U.S. Department of the Interior

U.S. Geological Survey

Techniques and Methods 5 A–8

Methods for the Preparation and Analysis of Solids and 

Suspended Solids for Total Mercury

Chapter 8 of

Book 5, Laboratory Analysis

Section A, Water Analysis
Methods for the Preparation and 

Analysis of Solids and Suspended 

Solids for Total Mercury

By Shane D. Olund, John F. DeWild, Mark L. Olson, and Michael T. Tate

Chapter 8 of

Book 5, Laboratory Analysis 

Section A, Water Analysis

Techniques and Methods 5 A–8

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.
iii

Contents

Abstract .......................................................................................................................................................... 1

Introduction ................................................................................................................................................... 1

Part 1. Method for the Digestion, Oxidation, and Analysis of Total Mercury in Solids ..................... 2

Scope and Application ........................................................................................................................ 2

Method Summary ................................................................................................................................ 2

Sample Collection and Preservation ................................................................................................ 2

Method Detection Limit ...................................................................................................................... 2

Reagents ............................................................................................................................................... 3

Standards .............................................................................................................................................. 3

Quality-Control Sample ....................................................................................................................... 4

Sample Preparation ............................................................................................................................. 4

Sample Analysis ................................................................................................................................... 5

Data Quality Objectives ............................................................................................................. 5

Analytical Equipment ................................................................................................................. 6

Data Analysis ........................................................................................................................................ 6

Acceptance Criteria ............................................................................................................................ 7

Method Performance .......................................................................................................................... 7

Part 2. Method for the Oxidation and Analysis of Total Mercury in Suspended Solids .................... 8

Scope and Application ........................................................................................................................ 8

Method Summary ................................................................................................................................ 8

Sample Collection and Preservation ................................................................................................ 8

Method Detection Limit ...................................................................................................................... 9

Reagents ............................................................................................................................................... 9

Standards ............................................................................................................................................ 10

Quality-Control Sample ..................................................................................................................... 10

Sample Preparation ........................................................................................................................... 11

Sample Analysis ................................................................................................................................. 11

Data Quality Objectives ........................................................................................................... 11

Analytical Equipment ............................................................................................................... 11

Data Analysis ...................................................................................................................................... 12

Acceptance Criteria .......................................................................................................................... 12

Method Performance ........................................................................................................................ 13

Summary ...................................................................................................................................................... 14

References ................................................................................................................................................... 15
iv

Tables

 1. Results from multiple analyses of solids for method detection limit (MDL) 

assay .............................................................................................................................................. 3

 2. Total mercury concentrations for multiple analyses of clay substrate and 

organic substrate solids samples ............................................................................................. 7

 3. Percent recovery data for the clay substrate, organic substrate, and sand 

substrate solids samples. Each sample was spiked with 1 nanogram of mercury. ......... 8

 4. Results from multiple analyses of particulate MESS-2 CRM for detection 

limit assay ..................................................................................................................................... 9

 5. Results for the analysis of MESS-2 CRM solution .............................................................. 13

 6. Results for the analysis of IAEA-405 CRM solution ............................................................ 14
v

Conversion Factors

Multiply By To obtain

Length

centimeter (cm) 3.94 x 10-1 inch (in)

millimeter (mm) 3.94 x 10-2 inch (in)

micrometer (μm) 3.94 x 10-5 inch (in)

Mass

gram (g) 3.53 x 10-2 ounce, avoirdupois (oz)

milligram (ng) 3.53 x 10-5 ounce, avoirdupois (oz)

microgram (μg) 3.53 x 10-8 ounce, avoirdupois (oz)

nanogram (mg) 3.53 x 10-11 ounce, avoirdupois (oz)

Volume

liter (L) 2.64 x 10-1 gallon (gal)

liter (L) 3.38 x 10-1 ounce, fl uid (oz)

milliliter (mL) 2.64 x 10-4 gallon (gal)

microliter (μL) 2.64 x 10-7 gallon (gal)

Flow

milliliters per minute (mL/min) 6.10 x 10-2 cubic inch per minute (in3

/min)

Pressure

pounds per square inch (psi) 6.89 kilopascal (kPa)

Resistivity

megohm centimeter (MΩ-cm) 3.94 x 10-1 megohm inch (MΩ-in)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

 °F=(1.8×°C)+32

Concentrations for suspended solids samples are in nanograms per liter (ng/L).

