GLC-ECD) method................................................... 53
4-1-1 Biological samples (fish, shellfish, human blood, and tissues such asumbilical cord) ................................................................................................. 545

4-1-2 Biological samples containing relatively high concentrations of mercury,particularly fish and shellfish (Simplified method) ......................................... 65
4-1-3 Urine ....................................................................................................... 73
4-1-4 Sediment/soil .......................................................................................... 80
4-1-5 Water....................................................................................................... 88
4-2 Determination by the hydrochloric acid leaching/toluene extraction/gasliquid chromatography with electron capture detection (GLC-ECD) method..... 97
4-2-1 Hair ......................................................................................................... 97
References .............................................................................................................. 104

6

1. Introduction
Obtaining reliable analytical data for mercury requires the following:
appropriate sample collection; pre-treatment for analysis; the selection of ameasurement method and preparation method for sample test solutions suited to thesamples; experience in their use; and confirmation of the reliability of one's own
analytical data. In addition, when performing an analysis, one must regularly pay
attention to preventing contamination of the samples by keeping the laboratory
clean; providing appropriate ventilation; and adequately washing glassware, tools,
and containers.
When evaluating the adverse health effects of mercury and clarifying its
dynamics and pathways in humans and in the environment, in addition to
performing a quantitative analysis for total mercury, one should also perform
separate quantitative analyses for methylmercury and inorganic mercury. Thismanual first provides a description of sampling followed by descriptions of theanalytical methods for total mercury and methylmercury for each target sample.
It should be noted that, for mercury analysis of fish and shellfish, water, air,soil (content and its elutriation) and the like, the following official regulations havebeen laid down, among others: "Provisional Regulatory Standards for Fish andOther Marine Products" (Director-General Notification No. 99, Environmental
Health Bureau, Ministry of Health and Welfare, dated July, 23, 1973); the method
listed in the table attached to Environment Agency Notice No. 59 issued in Dec.
1971 (Environmental Quality Standards for Water Pollution); the Manual of
Measuring Methods for Hazardous Air Pollutants (Air Environment Regulation No.
88, dated March 31, 1999); and Ministry of the Environment Notice No. 19, dated
March, 6, 2003. In cases where analysis is a requirement of the official regulation,an analytical method suitable for each case may be used. Further, a number of othermethods for mercury analysis have been reported. When using any of theseanalytical methods, one should of course practice careful quality control/quality
7

assurance of the obtained data, including simultaneous determination of suitable
certified reference materials (CRMs).
Currently, the CRMs prepared for the quality control/quality assurance ofanalytical values for mercury as well as methylmercury in various biological andenvironmental matrices are commercially available from several organizations,
including the IAEA (International Atomic Energy Agency, Analytical Quality
Control Services), NIST (National Institute of Standards and Technology, Office ofStandard Reference Materials, USA), NRCC (National Research Council of
Canada), and NIES (National Institute for Environmental Studies, Japan). These
CRMs may be used as needed.

8

2. Sampling
2-1 Environmental samples
2-1-1 Biological samples (fish and shellfish)

Water pollution caused by methylmercury can be monitored conveniently
by measuring the bioaccumulation of mercury in fish. Further, monitoring the
mercury in fish and shellfish eaten most often by people in a particular region is asuitable means of evaluating human exposure levels, because human exposure tomethylmercury occurs mostly through the consumption of fish and shellfish. In
addition, since most mercury present in fish is in the form of methylmercury, themeasurement of total mercury in fish can be used to evaluate methylmercury intake
by humans. However, methylmercury should also be measured in cases where
extremely high values appear and in cases involving consumption of whale meatand organ tissues whose proportion of methylmercury to total mercury is notalways constant.
When collecting fish samples, record the sampling date, location, species,
and ages. Also measure the weight and length and the like. For fish, collect 10-20
grams of the edible portion, place it in polyethylene bags, and store it in a freezer.
For shellfish, divide the muscle, digestive tract contents, and adductor muscle (forsnails, which lack an adductor muscle, divide the edible portion), place the portionsin polyethylene bags, and store in a freezer. Since particles of bottom sediment areoften contained in the digestive tracts of shellfish, remove these particles before
storage.
According to Japan’s Food Hygiene Act, the provisional regulatory standard
for mercury in fish and shellfish is 0.4 mg/kg (wet weight) as total mercury. The
background level of total mercury in fish and shellfish is considered to be 0.01-0.1
mg/kg (wet weight).
92-1-2 Water

When the source of contamination is directly connected to a river, lake,
marsh, or ocean, or when contamination is expected to have spread from a river to alake, marsh, or ocean, take water samples from the various areas. Use a Bandon
water sampler or the like to collect the water samples, preferably at 20-30 cm below
the surface. Take great care to prevent bottom sediment from entering water
samples collected near the bottom. In principle, collect seawater samples at hightide and avoid windy or rainy days. For lakes, marshes, and ocean regions, clearlystate the collection date, location, general water quality, position relative tocontamination source, and other information.
Keep water samples in a sealable glass or Teflon container that has been
well washed with hydrochloric acid or other agents before being transported. For
total mercury, Japan’s Effluent Standard and Environmental Quality Standard are
0.005 mg/L (ppm) and 0.0005 mg/L (ppm), respectively, according to Environment
Agency Notice No. 64 (September 1974) based on the Water Pollution Control Law
in Japan. For alkyl mercury, both the Effluent Standard and Environmental Quality
Standard state that it must not be detectable at the detection limit of 0.0005 mg/L(ppm) when analyzed with the official methods provided by the Water Pollution
Control Law. When a contamination accident causes a sudden release ofwastewater containing high levels of mercury, the levels of total mercury and alkyl
mercury must be evaluated according to these official standards. The backgroundlevels of total mercury are generally 0.5-3 ng/L (ppt) for ocean water, 2-15 ng/L(ppt) for shore water, and 1-3 ng/L (ppt) for rivers and lakes.

102-1-3 Sediment/soil

When collecting soil samples, vary the frequency of sample collection
depending on the plane position of the mercury pollution source and the extent of
the suspected contamination. While various methods for collecting soil samples
from the site have been proposed, Japan’s Soil Pollution Countermeasures Law(Ministry of the Environment, 2003) implemented in 2003 provides detailed
descriptions of the methods for collecting soil samples. These methods served as
the basis for the sampling methods provided in this manual. Briefly, in mostpollution situations, collect one sample per 100 m2 (based on a 10 m × 10 m grid).
At sites where the pollution record suggests the risk of pollution is not extreme,
obtain one sample by mixing samples obtained at five spots per 900 m2 (based on a
30 m × 30 m grid). With this five-spot mixing method, collect individual samples
from a total of five spots: the center point of each grid and four subpoints set
around it. Combine these five samples to obtain one final composite sample. Thisenhances the representativeness of the soil samples obtained from each grid.
Although the locations of the four subpoints are not precisely set out, it is desirable
to collect the four samples at points north, south, east, and west of the center point.
At each sampling point, collect the soil samples between the soil surface
and 50 cm below the soil. Specifically, collect the individual samples from two
separate regions, one between the soil surface and a point 5 cm below the surface,
and the other in the area from 5 cm to 50 cm below the soil surface. After collecting
the soil samples, remove most foreign objects (pebbles, roots, etc.) from eachsample and homogenize each sample by mixing with the quarter method. Afterhomogenization, mix an equal weight of each sample to obtain a final composite
sample. Similarly, for the five-spot mixing method, mix an equal weight of each of
the five samples (homogenized with the soil pre-treatment method mentioned
above) to obtain one composite sample for the mercury analyses.
11For rivers, sampling points allowing easy collection of the bottom sedimentare chosen at intervals of 50-200 m downstream from the discharge point ofindustrial wastewater or city drains; moreover, it is desirable that about two points
upstream be set for collection of bottom sediment as the control. The collection
spots for the sediment samples are usually specified as both riverbanks and thecenter of the river. Where the river is wide, increase the number of sampling points.
For lakes, marshes, and ocean areas, radially center the sampling points on
the release point or mouth of the river and conduct a grid survey as needed.
As for the sampling methods, the Ekman dredge sampler is used forcollection of the surface layer sediment of rivers, lakes, marshes, and seashores,
whereas the core sediment sampler is used to collect columnar samples that allow
for estimation of the sedimentary state and the history of mercury contamination
and accumulation.
Clean the collected bottom sediment of wood pieces, pebbles, shells, anddust and pass it through a 2-mm mesh sieve to prepare a sample. If the sample has ahigh water content, centrifuge it to remove the supernatant and mix well tohomogenize it before submitting it for analysis. Record the date, location, andgeneral conditions (appearance, color, smell, impurities, etc.).
Although glass containers are best for the collected samples, other sealedcontainers may also be used. Wash the containers well beforehand withhydrochloric acid or another agent. Store the samples in a cool dark place. Samples
containing metallic mercury or divalent mercury should be stored in a freezer.
Generally, the mercury level in soil is less than 0.2 mg/kg of dry weight(ppm). When the total mercury level in soil is found to exceed a few mg/kg (ppm),
the risk exists that the mercury will migrate from the soil into other environmental
sectors. In such cases, mercury contamination in nearby water systems must also be
investigated.
12

2-1-4 Plants

Plants normally exhibit little biological magnification of heavy metals andtherefore are not suitable for evaluating contamination. However, lichens havevarious properties that make them suitable as a biological indicator of air pollutants.
As with other rootless air plants, they absorb nutrients directly from the air,accumulate metals efficiently, and exhibit resistance to high concentrations ofmetals in their tissues.
Lichens are widely distributed geographically, making them suitable for not
only domestic but also international evaluations of air pollution. In fact, lichens(including the Parmelia and Usunera species) have often been used in research toevaluate air pollution caused by mercury and various other heavy metal pollutants,
and Garty (2001) has reported a related review article. Lichens, which usually growon trees or branches, are collected, washed well with water, cleaned of wood pieces
and dust, and air-dried to make a sample. For mercury analysis, place a few gramsof the sample in a vial and cut it into pieces with dissection scissors.

132-1-5 Atmosphere/air

Air samples are collected when mercury pollution is believed to be present
in the atmosphere or indoor environment. Since mercury concentrations in theatmosphere vary greatly, sampling points must be selected in order to clarify the
mercury distribution with consideration given to prevailing winds and the distancefrom the contamination source. To obtain air samples from the general indoor
environment and indoor environment of workrooms, etc., divide the room into agrid of 3 m square (with the width of the grid adjusted to accommodate the scale of
the work environment) and collect samples at the intersections of the grids. In
consideration of possible human exposure, set sampling points at 1 to 2 m above
ground. To collect mercury in the atmosphere or in the indoor air, place anabsorbing solution comprising 20 ml of 0.1% potassium permanganate and 1N
sulfuric acid in an impinger or similar bubbler. To sample the air, use a suction
pump to draw the air into the absorbing solution from the sampling point at a flowrate of 1 L/min. for a given time.
Because commercially available potassium permanganate often contains
mercury, dissolve it in 1N sulfuric acid and boil it to generate a precipitate of MnO2.
Cool and filter it for use as an absorbing solution. This procedure can remove all
mercury content and render the absorbance of the blank test solution almost zero.
The absorbing solution obtained in this manner can collect mercury vapor
efficiently, and one bubbler containing absorbing solution is usually sufficient.
If the absorbing solution has evaporated and decreased in volume after the
air samples have been drawn, top up the absorbing solution to a fixed volume tomake a test sample. Separately from this sample, take two identical volumes ofabsorbing solution that have not been aerated. Set aside one volume as a blank test
solution; to the other, add a fixed volume of inorganic mercury (II) standard
solution to create a standard test solution.
14

At measurement, add 10% hydroxylamine hydrochloride dropwise to
decolorize the potassium permanganate; determine the mercury concentration in thesample test solution by cold vapor atomic absorption spectrometry, as with theother samples. Using the volume of air collected, calculate the mercury
concentration in the air sample. This method can be widely applied to tests of theenvironmental atmosphere, the air of a work environment, and the gas discharged
from an emission source or the like.
For mercury in the atmosphere, standard values have not been established inJapan for either the environment or the generating source. However, the Japan
Society of Industrial Health recommends a concentration of 0.025 mg/m3 as thepermissible concentration of mercury vapor in the work environment.

15

2-2 Human samples
Mercury in biological samples -usually hair, blood, urine or umbilical cordis measured in order to evaluate the level of human exposure and body-burden.

2-2-1 Hair

The mercury concentration in hair is often used as a biomarker formethylmercury exposure because it reflects the concentration in the blood at thetime the hair was formed. At the same time, a hair sample provides a simple andnoninvasive sampling method as well as a storage method offering good sample
preservation. The mercury concentration in hair is generally detected at 250-300
times the blood concentration. Since the hair grows at a rate of roughly 1 cm permonth, evaluation of past exposure is possible. However, the mercury concentrationin hair can increase as a result of adhesion of external mercury vapor and inorganic
mercury, decrease as a result of hair treatments such as permanents, and be
influenced by the sample collection site.
In cases of no exposure to external inorganic mercury or mercury vapor,almost all mercury in hair is in the form of methylmercury; therefore, the level ofmethylmercury exposure from diet can be evaluated by measuring total mercury.
However, since people involved in gold mining and gold refining have a high riskof contamination from metallic mercury and mercury vapor, evaluation of actual
methylmercury exposure is possible only by measuring methylmercury as well as
total mercury in hair. Hair samples should be obtained from the occipital area of thehead and should include at least 20 strands of hair measuring 1 cm long (about 10
mg in total) cut with scissors at the hair root. Tie the root ends of the sampled hairstrands together with a cotton thread or affix to adhesive tape or the like so that theroot ends can be identified. Place the sample in a polyethylene bag and store at16

room temperature. Among the general population in Japan, the mercury
concentration in hair is in the range of 1-5 ppm and seldom exceeds 10 ppm.

2-2-2 Blood

For people who eat large quantities of fish and shellfish, the mercury
concentration ratio of red blood cells to plasma (serum) is approximately 10:1, andmost mercury contained in the red blood cells is in the form of methylmercury;
therefore, the methylmercury exposure can be evaluated by measuring total
mercury in blood. It is believed that 50% of inorganic mercury is present in theplasma and the mercury concentration in the plasma increases in relation to theamount of inorganic mercury accumulated in the kidneys. Thus, the exposure to
inorganic mercury/mercury vapor can be evaluated by measuring the total mercury
in plasma.
A blood sample in the range of several milliliters is collected as usual froma vein into an injection tube already containing an anticoagulant (heparin) andtransferred into a sealed container. The sample is then centrifuged at 3,000 rpm for
10 minutes to separate the red blood cells from plasma. Samples to be stored for along period of time should be frozen. While the mercury concentration in the bloodof the general population in Japan generally does not exceed 40 ng/g, people whose
diet is rich in fish sometimes have higher values.

172-2-3 Urine

Most mercury present in the urine is in the form of inorganic mercury. The
mercury concentration in the urine increases in relation to the level of inorganic
mercury accumulated in the kidneys. Accordingly, the total mercury value in theurine is an important biomarker for evaluating inorganic mercury/mercury vapor
exposure. On the other hand, leaking of methylmercury into urine may occur inthose with renal disease.
Since the mercury concentration in the urine also varies with the excretionrate, it is necessary to correct it with the creatinine concentration in the urine or tocollect the urine sample at a designated time.
Generally, as in usual urinalysis, 50-100 ml of urine is collected as a sample
in a paper cup in the early morning. The sample is then stored under refrigeration ina polyethylene container. Samples to be stored for more than one month should be
frozen. Since urine contains many inorganic salts, even fresh urine may generate
precipitate. Thus, the sample must be homogenized by shaking before analysis. A
method also exists where the solubility of the salts is increased by lowering the pHof the urine sample by adding a small amount of hydrochloric acid. Take steps toensure that microorganisms do not proliferate, as they may cause inorganic mercury
to reduce to mercury vapor, which will escape and be lost. It is believed that the
average mercury level in the urine of the general population in a region without any
particular mercury exposure is less than 10 ng/ml.