Concentrations for solids samples are in nanograms per grams (ng/g).
vi

Abbreviated Water-Quality Units

g gram

mg milligram (10-3 grams)

μg micrograms (10-6 grams)

ng nanograms (10-9 grams)

L liters

mL milliliters (10-3 liters)

μL microliters (10-6 liters)

mg/L milligrams per liter (parts per million)

μg/L micrograms per liter (parts per billion)

ng/L nanograms per liter (parts per trillion)

ng/g nanograms per gram (parts per billion)

cm centimeters (10-2 meters)

mm millimeters (10-3 meters)

μm micron (10-6 meters)

mL/min milliliters per minute

MΩ-cm megohm centimeter

Mmol mega moles (106

 moles)

Abbreviations and Acronyms

Ar argon

BDL batch detection limit

BrCl bromine monochloride

CRM certified reference material

CVAFS cold vapor atomic fluorescence spectroscopy

DQO data quality objective

HCl hydrochloric acid

Hg mercury

Hg0

 gaseous mercury

HgS cinnabar

HgT total mercury

HNO3

 nitric acid

I.D. inside diameter

KBr potassium bromide

KBrO3

 potassium bromate

MDL method detection limit

N2

 nitrogen

NIST National Institute of Standards and Technology

NH2

OH*HCl hydroxylamine hydrochloride

O.D. outside diameter

psi pounds per square inch

QA quality assurance

QCS quality-control sample

QFF quartz fiber filter

SnCl2

 stannous chloride

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

WDML Wisconsin District Mercury Lab
Abstract

The methods documented in this report are utilized 

by the Wisconsin District Mercury Lab for analysis of total 

mercury in solids (soils and sediments) and suspended solids (isolated on filters). Separate procedures are required 

for the different sample types. For solids, samples are prepared by room-temperature acid digestion and oxidation 

with aqua regia. The samples are brought up to volume 

with a 5 percent bromine monochloride solution to ensure 

complete oxidation and heated at 50°C in an oven overnight. Samples are then analyzed with an automated flow 

injection system incorporating a cold vapor atomic fluorescence spectrometer. A method detection limit of 0.3 ng 

of mercury per digestion bomb was established using multiple analyses of an environmental sample. Based on the 

range of masses processed, the minimum sample reporting 

limit varies from 0.6 ng/g to 6 ng/g. Suspended solids 

samples are oxidized with a 5 percent bromine monochloride solution and held at 50°C in an oven for 5 days. The 

samples are then analyzed with an automated flow injection system incorporating a cold vapor atomic fluorescence 

spectrometer. Using a certified reference material as a 

surrogate for an environmental sample, a method detection 

limit of 0.059 ng of mercury per filter was established. The 

minimum sample reporting limit varies from 0.059 ng/L to 

1.18 ng/L, depending on the volume of water filtered.

Introduction

Since the mid-1980’s, scientists have redefined 

our understanding of the sources, cycling processes and 

pathways, and levels of mercury (Hg) in various environmental media. Much of this improved understanding 

has been facilitated through the advancement of sampling and analytical procedures that pointed to low-level 

atmospheric deposition as the key Hg source reaching all 

aquatic ecosystems across the globe. In addition, even 

though most soils, sediments, and suspended particulates 

in surface waters have been relatively enriched with Hg 

over time, concentrations are still quite low and remain a 

significant analytical challenge to quantify accurately. The 

dominant repository for the vast majority of Hg released to 

the environment over the past 100 years has been surficial soils and sediments (soils and sediments: 947 Mmol; 

atmosphere: 17 Mmol; oceans: 36 Mmol)(Mason and others, 1994). Thus, our ability to quantify and monitor these 

large pools of Hg is critical for assessing and continuing to 

improve our understanding of the global Hg problem. The 

precise chemical composition of Hg in soils, sediments, 

and suspended particulates remains difficult to quantify 

analytically, although in most instances it is inorganic, 

divalent Hg that is most likely sorbed to fine-grained, 

organic substrates (Wiener and others, 2003). Lacking species-specific methods, most researchers report total mercury (HgT) and methylmercury concentrations for solidphase environmental samples (DeWild and others, 2004). 

At sites distant from point sources, most soil and sediment 

Hg is derived from atmospheric deposition, and HgT levels 

range from about ten to several hundred nanograms per 

gram (ng/g, dry weight) (Nater and Grigal, 1992; Krabbenhoft and others, 1999). Near point sources, especially 

cinnabar (HgS) deposits or abandoned placer mines, Hg 

concentrations can be considerably higher, generally in 

the part per million range (Krabbenhoft and others, 1999; 

Biester et al. 2000; and Gustin et al. 2000). With such a 

wide range of concentrations observable in soils and sediments, several factors must be considered when attempting 

to quantify HgT in soils, sediment, and suspended particulates, including: (1) sample contamination due to improper 

sample handling or Hg-contaminated sampling devices; (2) 

natural heterogeneity of native materials; and, (3) matrix 

interferences and incomplete oxidation of samples.

This document describes the methods used by the 

U.S. Geological Survey (USGS) Wisconsin District 

Methods for the Preparation and Analysis of Solids and 

Suspended Solids for Total Mercury

Olund, S.D., DeWild, J.F., Olson, M.L., and Tate, M.T.
2 Methods for the Preparation and Analysis of Solids and Suspended Solids for Methylmercury

Mercury Laboratory (WDML) in Middleton, Wisconsin, 

to analyze solids and suspended solids samples for HgT 

concentration and to document a method detection limit 

(MDL) for these sample media using the described techniques. Because the WDML employs different procedures 

for the preparation of solids (soils and sediments) and for 

suspended solids that are collected (isolated) on filters, 

the procedures, MDL’s, and method performance are 

presented separately in this report. In addition, although 

this document will not address the need to practice “tracemetal-clean” methods during sample collection (Olson and 

DeWild, 1999), the utmost care should be taken to ensure 

reliable results when acquiring environmental samples for 

trace Hg levels.

The WDML gratefully acknowledges support for 

this study from the USGS Toxic Substances Hydrology 

Program.

Part 1. Method for the Digestion, 

Oxidation, and Analysis of Total 

Mercury in Solids

Scope and Application

This method is suitable for the determination of HgT 

in solids collected from terrestrial and aquatic environments. Samples can consist of soils or bed sediments and 

can be processed wet or freeze-dried. The minimum mass 

of Hg that is detectable is 0.3 ng per digestion bomb. The 

upper range can be extended to meet most samples by 

controlling the amount of material processed and through 

dilutions of the digestate. All samples are reported in ng/g 

dry weight.

Method Summary

An aliquot of solid material homogenized with a 

Teflon policeman is digested and oxidized in a Teflon 

digestion bomb with aqua regia at room temperature 

overnight to convert all Hg to Hg2+. The digested sample is 

then diluted to volume with 5 percent bromine monochloride (BrCl). After dilution, the sample is pre-reduced with 

hydroxylamine hydrochloride (NH2

OH*HCl) to remove 

any free halogens, then reduced with stannous chloride 

(SnCl2) to convert Hg2+ to gaseous mercury (Hg0). The Hg0

is purged, captured on a gold trap, thermally desorbed, and 

then detected using a cold vapor atomic fluorescence spectrometer (CVAFS). This method can be used to determine 

HgT concentrations in solid samples with a method detection limit of 0.3 ng in a digestion bomb.

Sample Collection and Preservation

HgT analysis is extremely sensitive to contamination; therefore, care must be taken to avoid contamination 

during sample collection and analysis. Sample collection should be conducted using clean hands/dirty hands 

protocol (Olson and DeWild, 1999). Solids samples are 

collected and placed into precleaned vials. Collection and 

analysis equipment is cleaned according to the procedures 

outlined in DeWild and others (2002). Vials can consist of 

Teflon, cleaned according to DeWild and others (2002), 

baked glass vials (prepared by heating to 550°C for 4 

hours), or acid-rinsed polycarbonate vials. Samples are 

frozen as soon as possible after collection, shipped to the 

lab on dry ice by overnight mail, and held at a temperature 

of -15°C or less until processing. The WDML has not 

performed a holding time study; however, a frozen certified reference material (CRM) certified for Hg is available 

through the National Institute of Standards and Technology (NIST) and is stable for a duration of 9 years.