18

2-2-4 Umbilical cord

When food containing methylmercury is ingested by the mother during
pregnancy, the methylmercury easily passes through the placenta, transferring fromthe mother's body to the fetus and exposing the fetus to the methylmercury. One
prime example of this was the occurrence of many fetal cases of Minamata diseaseaccompanied by severe cerebral palsy-like symptoms. This was caused by pregnant
mothers’ ingestion of fish and shellfish highly contaminated with methylmercury
when Minamata disease was prevalent in Japan. Mercury in the umbilical cord isused as a suitable biomarker of methylmercury exposure during the fetal period
because the mercury concentration in the umbilical cord is highly correlated withthat in umbilical cord blood, and most mercury occurring in the umbilical cord is in
the form of methylmercury. Several centimeters of the fetus side of the umbilicalcord are collected at delivery and washed with physiological saline to remove theblood. The sample is stored frozen until the time of analysis.
The umbilical cord sample can also be stored as a dry sample for a long
period if air-dried after collection. In addition, since it is a tradition in Japan forfamilies to store the umbilical cord with care, each child's mercury exposure at birth
can be evaluated by measuring the mercury content. Umbilical cords that predate
the 1970s, however, often contain much higher amounts of inorganic mercury due
to the application of mercurochrome (an antimicrobial containing mercury), which
was widely used as an external preparation; therefore, it is necessary to measure
methylmercury in such cases. The stored umbilical cord is soaked in water tomoisten it, washed with water to remove the blood and other adhering substances,
and air-dried to prepare the sample for analysis.
The concentration of methylmercury in the umbilical cord in the general
population in Japan is considered to be around 0.1 µg/g (dry weight). It has been19

reported that the methylmercury concentration in the umbilical cord can be as highas several µg/g (dry weight) in children born during the Minamata disease outbreak.
Conversion table
1 ppm = 1 mg/kg (L) = 1 µg/g (ml) = 1 ng/mg (µl)
1 ppb = 1 µg/kg (L) = 1 ng/g (ml)1 ppt = 1 ng/kg (L)203. Analytical Method for Total Mercury
The conventional methods for measuring total mercury include absorption
spectrometry (dithizone colorimetry), neutron activation analysis, and cold vapor
atomic absorption spectrometry. In absorption spectrometry, dithizone forms acomplex with the metal ions and produces a colored organic solution. The color
intensity varies with the mercury concentration. Although this method has beenused historically because of the simplicity of the procedures, its use declined
greatly with the introduction of highly sensitive atomic absorption spectrometry in
the 1960s.
In neutron activation analysis, thermal neutrons in a nuclear reactor are
irradiated and gamma radiation from generated 197Hg is measured for comparative
quantification with the standard sample. This enables nondestructive analysis inwhich the sample is analyzed directly without any pre-treatment such asconcentration, and it is highly precise and sensitive. However, it is not usedfrequently due to its high cost, the need for a nuclear reactor, and the need for an
expensive counting apparatus, not to mention the safety requirements for handlingradioactive materials.
In cold vapor atomic absorption spectrometry, mercury is converted intoelemental mercury vapor, which is introduced into an absorption cell and theabsorption measured at 253.7 nm for determination of the quantity. It is a much
more sensitive method as compared with conventional flame atomic absorption
spectrometry. Other advantages include its ability to measure mercury in thesamples with a UV spectrophotometer or a simple mercury lamp. It is roughlyclassified into the reduction/aeration procedure and the sample combustion
procedure according to the generation mode for mercury in the elemental form. The
former involves wet digestion with a mixture of strong acids followed by theaddition of a reducing agent to generate elemental mercury vapor (Hg0). In thelatter, elemental mercury vapor (Hg0) is generated through direct combustion of the21

sample to be analyzed. Currently, the most common method is based on the former
technique.
Herein we describe -among these highly sensitive analytical methods- a
method involving wet digestion, reduction and cold vapor atomic absorption
spectrometry (CVAAS) (the circulation-open air flow system), which offers
substantial improvements over the conventional method.

22

3-1 Determination by the wet digestion/reduction/cold vapor atomic
absorption spectrometry (CVAAS) (circulation-open air flow system)
Principle
The present method involving reduction and cold vapor atomic absorption
spectrometry (CVAAS) (circulation-open air flow system) is, in principle, similar
to the conventional circulation system in that the method includes the following:
reduction of Hg2+ ions in the sample test solution with stannous chloride to
generate elemental mercury vapor (Hg0); and the introduction of mercury vapor
into the photo-absorption cell for the measurement of absorbance at 253.7 nm.
However, unlike the conventional closed system in which the elemental mercury
vapor generated is continuously circulated with a diaphragm pump through areaction vessel, a U-shaped tube packed with a drying agent, and the photoabsorption cell, the present method uses a circulation-open air flow system asshown in Figure 1. The apparatus constitutes a closed system and comprises adiaphragm pump, reaction vessel, acid gas trap, moisture trap (ice bath), and a 4way cock. During its operation, the elemental vapor generated by the addition ofstannous chloride is circulated via the 4-way cock at a flow rate of 1-1.5 L/min. for
30 seconds to homogenize the concentration in the gas phase. The 4-way cock isthen rotated by 90° to introduce the gas phase into the photo-absorption cell all at
once. The measurement is completed within one minute per sample with thisapparatus, which can measure even 0.1 ng of mercury with high accuracy.
Additionally, in the method for preparing the sample test solution for thepresent method, the conventional wet digestion method is improved by the use of a
50-ml flask with a long neck (at least 10 cm), such as a thick-walled volumetricflask1 with a ground glass stopper, as well as a mixed acid system with an increased
rate of sulfuric acid, HNO3-HClO4-H2SO4 (1+1+5), that already contains perchloric
acid, for the sample digestion. This is innovative in that sample digestion can be23completed in a relatively short time without loss of mercury. It is a simple method
where the sample is subjected to wet digestion on a hot plate at 200-230°C for 30
minutes and cooled followed by topping up to a fixed volume with water. Thismethod can be applied directly to the digestion of biological samples including hair,blood, and fish as well as various solid samples such as sediment and soil. A reflux
condenser is not required during heating.

Figure 1. Schematic Diagram of Reduction/Cold Vapor Atomic Absorption
Spectrometry (CVAAS) (Circulation-Open Air Flow System)2

Procedural Notes
24

1. A thick-walled volumetric flask made of PyrexR, available from Koei Co. Ltd.,
Kumamoto, Japan, is recommended for safety reasons. If it is unavailable, acommercially available volumetric flask made of PyrexR may be used. In
addition, a test tube made of PyrexR (21 mm in diameter and 200 mm inheight) may be used instead of a volumetric flask, and an aluminum blockheater may be used instead of a hot plate for wet digestion of the sample using
the same procedure as described above.
2.

The automated apparatus based on this principle is commercially available as a
Model Hg-201 Semi-automated Mercury Analyzer (Sanso Seisakusho Co. Ltd.,Tokyo, Japan).

25

3-1-1 Biological samples (including fish, shellfish, human blood, urine, andtissues such as umbilical cord)This method is applied to biological samples such as fish, shellfish, humanblood, urine and tissues such as umbilical cord. Before being weighed, the sample
is placed in a vial, cut into fine pieces with dissection scissors, and homogenized toa rough pasty state to prepare it for analysis. Liquid samples such as blood are
mixed well with a Pasteur pipette with a rubber bulb in preparation for analysis.
a. Reagents(1)

HNO3-HClO4 (1+1): Mix 100 ml of perchloric acid (for measurement of toxic
metals) into 100 ml of nitric acid (for measurement of toxic metals). (Store ina cool dark place.)(2)

H2SO4: Sulfuric acid (for measurement of toxic metals)(3)

Distilled water: Distill deionized water and store in a clean glass container.

(4)

HCl: Hydrochloric acid (analytical grade)(5)

10% SnCl2 solution: Dissolve 10 g of tin (II) chloride dihydrate (analyticalgrade), SnCl2 ·2H2O, in 9 ml of HCl and dilute to 100 ml with distilled water.
Aerate with N2 gas (100 ml/min., 20-30 minutes) to expel any mercury fromthe solution.

(6)

5N NaOH: Dissolve 20 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 100 ml.

(7)

0.1N NaOH: Dilute 5 N NaOH 50-fold with distilled water.

(8)

0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)(9)

Methylmercury standard solution1: Weigh out 12.5 mg of CH3HgCl(authentic standard) in a 100-ml volumetric flask, dissolve in toluene to make26

a final volume of 100 ml, and store as stock solution. Dilute the stock solution
100-fold with toluene to obtain a methylmercury standard solution. One ml ofthis solution contains 1.0 µg of Hg.
(10) Methylmercury-cysteine solution: Transfer 0.5 ml of the methylmercury
standard solution and 5 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube with a glass stopper. Shake for 3 minutes with ashaker to extract methylmercury into the aqueous phase. Centrifuge at 1,200rpm for 3 minutes and draw off and discard the organic phase (upper phase).
Seal the tube and store in a cool dark place. (Prepare a fresh solution monthly).
One ml of this solution contains 0.1 µg of Hg.
(11) 1N H2SO4: Gradually add 30 ml of sulfuric acid (for measurement of toxic
metals) to distilled water to make a final volume of 1,000 ml.
(12) 1% acidic KMnO4 solution for collecting mercury: Dissolve 1 g of potassium
permanganate (analytical grade) in 100 ml of 1N H2SO4.
(13) 0.5% KMnO4 solution: Dissolve 0.5 g of potassium permanganate (analyticalgrade) in distilled water to make a final volume of 100 ml.
(14) Toluene: C6H5CH3 (reagent grade for residual pesticide analyses)b. Instruments and equipment(1)

Mercury analyzer2 Model Hg-201 Semi-Automated Mercury Analyzer (Sanso
Seisakusho Co., Ltd.)(2)

Hot plate: Capable of attaining a surface temperature of 250°C(3)

Sample digestion flask3: 50-ml thick-walled volumetric flask made of Pyrex(150 mm total height, 13 mm inlet diameter)(4)

Volumetric flasks: 10, 100, and 1,000 ml(5)

Measuring pipettes: 0.2, 0.5, 1.5, and 10 ml(6)

Vial: 20-ml scintillation vial
27

(7)

10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter × 100
mm in length(8)

Dissection scissors(9)

Multi-flow meter: V4-type flow meter multi-kit (Kojima Instruments Inc.)(10) Reciprocal shaker(11) Centrifuge
Note: Prior to use, thoroughly wash all laboratory glassware and sample containers
to be used in the analysis with a 0.5% KMnO4 solution. Rinse with water until thecolor of the KMnO4 solution is no longer visible.
c. Preparation of sample test solution
Precisely weigh out a homogenized sample (0.5 g maximum of wet weight)
and place at the bottom of a sample digestion flask. (For dry samples such asumbilical cord, weigh out precisely 0.1 g and add 0.5 ml of distilled water tomoisten beforehand.) Add 1 ml of distilled water, 2 ml of HNO3-HClO4 (1+1), and
5 ml of H2SO4 in turn and heat on a hot plate at 200-230°C for 30 minutes Allow tocool, add distilled water to make a fixed volume of 50 ml, mix well, and use theresulting solution as the sample test solution.
For urine samples, add 2 ml of HNO3-HClO4 (1+1) and 5 ml of H2SO4 to asample digestion flask beforehand. Gradually add a fixed volume (usually 2 ml) of
the urine sample while stirring slowly. Heat and treat it in a manner similar to theabove procedure to prepare the sample test solution4. Separately, transfer 0 and 1.0
ml of methylmercury-cysteine solution (0.10 µg Hg/ml) into two sample digestion
flasks (corresponding to 0 and 0.10 µg Hg). Add 1 ml of distilled water only to theformer (the blank) followed by 2 ml of HNO3-HClO4 (1+1) and 5 ml of H2SO4 in
turn. Follow the same steps as indicated above for preparation of the sample test
solutions to make a blank test solution and a standard test solution for themeasurement of total mercury.
28

d. Test procedures and calculations
Test procedures
Gently transfer fixed volumes V ml (usually 5 ml, to a maximum of 10 ml)of each of the blank test solution, the standard test solution, and the sample test
solution into the reaction vessel of the mercury analyzer and apply the stopper. Add
1 ml of 10% SnCl2 solution with the accessory dispenser and push the start button.
The diaphragm pump will run and the generated elemental mercury vapor will becirculated through the 4-way cock between the reaction vessel and the acidic gas
trap for 30 seconds to homogenize the concentration in the gas phase, while theacidic gas generated from the sample test solution is collected in the alkaline
solution. After 30 seconds, the 4-way cock will turn automatically by 90°, allowing
the introduction of mercury vapor into the photo-absorption cell through an ice bathfor measurement of the absorbance. The readings of the recorder will increase
sharply and decrease with a sharp peak. When the recorder reading begins todecrease, open the cock on the lower part of the reaction vessel to discard thesolution inside, close it again, and allow it to aerate until it returns to the baseline.
Push the reset button to start the next measurement.5
Calculation
The peak heights (mm) obtained after measurement of fixed volumes V ml6
of each of the blank, the standard, and the sample test solutions (or their diluted
solutions) for the total mercury analysis are labeled Pbl, Pstd, and Ps, respectively.
The total mercury concentration in the sample is calculated with the following
formula7:
Total mercury concentration in the sample (µg/g) = 0.10 µg ×
(Ps–Pbl)/(Pstd–Pbl) × dilution factor × 1/sample weight (g)29For blood and urine samples, the mercury concentrations are usually
expressed in ng/g and ng/ml, respectively, and thus calculated with the following
formula:Total mercury concentration in blood or urine (ng/g or ml) = 100 ng ×
(Ps–Pbl)/(Pstd–Pbl) × dilution factor × 1/sample amount (g or ml)
Procedural Notes
1.

Although a standard solution of inorganic mercury (II) is commonly used as astandard solution for the analysis of total mercury in the sample, the present
method uses a methylmercury-cysteine solution as the standard solution, thesame used for methylmercury analysis. Similarly to the samples, it is subjected
to wet digestion in order to make a standard test solution for total mercury
measurement. This is an effort to avoid measurement errors caused by the useof a different standard solution, because most mercury contained in fish andshellfish is in the form of methylmercury, and the total mercury as well as
methylmercury in the sample are commonly measured at the same time.
Methylmercury in the organic solvent is extremely stable. Even 1 ppm of
methylmercury in a toluene solution can be used for several years if stored
frozen to prevent volatilization of the solvent. When the preparation of astandard solution for total mercury measurement using the present method
unavoidably requires the use of an inorganic mercury (II) standard, thefollowing method is recommended for its stability, good storage characteristics,
and other advantages.
Inorganic mercury standard solution: Weigh out 13.5 mg of mercury (II)chloride (standard) in a 100-ml volumetric flask, dissolve in 4 ml of HNO3HClO4 (1+1) and 10 ml of H2SO4 added in turn, and top up to the mark with
distilled water to make a stock mercury solution (1 ml of the stock mercury
solution = 100 µg Hg). The stock mercury solution obtained in such way will30

be stable for several years if sealed and stored in a cool dark place. At every
use, the stock solution is diluted 1,000 times with the above blank test solution
to make a mercury standard solution (1 ml of this solution = 0.10 µg Hg). In
addition, when a commercially available standard solution is used, the blanktest solution is similarly used to dilute it appropriately.
2.

The automated apparatus based on this principle is commercially available as a
Model Hg-201 Semi-automated Mercury Analyzer (Sanso Seisakusho Co. Ltd.,Tokyo, Japan).

3. A thick-walled volumetric flask made of PyrexR, available from Koei Co. Ltd.,
Kumamoto, Japan, is recommended for safety reasons. If it is unavailable, acommercially available volumetric flask made of PyrexR may be used. In
addition, a test tube made of PyrexR (21 mm in diameter and 200 mm inheight) may be used instead of a volumetric flask, and an aluminum blockheater may be used instead of a hot plate for wet digestion of the sample using
the same procedure as described above.
4.

For urine samples, placing the sample in a sample digestion flask and adding
HNO3-HClO4 (1+1) and sulfuric acid in turn -as is the case with the otherbiological samples- may result in sudden violent reactions accompanied by therisk of overflow of the mixture from the container. To avoid this risk andensure safe operation, place the acids in the sample digestion flask first andthen add the urine sample gradually while swirling the sample digestion flask.

5.

Unless sufficient time for purging (at least 15 seconds) has elapsed after
measurement of the sample, residues from the former test solution may
continue to have an effect. Particularly when measurement of a sample with alow concentration follows measurement of a sample with a high concentration,a measurement should be carried out between them with distilled water inorder to confirm that the value has decreased to the background level.
31

6.

The equilibrium concentration between the aqueous phase and the gas phase of
reduced and vaporized mercury vapor may differ depending on the acidconcentration and volume of the sample test solution at measurement.
Therefore, the blank test solution is used for dilution of the sample test
solution and both the sample test solution and the standard test solution aremeasured under the same conditions in every respect (acid concentration andvolume).

7.

In atomic absorption spectrometry, the multi-point calibration curve method is
not always required because the linear range of the calibration curve is wide.
Therefore, a one-point calibration curve method is often used as well.
Moreover, in addition to the blank solution, choose the most suitableconcentration of the standard test solution from, for example, 0.02, 0.05, or
0.10 µg Hg/50 ml for a total mercury measurement with a peak height close tothat of the sample test solution. In this case, use the same volume of both thestandard test solution and sample test solution during the measurements. This
will facilitate quantification.

32

Biological samples,(0.5 g max. of wet weight)
Sample digestion flask
Distilled water, 1 ml
HNO3-HClO4 (1+1), 2 ml
H2SO4, 5 ml
Heat at 200-230°C for 30 min.
Digested samples
Cool.
Top up to 50 ml with distilled water.
Test solution, a fixed volume (usually 5 ml)
10% SnCl2 solution, 1 ml
CVAAS

Flow Chart 1. Determination of Total Mercury in Biological Samples (fish,shellfish, human hair, blood, and tissues such as umbilical cord)

Sample digestion flask
HNO3-HClO4 (1+1), 2 ml
H2SO4, 5 ml
Urine samples, 2 ml
Add dropwise while swirling slowly.
Heat at 200-230°C for 30 min.
Digested samples
Cool.
Top up to 50 ml with distilled water.
Test solution, a fixed volume (usually 5 ml)
10% SnCl2 solution, 1 ml
CVAAS

Flow Chart 2. Determination of Total Mercury in Urine

33

3-1-2 Hair

Weigh 20-30 mg of hair sample in a beaker, wash with neutral detergent(diluted 100-fold) and distilled water by decantation, and wash again with a small
amount of acetone to remove the water. Remove the residual acetone under reducedpressure. Transfer the hair sample into a 20 ml vial and cut into an approximately
powdery state with dissection scissors to make a sample for analysis.
a. Reagents(1)

Acetone: CH3COCH3 (analytical grade)(2)

Ethanol: C2H5OH (analytical grade)(3)

HNO3-HClO4 (1+1): Mix 100 ml of perchloric acid (for measurement of toxic
metals) into 100 ml of nitric acid (for measurement of toxic metals). (Store ina cool dark place.)(4)

H2SO4: Sulfuric acid (for measurement of toxic metals)(5)

Distilled water: Distill deionized water and store in a clean glass container.

(6)

HCl: Hydrochloric acid (analytical grade)(7)

10% SnCl2 solution: Dissolve 10 g of tin (II) chloride dihydrate (analyticalgrade), SnCl2 ·2H2O, in 9 ml of HCl and dilute to 100 ml with distilled water.
Aerate with N2 gas (100 ml/min., 20-30 minutes) to expel any mercury fromthe solution.

(8)

5N NaOH: Dissolve 20 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 100 ml.

(9)

0.1N NaOH: Dilute 5 N NaOH 50-fold with distilled water.