Method Detection Limit

Although samples are reported in ng/g dry weight, 

the MDL represented as a mass is the most effective way 

for the WDML to evaluate detection. It is not possible to 

consistently weigh out 100 mg of solids for every sample, 

which is the target sample size the WDML uses. Because 

varying amounts of solids are processed, using an MDL 

based on mass per aliquot allows a direct comparison 

of the amount of mercury in the sample digestate to the 

consistent value of 0.3 ng. Although the target mass for 

sample processing is 100 mg, the actual mass varies from 

50 mg to 500 mg. This operational mass range yields a 

minimum sample reporting limit of 0.6 ng/g to 6 ng/g, as 

processed.

To demonstrate that the WDML can accurately quantify HgT in solid samples at environmentally important 

levels, an MDL study was performed. Even though wet 

samples were used for this study, the MDL is applicable 

to both wet and freeze-dried solid samples. The MDL 

reflects the mass of Hg in a digestion bomb, and is used 

to evaluate the mass of Hg in samples regardless of their 

condition (wet or freeze-dried) at the time of digestion. 
An MDL of 0.3 ng of HgT was determined according to 

U.S. Environmental Protection Agency (USEPA) protocol (U.S. Environmental Protection Agency, 1990) from 

multiple analyses of a solid sample that was primarily 

clay (table 1). The sample was mixed thoroughly, and ten 

aliquots were transferred into Hg clean Teflon digestion 

bombs. The target mass of 100 mg was not achieved for 

each aliquot; therefore, the mass detected per bomb was 

converted to a 100 mg equivalency. The samples were 

analyzed over ten days.

Reagents

Upon receipt at the laboratory or on the day of preparation, reagent containers should be labeled with the date 

received or made and the initials of the person preparing 

them.

A. Reagent water. Ultra-pure reagent grade water 

containing less than 0.1 ng/L Hg with a resistance 

greater than 18 MΩ-cm starting from a prepurified source (distilled, reverse osmosis, and others). 

The water is delivered through a 0.2 μm filter, as 

obtained from a Millipore Academic water-purification system or equivalent.

B. Hydrochloric acid (HCl). EM Science Omni Pure 

HCl (containing less than 5 ng/L Hg) or equivalent. 

C. Bromine monochloride. Dissolve 10.8 g of 

reagent grade potassium bromide (KBr) in a Hg 

clean Teflon or glass bottle containing 1L of 

concentrated HCl. Place a Teflon coated stir bar 

into the bottle and stir for 1 hour or until dissolved. 

Slowly add 15.2 g reagent grade potassium bromate (KBrO3

) to the bottle while stirring. CAUTION: This needs to be done slowly and in a fume 

hood because large quantities of free halogens 

are produced. Addition of KBrO3 to the solution 

should produce a color change from yellow to red 

to orange. Cap bottle loosely and stir for an additional hour. Prepare fresh monthly.

D. Nitric Acid (HNO3

). EM Science Omni Pure 

HNO3 (containing less than 5 ng/L Hg) or equivalent.

E. Stannous chloride. Add 30 g SnCl2 to 50 mL 

concentrated HCl in a dark 2.5 L glass bottle. Add 

950 mL reagent water. Purge with Hg free nitrogen 

(N2) at 30 mL/min during initial start up and during 

analysis. Prepare fresh monthly.

F. Hydroxylamine hydrochloride. Dissolve 30 g of 

NH2OH*HCl in a Teflon bottle containing 100 mL 

reagent water. Add 10 μL SnCl2 to the solution and 

purge with Hg free N2 at 300 mL/min for 1 hour. 

Prepare fresh every 6 months. 

G. Nitrogen. Grade 5.0 (ultra high purity) N2 that is 

passed through a gold bead trap attached to the 

outlet of the tank to remove any Hg. 