(10) 0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)34

(11) Methylmercury standard solution: Weigh out 12.5 mg of CH3HgCl (authentic
standard) in a 100-ml volumetric flask, dissolve in toluene to make a final
volume of 100 ml, and store as stock solution. Dilute the stock solution 100fold with toluene to obtain a methylmercury standard solution. One ml of thissolution contains 1.0 µg of Hg.
(12) Methylmercury-cysteine solution: Transfer 0.5 ml of the methylmercury
standard solution and 5 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube fitted with a stopper. Shake for 3 minutes with ashaker to extract methylmercury into the aqueous phase. Centrifuge at 1,200rpm for 3 minutes and draw off and discard the organic phase (upper phase).
Seal the tube and store in a cool dark place. (Prepare a fresh solution
monthly.) One ml of this solution contains 0.1 µg of Hg.
(13) 1N H2SO4: Gradually add 30 ml of sulfuric acid (for measurement of toxic
metals) to distilled water to make a final volume of 1,000 ml.
(14) 1% acidic KMnO4 solution for collecting mercury: Dissolve 1 g of potassium
permanganate (analytical grade) in 100 ml of 1N H2SO4.
(15) 0.5% KMnO4 solution: Dissolve 0.5 g of potassium permanganate (analyticalgrade) in distilled water to make a final volume of 100 ml.
(16) Toluene: C6H5CH3 (reagent grade for residual pesticide analyses)b. Instruments and equipment(1)

Mercury analyzer: Model Hg-201 Semi-automated Mercury Analyzer (Sanso
Seisakusho Co., Ltd., Tokyo, Japan)(2)

Hot plate: Capable of attaining a surface temperature of 250°C(3)

Sample digestion flask: 50-ml thick-walled volumetric flask made of Pyrex(150 mm total height, 13 mm inlet diameter)(4)

Volumetric flasks: 10, 100, and 1,000 ml(5)

Measuring pipettes: 0.2, 0.5, 1.5, and 10 ml
35

(6)

Vial: 20-ml scintillation vial

(7)

10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter × 100
mm in length(8)

Dissection scissors(9)

Multi-flow meter: V4-type flow meter multi-kit (Kojima Instruments Inc.)(10) Reciprocal shaker(11) Centrifuge(12) Beaker
Note: Prior to use, thoroughly wash all laboratory glassware and sample containers
to be used during the analysis with 0.5% KMnO4 solution. Rinse with water until
the color of the KMnO4 solution is no longer visible.
c. Preparation of test solution
Precisely weigh out a finely cut sample (usually around 10 mg) and place ina sample digestion flask. Add 1 ml of distilled water, 2 ml of HNO3-HClO4 (1+1),
and 5 ml of H2SO4 in turn. Heat on a hot plate at 200-230°C for 30 minutes. Allow
to cool, add distilled water to make a fixed volume, and use the resulting solution as
the sample test solution.
Separately, transfer 0 and 1.0 ml of methylmercury-cysteine solution (100ng Hg/ml) into two sample digestion flasks (corresponding to 0 and 100 ng Hg).
Add 1 ml of distilled water to only the former (the blank) followed by 2 ml of
HNO3-HClO4 (1+1) and 5 ml of H2SO4 in turn. To obtain a blank test solution andstandard test solution for the measurement of total mercury, follow the sameprocedures as indicated above for preparation of the sample test solution.
d. Test procedures and calculation
Test procedures
36Gently transfer a fixed volume, V ml (normally 5 ml, to a maximum of 10ml) of each of the blank test solution, standard test solution for measurement of
total mercury, and the sample test solution into the reaction vessel of the mercury
analyzer and apply the stopper. Add 1 ml of 10% SnCl2 solution with the accessory
dispenser and push the start button. The diaphragm pump will run and thegenerated mercury vapor will be circulated through the 4-way cock between thereaction vessel and the acidic gas trap for 30 seconds to homogenize theconcentration in the gas phase while the acidic gas generated from the test solution
is collected in the alkaline solution. After 30 seconds, the 4-way cock will turnautomatically by 90°, allowing the introduction of mercury vapor into the photoabsorption cell through the ice bath for measurement of the absorbance. The
readings of the recorder will increase sharply and decrease with a sharp peak. Whenthe reading of the recorder begins to decrease, open the cock on the lower part of
the reaction vessel to discard the solution inside, close it again, and allow it toaerate until it returns to the baseline. Push the reset button to start the next
measurement.
d. Test procedures and calculation
Calculation
The peak heights (mm) obtained after measurement of fixed volumes V mlof each of the blank, the standard, and the sample test solutions (or their diluted
solutions) for the total mercury analysis are labeled Pbl, Pstd, and Ps, respectively.
The total mercury concentration in the sample is calculated with the following
formula:Total mercury concentration in the sample (ng/mg) =100 ng ×
(Ps–Pbl)/(Pstd–Pbl) × dilution factor ×1/sample weight (mg)37

For the basics of total mercury analysis, see pp. 30-32 for the Procedural
Notes to “3-1-1 Biological Samples (including fish, shellfish, human blood, urine
and tissues such as umbilical cord).”Hair sample (around 10 mg)

Sample digestion flask
Distilled water, 1 ml
HNO3-HClO4 (1+1), 2 ml
H2SO4, 5 ml
Heat at 200-230°C for 30 min.
Digested samples
Cool.
Top up to 50 ml with distilled water.
Test solution, a fixed volume (usually 5 ml)
10% SnCl2 solution, 1 ml
CVAAS

Flow Chart 3. Determination of Total Mercury in Hair38

3-1-3 Sediment/soil

Remove wood pieces, pebbles, shells, and dust from the collected sedimentor soil sample. Homogenize the sample with the quarter method and pass it througha 2.0 mm mesh sieve to make a sample for analysis. If the sample has a high watercontent, centrifuge it to remove the supernatant and mix well to homogenize it
before subjecting it to analysis.
a. Reagents(1)

HNO3-HClO4 (1+1): Mix 100 ml of perchloric acid (for measurement of toxic
metals) into 100 ml of nitric acid (for measurement of toxic metals). (Store ina cool dark place.)(2)

H2SO4: Sulfuric acid (for measurement of toxic metals)(3)

Distilled water: Distill deionized water and store in a clean glass container.

(4)

HCl: Hydrochloric acid (analytical grade)(5)

10% SnCl2 solution: Dissolve 10 g of tin (II) chloride dihydrate (analyticalgrade), SnCl2 ·2H2O, in 9 ml of HCl and dilute to 100 ml with distilled water.
Aerate with N2 gas (100 ml/min., 20-30 minutes) to expel any mercury fromthe solution.

(6)

5N NaOH: Dissolve 20 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 100 ml.

(7)

0.1N NaOH: Dilute 5N NaOH 50-fold with distilled water.

(8)

0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)(9)

Methylmercury standard solution: Weigh out 12.5 mg of CH3HgCl (authentic
standard) in a 100-ml volumetric flask, dissolve in toluene to make a final
volume of 100 ml, and store as stock solution. Dilute the stock solution 10039

fold with toluene to obtain a methylmercury standard solution. One ml of thissolution contains 1.0 µg of Hg.
(10) Methylmercury-cysteine solution: Transfer 0.5 ml of the methylmercury
standard solution and 5 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube fitted with a stopper. Shake for 3 minutes with ashaker to extract methylmercury into the aqueous phase. Centrifuge at 1,200rpm for 3 minutes and draw off and discard the organic phase (upper phase).
Seal the tube and store in a cool dark place. (Prepare a fresh solution monthly).
One ml of this solution contains 0.1 µg of Hg.
(11) 1N H2SO4: Gradually add 30 ml of sulfuric acid (for measurement of toxic
metals) to distilled water to make a final volume of 1,000 ml.
(12) 1% acidic KMnO4 solution for collecting mercury: Dissolve 1 g of potassium
permanganate (analytical grade) in 100 ml of 1N H2SO4.
(13) 0.5% KMnO4 solution: Dissolve 0.5 g of potassium permanganate (analyticalgrade) in distilled water to make a final volume of 100 ml.
(14) Toluene: C6H5CH3 (reagent grade for residual pesticide analyses)b. Instruments and equipment(1)

Mercury analyzer: Model Hg-201 Semi-Automated Mercury Analyzer (Sanso
Seisakusho Co., Ltd.)(2)

Hot plate: Capable of attaining a surface temperature of 250°C(3)

Sample digestion flask: 50-ml thick-walled volumetric flask made of Pyrex(150 mm total height, 13 mm inlet diameter)(4)

Volumetric flasks: 10, 100, and 1,000 ml(5)

Measuring pipettes: 0.2, 0.5, 1.5, and 10 ml(6)

Vial: 20-ml scintillation vial

(7)

10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter × 100
mm in length
40

(8)

Dissection scissors(9)

Multi-flow meter: V4-type flow meter multi-kit (Kojima Instruments Inc.)(10) Reciprocal shaker(11) Centrifuge(12) Porcelain crucible
Note: Prior to use, thoroughly wash all laboratory glassware and sample containers
to be used during the analysis with 0.5% KMnO4 solution. Rinse with water until
the color of the KMnO4 solution is no longer visible.
c. Preparation of sample test solution
Precisely weigh out a homogenized sample (0.5 g maximum of wet weight)
in the bottom of a sample digestion flask. Add 1 ml of distilled water, 2 ml of
HNO3-HClO4 (1+1), and 5 ml of H2SO4 in turn followed by heat treatment on a hot
plate at 200-230°C for 30 minutes. Allow to cool, add distilled water to make afixed volume of 50 ml, mix well, and use the resulting solution as the sample test
solution.
Separately, transfer 0 and 1.0 ml of methylmercury-cysteine solution (0.10µg Hg/ml) into two sample digestion flasks (corresponding to 0 and 0.10 µg Hg).
Add 1 ml of distilled water to only the former (the blank) followed by 2 ml of
HNO3-HClO4 (1+1) and 5 ml of H2SO4 in turn. To obtain a blank test solution andstandard test solution for the measurement of total mercury, follow the same steps
as indicated above for preparation of the sample test solution.
For wet samples, weigh out about 10-20 g of the sample into a porcelain
crucible of known weight. Place it in a drying oven at 105°C and dry for 2 to 3
hours. Allow it to cool in a desiccator and weigh it to obtain the ratio of wet
weight/dry weight (WW/DW).
d. Test procedures and calculation
Test procedures
41

Gently transfer a fixed volume, V ml (normally 5 ml, to a maximum of 10ml) of each of the blank test solution, standard test solution and the sample test
solution into the reaction vessel of the mercury analyzer and apply the stopper. Add
1 ml of 10% SnCl2 solution with the accessory dispenser and push the start button.
The diaphragm pump will run and the generated elemental mercury vapor will becirculated through the 4-way cock between the reaction vessel and the acidic gas
trap for 30 seconds to homogenize the concentration in the gas phase, while theacidic gas generated from the test solution is collected in the alkaline solution.
After 30 seconds, the 4-way cock will turn automatically by 90°, allowing the
introduction of the elemental mercury vapor into the photo-absorption cell throughthe ice bath for measurement of the absorbance. The readings of the recorder will
increase sharply and decrease with a sharp peak. When the reading of the recorder
begins to decrease, open the cock on the lower part of the reaction vessel to discard
the solution inside, close it again, and allow it to aerate until it returns to thebaseline. Push the reset button to start the next measurement.
Calculation
The peak heights (mm) obtained after measurement of fixed volumes V ml
(usually 5 ml, maximum 10 ml) of each of the blank, the standard, and the sample
test solutions (or their diluted solutions) for the total mercury analysis are labeledPbl, Pstd, and Ps, respectively. The total mercury concentration (µg/g of dry
weight) in the sample is calculated with the following formula:
Total mercury concentration in the sample (µg/g) = 0.10 µg ×
(Ps–Pbl)/(Pstd–Pbl) × dilution factor × 1/sample weight (g) × WW/DW
WW/DW: ratio of wet weight/dry weight42

Note: For the basics of total mercury analysis, see pp. 30-32 for the Procedural
Notes to “3-1-1 Biological Samples (including fish, shellfish, human blood,urine and tissues such as umbilical cord).”Sediment/soil samples(0.5 g max. of wet weight)
Sample digestion flask
Distilled water, 1 ml
HNO3-HClO4 (1+1), 2 ml
H2SO4, 5 ml
Heat at 200-230°C for 30 min.
Digested samples
Cool.
Top up to 50 ml with distilled water.
Test solution, a fixed volume (usually 5 ml)
10% SnCl2 solution, 1 ml
CVAAS

Flow Chart 4. Determination of Total Mercury in Sediment/Soil43

3-1-4 Water1

After collection of water, the water sample brought to the laboratory isusually filtered with a 0.45-µm membrane filter to make a sample for analysis. It is
desirable to analyze the mercury as soon as possible. Total water may be used as asample for convenience.
a. Reagents(1)

HNO3-HClO4 (1+1): Mix 100 ml of perchloric acid (for measurement of toxic
metals) into 100 ml of nitric acid (for measurement of toxic metals). (Store ina cool dark place.)(2)

H2SO4: Sulfuric acid (for measurement of toxic metals)(3)

Distilled water: Distill deionized water and store in a clean glass container.

(4)

HCl: Hydrochloric acid (analytical grade)(5)

10% SnCl2 solution: Dissolve 10 g of tin (II) chloride dihydrate (analyticalgrade), SnCl2 ·2H2O, in 9 ml of HCl and dilute to 100 ml with distilled water.
Aerate with N2 gas (100 ml/min., 20-30 minutes) to expel any mercury fromthe solution.

(6)

5N NaOH: Dissolve 20 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 100 ml.

(7)

0.1N NaOH: Dilute 5N NaOH 50-fold with distilled water.

(8)

Purified 0.01% dithizone-toluene2: Dissolve 0.011 g of diphenylthiocarbazone,
C6H5N:NCSNHNHC6H5, in 100 ml of toluene in a 200-ml separatory funnel.
Add 50 ml of 0.1N NaOH and shake briefly to extract the dithizone into theaqueous phase (bottom phase). After allowing it to settle, transfer the bottom
phase into a glass container fitted with a glass stopper. Add 1N HCl dropwise
to make the solution slightly acidic (blackish-green crystals will precipitate).
Add 100 ml of toluene and shake to obtain purified 0.01% dithizone-toluene.
44

Allow the phases to separate, draw off and discard the bottom phase, and seal.
Store in a cool dark place. (Prepare a fresh solution for each analysis.)(9)0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)(10) Methylmercury standard solution: Weigh out 12.5 mg of CH3HgCl (authentic
standard) in a 100-ml volumetric flask, dissolve in toluene to make a final
volume of 100 ml, and store as stock solution. Dilute the stock solution 100fold with toluene to obtain a methylmercury standard solution. One ml of thissolution contains 1.0 µg of Hg.
(11) Methylmercury-cysteine solution: Transfer 0.5 ml of the methylmercury
standard solution and 5 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube fitted with a glass stopper. Shake for 3 minutes with ashaker to extract methylmercury into the aqueous phase. Centrifuge at 1,200rpm for 3 minutes and draw off and discard the organic phase (upper phase).
Seal the tube and store in a cool dark place. (Prepare a fresh solution monthly).
One ml of this solution contains 0.1 µg of Hg.
(12) 1N H2SO4: Gradually add 30 ml of sulfuric acid (for measurement of toxic
metals) to distilled water to make a final volume of 1,000 ml.
(13) 1% acidic KMnO4 solution for collecting mercury: Dissolve 1 g of potassium
permanganate (analytical grade) in 100 ml of 1N H2SO4.
(14) 0.5% KMnO4 solution: Dissolve 0.5 g of potassium permanganate (analyticalgrade) in distilled water to make a final volume of 100 ml.
(15) 20N H2SO4: Transfer about 350 ml of distilled water into a 1-L volumetricflask. Gradually add 600 ml of sulfuric acid (for measurement of toxic metals)
while stirring in ice water. After it returns to room temperature, add distilledwater to make a final volume of 1,000 ml.
45

(16) 10N NaOH: Dissolve 400 g of sodium hydroxide (analytical grade) to make a
final volume of 1,000 ml.
(17) 10% NH2OH·HCl solution: Dissolve 10 g of hydroxylamine hydrochloride(analytical grade) in distilled water to make a final volume of 1,000 ml.
(18) 10% EDTA solution: Dissolve 10 g of tetrasodium ethylenediaminetetraacetate(analytical grade), C10H12N2O8Na4·4H2O, in distilled water to make a final
volume of 100 ml.
(19) Toluene: C6H5CH3 (reagent grade for residual pesticide analyses)b. Instruments and equipment(1)

Mercury analyzer: Model Hg-201 Semi-Automated Mercury Analyzer (Sanso
Seisakusho Co., Ltd.)(2)

Hot plate: Capable of attaining a surface temperature of 250°C(3)

Sample digestion flask: 50-ml thick-walled volumetric flask made of Pyrex(150 mm total height, 13 mm inlet diameter)(4)

Volumetric flasks: 10, 100, and 1,000 ml(5)

Measuring pipettes: 0.2, 0.5, 1.5, and 10 ml(6)

2-L separatory funnel(7)10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter × 100
mm in length(8)

Rotary evaporator(9)