H. Argon (Ar). Grade 5.0 (ultra high purity) Ar that 

is passed through a gold bead trap attached to the 

outlet of the tank to remove any Hg. 

Standards

The stock and substock standards should by stored 

outside of the clean laboratory to prevent contamination of 

the entire lab. To clean a volumetric flask, fill to approximately 20 percent total volume with 50 percent HNO3

, 

place the ground glass stopper on its side over the opening 

to prevent pressure buildup, and reflux on a hotplate for 4 

hours.

A. Stock standard (1x109

 ng/L (1000 mg/L)). Commercially available Hg standard verified against an 

Part 1. Method for the Digestion, Oxidation, and Analysis of Total Mercury in Solids 3

Table 1. Results from multiple analyses of solids for method 

detection limit (MDL) assay.

[All masses in nanograms (ng) of mercury per 100 milligrams (mg) of 

solids]

Clay Substrate

1.39

1.53

1.73

1.55

1.60

1.40

1.43

1.20

1.60

1.42

Average 1.49

Standard deviation 0.1

Percent relative standard deviation 10.0

Detection limit 

(standard deviation x 2.821*) 0.3

*students T-value at the 99 percent confidence interval for n=10
4 Methods for the Preparation and Analysis of Solids and Suspended Solids for Methylmercury

NIST standard reference material. All subsequent 

standards are prepared using the stock standard. 

Before preparing other standards, ensure the 

expiration date of the stock standard has not been 

exceeded. 

B. Substock standard (1x106

 ng/L (1000 μg/L)). 

Dispense approximately 50 mL of reagent grade 

water and 5 mL of BrCl into a 100 mL Hg clean 

class A volumetric flask. Pipette 100 μL of the 

stock standard into the flask and bring to volume 

with reagent water. 

C. Working standard (1000 ng/L). Dispense approximately 500 mL of reagent grade water and 5 mL 

of BrCl into a 1.0 L Hg clean class A volumetric 

flask. Pipette 1.0 mL of the substock standard into 

the flask and bring to volume with reagent water. 

Prepare fresh every six months.

D. Analytical standards. Analytical standards range 

from 1 ng/L to 40 ng/L, and the standards should 

span the expected concentrations of the samples to 

be analyzed. Dispense approximately 500 mL of 

reagent grade water and 5 mL of BrCl into a 1.0 L 

Hg clean class A volumetric flask. Pipette a volume 

of working standard into the flask that yields the 

desired concentration of the analytical standard and 

bring to volume with reagent water. For a 1 ng/L 

analytical standard, 1.0 mL of the working standard 

would be added. The analytical standard must be 

compared to the previous analytical standard and 

agree within ± five percent. Prepare fresh every six 

months.

Quality-Control Sample

The quality-control sample (QCS) will be prepared 

from a commercially available Hg standard. The standard 

will be of a different source or lot than the standard used to 

prepare the analytical standards. The QCS is used throughout analysis to verify statistical control.

A. Quality-control stock standard (1x1010 ng/L 

(10,000 mg/L)). Prepared from NIST standard reference material 3133. All subsequent quality-control standards and samples are prepared using this 

stock standard. Before preparing other standards, 

ensure the expiration date of the stock standard has 

not been exceeded.

B. Quality-control substock standard (1x107 ng/L 

(10,000 μg/L)). Dispense approximately 50 mL of 

reagent grade water and 5 mL of BrCl into a 100 

mL Hg clean class A volumetric flask. Pipette 100 

μL of the quality-control stock standard into the 

flask and bring to volume with reagent water. 

C. Quality-control working standard (1000 ng/L). 

Dispense approximately 500 mL of reagent grade 

water and 5 mL of BrCl into a 1.0 L Hg clean class 

A volumetric flask. Pipette 100 μL of the qualitycontrol substock standard into the flask and bring 

to volume with reagent water. Prepare fresh every 

six months.