Magnetic stirrer(10) Multi-flow meter: V4-type flow meter multi-kit (Kojima Instruments Inc.)(11) Reciprocal shaker(12) Centrifuge
Note: Prior to use, thoroughly wash all laboratory glassware and sample containers
to be used during the analysis with 0.5% KMnO4 solution. Rinse with water until
the color of the KMnO4 solution is no longer visible.
46

c. Preparation of sample test solution
Transfer 2 L of a water sample into a 2 L separatory funnel. Add 10 ml of
20N H2SO4 and 5 ml of 0.5% KMnO4 solution, mix by shaking, and let stand for 5
minutes. Neutralize with 20 ml of 10N NaOH, add 5 ml of 10% NH2OH·HCl
solution, and shake. Let stand for 20 minutes. 3 Add 5 ml of 10% EDTA solution to
the mixture and mix by shaking. Add precisely 10 ml of purified 0.01% dithizonetoluene followed by vigorous shaking for 1 minute to extract the mercury in thesample. Let stand for at least 1 hour, avoiding direct sunlight. Discard the aqueous
phase (lower phase). Transfer the toluene phase preferably into a 10-ml conicalcentrifuge tube fitted with a glass stopper and centrifuge at 1,200 rpm for 3 minuteswith the glass stopper in place. (When an emulsion is formed, add 0.5 g ofanhydrous sodium sulfate and shake followed by centrifugation to remove thelower phase.) Transfer a fixed volume (usually 7 ml) of the toluene phase into asample digestion flask. With a rotary evaporator, evaporate to dryness on a water
bath at 60°C. Add 1 ml of distilled water, 2 ml of HNO3-HClO4 (1+1), and 5 ml of
H2SO4 and heat on a hot plate at 200-230°C for 30 minutes. Allow to cool and add
distilled water to obtain a fixed volume of 50 ml. Mix well and use this as a sample
test solution. Separately, choose a sample with a lower mercury content based on
the type of water sample. To each of the 2-L water samples chosen, add 0 and 0.2
ml of methylmercury-cysteine solution (100 ng Hg/ml; corresponding to 0 and 20
ng Hg). Follow the above preparation procedures for sample test solutions to obtaina blank test solution and standard test solution for the measurement of total mercury.
d. Test procedures and calculation
Test procedures
Gently transfer a fixed volume, V ml (normally 10 ml) of the blank test
solution, standard test solution, and the sample test solution into the reaction vessel47

in the mercury analyzer and apply the stopper. Add 1 ml of 10% SnCl2 solution
with the accessory dispenser and push the start button. The diaphragm pump will
run and the generated elemental mercury vapor will be circulated through the 4-way
cock between the reaction vessel and the acidic gas trap for 30 seconds tohomogenize the concentration in the gas phase, while the acidic gas generated fromthe test solution is collected in the alkaline solution. After 30 seconds, the 4-way
cock will turn automatically by 90°, allowing the introduction of the elemental
mercury vapor into the photo-absorption cell through the ice bath for measurementof the absorbance. The readings of the recorder will increase sharply and decrease
with a sharp peak. When the reading of the recorder begins to decrease, open the
cock on the lower part of the reaction vessel to discard the solution inside, close it
again, and allow it to aerate until it returns to the baseline. Push the reset button tostart the next measurement
Calculation
The peak heights (mm) obtained after measurement of fixed volumes V ml
(normally 10 ml) of each of the blank, the standard, and the sample test solutions(or their diluted solutions) are labeled Pbl, Pstd, and Ps, respectively. The total
mercury concentration in the sample is calculated with the following formula:
Total mercury concentration in the sample (ng/L) = 20 ng × (Ps–Pbl)/(Pstd–Pbl)
× dilution factor × 1/ sample volume (L)Procedural Notes
1.

Since concentrations of mercury in water samples are extremely low andusually at the ng/L level, pre-concentration of the mercury in the sample isrequired for measurement of the mercury. In the present method, quantitativeand efficient pre-concentration is performed by extracting the mercury with asmall volume of 0.01% dithizone-toluene after ionization of all the mercury
48

species in the sample with potassium permanganate in an acidic medium withsulfuric acid. This uses the chemical properties of dithizone: it combines easily
with ionic mercury species to form a complex salt that is insoluble in water but
soluble in organic solvents such as toluene. After pre-concentration by
extracting the mercury with 0.01% dithizone-toluene, the extract is evaporated
to dryness under reduced pressure. Similar to the case of biological samples
and the like, the residue is subjected to wet digestion to prepare a sample test
solution for the total mercury analysis with CVAAS.
2.

Dithizone (diphenylthiocarbazone) is easily oxidized and usually contains its
oxidized form, diphenylthiocarbadiazone, as an impurity. As well, it
sometimes contains mercury or the like in the form of metal complex, although
the amount is minute. These impurities are highly soluble in organic solvents
but insoluble in alkaline solutions, whereas pure dithizone has the chemical
property of being soluble not only in organic solvents but also soluble inalkaline solutions by forming its salts. This property enables impurities to be
removed and dithizone to be purified for use.

3.

For samples containing large amounts of Cl- ions such as seawater, thetreatment of the sample with a combination of potassium permanganate andsulfuric acid causes oxidation of Cl- ions to Cl2 to occur during the treatment,
and the resulting Cl2, once generated, is difficult to reduce by treatment withhydroxylamine hydrochloride solution. This results in oxidation of dithizone in
the subsequent dithizone-toluene extraction step. Therefore, particularly forseawater samples, it is important to maintain the 5 minutes treatment time withpotassium permanganate. Further, after the addition and mixing of thehydroxylamine hydrochloride solution, allow at least 20 minutes of reaction
time before the EDTA treatment and dithizone-toluene extraction procedures.

49

For the basics of total mercury analysis, see pp. 30-32 for the Procedural
Notes to “3-1-1 Biological Samples (including fish, shellfish, human blood, urine
and tissues such as umbilical cord).”50

Sample, 2 L (2 L separatory funnel)
Add 10 ml of 20N H2SO4 and mix.
Add 5 ml of 0.5% KMnO4 solution and mix.
Let stand for 5 min.
Add 20 ml of 10N NaOH and mix to neutralize.
Add 5 ml of 10% NH2OH·HCl solution, mix, and allow to stand for 20 min.
Add 5 ml of 10% EDTA solution and mix.
Add 10 ml of purified 0.01% dithizone-toluene and vigorously shake for 1
min.
Allow to stand for at least 1 hr.
Organic phase(10-ml conical centrifuge tube)

Aqueous phase(When an emulsion is formed, add 0.5 g of Na2SO4 and shake.)
Centrifuge at 1,200 rpm for 3 min.
Organic phase, 7 ml (sample digestion flask)
Evaporate to dryness.
Residue
Distilled water, 1 ml
HNO3-HClO4 (1+1), 2 ml
H2SO4, 5 ml
Heat at 200-230°C for 30 min.
Digested sample
Allow to cool.
Top up to 50 ml with distilled water.
Test solution, a fixed volume (usually 10 ml)
10% SnCl2 solution, 1 ml
CVAAS

Flow Chart 5. Determination of Total Mercury in Water51

4. Analytical Method for Methylmercury
For measurement of organic mercury, gas-liquid chromatography withelectron capture detection (GLC-ECD) is used for selective analysis ofmethylmercury and other organomercury compounds. Because this techniqueprovides good separation and superior sensitivity for analyzing organomercury
halides, it has been widely used for the determination of methylmercury in various
kinds of biological and environmental samples.
Briefly, the analytical procedure involves the extraction of methylmercury
in the samples as its halide into an organic solvent after acidification; the backextraction into a cysteine- or glutathione-aqueous solution; the re-extraction into anorganic solvent; and measurement of methylmercury by GLC-ECD. As analternative, methylmercury can be determined by CVAAS, which measureselemental mercury vapor generated from a heated sample test solution obtained
from similar methylmercury extraction procedures. However, in this direct
extraction procedure with organic solvent, a solid emulsion is often formed during
the extraction process, particularly with fish and other biological samples. This
makes the following steps complicated and causes the extraction efficiency of
methylmercury to vary with the type of sample. While several pre-treatment
methods are proposed to overcome the above drawbacks, we describe herein thefollowing two methods: determination by the dithizone extraction/GLC-ECD
method, which is suitable for methylmercury in various types of biological andenvironmental

specimens;

and

the

hydrochloric

acid

leaching/toluene

extraction/GLC-ECD method for the determination of methylmercury in hair.

524-1 Determination by the dithizone extraction/gas-liquid
chromatography with electron capture detection (GLC-ECD) method
Principle
The dithizone extraction/GLC-ECD method was established as an analyticalmethod for methylmercury in various biological and environmental matrices. It isbased on the following two advantages of dithizone extraction, which was widelyused for colorimetry of inorganic and organic mercury species prior to theintroduction of atomic absorption in the late 1960s: it has much higher extraction
efficiency than that of direct solvent extraction, facilitating the extraction
separations of trace amounts of mercury from samples with a small portion of thesolution; and alkyl mercuric dithizonate, as soon as it is injected into GLC, reacts
with Cl- in the column to give its chloride form for quantitative detection.
Briefly, this method involves the following steps: pre-treatment of thesample, dithizone extraction, back-extraction into alkaline sodium sulfide, dithizone
re-extraction, and GLC measurement. Appropriate pre-treatment to accommodate
the characteristics of the composition of each sample enables efficient extraction of
methylmercury with a small portion of dithizone-toluene solution. After dithizonetoluene extraction, test solutions are prepared with all common procedures,
followed by measurement with GLC-ECD. To accommodate the principle used forthis method, pack several centimeters of sodium chloride at the injection port of thecolumn on top of the packing material for GLC.

53

4-1-1 Biological samples (fish, shellfish, human blood, and tissues such asumbilical cord)1

This method is applicable to protein-rich biological samples such as fish,shellfish, human blood and tissues such as umbilical cord. For a solid sample, place
it into a vial, cut it into small pieces with dissection scissors, and homogenize to apasty state to obtain a sample for analysis. For liquid samples such as blood, mix
well with a Pasteur pipette with a bulb or the like so that it is homogenized foranalysis.
a. Reagents(1)

Toluene: C6H5CH3 (pesticide analysis grade)(2)

Hexane: CH3(CH2) 4CH3 (pesticide analysis grade)(3)

Ethanol: C2H5OH (analytical grade)(4)

Distilled water: Distill deionized water and store in a clean glass container.

(5)

1N KOH-ethanol: Dissolve 56.11 g of potassium hydroxide (analytical grade)in ethanol to make a final volume of 1,000 ml. (Store in a cool dark place.)(6)

1N HCl: Mix 90 ml of hydrochloric acid (analytical grade) with distilledwater to obtain a final volume of 1,000 ml.

(7)

20% EDTA solution: Dissolve 20 g of tetrasodium ethylenediaminetetraacetate(analytical grade), C10H12N2O8Na4·4H2O, in distilled water to make a final
volume of 100 ml.

(8)

1N NaOH: Dissolve 40 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 1,000 ml.

(9)

0.1N NaOH: Dilute 1N NaOH 10-fold with distilled water.

(10) Purified 0.01% dithizone solution2: Dissolve 0.011 g of diphenylthiocarbazone,
C6H5N:NCSNHNHC6H5, in 100 ml of toluene in a 200-ml separatory funnel.
Add 50 ml of 0.1N NaOH and shake briefly to extract the dithizone into the54aqueous phase (bottom phase). After allowing the phases to separate, transfer
the bottom phase into a glass container fitted with a glass stopper. Add 1N
HCl dropwise to make the solution slightly acidic (blackish-green crystals
will precipitate). Add 100 ml of toluene and shake to obtain purified 0.01%
dithizone-toluene. Allow the phases to separate, draw off and discard thebottom phase, and seal. Store in a cool dark place. (Prepare a fresh solution
for each analysis.)(11) Alkaline sodium sulfide solution: Dissolve 0.15 g of Na2S·9H2O (analyticalgrade) in 10 ml of distilled water in a 10-ml conical centrifuge tube fitted witha glass stopper to make the sodium sulfide stock solution. (Prepare a fresh
solution monthly. Store in a cool dark place.) At each use, transfer 0.1 ml of
the stock solution into a 100-ml glass container fitted with a glass stopper, add
50 ml of 0.1N NaOH and 50 ml of ethanol, and mix to obtain an alkaline
sodium sulfide solution. (One ml of this solution contains 5 µg of Na2S.)(12) Walpole's buffer: Mix 200 ml of 1M CH3COONa and about 200 ml of 1N
HCl to adjust to pH 3.0.
(13) 0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)(14) Methylmercury standard solution: Weigh out 12.5 mg of methylmercury
chloride, CH3HgCl (authentic standard) in a 100-ml volumetric flask, dissolve
in toluene to make a final volume of 100 ml, and store as a stock solution.
Dilute the stock solution 100-fold with toluene to obtain the methylmercury
standard solution. One ml of this solution contains 1,000 ng of Hg.
(15) Methylmercury-cysteine solution: Transfer 0.5 ml of the methylmercury
standard solution and 5 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube fitted with a stopper. Shake for 3 minutes with ashaker to extract the methylmercury to the aqueous phase. Centrifuge at 1,20055

rpm for 3 minutes and draw off and discard the organic phase (upper phase).
Seal the tube and store in a cool dark place. (Prepare a fresh solution monthly).
One ml of this solution contains 0.1 µg of Hg.
(16) Anhydrous sodium sulfate: Anhydrous sodium sulfate (pesticide analysis
grade) heated at 500°C for 2-3 hours (stored in a desiccator)(17) N2 gas
Note: For the above reagents (6)-(9), (11), and (12), prepare the required amounts
in advance, add a 1/2 volume of toluene, wash by shaking in a separatory funnel.
Confirm beforehand that no peaks appear that could interfere with the measurement
by GLC-ECD.
b. Instruments and equipment(1)

Gas-liquid chromatograph with electron capture detector (GLC-ECD)(2)

Multi-flow meter: Model V4 flow meter multi-kit (Kojima Instruments Inc.)(3)

Centrifuge(4)

Reciprocal shaker(5)Isothermal bath

(6)

Magnetic stirrer(7)

Aspirator(8)

Vortex mixer(9)

pH mater(10) Volumetric flasks: 10, 100, and 1,000 ml(11) Measuring pipettes: 0.2, 0.5, 1.5, and 10 ml(12) Pasteur pipettes(13) Separatory funnels: 100, 200, and 1,000 ml(14) Glass containers with glass stoppers: 100, 200, and 500 ml(15) Glass container with screw cap: 1,000 ml(16) 40-ml conical centrifuge tube with a glass stopper
56

(17) 10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter × 100
mm in length(18) Vial: 20-ml scintillation vial
(19) Dissection scissors
Note: Thoroughly wash all glassware with toluene prior to use. Confirm in advancethat no peaks appear that could interfere with measurement by GLC-ECD.
Gas-liquid chromatographic conditions:
Either of the following three different columns can be used for the analysis:i) 3.0 mm × 0.75-1.0 m glass column packed with Hg-20A on Uniport HP (AWDMCS, 60-80 mesh, GL Science Co., Ltd., Tokyo, Japan).
ii) 3.0 mm × 0.75-1.0 m glass column packed with 10% KOCL-Hg on
Chromosorb W (AW-DMCS, 60-80 mesh, J-Science Co., Ltd., Kyoto, Japan).
iii) 3.0 mm × 2.0 m glass column packed with 5-10% poly-diethylene glycol
succinate (DEGS) on Chromosorb W (AW-DMCS).
After packing the column, pack about 2-3 cm of NaCl, previously heated at
500°C for 2-3 hours, on top of the packing material (at the injection port).
Temperature: Column oven: 140-160°C, Injection port: 180°C, Detector oven:
200°C
Carrier gas: N2, 30-40 ml/min.
c. Preparation of sample test solution
Methylmercury extraction
Precisely weigh out a homogenized sample (usually 0.2-0.5 g as wet weight,
about 0.1 g for a dry sample) and place in the bottom of a 40-ml screw-capped
conical centrifuge tube. (For a dry sample, add 0.5 ml of distilled water to moisten
after weighing.) Add 10 ml of 1N KOH-ethanol. Seal tightly and heat in an
isothermal bath at 100°C for 1 hour and occasionally swirl gently.3 Allow to cool,57

add 10 ml of 1N HCl and 5 ml of hexane in turn, and shake for 3 minutes with areciprocal shaker. Centrifuge at 2,500 rpm for 3 minutes. Draw off and discard thehexane phase (upper phase) to remove fatty materials.4 Add 2 ml of 20% EDTA
and mix well.5 Add 5 ml of purified 0.01% dithizone-toluene. Shake for 3 minutes
to extract methylmercury as its dithizonate (complex) into the toluene phase. Allow
the phases to separate. Draw off and discard the aqueous phase (lower phase).
Centrifuge at 2,500 rpm for 3 minutes and further draw off and discard as much of
the remaining aqueous phase (lower phase) as possible.
Clean-up
Add 3 ml of 1N NaOH to the toluene phase and shake for 3 minutes to wash
and remove excess dithizone. (For a blood sample, add 0.5 g of anhydrous sodium
sulfate to the toluene phase and shake for 3 minutes prior to this step, followed bywashing with 3 ml of 1N NaOH).6 Allow the phases to separate. Draw off anddiscard the aqueous phase (lower phase). Centrifuge at 2,500 rpm for 3 minutes toobtain a clear toluene phase. Transfer a fixed volume (usually 3 ml) of the toluene
phase into a 10-ml conical centrifuge tube with glass stopper. Add 2 ml of alkaline
sodium sulfide solution and shake for 3 minutes to back-extract the methylmercury
into the aqueous phase.7 Centrifuge at 1,200 rpm for 3 minutes with the glass
stopper attached. Draw off and discard the toluene phase (upper phase) carefully.
Add 2 ml of toluene to the aqueous phase and shake for 3 minutes to wash theaqueous phase. Centrifuge again at 1,200 rpm for 3 minutes with the glass stopper
attached. Draw off and discard the toluene phase (upper phase). Add 1N HCl (3-5drops) to make the solution slightly acidic.8 With a Pasteur pipette, aerate thesolution with N2 gas through a multi-flow meter for 3 minutes (50 ml/min.) to expel
the excess sulfide ions as hydrogen sulfide gas. Subsequently, add 2 ml of
Walpole's buffer while washing the tip of the Pasteur pipette. Mix well with avortex mixer. Add a fixed volume of purified 0.01% dithizone-toluene (0.2-1.0 ml,
58

usually 0.5 ml) and shake to extract methylmercury. Centrifuge at 1,200 rpm for 3
minutes with the glass stopper attached. Draw off and discard the aqueous phase(lower phase). Add 3 ml of 1N NaOH to the toluene phase and shake for 3 minutes
to wash and remove the excess dithizone. Allow the phases to separate. Draw off
and discard the aqueous phase (lower phase). Centrifuge at 1,200 rpm for 3 minuteswith the glass stopper attached. Again draw off and discard as much of theremaining aqueous phase (lower phase) as possible. Acidify the solution by adding
2 drops of 1N HCl to the toluene phase and mix with a vortex mixer. Centrifuge at
1,200 rpm for 3 minutes with the glass stopper attached. Draw off and discard thehydrochloric acid phase (lower phase). Use the resulting solution as the sample test
solution.
Separately, depending on the expected mercury concentrations in thesamples, transfer 0-0.20 ml of methylmercury-cysteine solution (corresponding to
0-0.020 µg Hg) into 40-ml screw-capped conical centrifuge tubes and add 10 ml of
1N KOH-ethanol. Follow the same steps as indicated above for preparing thesample test solution to make methylmercury standard test solutions for thecalibration curve. Protect the test solutions from light after preparation.
d. Test procedures and calculations
With a micro-syringe, inject into the GLC a fixed volume (usually 2-5 µl) of
each of the sample test solutions (or their toluene-diluted solutions), the blank andmethylmercury standard test solutions for the calibration curve. Calculate themethylmercury concentration in the sample (µg/g) by comparing the peak height ofthe sample test solution with the calibration curve obtained from the standard test
solutions. 9
Procedural Notes
59

1.

This method involves the digestion of proteins in the sample by heating with
1N KOH-ethanol, removal of free fatty materials by washing with hexane
under a slightly acidic condition, and quantitative extraction separation of
methylmercury in the sample into the toluene phase as its dithizonate, followed
by clean-up with an alkaline sodium sulfide solution and re-extraction with asmall portion of 0.01% dithizone-toluene.

2.

Dithizone (diphenylthiocarbazone) is easily oxidized, and its oxidized form
(diphenylthiocarbadiazone) is contained as an impurity that causes interferingpeaks on the gas chromatogram. Therefore, utilizing pure dithizone’s uniquechemical property of forming a water-soluble salt that dissolves in alkaline
solution, prepare a fresh dithizone-toluene solution for each analysis.

3.

If not tightly sealed, the solution may boil during heating. In such a case,remove the container, cool well with tap water, close the screw cap again sothat the gas does not leak, and continue the heating. If the volume of thesolution has been reduced without any apparent boiling, repeat the procedurefrom the beginning.

4.

To remove the upper phase or lower phase from the test tube, use the SuctionRemoval System with a Pasteur pipette connected with a flexible tube througha waste liquid collector to an aspirator, as shown in Figure 2. Briefly, toremove the upper phase (organic phase), perform suctioning by positioning the
tip of the Pasteur pipette on the surface of the upper phase down along theinside wall of the test tube in order to draw off most of the upper phase. When
only a little upper phase remains, keep the tip of the Pasteur pipette a few mm
above the surface of the organic phase and continue to draw off. With thistechnique, only the organic phase, which has a lower specific gravity than thatof the lower phase (aqueous phase) and high volatility, is drawn off together
with air, allowing for almost complete removal of the organic phase. To draw
off and discard the lower of the two phases separated in the test tube, squeeze
60the flexible tube with the fingers to stop the suction of the Pasteur pipette.
Position the tip of the Pasteur pipette at the bottom of the test tube and adjust
the pressure on the tube to slowly draw up the lower phase. When the lower
phase is almost completely removed, squeeze the flexible tube to stop thesuction and remove the Pasteur pipette. This makes it possible to remove only
the lower phase. Because these procedures require some skill and precision,practice each procedure beforehand.
5.

Before dithizone extraction, add the EDTA solution and mix by shaking inorder to mask Fe ions and other metal ions contained in the samples,particularly blood samples and the like.

6.

This procedure allows the methylmercury-dithizone complex (methylmercury
dithizonate) to remain in the toluene phase; however, excess dithizone in thetoluene phase forms water-soluble salt in the alkaline solution, which can betransferred into the aqueous phase. This dithizone removal procedure
maintains the methylmercury-dithizonate in the toluene phase without any loss.
One such dithizone-removal procedure with alkali washing is usually
sufficient. However, if a clear toluene phase is not obtained, repeat thisprocedure.
For blood samples, black suspended matter generated during dithizone-toluene
extraction colors the final sample test solution, often resulting in theappearance of interfering peaks on the gas chromatogram. To prevent this, add
0.5 g of anhydrous sodium sulfate and shake, before performing the alkali
washing.

7. Methylmercury dithizonate in the toluene phase reacts with excess sulfide ions,forming a water-soluble complex that can be transferred into the aqueous
phase. In order to perform an efficient one-time extraction procedure, use an
alkaline ethanol solution of sodium sulfide.
61

8.

To confirm the volume of 1N HCl required to be added for slight acidificationof the solution, transfer 2 ml of alkaline sodium sulfide solution into another10-ml test tube in advance and add a few drops of 0.01% dithizone solution asa pH indicator to obtain a yellow or orange color. Add 1N HCl to thisdropwise until the color changes to blue. The number of drops of 1N HCl
added is the amount of 1N HCl required to acidify the solution slightly.

9.

Generally, in GLC measurement, the linear range of the calibration curve isnarrow. Take notice of this, particularly when taking measurements, andundertake appropriate dilution so that the peak height of the sample test
solution is in the linear range. When linearity is confirmed throughmeasurement of the methylmercury standard test solution for preparation of
the calibration curve, the methylmercury concentration in the sample may be
calculated according to the following equation using the peak height (mm) of
the standard test solution (Pstd) of, for example, 0.020 µg Hg.
Methylmercury concentration in the sample (µg/g or ml) = 0.020 µg ×
(Ps–Pbl)/(Pstd–Pbl) × dilution factor × 1/sample weight (g)Ps: peak height (mm) of the sample test solution
Pbl: peak height (mm) of the blank test solution

62

Figure 2. Suction-Removal System for Separation of Liquid Phases

63Sample, 0.2-0.5 g wet weight (40-ml screw-capped conical centrifuge tube)
Add 10 ml of 1N KOH-ethanol.
Seal tightly and heat at 100°C for 1 hr.
Add 10 ml of 1N HCl and mix to acidify slightly.
Add 5 ml of hexane and shake for 3 min.
Centrifuge at 2,500 rpm for 3 min.
Aqueous phase
Organic phase
Add 2 ml of 20% EDTA and mix.
Add 5 ml of purified 0.01% dithizone-toluene and shake for 3 min.
Centrifuge at 2,500 rpm for 3 min.
Organic phase(For blood, add 0.5 g of Na2SO4 and shake.)
Add 3 ml of 1N NaOH and shake for 3 min.
Centrifuge at 2,500 rpm for 3 min.

Aqueous phase

Organic phase, 3 ml (10-ml conical centrifuge tube)
Aqueous phase
Add 2 ml of alkaline sodium sulfide solution and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Aqueous phase
Add 2 ml of toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.

Organic phase

Aqueous phase
Organic phase
Add 3-5 drops of 1N HCl to acidify slightly.
Aerate the sample with N2 gas for 3 min. at 50 ml/min.
Add 2 ml of Walpole's buffer and mix.
Add 0.5 ml of purified 0.01% dithizone-toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Organic phase
Aqueous phase
Add 3 ml of 1N NaOH and shake for 3 min.
Allow to stand for a while and discard the lower phase.
Centrifuge at 1,200 rpm for 3 min.
Organic phase
Add 2 drops of 1N HCl and vortex mix.
Centrifuge at 1,200 rpm for 3 min.
GLC-ECD

Aqueous phase

Hydrochloric acid phase

Flow Chart 6. Determination of Methylmercury in Biological Samples(fish, shellfish, human blood, and tissues such as umbilical cord)644-1-2 Biological samples containing relatively high concentrations of
mercury, particularly fish and shellfish (Simplified method)1

As described above, the analytical method for methylmercury in biologicalsamples using the dithizone extraction/GLC-ECD method is widely applied forquantitative determination of trace amounts of methylmercury in proteinous
samples that include fish, shellfish, blood, and human tissues. However, when thesample test solution is prepared according to this method for fish, shellfish, and theother biological samples containing relatively high concentrations of mercury,
substantial dilution of the sample test solution is unavoidable at measurement inmost cases. For such samples, a method is available wherein the collected volumeof the toluene phase used in back-extraction is reduced in the clean-up step. The
following method, in which the above analytical procedures are partially simplified,can also be applied when a high mercury concentration is expected from themeasurement of total mercury.
a. Reagents(1)

Toluene: C6H5CH3 (pesticide analysis grade)(2)

Hexane: CH3(CH2)4CH3 (pesticide analysis grade)(3)

Ethanol: C2H5OH (analytical grade)(4)

Distilled water: Distill deionized water and store in a clean glass container.

(5)

1N KOH-ethanol: Dissolve 56.11 g of potassium hydroxide (analytical grade)in ethanol to obtain a final volume of 1,000 ml. (Store in a cool dark place.)(6)

1N HCl: Mix 90 ml of hydrochloric acid (analytical grade) with distilledwater to obtain a final volume of 1,000 ml.

(7)

20% EDTA solution: Dissolve 20 g of tetrasodium ethylenediaminetetraacetate(analytical grade), C10H12N2O8Na4·4H2O, in distilled water to make a final
volume of 100 ml.
65

(8)

1N NaOH: Dissolve 40 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 1,000 ml.

(9)

0.1N NaOH: Dilute 1N NaOH 10-fold with distilled water.

(10) Purified 0.01% dithizone-toluene: Dissolve 0.011 g of diphenylthiocarbazone,
C6H5N:NCSNHNHC6H5, in 100 ml toluene in a 200-ml separatory funnel.
Add 50 ml of 0.1N NaOH and shake briefly to extract the dithizone into theaqueous phase (bottom phase). After allowing the phases to separate, transfer
the bottom phase into a glass container fitted with a glass stopper. Add 1N
HCl dropwise to make the solution slightly acidic (blackish-green crystals
will precipitate). Add 100 ml of toluene and shake to obtain purified 0.01%
dithizone-toluene. Allow the phases to settle, draw off and discard the bottom
phase, and seal. Store in a cool dark place. (Prepare a fresh solution for eachanalysis.)(11) Alkaline sodium sulfide solution: Dissolve 0.15 g of Na2S·9H2O (analyticalgrade) in 10 ml of distilled water in a 10-ml conical centrifuge tube fitted witha glass stopper to make the sodium sulfide stock solution. (Prepare a fresh
solution monthly. Store in a cool dark place.) At each use, transfer 0.1 ml of
the stock solution into a glass container fitted with a glass stopper, add 50 mlof 0.1N NaOH and 50 ml of ethanol, and mix to obtain an alkaline sodium
sulfide solution. (One ml of this solution contains 5 µg of Na2S.)(12) Walpole's buffer: Mix 200 ml of 1M CH3COONa and about 200 ml of 1N
HCl to adjust to pH 3.0.
(13) 0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)(14) Methylmercury standard solution: Weigh out 12.5 mg of methylmercury
chloride, CH3HgCl (authentic standard) in a 100-ml volumetric flask, dissolve
in toluene to make a final volume of 100 ml, and store as a stock solution.
66

Dilute the stock solution 100-fold with toluene to obtain the methylmercury
standard solution. One ml of this solution contains 1.0 µg of Hg.
(15) Methylmercury-cysteine solution: Transfer 0.5 ml of the methylmercury
standard solution and 5 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube fitted with a stopper. Shake for 3 minutes with areciprocal shaker to extract the methylmercury into the aqueous phase.
Centrifuge at 1,200 rpm for 3 minutes and draw off and discard the organic
phase (upper phase). Seal the tube and store in a cool dark place. (Prepare a
fresh solution monthly). One ml of this solution contains 0.1 µg of Hg.
(16) N2 gas
Note: For the above reagents (6)-(9), (11), and (12), prepare the required amounts
in advance, add a 1/2 volume of toluene, and wash by shaking. Confirm beforehandthat no peaks appear that could interfere with the measurement by GLC-ECD.
b. Instruments and equipment(1)

Gas-liquid chromatograph equipped with electron capture detector (GLCECD)(2)

Multi-flow meter: Model V4 flow meter multi-kit (Kojima Instruments Inc.)(3)

Centrifuge(4)

Reciprocal shaker(5)Isothermal bath

(6)

Magnetic stirrer(7)

Aspirator(8)

Vortex mixer(9)

pH mater(10) Volumetric flasks: 10, 100, and 1,000 ml(11) Measuring pipettes: 0.2, 0.5, 1.5, and 10 ml(12) Pasteur pipettes
67(13) Separatory funnels: 100, 200, and 1,000 ml(14) Glass containers with glass stoppers: 100, 200, and 500 ml(15) Glass container with screw cap: 1,000 ml(16) 40-ml conical centrifuge tube with glass stopper(17) 10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter × 100
mm in length(18) Vial: 20-ml scintillation vial
(19) Dissection scissors
Note: Thoroughly wash all glassware with toluene before use. Confirm in advancethat no peaks appear that could interfere with measurement.
Gas-liquid chromatographic conditions:
Either of the following three different columns can be used for the analysis:i) 3.0 mm × 0.75-1.0 m glass column packed with Hg-20A on Uniport HP (AWDMCS, 60-80 mesh, GL Science Co., Ltd., Tokyo, Japan).
ii) 3.0 mm × 0.75-1.0 m glass column packed with 10% KOCL-Hg on
Chromosorb W (AW-DMCS, 60-80 mesh, J-Science Co., Ltd., Kyoto, Japan).
iii) 3.0 mm × 2.0 m glass column packed with 5%-10% poly-diethylene glycol
succinate (DEGS) on Chromosorb W (AW-DMCS).
After packing the column, pack about 2-3 cm of NaCl, previously heated at
500°C for 2-3 hours, on top of the packing material (at the injection port).
Temperature: Column oven: 140-160°C, Injection port: 180°C, Detector oven:
200°C
Carrier gas: N2, 30-40 ml/min.
c. Preparation of sample test solution
Methylmercury extraction
68Precisely weigh out a homogenized sample (usually 0.2-0.5 g as wet weight,
about 0.1 g for a dry sample) and place in the bottom of a 40-ml screw-capped
conical centrifuge tube. (For a dry sample, add 0.5 ml of distilled water to moisten
after weighing.) Add 10 ml of 1N KOH-ethanol. Seal tightly and heat in an
isothermal bath at 100°C for 1 hour, occasionally swirling gently. Allow to cool,
add 10 ml of 1N HCl and 5 ml of hexane in turn, and shake for 3 minutes with areciprocal shaker. Centrifuge at 2,500 rpm for 3 minutes. Draw off and discard thehexane phase (upper phase) to remove fatty materials. Add 2 ml of 20% EDTA andmix well. Add 5 ml of purified 0.01% dithizone-toluene. Shake for 3 minutes toextract methylmercury as its dithizonate (complex) into the toluene phase. Allow
the phases to separate. Draw off and discard the aqueous phase (lower phase).
Centrifuge at 2,500 rpm for 3 minutes to obtain a clear toluene phase.
Clean-up
Transfer 1.0 ml of the toluene phase into a 10-ml conical centrifuge tube
with glass stopper. 2 Add 2 ml of alkaline sodium sulfide solution and shake for 3
minutes to back-extract the methylmercury into the aqueous phase. Centrifuge at
1,200 rpm for 3 minutes with the glass stopper attached. Draw off and discard thetoluene phase (upper phase) carefully. Add 2 ml of toluene to the aqueous phaseand shake for 3 minutes to wash the aqueous phase. Centrifuge again at 1,200 rpm
for 3 minutes with the glass stopper attached. Draw off and discard the toluene
phase (upper phase). Add 1N HCl (3-5 drops) to make the solution slightly acidic.
With a Pasteur pipette, aerate the solution with N2 gas through a multi-flow meterfor 3 minutes (50 ml/min.) to expel the excess sulfide ions as hydrogen sulfide gas.
Subsequently, add 2 ml of Walpole's buffer while washing the tip of the Pasteur
pipette. Mix well with a vortex mixer. Add 1.0 ml of toluene and shake for 3
minutes (for re-extraction of methylmercury together with excess dithizone).3
Centrifuge at 1,200 rpm for 3 minutes with the glass stopper attached. Draw off anddiscard the aqueous phase (lower phase). Add 3 ml of 1N NaOH to the toluene
69phase and shake to wash and remove the excess dithizone. Allow the phases toseparate. Draw off and discard the aqueous phase (lower phase). Centrifuge at
1,200 rpm for 3 minutes with the glass stopper attached. Draw off and discard asmuch of the remaining aqueous phase (lower phase) as possible. Acidify thesolution by adding 2 drops of 1N HCl and mix with a vortex mixer. Centrifuge at
1,200 rpm for 3 minutes with the glass stopper attached. Draw off and discard thehydrochloric acid phase (lower phase). Use the resulting solution as the sample test
solution.
Separately, depending on the expected mercury concentrations in thesamples, transfer 0-1.0 ml of methylmercury-cysteine solution (corresponding to 00.10 µg Hg) into 40-ml screw-capped conical centrifuge tubes and add 10 ml of 1N
KOH-ethanol. Follow the same steps as indicated above for preparing the sample
test solution to obtain methylmercury standard test solutions for the calibration
curve. Protect the test solutions from light after preparation.
d. Test procedures and calculations
With a micro-syringe, inject into the GLC a fixed volume (usually 2-5 µl) of
each of the sample test solutions (or their toluene-diluted solutions), the blank andmethylmercury standard test solutions for the calibration curve. Calculate themethylmercury concentration in the sample (µg/g) by comparing the peak height ofthe sample test solution with the calibration curve obtained from the blank andmethylmercury standard test solutions.
Procedural Notes
1.