D. Quality-control samples. Concentrations for QCS 

should represent the concentrations of the environmental samples being analyzed. A 5 ng/L, 10 ng/L 

and 30 ng/L QCS are used to represent the range of 

samples encountered. The 5 ng/L and 10 ng/L QCS 

would be used for lower concentrations, and the 10 

ng/L and 30 ng/L QCS would be used for higher 

concentratoins. Dispense approximately 500 mL of 

reagent grade water and 5 mL BrCl into a 1.0 L Hg 

clean class A volumetric flask. Pipette the appropriate amount of quality-control working standard 

into the flask to yield the desired QCS concentration and dilute to volume with reagent water. For 

a 5 ng/L QCS, add 5 mL of the quality-control 

working standard. The new QCS must be verified 

against the previous QCS and agree within ± five 

percent. A new QCS should be made fresh every 

six months.

Sample Preparation

Prior to analysis, solids samples are digested and 

oxidized to ensure complete conversion of Hg to Hg2+. 

Any number of samples may be prepared in a digestion 

batch. For every 10 environmental samples, there will be a 

method blank, a CRM sample, and one of the 10 environmental samples will be prepared in triplicate. A minimum 

of three method blanks must be created for a digestion 

batch. A method blank is an empty Teflon digestion bomb 

that has all the reagents added and is carried through all 

the steps that a sample would undergo.

Solids samples are completely thawed, then thoroughly homogenized using a Teflon policeman. A small 

aliquot, approximately 100 mg, is transferred to a Teflon 

digestion bomb using the policeman. The exact mass 
transferred is recorded to the nearest tenth of a mg, as 

well as the bomb ID. When all the solids are transferred 

to the digestion bombs, 6 mL of HCl and 2 mL of HNO3

are added. This combination of HCl and HNO3, in a 3:1 

ratio, creates aqua regia, a strong oxidizing solution. The 

bombs are loosely capped and placed in a fume hood for 

one hour. After the hour has expired, the bombs are then 

wrench-tightened, and allowed to react overnight at room 

temperature. After 24 hours, the bombs are diluted with 22 

mL of 5 percent BrCl to a total volume of 30 mL. When 

the samples have been diluted, they are wrench-tightened 

and placed in an oven at 50°C overnight, after which time 

they are ready for analysis.

Sample Analysis

After the digestion bombs are removed from the oven, 

the digestate is thoroughly mixed, an aliquot is transferred 

to a 60-mL Teflon vial containing 50 μL NH2

OH*HCl, and 

diluted to 50 mL. These diluted samples are then analyzed 

according to USEPA Method 1631, Revision E (U.S. Environmental Protection Agency, 2002) utilizing an automated 

flow injection system. An analytical batch consists of 12 

vials bracketed by the appropriate high level and low level 

QCS. Eleven vials contain samples, and the twelfth vial 

is a matrix spike of an environmental sample contained in 

one of the previous 11 vials. All samples are analyzed in 

duplicate from their respective vials and must fall within 

the calibration range. If they do not, they must be diluted 

further in a fresh 60-mL Teflon vial. A sample can consist 

of a method blank, a CRM, or an environmental sample. 

Data Quality Objectives

Data Quality Objectives (DQOs) have been established to evaluate statistical control over the analytical 

system during the analysis.

A. Correlation coefficient. The correlation coefficient of the standard curve using a simple linear 

regression forcing zero must be 0.995 or greater. If 

the standard curve does not meet the objective, the 

system is deemed out of control, and sample analysis cannot proceed. The issue must be resolved, and 

an acceptable standard curve needs to be generated 

before analyzing samples.

B. Quality-control samples. The analytically determined QCS concentrations must have a percent 

recovery of 90 to 110 percent when compared to 

the actual concentration. If either QCS fails to meet 

criteria, the samples that were bracketed must be 

reanalyzed until they are bracketed by acceptable 

QCS or until volume is exhausted. If no sample 

volume remains and either bracketing QCS does 

not meet the DQO, then the environmental samples 

in that batch must be prepared again if the remaining sample mass is sufficient. If the sample cannot 

be prepared again, the samples are flagged with a 

quality assurance (QA) flag, indicating failure of 

QCS during analysis.