This method is applied to determination of methylmercury in biologicalsamples (particularly those of fish and shellfish) containing relatively highconcentrations of mercury (exceeding 0.1 ppm). This method differs from that
described in 4-1-1 in the following points: after 0.01% dithizone-toluene
70extraction, omit 1N NaOH washing and the subsequent centrifugal separation;in the methylmercury re-extraction step, the extraction can be performed withtoluene alone instead of 0.01% dithizone-toluene. In addition, this method has
the advantage that an obvious change of color in the step of slight acidification
readily indicates the need to expel excess sulfide ions because dithizone, which
serves as a pH indicator, has already been extracted into the aqueous phase andcolored the solution during the preceding back-extraction with the alkaline
sodium sulfide solution.
2.

In this process, methylmercury dithizonate as well as free dithizone in 0.01%
dithizone-toluene are transferred at the same time into the alkaline sodium
sulfide solution; therefore, the volume of the 0.01% dithizone-toluene extract
to be used for back-extraction into alkaline sodium sulfide is limited to 1 ml.

3.

In this procedure, methylmercury together with dithizone, which has been in
the free form in the aqueous phase, is re-extracted into toluene. Therefore,
conduct re-extraction with this method using only toluene in a volume of 1 ml,
the same as that of the 0.01% dithizone-toluene extract used.

For the basics of methyl mercury analysis, see pp. 60-62 for the Procedural
Notes to “4-1-1 Biological samples (fish, shellfish, human blood, and tissues suchas umbilical cord)”71

Sample, 0.2-0.5 g wet weight (40-ml screw-capped conical centrifuge tube)
Add 10 ml of 1N KOH-ethanol.
Seal tightly and heat at 100°C for 1 hr.
Add 10 ml of 1N HCl and mix to slightly acidify.
Add 5 ml of hexane and shake for 3 min.
Centrifuge at 2,500 rpm for 3 min.
Aqueous phase

Organic phase

Add 2 ml of 20% EDTA and mix.
Add 5 ml of purified 0.01% dithizone-toluene and shake for 3 min.
Centrifuge at 2,500 rpm for 3 min.
Organic phase, 1 ml (10-ml conical centrifuge tube)

Aqueous phase

Add 2 ml of alkaline sodium sulfide solution and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Aqueous phase

Organic phase

Add 2 ml of toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Aqueous phase

Organic phase

Add 3-5 drops of 1N HCl to acidify slightly.
Aerate the sample with N2 gas for 3 min. at 50 ml/min.
Add 2 ml of Walpole's buffer and mix.
Add 1.0 ml of toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Organic phase

Aqueous phase

Add 3 ml of 1N NaOH and shake for 3 min.
Allow to stand and discard the aqueous layer.
Centrifuge at 1,200 rpm for 3 min.
Organic phase

Aqueous phase

Add 2 drops of 1N HCl and vortex mix.
Centrifuge at 1,200 rpm for 3 min.
GLC-ECD

Hydrochloric acid phase

Flow Chart 7. Determination of Methylmercury in Biological Samples Containing
Relatively High Concentrations of Mercury, Particularly Fish and
Shellfish (Simplified Method)72

4-1-3 Urine

a. Reagents(1)

Toluene: C6H5CH3 (pesticide analysis grade)(2)

Ethanol: C2H5OH (analytical grade)(3)

Distilled water: Distill deionized water and store in a clean glass container.

(4)

1N KOH-ethanol: Dissolve 56.11 g of potassium hydroxide (analytical grade)in ethanol to obtain a final volume of 1,000 ml. (Store in a cool dark place.)(5)

1N HCl: Mix 90 ml of hydrochloric acid (analytical grade) with distilledwater to obtain a final volume of 1,000 ml.

(6)

20% EDTA solution: Dissolve 20 g of tetrasodium ethylenediaminetetraacetate(analytical grade), C10H12N2O8Na4·4H2O, in distilled water to make a final
volume of 100 ml.

(7)

1N NaOH: Dissolve 40 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 1,000 ml.

(8)

0.1N NaOH: Dilute 1N NaOH 10-fold with distilled water.

(9)

Purified 0.01% dithizone-toluene: Dissolve 0.011 g of diphenylthiocarbazone,
C6H5N:NCSNHNHC6H5, in 100 ml of toluene in a 200-ml separatory funnel.
Add 50 ml of 0.1N NaOH and shake briefly to extract the dithizone into theaqueous phase (bottom phase). After allowing the phases to separate, transfer
the bottom phase into a glass container fitted with a glass stopper. Add 1N
HCl dropwise to make the solution slightly acidic (blackish-green crystals
will precipitate), add 100 ml of toluene, and shake to obtain purified 0.01%
dithizone-toluene. Allow the phases to settle, draw off and discard the bottom
phase, and seal. Store in a cool dark place. (Prepare a fresh solution for eachanalysis.)(10) Alkaline sodium sulfide solution: Dissolve 0.15 g of Na2S·9H2O (analyticalgrade) in 10 ml of distilled water in a 10-ml conical centrifuge tube fitted with73

a glass stopper to make the sodium sulfide stock solution. (Prepare a fresh
solution monthly. Store in a cool dark place.) At each use, transfer 0.1 ml of
the stock solution into a glass container fitted with a glass stopper, add 50 mlof 0.1N NaOH and 50 ml of ethanol, and mix to obtain an alkaline sodium
sulfide solution. (One ml of this solution contains 5 µg of Na2S.)(11) Walpole's buffer: Mix 200 ml of 1M CH3COONa and about 200 ml of 1N
HCl in 600 ml of distilled water to adjust to pH 3.0.
(12) 0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)(13) Methylmercury standard solution: Weigh out 12.5 mg of methylmercury
chloride, CH3HgCl (authentic standard) in a 100-ml volumetric flask, dissolve
in toluene to make a final volume of 100 ml, and store as stock solution.
Dilute the stock solution 100-fold with toluene to obtain the methylmercury
standard solution. One ml of this solution contains 1,000 ng of Hg.
(14) Methylmercury-cysteine solution: Transfer 0.5 ml of the methylmercury
standard solution and 5 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube fitted with a stopper. Shake for 3 minutes with areciprocal shaker to extract the methylmercury into the aqueous phase.
Centrifuge at 1,200 rpm for 3 minutes and draw off and discard the organic
phase (upper phase). Seal the tube and store in a cool dark place. (Prepare a
fresh solution monthly). One ml of this solution contains 0.1 µg of Hg.
(15) Anhydrous sodium sulfate: Anhydrous sodium sulfate (pesticide analysis
grade) heated at 500°C for 2-3 hours (stored in a desiccator)(16) N2 gas
Note: For the above reagents (5)-(8), (10) and (11), prepare the required amount
before use, add a 1/2 volume of toluene, and wash by shaking. Confirm beforehandthat no peaks appear that could interfere with the measurement by GLC-ECD.
74

b. Instruments and equipment(1)

Gas-liquid chromatograph equipped with electron capture detector (GLCECD)(2)

Multi-flow meter: Model V4 flow meter multi-kit (Kojima Instruments Inc.)(3)

Centrifuge(4)

Reciprocal shaker(5)

Magnetic stirrer(6)

Aspirator(7)

Vortex mixer(8)

pH mater(9)

Volumetric flasks: 10, 100, and 1,000 ml(10) Measuring pipettes: 0.2, 0.5, 1.5, and 10 ml(11) Pasteur pipettes(12) Separatory funnels: 100, 200, and 1,000 ml(13) Glass containers with glass stopper: 100, 200, and 500 ml(14) Glass container with screw cap: 1,000 ml(15) 50-ml round-bottom centrifuge tube with glass stopper(16) 10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter × 100
mm in length
Note: Thoroughly wash all glassware with toluene before use. Confirm in advancethat no peaks appear that could interfere with the measurement by GLC-ECD.
Gas-liquid chromatographic conditions:
Either of the following three different columns can be used for the analysis:i) 3.0 mm × 0.75-1.0 m glass column packed with Hg-20A on Uniport HP (AWDMCS, 60-80 mesh, GL Science Co., Ltd., Tokyo, Japan).
75ii) 3.0 mm × 0.75-1.0 m glass column packed with 10% KOCL-Hg on
Chromosorb W (AW-DMCS, 60-80 mesh, J-Science Co., Ltd., Kyoto, Japan).
iii) 3.0 mm × 2.0 m glass column packed with 5%-10% poly-diethylene glycol
succinate (DEGS) on Chromosorb W (AW-DMCS).
After packing the column, pack about 2-3 cm of NaCl, previously heated at
500°C for 2-3 hours, on top of the packing material (at the injection port).
Temperature: Column oven: 140-160°C, Injection port: 180°C, Detector oven:
200°C
Carrier gas: N2, 30-40 ml/min.
c. Preparation of sample test solution
Methylmercury extraction
Transfer a urine sample (usually 20 ml) into a 50-ml round-bottom
centrifuge tube fitted with a glass stopper. Add 10 ml of 1N KOH-ethanol andshake for 5 minutes. Add 10 ml of HCl and mix to acidify the sample slightly. Add
2 ml of 20% EDTA and mix well. Add 5 ml of purified 0.01% dithizone-toluene
and shake for 3 minutes to extract methylmercury in the sample. Centrifuge at
1,200 rpm for 3 minutes with the attached grass stopper. Draw off and discard theaqueous phase (lower phase). Add 0.5 g of anhydrous sodium sulfate to the toluene
phase and shake for 5 minutes. Centrifuge again at 1,200 rpm for 3 minutes withthe attached grass stopper. Draw off and discard as much of the remaining aqueous
phase (lower phase) as possible.
Clean-up
Add 3 ml of 1N NaOH to the toluene phase and shake for 3 minutes toremove excess dithizone in the toluene phase. Centrifuge at 1,200 rpm for 3
minutes with the glass stopper attached. Draw off and discard the aqueous phase(lower phase). Repeat the washing with 3 ml of 1N NaOH for the clean-up. Allow
the phases to separate. Draw off and discard the aqueous phase. Centrifuge at 1,200rpm for 3 minutes to obtain a clear toluene phase. (If the emulsion still remains in76

the toluene phase, draw off and discard the lower phase. Add about 0.5 g ofanhydrous sodium sulfate and shake. Perform centrifugal separation and discard thelower phase. )Transfer a fixed volume (usually 3 ml) of the toluene phase into a 10-ml
conical centrifuge tube with a glass stopper. Add 2 ml of alkaline sodium sulfide
solution and shake for 3 minutes to back-extract the methylmercury into theaqueous phase. Centrifuge at 1,200 rpm for 3 minutes with the glass stopper
attached. Carefully draw off and discard the toluene phase (upper phase). Add 2 mlof toluene to the aqueous phase and shake for 3 minutes to wash the aqueous phase.
Centrifuge again at 1,200 rpm for 3 minutes with the glass stopper attached. Draw
off and discard the toluene phase (upper phase). Add 1N HCl (3-5 drops) to makethe solution slightly acidic. With a Pasteur pipette, aerate the solution with N2 gas
through a multi-flow meter for 3 minutes (50 ml/min.) to expel the excess sulfide
ions as hydrogen sulfide gas. Subsequently, add 2 ml of Walpole's buffer whilewashing the tip of the Pasteur pipette and mix well with a vortex mixer. Add a fixedvolume of purified 0.01% dithizone solution (0.2-1.0 ml, usually 0.5 ml) and shakefor 3 minutes to extract methylmercury. Centrifuge at 1,200 rpm for 3 minutes withthe glass stopper attached. Draw off and discard the aqueous phase (lower phase).
Add 3 ml of 1N NaOH to the toluene phase and shake for 3 minutes to remove theexcess dithizone. Allow the phases to separate. Draw off and discard the aqueous
phase (lower phase). Centrifuge at 1,200 rpm for 3 minutes with the glass stopper
attached. Again draw off and discard as much of the aqueous phase (lower phase)as possible. Acidify the solution by adding 2 drops of 1N HCl to the toluene phaseand mix with a vortex mixer. Centrifuge at 1,200 rpm for 3 minutes with the glass
stopper attached. Draw off and discard the hydrochloric acid phase (lower phase).
Use the resulting solution as the sample test solution.
Separately, place 20 ml of distilled water in each of three 50-ml screwcapped round-bottom centrifuge tubes. Add 0, 0.050, and 0.10 ml (corresponding to77

0, 5, and 10 ng Hg) of methylmercury-cysteine solution, respectively. Subject thesesamples to the same procedures indicated above for preparing the sample test
solutions to obtain a blank test solution and methylmercury standard test solutions
for calibration. Store these test solutions in a cool dark place after preparation.
d. Test procedures and calculations
With a micro syringe, inject into the GLC a fixed volume (usually2-5 µl) of
each of the sample test solutions (or their toluene-diluted solutions), blank andmethylmercury standard test solutions. Calculate the methylmercury concentrationin the urine sample (ng/ml) by comparing the peak height of the sample test
solution with the calibration curve obtained from the blank and standard test
solutions.
Alternatively, when the linearity is confirmed by measurement of themethylmercury standard test solutions for calibration, calculate the concentration of
methylmercury in the sample with the following equation using the peakheight(mm) of the standard test solution (Pstd) of, for example, 10 ng Hg.
Methylmercury concentration in the urine sample (ng/ml) = 10 ng ×
(Ps–Pbl)/(Pstd–Pbl) × 1/sample volume (ml)Ps: peak height (mm) of sample test solution
Pbl: peak height (mm) of blank test solution
Note: For the basics of methyl mercury analysis, see pp. 60-62 for the Procedural
Notes to “4-1-1 Biological samples (fish, shellfish, human blood, and tissues suchas umbilical cord)”78

Sample, 20 ml (50-ml round-bottom centrifuge tube)
Add 10 ml of 1N KOH-ethanol and shake for 5 min.
Add 10 ml of 1N HCl and mix to acidify slightly.
Add 2 ml of 20% EDTA and mix.
Add 5 ml of purified 0.01% dithizone-toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Organic phase

Aqueous phase

Add 0.5 g of anhydrous Na2SO4 and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Organic phase

Aqueous phase

Add 3 ml of 1N NaOH and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Repeat this step once.
Organic phase, 3 ml (10-ml conical centrifuge tube)

Aqueous phase

Add 2 ml of alkaline sodium sulfide solution and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Aqueous phase

Organic phase

Add 2 ml of toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Aqueous phase

Organic phase

Add 3-5 drops of 1N HCl to acidify slightly.
Aerate with N2 gas at 50 ml/min. for 3 min.
Add 2 ml of Walpole’s buffer and mix.
Add 0.5 ml of purified 0.01% dithizone-toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Organic phase

Aqueous phase

Add 3 ml of 1N NaOH and shake for 3 min.
Allow to stand. Discard the aqueous phase.
Centrifuge at 1,200 rpm for 3 min.
Organic phase

Aqueous phase

Add 2 drops of 1N HCl and vortex mix.
Centrifuge at 1,200 rpm for 3 min.
GLC-ECD

Hydrochloric acid phase

Flow Chart 8. Determination of Methylmercury in Urine
79

4-1-4 Sediment/soila. Reagents(1)

Toluene: C6H5CH3 (pesticide analysis grade)(2)

Ethanol: C2H5OH (analytical grade)(3)

Distilled water: Distill deionized water and store in a clean glass container.

(4)

1N KOH-ethanol: Dissolve 56.11 g of potassium hydroxide (analytical grade)in ethanol to obtain a final volume of 1,000 ml. (Store in a cool dark place.)(5)

1N HCl: Mix 90 ml of hydrochloric acid (analytical grade) with distilledwater to obtain a final volume of 1,000 ml.

(6)

20% NH2OH·HCl solution: Dissolve 20 g of hydroxylamine hydrochloride indistilled water to make a final volume of 100 ml.

(7)

20% EDTA solution: Dissolve 20 g of tetrasodium ethylenediaminetetraacetate(analytical grade), C10H12N2O8Na4·4H2O, in distilled water to make a final
volume of 100 ml.

(8)

1N NaOH: Dissolve 40 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 1,000 ml.

(9)

0.1N NaOH: Dilute 1N NaOH 10-fold with distilled water.

(10) Purified 0.01% dithizone-toluene: Dissolve 0.011 g of diphenylthiocarbazone,
C6H5N:NCSNHNHC6H5, in 100 ml of toluene in a 200-ml separatory funnel.
Add 50 ml of 0.1N NaOH and shake briefly to extract the dithizone into theaqueous phase (bottom phase). After allowing the phases to separate, transfer
the bottom phase into a glass container fitted with a glass stopper. Add 1N
HCl dropwise to make the solution slightly acidic (blackish-green crystals
will precipitate). Add 100 ml of toluene and shake to obtain purified 0.01%
dithizone-toluene. Allow the phases to settle, draw off and discard the bottom
phase, and seal. Store in a cool dark place. (Prepare a fresh solution for eachanalysis.)80

(11) Alkaline sodium sulfide solution: Weigh out 0.15 g of Na2S·9H2O (analyticalgrade) in a 10-ml conical centrifuge tube with a glass stopper and dissolve in
10 ml of distilled water to make the sodium sulfide stock solution. (Prepare a
fresh solution monthly. Store in a cool dark place.) At each use, transfer 0.1
ml of the stock solution into a glass container with a glass stopper, add 50 mlof 0.1N NaOH and 50 ml of ethanol, and mix to make an alkaline sodium
sulfide solution. (One ml of this solution contains 5 µg of Na2S.)(12) Walpole's buffer: Mix 200 ml of 1M CH3COONa and about 200 ml of 1N
HCl in 600 ml of distilled water to adjust to pH 3.0.
(13) Anhydrous sodium sulfate: Anhydrous sodium sulfate (pesticide analysis
grade) heated at 500°C for 2-3 hours (stored in a desiccator)(14) 0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)(15) Methylmercury standard solution: Weigh out 12.5 mg of methylmercury
chloride, CH3HgCl (authentic standard) in a 100-ml volumetric flask, dissolve
in toluene to make a final volume of 100 ml, and store as a stock solution.
Dilute the stock solution 100-fold with toluene to make the methylmercury
standard solution. One ml of this solution contains 1,000 ng of Hg.
(16) Methylmercury-cysteine solution: Transfer 0.5 ml of the methylmercury
standard solution and 5 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube with a stopper. Shake for 3 minutes with a reciprocal
shaker to extract the methylmercury to the aqueous phase. Centrifuge at 1,200rpm for 3 minutes with the glass stopper attached and draw off and discard theorganic phase (upper phase). Seal the tube and store in a cool dark place.
(Prepare a fresh solution monthly). One ml of this solution contains 0.10 µgof Hg.
81

(17) Florisil: Florisil for column chromatography (60-100 mesh) heated at 130°C
for 2-3 hours (stored in a desiccator)(18) Florisil column: A glass column packed with 0.5 g of Florisil (60-100 mesh)and 0.5 g anhydrous sodium sulfate in turn(19) N2 gas
Note: For the above reagents (5)-(9), (11), and (12), prepare the required amounts
in advance, add a 1/2 volume of toluene, and wash by shaking. Confirm beforehandthat no peaks appear that could interfere with the GLC measurement ofmethylmercury.
b. Instruments and equipment(1)

Gas-liquid chromatograph equipped with electron capture detector (GLCECD)(2)

Multi-flow meter: Model V4 flow meter multi-kit (Kojima Instruments Inc.)(3)

Centrifuge(4)

Reciprocal shaker(5)

Magnetic stirrer(6)

Aspirator(7)

Vortex mixer(8)

pH mater(9)

Volumetric flasks: 10, 100, and 1,000 ml(10) Measuring pipettes: 0.2, 0.5, 1.5, and 10 ml(11) Pasteur pipettes(12) Separatory funnels: 100, 200, and 1,000 ml(13) Glass containers with glass stoppers: 100, 200, and 500 ml(14) Glass container with a screw cap: 1,000 ml(15) 50-ml screw-capped round-bottom centrifuge tube
82

(16) 10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter × 100
mm in length(17) Cotton wool(18) Porcelain crucible
Note: Thoroughly wash all glassware with toluene before use. Confirm in advancethat no peaks appear that could interfere with the GLC measurement ofmethylmercury. If a peak appears, perform heat treatment at 300°C for 30 minutes.
Gas-liquid chromatographic conditions:
Either of the following three different columns can be used for the analysis:i) 3.0 mm × 0.75-1.0 m glass column packed with Hg-20A on Uniport HP (AWDMCS, 60-80 mesh, GL Science Co., Ltd., Tokyo, Japan).
ii) 3.0 mm × 0.75-1.0 m glass column packed with 10% KOCL-Hg on
Chromosorb W (AW-DMCS, 60-80 mesh, J-Science Co., Ltd., Kyoto, Japan).
iii) 3.0 mm × 2.0 m glass column packed with 5%-10% poly-diethylene glycol
succinate (DEGS) on Chromosorb W (AW-DMCS).
After packing the column, pack about 2-3 cm of NaCl, previously heated at
500°C for 2-3 hours, on top of the packing material (at the injection port).
Temperature: Column oven: 140-160°C, Injection port: 180°C, Detector oven:
200°C
Carrier gas: N2, 30-40 ml/min.
c. Preparation of sample test solution
Methylmercury extraction
Precisely weigh out a homogenized sample (usually 0.2-0.5 g as wet weight,
around 0.1 g for a dry sample) in the bottom of a 50-ml screw-capped round-bottom
centrifuge tube. (For a dry sample, add 0.5 ml of distilled water to moisten after
weighing.) Add 10 ml of 1N KOH-ethanol. Stir and crush well with a glass rod and83shake for 20 minutes with a reciprocal shaker and add 10 ml of 1N HCl to acidify
the sample solution slightly. Aerate the sample solution with N2 gas at 100 ml/min.
for 5 minutes while stirring with a magnetic stirrer. Add 2 ml of a 20%
NH2OH·HCl solution and 2 ml of a 20% EDTA solution in turn, and mix byshaking.1 Add 5 ml of purified 0.01% dithizone solution and shake for 3 minutes toextract methylmercury in the sample. Centrifuge at 2,500 rpm for 3 minutes. Usinga 5-ml measuring pipette provided with a small amount of cotton wool woundaround the tip, collect at least 4 ml from the toluene phase, being careful not to mix
the lower phase, and pass it through the Florisil column. Receive the eluate into a
10-ml conical centrifuge tube with a glass stopper.
Clean-up
Add 3 ml of 1N NaOH to the toluene phase and wash by shaking for 3
minutes to remove excess dithizone into the aqueous phase. Centrifuge at 1,200rpm for 3 minutes with the glass stopper attached. Draw off and discard as much of
the lower phase as possible. Add another 3 ml of 1N NaOH. Shake and wash
similarly. Allow the phases to separate. Draw off and discard the lower phase.
Centrifuge at 1,200 rpm for 3 minutes with the glass stopper attached. Transfer a
fixed volume (usually 3 ml) of the toluene phase into another 10-ml conicalcentrifuge tube with a glass stopper. Add 2 ml of alkaline sodium sulfide solution
and shake for 3 minutes to back-extract the methylmercury into the aqueous layer.
Centrifuge at 1,200 rpm for 3 minutes with the glass stopper attached and draw off
and discard the toluene phase (upper phase) carefully. Then, add 2 ml of toluene tothe aqueous phase and shake for 3 minutes to wash the aqueous phase. Centrifuge
again at 1,200 rpm for 3 minutes with the glass stopper attached. Draw off anddiscard the toluene phase (upper phase). Add 1N HCl (3-5 drops) to make thesolution slightly acidic. With a Pasteur pipette, aerate the solution with N2 gas
through a multi-flow meter at 50 ml/min. for 3 minutes to expel the excess sulfide
84

ions as hydrogen sulfide gas. Subsequently, add 2 ml of Walpole's buffer whilewashing the tip of the Pasteur pipette in turn and mix well with a vortex mixer. Adda fixed volume of purified 0.01% dithizone solution (0.2-1.0 ml, usually 0.5 ml)
and shake to extract methylmercury. Centrifuge at 1,200 rpm for 3 minutes with theglass stopper attached. Draw off and discard the aqueous phase (lower phase). Add
3 ml of 1N NaOH to the toluene phase, shake, and wash to remove the excess
dithizone. Allow the phases to separate. Draw off and discard the aqueous phase(lower phase). Centrifuge at 1,200 rpm for 3 minutes with the glass stopper
attached, and again draw off and discard as much of the aqueous phase (lower
phase) as possible. Acidify the solution by adding 2 drops of 1N HCl to the toluene
phase and stir with a vortex mixer. Centrifuge at 1,200 rpm for 3 minutes with theglass stopper attached. Draw off and discard the hydrochloric acid phase (lower
phase). Use the resulting solution as the sample test solution.
Separately, depending on the expected mercury concentrations in thesamples, transfer 0-0.20 ml of methylmercury-cysteine solution (corresponding to
0-0.020 µg Hg) into at least three 50-ml screw-capped round-bottom centrifuge
tubes. Add 10 ml of 1N KOH-ethanol and follow the same procedures as indicatedabove for preparing the sample test solutions to obtain the blank test solution andmethylmercury standard test solutions for the calibration curve. Store all these test
solutions in a cool dark place.
For wet samples, at collection of the samples for analysis, precisely weighabout 10-20 g of the sample into a porcelain crucible of known weight. Place it in adrying oven at 105°C and dry for 2-3 hours. Allow to cool in a desiccator, thenweigh to obtain the wet weight/dry weight ratio (WW/DW).
d. Test procedures and calculations
With a micro-syringe, inject into the GLC a fixed volume (usually 2-5 µl) of
each of the sample test solutions (or their toluene-diluted solutions), the blank and85the methylmercury standard test solutions for the calibration curve. Calculate themethylmercury concentration in the sample (µg/g wet weight) by comparing thepeak height of the sample test solution with the calibration curve obtained from theblank and standard test solutions. Convert the result to a dry weight (µg/g dryweight) with the wet weight/dry weight ratio determined for the sample with theprocedure indicated above.
Procedural Notes
1.

Before dithizone extraction, add hydroxylamine hydrochloride and EDTA
solution and mix by shaking to reduce oxidative substances and mask othermetal ions contained in the sample. This prevents dithizone from unnecessary
consumption/decomposition during the dithizone-toluene extraction process.
For the basics of methyl mercury analysis, see pp. 60-62 for the Procedural

Notes to “4-1-1 Biological samples (fish, shellfish, human blood, and tissues suchas umbilical cord)”86

Sample, 0.2-0.5 g wet weight (50-ml screw-capped centrifuge tube)
Add 10 ml of 1N KOH-ethanol, stir and crush with a glass rod.
Shake for 20 min.
Add 10 ml of 1N HCl to acidify slightly.
Aerate with N2 gas at 100 ml/min. for 5 min.
Add 2 ml of 20% NH2OH·HCl and mix.
Add 2 ml of 20% EDTA and mix.
Add 5 ml of purified 0.01% dithizone-toluene and shake for 3 min.
Centrifuge at 2,500 rpm for 3 min.
Organic phase (4 ml minimum)
Pass-through Florisil column

Aqueous phase

Organic phase (10-ml conical centrifuge tube)
Add 3 ml of 1N NaOH and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.

Aqueous phase

Organic phase, 3 ml (10-ml conical centrifuge tube)
Aqueous phase
Add 2 ml of alkaline sodium sulfide solution and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Aqueous phase
Add 2 ml of toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.

Organic phase

Aqueous phase
Organic phase
Add 3-5 drops of 1N HCl to acidify slightly.
Aerate with N2 gas at 50 ml/min. for 3 min.
Add 2 ml of Walpole’s buffer and mix.
Add 0.5 ml of purified 0.01% dithizone-toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Aqueous phase
Add 3 ml of 1N NaOH and shake for 3 min.
Allow phases to separate. Discard the aqueous phase.
Centrifuge at 1,200 rpm for 3 min.

Organic phase

Organic phase
Add 2 drops of 1N HCl and vortex mix.
Centrifuge at 1,200 rpm for 3 min.

Aqueous phase

GLC-ECD

Hydrochloric acid phase

Flow Chart 9. Determination of Methylmercury in Sediment/Soil87

4-1-5 Water

Similar to the method for total mercury analysis of water samples, thismethod involves the ionization and liberation of mercury compounds throughtreatment with potassium permanganate under sulfuric acid-acidification; preconcentration of the mercury by dithizone-toluene extraction; back-extraction of themethylmercury in the extract into alkaline sodium sulfide solution; re-extraction
with dithizone-toluene to clean up; and measurement by GLC-ECD.
a. Reagents(1)

Toluene: C6H5CH3 (pesticide analysis grade)(2)

Ethanol: C2H5OH (analytical grade)(3)

Distilled water: Distill deionized water and store in a clean glass container.

(4)

20N H2SO4: Transfer about 350 ml of distilled water into a 1-L volumetricflask. Gradually add 600 ml of sulfuric acid (for measurement of toxic metals)
while stirring in ice water. After it returns to room temperature, add distilledwater to a final volume of 1,000 ml.

(5)

10N NaOH: Dissolve 400 g of sodium hydroxide (analytical grade) to make a
final volume of 1,000 ml.

(6)

0.5% KMnO4 solution: Dissolve 0.5 g of potassium permanganate (analyticalgrade) in distilled water to make a final volume of 100 ml.

(7)

10% NH2OH·HCl solution: Dissolve 10 g of hydroxylamine hydrochloride indistilled water to make a final volume of 100 ml.

(8)

10% EDTA solution: Dissolve 10 g of tetrasodium ethylenediaminetetraacetate(analytical grade), C10H12N2O8Na4·4H2O, in distilled water to make a final
volume of 100 ml.

(9)

1N HCl: Mix 90 ml of hydrochloric acid (analytical grade) with distilledwater to obtain a final volume of 1,000 ml.
88

(10) 1N NaOH: Dissolve 40 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 1,000 ml.
(11) 0.1N NaOH: Dilute 1N NaOH 10-fold with distilled water.
(12) Purified 0.01% dithizone-toluene1: Dissolve 0.011 g of diphenylthiocarbazone,
C6H5N:NCSNHNHC6H5, in 100 ml of toluene in a 200-ml separatory funnel.
Add 50 ml of 0.1N NaOH and shake briefly to extract the dithizone into theaqueous phase (bottom phase). Allow the phases to separate. Transfer thebottom phase into a glass container fitted with a glass stopper. Add 1N HCl
dropwise to make the solution slightly acidic (blackish-green crystals will
precipitate), add 100 ml of toluene, and shake to obtain purified 0.01%
dithizone-toluene. Allow the phases to separate. Draw off and discard thebottom phase and seal. Store in a cool dark place. (Prepare a fresh solution foreach analysis.)(13) Alkaline sodium sulfide solution: Weigh out 0.15 g of Na2S·9H2O (analyticalgrade) in a 10-ml conical centrifuge tube fitted with a glass stopper anddissolve in 10 ml of distilled water to make a sodium sulfide stock solution.
(Prepare a fresh solution monthly. Store in a cool dark place.) At each use,transfer 0.1 ml of the stock solution into a glass container fitted with a glass
stopper, add 50 ml of 0.1N NaOH and 50 ml of ethanol, and mix to make analkaline sodium sulfide solution. (One ml of this solution contains 5 µg of
Na2S.)(14) Walpole's buffer: Mix 200 ml of 1M CH3COONa and about 200 ml of 1N
HCl in 600 ml of distilled water to adjust to pH 3.0.
(15) 0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)(16) Methylmercury standard solution: Weigh out 12.5 mg of methylmercury
chloride, CH3HgCl (authentic standard) in a 100-ml volumetric flask, dissolve89

in toluene to make a final volume of 100 ml, and store as stock solution.
Dilute the stock solution 100-fold with toluene to make a methylmercury
standard solution. One ml of this solution contains 1,000 ng of Hg.
(17) Methylmercury-cysteine solution: Transfer 0.5 ml of the methylmercury
standard solution and 5 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube fitted with a glass stopper. Shake for 3 minutes with areciprocal shaker to extract the methylmercury into the aqueous phase.
Centrifuge at 1,200 rpm for 3 minutes with the glass stopper attached anddraw off and discard the organic phase (upper phase). Seal the tube and store
as a stock solution in a cool dark place. (Prepare a fresh solution monthly). At
each use, dilute the stock solution 10-fold with distilled water to make amethylmercury-cysteine solution for preparing calibration samples for water
methylmercury analysis. One ml of this solution contains 10 ng of Hg.
(18) Anhydrous sodium sulfate: Anhydrous sodium sulfate (pesticide analysis
grade) heated at 500°C for 2-3 hours (stored in a desiccator)(19) N2 gas
Note: For the above reagents(5), (7)-(11), (13), and (14), prepare the required
amounts in advance, add a 1/2 volume of toluene, and wash by shaking in a
separatory funnel. Confirm beforehand that no peaks appear that could interferewith the GLC measurement of methylmercury.
b. Instruments and equipment(1)

Gas-liquid chromatograph equipped with electron capture detector (GLCECD)(2)

Multi-flow meter: Model V4 flow meter multi-kit (Kojima Instruments Inc.)(3)

Centrifuge(4)

Reciprocal shaker(5)

Magnetic stirrer
90

(6)

Aspirator(7)

Vortex mixer(8)

pH mater(9)

Volumetric flasks: 10, 100, and 1,000 ml(10) Measuring pipettes: 0.2, 0.5, 5, and 10 ml(11) Pasteur pipettes(12) Separatory funnels: 100, 200, 1,000, and 2,000 ml(13) Glass containers with glass stoppers: 100, 200, and 500 ml(14) Glass container with screw cap: 1,000 ml(15) 35-ml conical centrifuge tube with glass stopper(16) 10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter × 100
mm in length
Note: Thoroughly wash all glassware with toluene before use. Confirm in advancethat no peaks appear that could interfere with the GLC measurement ofmethylmercury.
Gas-liquid chromatographic conditions:
Either of the following three different columns can be used for the analysis:i) 3.0 mm × 0.75-1.0 m glass column packed with Hg-20A on Uniport HP (AWDMCS, 60-80 mesh, GL Science Co., Ltd., Tokyo, Japan).
ii) 3.0 mm × 0.75-1.0 m glass column packed with 10% KOCL-Hg on
Chromosorb W (AW-DMCS, 60-80 mesh, J-Science Co., Ltd., Kyoto, Japan).
iii) 3.0 mm × 2.0 m glass column packed with 5%-10% poly-diethylene glycol
succinate (DEGS) on Chromosorb W (AW-DMCS).
After packing the column, pack about 2-3 cm of NaCl, previously heated at
500°C for 2-3 hours, on top of the packing material (at the injection port).
Temperature: Column oven: 140-160°C, Injection port: 180°C, Detector oven:
200°C
91