RQCS = (CA/CT) * 100, (1)

where

RQCS = percent recovery for the QCS

CA = Analytically determined concentration of the 

QCS, in ng/L

CT = Theoretical concentration of the QCS, in ng/L

C. Duplicate analysis. The percent difference 

between duplicate analyses taken from the same 

vial for a sample must be less than 10 percent. If 

the percent difference for the sample is greater than 

10 percent, the sample must be rerun if volume 

permits. If the sample cannot be analyzed again, 

that specific sample must be prepared again if the 

remaining sample mass is sufficient. If the sample 

cannot be prepared again, the sample is flagged 

with a QA flag indicating a percent difference 

failure.

% Diff = |C1

 – C2|/CAVE * 100, (2)

where

% Diff = Percent difference for duplicate analysis

C1

 = Concentration of digestate for first sample 

analysis, in ng/L

C2

 = Concentration of digestate for second sample 

analysis, in ng/L

CAVE = Average concentration of both analyses, 

in ng/L

D. Matrix spikes. One sample in the analytical batch 

is spiked with a known amount of Hg. The percent 

recovery of the spike must be 90 to 110 percent. 

If the matrix spike does not meet criteria, another 

matrix spike is run on that sample, volume permitting, as well as another sample. If the new matrix 

spikes do not meet criteria, the batch is flagged 

with a QA flag indicating a potential matrix interference problem with the samples. 

Part 1. Method for the Digestion, Oxidation, and Analysis of Total Mercury in Solids 5
6 Methods for the Preparation and Analysis of Solids and Suspended Solids for Methylmercury

RSP = (CSP – CUN)/(SM /V) * 100, (3)

where

RSP = Percent recovery for matrix spike

CSP = Concentration of the spiked sample, in ng/L

CUN = Concentration of the unspiked sample, in 

ng/L

SM = Mass of the spike, in ng

V = Total volume in autosampler vial, in L

Analytical Equipment

A. Regulator capable of supplying 30 pounds per 

square inch (psi) of pressure.

B. Detector. The detector is a commercially available 

Model 2600 CVAFS mercury detector from Tekran 

(Toronto, ON) equipped with a mass flow controller capable of measuring 30 mL/min and an auxiliary flow meter capable of measuring 300 mL/min.

C. Autosampler. The Model 2630 automatic sample 

changer from Tekran holds four racks of 12 60-mL 

autosampler vials and contains a rinse station.

D. Peristaltic pump. The Model 2610 peristaltic 

pump from Tekran flushes the rinse station and 

pumps sample, reagents, and rinse water to the 

gas/liquid separator. The pump also removes waste 

from the gas/liquid separator and overflow from the 

rinse station.

E. Gold-coated glass bead trap. The gold-coated 

glass bead trap is constructed of a 7-mm outside 

diameter (O.D.) quartz tube, 10 cm long and with 

a constriction 3 cm from the outlet end. A plug of 

quartz wool is placed into the inlet end, about 0.7 

g (filling about 3.5 cm in the tube) of gold-coated 

glass beads are added, and the inlet end is plugged 

with another piece of quartz wool. After the traps 

are packed, another constriction is added at the 

inlet end. Female fittings for gold traps are made 

from small pieces of 6-mm inside diameter (I.D.) 

monobarb Teflon tubing. 

F. Soda lime trap. The soda lime trap is supplied 

with the Tekran Model 2600 CVAFS mercury 

detector. The trap is filled with 4-8 mesh soda 

lime. The soda lime trap captures moisture and free 

halogens that are generated by purging the sample. 

The soda lime trap removes these constituents 

before they can reach the gold trap. Moisture will 

create interferences with the Hg detector and free 

halogens will destroy the gold trap.

G. Rinse water reservoir. 5-L Teflon carboy filled 

with reagent water and acidified to 1 percent with 

HCl. 

H. Stannous chloride reservoir. SnCl2

 solution is 

placed into a dark 2.5-L glass bottle and slowly 

purged with N2 throughout the analysis.

Data Analysis

 The following formulas are used to calculate concentrations.