Carrier gas: N2, 30-40 ml/min.
c. Preparation of sample test solution
Methylmercury extraction
Transfer 2 L of a water sample into a 2-L separatory funnel. Add 10 ml of
20N H2SO4 and 5 ml of a 0.5% KMnO4 solution. Mix and let stand for 5 minutes.
Add 20 ml of 10N NaOH and mix by shaking to neutralize. Add 5 ml of a 10%
NH2OH·HCl solution and shake for several seconds to mix. Let stand for 20
minutes. Add 5 ml of 10% EDTA solution and mix by shaking.2 Add 10 ml ofpurified 0.01% dithizone-toluene and shake vigorously for 1 minute to extract the
methylmercury in the sample. Let stand for at least 1 hour out of direct sunlight.
Discard the aqueous phase (lower phase).
Clean-up
Transfer as much of the toluene phase as possible into a 35-ml conicalcentrifuge tube fitted with a glass stopper. Attach the glass stopper and centrifuge at
1,200 rpm for 3 minutes. Draw off and discard the aqueous phase (lower phase).
(For analysis with unfiltered water, if emulsification occurs, remove the lower
aqueous phase, add about 0.5 g of anhydrous sodium sulfate, and shake followed bycentrifugal separation to remove the lower phase.) Add 5 ml of 1N NaOH and washby shaking for 3 minutes to remove excess dithizone. Centrifuge at 1,200 rpm for 3
minutes with the glass stopper attached. Draw off and discard the aqueous phase(lower phase). Again add 5 ml of 1N NaOH and repeat this washing procedure.
After centrifugal separation, draw off and discard the lower phase. Transfer a fixedvolume (usually 7 ml) of the toluene phase to a 10-ml conical centrifuge tube with aglass stopper. Add 2 ml of alkaline sodium sulfide solution and shake for 3 minutes
to back-extract the methylmercury into the aqueous phase. Centrifuge at 1,200 rpm
for 3 minutes with the glass stopper attached. Carefully draw off and discard thetoluene phase (upper phase). Add 2 ml of toluene to the aqueous phase and shake92

for 3 minutes to wash the aqueous phase. Centrifuge again at 1,200 rpm for 3
minutes with the glass stopper attached. Draw off and discard the toluene phase(upper phase). Add 1N HCl (3-5 drops) to make the solution slightly acidic. With a
Pasteur pipette, aerate the sample solution with N2 gas through a multi-flow meterat 50 ml/min. for 3 minutes to expel the excess sulfide ions as hydrogen sulfide gas.
Subsequently, add 2 ml of Walpole's buffer while washing the tip of the Pasteur
pipette. Mix well with a vortex mixer. Add a fixed volume of purified 0.01%
dithizone-toluene (usually 0.2 ml) and shake for 3 minutes to extract
methylmercury. Centrifuge at 1,200 rpm for 3 minutes with the glass stopper
attached. Draw off and discard the aqueous phase (lower phase). Add 3 ml of 1N
NaOH to the toluene phase and wash by shaking for 3 minutes to remove the excess
dithizone. Let stand to allow the two phases to separate. Draw off and discard theaqueous phase (lower phase). Centrifuge at 1,200 rpm for 3 minutes with the glass
stopper attached, and again draw off and discard as much of the remaining aqueous
phase (lower phase) as possible. Acidify the solution by adding 2 drops of 1N HCl
and mix with a vortex mixer. Centrifuge at 1,200 rpm for 3 minutes with the glass
stopper attached. Draw off and discard the hydrochloric acid phase (lower phase) tomake a sample test solution.
Separately, choose the water sample with the lowest mercury concentrationand transfer 2 L each to three 2-L separatory funnels. Add 0, 0.10, and 0.20 ml ofmethylmercury-cysteine solution (corresponding to 0, 1.0 and 2.0 ng Hg),
respectively. Subject the samples to the same procedures as indicated above forpreparing sample test solutions to make a blank test solution and methylmercury
standard test solutions, respectively. Store these test solutions in a cool dark place
after preparation.
d. Test procedures and calculations
93

With a micro-syringe, inject into the GLC a fixed volume (usually 2-5 µl) of
each of the sample test solutions (or their toluene-diluted solutions), and the blankand methylmercury standard test solutions. Calculate the methylmercury
concentration in the water sample (ng Hg/L) by comparing the peak height of thesample test solution with the calibration curve obtained from the blank and standard
test solutions. Alternatively, when the linearity is confirmed by measurement of themethylmercury standard test solutions for preparation of the calibration curve, themethylmercury concentration in the sample can be calculated according to thefollowing equation using the peak height of the standard test solution (Pstd) of, forexample, 2 ng Hg.
Methylmercury concentration in the water sample (ng/L) = 2 ng ×
(Ps–Pbl)/(Pstd–Pbl) × dilution factor × 1/ water sample (L)Ps: peak height (mm) of the sample test solution
Pbl: peak height (mm) of the blank test solution
Procedural Notes
1.

Dithizone (diphenylthiocarbazone) is easily oxidized and usually contains its
oxidized form (diphenylthiocarbadiazone) as an impurity that causesinterfering peaks on the gas chromatogram. Therefore, utilizing puredithizone’s unique chemical property of forming a water-soluble salt that
dissolves in alkaline solution, prepare a fresh dithizone-toluene solution foreach analysis.

2.

In preparing sample test solutions for water samples, add hydroxylaminehydrochloride to reduce the remaining potassium permanganate and add
EDTA solution to mask other metal ions contained in the sample. Thus, add
both to prevent unnecessary consumption of dithizone by metal ions andoxidation during dithizone-toluene extraction.
94

For the basics of methyl mercury analysis, see pp. 60-62 for the Procedural
Notes to “4-1-1 Biological samples (fish, shellfish, human blood, and tissues suchas umbilical cord)”95

Sample, 2 L (2-L separatory funnel)
Add 10 ml of 20N H2SO4 and mix to acidify.
Add 5 ml of 0.5% KMnO4 solution, mix, and let stand for 5 min.
Add 20 ml of 10N NaOH and mix to neutralize.
Add 5 ml of 10% NH2OH·HCl solution, mix, and let stand for 20 min.
Add 5 ml of 10% EDTA solution and mix.
Add 10 ml of 0.01% dithizone-toluene and shake for 3 min.
Let stand for at least 1 hr.
Organic phase (35-ml conical centrifuge tube)

Aqueous phase(When an emulsion is formed, add 0.5 g of anhydrous Na2SO4 and shake.)
Centrifuge at 1,200 for 3 min.
Organic phase

Aqueous phase

Add 5 ml of 1 N NaOH and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Organic phase, 7 ml (10-ml conical test tube)

Aqueous phase

Add 2 ml of alkaline sodium sulfide solution and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Aqueous phase

Organic phase

Add 2 ml of toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Aqueous phase

Organic phase

Add 3-5 drops of 1N HCl to acidify slightly.
Aerate with N2 gas at 50 ml/min. for 3 min.
Add 2 ml of Walpole’s buffer and mix.
Add 0.2 ml of purified 0.01% dithizone-toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Organic phase

Aqueous phase

Add 3 ml of 1N NaOH and shake for 3 min.
Allow to stand. Discard the aqueous phase.
Centrifuge at 1,200 rpm for 3 min.
Organic phase

Aqueous phase

Add 2 drops of 1N HCl and vortex mix.
Centrifuge at 1,200 rpm for 3 min.
GLC-ECD

Hydrochloric acid phase

Flow Chart 10. Determination of Methylmercury in Water
96

4-2

Determination

by

the

hydrochloric

acid

leaching/toluene

extraction/gas-liquid chromatography with electron capture detection(GLC-ECD) method
Methylmercury analysis for hair sampling can be performed more simply
with a method different from that presented above. Briefly, this method involves
immersion of the sample in 2N HCl, heating at 100°C for 5 minutes to leach out
methylmercury from the sample, methylmercury extraction into toluene, anddetermination by GLC-ECD.

4-2-1 Hair

Transfer several tens of milligrams of the sample into a beaker. Wash withneutral detergent(diluted 100-fold) and distilled water by decantation. Add a small
volume of acetone to the sample to remove the remaining water. Remove theacetone under reduced pressure. Transfer the sample into a 20-ml vial and cut it
into fine pieces with dissection scissors.
a. Reagents(1)

Toluene: C6H5CH3 (pesticide analysis grade)(2)

Ethanol: C2H5OH (analytical grade)(3)

Distilled water: Distill deionized water and store in a clean glass container.

(4)

2N HCl: Mix 180 ml of hydrochloric acid (analytical grade) with distilledwater to obtain a final volume of 1,000 ml.

(5)

1N NaOH: Dissolve 40 g of sodium hydroxide (analytical grade) in distilledwater to make a final volume of 1,000 ml.

(6)

0.1N NaOH: Dilute 1N NaOH 10-fold with distilled water.

97

(7)

0.1% L-cysteine solution: Dissolve 10 mg of L-cysteine hydrochloride,
HSCH2CH(NH2)COOH·HCl·H2O, in 10 ml of 0.1N NaOH. (Prepare a fresh
solution for each analysis.)(8)

Methylmercury standard solution: Weigh out 12.5 mg of methylmercury
chloride, CH3HgCl (authentic standard) in a 100-ml volumetric flask, dissolve
in toluene to make a final volume of 100 ml, and store as stock solution.
Dilute the stock solution 100-fold with toluene to make the methylmercury
standard solution. One ml of this solution contains 1,000 ng of Hg.

(9)Methylmercury-cysteine solution: Transfer 2 ml of the methylmercury
standard solution and 2 ml of the 0.1% L-cysteine solution into a 10-ml
conical centrifuge tube with a glass stopper. Shake for 3 minutes with areciprocal shaker to extract the methylmercury into the aqueous phase.
Centrifuge at 1,200 rpm for 3 minutes with the glass stopper attached anddraw off and discard the organic phase (upper phase). Seal the tube and store
in a cool dark place. (Prepare a fresh solution monthly). One ml of thissolution contains 1,000 ng of Hg.

Note: For the above reagents (5) and (6), prepare the required amounts in advance,
add a 1/2 volume of toluene, and wash by shaking in a separatory funnel. Confirm
beforehand that no peaks appear that could interfere with the measurement ofmethylmercury by GLC-ECD.
b. Instruments and equipment(1)

Gas-liquid chromatograph equipped with electron capture detector (GLCECD)(2)

Centrifuge(3)

Reciprocal shaker(4)Isothermal bath: Use polyethylene glycol 400.

(5)Aspirator
98

(6)Volumetric flasks: 10, 100, and 1,000 ml(7)

Measuring pipettes: 0.2, 1, 5, and 10 ml(8)

Pasteur pipettes(9)Separatory funnel: 1,000 ml(10) Glass container with glass stopper: 500 ml(11) Beaker: 100 ml(12) 10-ml screw-capped round-bottom centrifuge tube: 16.5 mm in diameter ×
105 mm in length(13) 10-ml conical centrifuge tube with glass stopper: 16.5 mm in diameter, 100
mm in length(14) Vial: 20-ml scintillation vial
(15) Glass wool or cotton wool(16) Dissection scissors
Note: Thoroughly wash all glassware with toluene before use. Confirm in advancethat no peaks appear that could interfere with measurement of methylmercury by
GLC-ECD. If a peak appears, perform heat treatment at 300°C for 30 minutes.
Gas-liquid chromatographic conditions:
Either of the following three different columns can be used for the analysis:i) 3.0 mm × 0.75-1.0 m glass column packed with Hg-20A on Uniport HP (AWDMCS, 60-80 mesh, GL Science Co., Ltd., Tokyo, Japan).
ii) 3.0 mm × 0.75-1.0 m glass column packed with 10% KOCL-Hg on
Chromosorb W (AW-DMCS, 60-80 mesh, J-Science Co., Ltd., Kyoto, Japan).
iii) 3.0 mm × 2.0 m glass column packed with 5%-10% poly-diethylene glycol
succinate (DEGS) on Chromosorb W (AW-DMCS).
After packing the column, pack about 2-3 cm of NaCl, previously heated at
500°C for 2-3 hours, on top of the packing material (at the injection port).
99

Temperature: Column oven: 140-160°C, Injection port: 180°C, Detector oven:
200°C
Carrier gas: N2, 30-40 ml/min.
c. Preparation of sample test solutions
Precisely weigh out a finely cut hair sample (usually around 10 mg) andtransfer into a 10-ml screw-capped round-bottom centrifuge tube. Add 2 drops ofethanol to moisten the sample. With a glass rod, insert a small amount of glass woolor cotton wool into the tube and press lightly on the sample to cover it. Gently place
3 ml of 2N HCl onto the glass wool or cotton, taking care to keep the sample below
the surface. Seal tightly and heat in an isothermal bath at 100°C for 5 minutes toelute methylmercury from the sample.1 Allow to cool and invert it to mix.
Centrifuge at 1,200 rpm for 3 minutes. Transfer 1 ml of the supernatant into a 10ml conical centrifuge tube provided with a glass stopper. Add 2 ml of toluene andshake for 3 minutes to extract the methylmercury present in the HCl phase into thetoluene phase.2 Centrifuge at 1,200 rpm for 3 minutes. Draw off and remove thelower phase3 to make a sample test solution.
Separately, transfer 0, 0.050, and 0.10 ml of a methylmercury-cysteine
solution (corresponding to 0, 50, and 100 ng Hg) into three 10-ml screw-cappedround-bottom centrifuge tubes, respectively, and add 2N HCl to make a final
volume of 3 ml. Subject these solutions to the procedures indicated in the method
for preparing test solutions to make methylmercury standard test solutions for thecalibration curve. Protect all the test solutions from light after preparation.
d. Test procedures and calculations
With a micro-syringe, inject into the GLC a fixed volume (usually 2-5 µl) of
each of sample test solutions (or their toluene-diluted solutions), and the blank andmethylmercury standard test solutions. Calculate the methylmercury concentration100

in the hair sample (ng/mg) by comparing the peak height of the sample test solution
with the calibration curve obtained from the blank and methylmercury standard test
solutions.
Alternatively, when the linearity is confirmed by measurement of themethylmercury standard test solutions for preparation of the calibration curve, themethylmercury concentration in the sample can be calculated according to thefollowing equation using the peak height of the standard test solution (Pstd) of, forexample, 100 ng Hg.
Methylmercury concentration in the sample (ng/mg) = 100 ng ×
(Ps–Pbl)/(Pstd–Pbl) × dilution factor × 1/sample weight (mg)Ps: Peak height (mm) of sample test solution
Pbl: Peak height (mm) of blank test solution
Procedural Notes
1.

Although the leaching of methylmercury in hair samples with dilutehydrochloric acid proceeds gradually at normal temperatures, it is accelerated
by heating. When using 2N HCl, heating at 100°C causes it to elute almost
completely within several minutes; exceeding 10 minutes causes other organic
substances to elute, resulting in the appearance of interfering peaks on the gas
chromatogram. A heating time of 5 minutes is sufficient under the conditionsof this method. Do not exceed 10 minutes of heating time.

2.

In order to transfer the methylmercury in the HCl eluate quantitatively into thetoluene phase in this extraction step, use a toluene volume at least twice that of
the HCl eluate for extraction.

3.

To remove the upper phase or lower phase in the test tube, use the SuctionRemoval System with a Pasteur pipette connected with a flexible tube througha waste liquid collector to an aspirator, as shown in Figure 2. Briefly, toremove the upper phase (organic phase), perform suctioning by positioning the101

tip of the Pasteur pipette on the surface of the upper phase down along theinside wall of the test tube in order to draw off most of the upper phase. When
only a little upper phase remains, keep the tip of the Pasteur pipette a few mm
above the surface of the organic phase and continue to draw off. With thistechnique, only the organic phase, which has a lower specific gravity than thatof the lower phase (aqueous phase) and high volatility, is drawn off together
with air, allowing for almost complete removal of the organic phase. To draw
off and discard the lower of the two phases separated in the test tube, squeeze
the flexible tube with the fingers to stop the suction of the Pasteur pipette.
Position the tip of the Pasteur pipette at the bottom of the test tube and adjust
the pressure on the flexible tube to slowly draw up the lower phase. When thelower phase is almost completely removed, squeeze the flexible tube to stop
the suction and remove the Pasteur pipette. This makes it possible to remove
only the lower phase. Because these procedures require some skill andprecision, practice each procedure beforehand.

102

Sample, around 10 mg (10-ml screw-capped centrifuge tube)
Add 2 drops of ethanol.
Cover with a small amount of glass wool or cotton wool.
Slowly add 3 ml of 2N HCl.
Seal tightly and heat at 100°C for 5 min.
Allow to cool and mix.
Centrifuge at 1,200 rpm for 3 min.
Hydrochloric acid phase, 1 ml (10-ml conical centrifuge tube)
Add 2 ml of toluene and shake for 3 min.
Centrifuge at 1,200 rpm for 3 min.
Organic phase

Hydrochloric acid phase

GLC-ECD

Flow Chart 11. Determination of Methylmercury in Hair

103

References
1) Kanno, J., Akagi, H., Takabatake, E.: A method for determination of
methylmercury in environmental samples, particularly in sediment, Japanese
Journal of Toxicology and Environmental Health (Eisei kagaku), 31, 260-268(1985). (in Japanese).
2) Akagi, H.: Analysis of methylmercury in fish and shellfish by dithizone
extraction-gas chromatography, Japanese Journal of Hygiene, 40, 293 (1985).
(in Japanese).
3) Matsuo, N., Suzuki, T., Akagi, H.: Mercury concentration in organs ofcontemporary Japanese, Archives of Environmental Health, 44(3), 298-303(1989).
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J.R.D., Oliveira, R.B., Haraguchi, K., Pfeiffer, W.C., Takizawa, Y., Kato, H.:
Human exposure to mercury due to gold mining in the Tapajos river basin,
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1049) Kehrig, H.A., Malm, O., Akagi, H., Guimaraes, J.R.D., Torres, J.P.M.:
Methylmercury in fish and hair from Balbina Reservoir, Brazilian Amazon,
Environmental Research, Section A 77, 84-90 (1998).
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estimation from umbilical cord concentrations in patients with Minamata disease,
Environmental Research, Section A 77, 98-103 (1998).
11) Akagi, H., Castillio, E.S., Cortes-Maramba, N., Francisco-Rivera, A.T.,
Timbang, T.D.: Health assessment for mercury exposure among schoolchildren
residing near a gold processing and refining plant in Apokon, Tagum, Davao delNorte, Philippines, The science of the Total Environment, 259, 31-43 (2000).
12) Logar, M., Horvat, M., Akagi, H., Ando, T., Tomiyasu, T., Fajon, V.:
Determination of total mercury and monomethylmercury compounds in water
samples from Minamata Bay, Japan: An interlaboratory comparative study ofdifferent analytical techniques, Applied Organometallic Chemistry, 15, 515-526(2001).
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Contamination and Toxicology, 68, 699-704 (2002)

105