CONCENTRATION OF DIGESTATE

Cng/L = (PA/S) * D, (4)

where

Cng/L = concentration of digestate, in ng/L

PA = peak area

S = slope of calibration line

D = dilution factor (50/sample aliquot volume in mL)

MASS OF Hg IN METHOD BLANK

MBB = Cng/L * VB, (5)

where

MBB = mass of Hg in method blank, in ng

Cng/L = concentration of digestate, in ng/L, 

 as determined in Equation 4

VB = volume of digestate originally in bomb, in L

MASS OF Hg IN BOMB FROM SAMPLE

MS = (Cng/L * VB) – MBB – AVE, (6)

where

MS = mass of Hg in sample bomb, in ng

Cng/L = concentration of digestate, in ng/L, 

 as determined in Equation 4

VB = volume of digestate originally in bomb, in L

MBB – AVE = average mass in all method blanks 

 for digestion batch
 ng/g CONCENTRATION OF SOLIDS SAMPLE

Cng/g = MS / WS, (7)

where

Cng/g = concentration of sample, in ng/g

MS = mass of Hg in sample bomb, in ng

WS = mass of solids in bomb, in g

Acceptance Criteria

Included with the digestion batch of environmental 

samples are method blanks, replicate analyses, and CRM 

samples. Each of these samples provides quality-control 

information used to evaluate the acceptability of the analytical runs. Typically, multiple analytical runs are necessary to analyze the entire digestion batch.

A. Method blanks. Method blanks are included in 

each digestion batch, with a minimum of 3 blanks 

per day of sample preparation. The method blanks 

are used to evaluate gross contamination and to 

correct for background Hg from reagents during 

digestion, oxidation, and analysis. Values obtained 

from these blanks are used to calculate a batch 

detection limit (BDL) for the digestion batch. The 

DQO for BDL is 0.3 ng.

BDL = 3 * σ, (8)

where

BDL = Batch detection limit

σ = Standard deviation of the method blanks for 

the digestion batch, in ng

B. Replicate analyses. One sample from each batch 

is prepared in triplicate to evaluate the precision of 

the method. DQOs for replicate analyses are a relative standard deviation of no more than 25 percent.

C. Certified reference material. There are CRM 

samples included in each batch that are used to 

evaluate the accuracy of the analytical run. DQOs 

for CRMs are 80 to 120 percent recovery.

Method Performance

To evaluate method performance, three separate 

solids samples were analyzed over 10 days, representing 

different types of materials. One was a predominately clay 

substrate, the second was an organic rich substrate, and the 

third was a sandy, mineral substrate. Each sample was set 

up in 20 separate bombs, with half of those having a 

1 ng Hg spike added to them to evaluate the digestion and 

oxidation processes.

Precision was evaluated by examining the percent 

relative standard deviation of the concentrations obtained 

from all analyses of the solid samples for each type of 

material. The percent relative standard deviation for the 

clay substrate was 10.0 and the organic rich substrate was 

12.8 (table 2). The sand substrate was not used to evaluate 

precision because the concentration of the samples was 

less than the MDL. Percent relative standard deviation was 

calculated using the formula:

PERCENT RELATIVE STANDARD DEVIATION

% RSD = (CSTDEV /CAVE) * 100 (9)

where

% RSD = percent relative standard deviation

CSTDEV = standard deviation of all samples

CAVE = average concentration of all samples

Accuracy was evaluated by calculating the percent 

recovery for the matrix spikes versus the unspiked samples. All three substrates were used to evaluate accuracy 

because a known amount of Hg was added to the digestion bomb and a recovery could be based on that addition. 

Percent recoveries were calculated using the formula:

Part 1. Method for the Digestion, Oxidation, and Analysis of Total Mercury in Solids 7

Table 2. Total mercury concentrations for multiple analyses 

of clay substrate and organic substrate solids samples

[All concentrations in nanograms per gram (ng/g) wet weight]

Clay 

Substrate

Organic 

Substrate

13.9 12.6

15.3 10.1

17.3 12.5

15.5 13.0

16.0 11.4

14.0 11.4

14.3 11.9

12.0 11.9

16.0 16.0

14.2 11.3

Average 14.9 12.2

Standard deviation 1.5 1.6

Percent relative standard 

deviation 10.0 12.8
8 Methods for the Preparation and Analysis of Solids and Suspended Solids for Methylmercury

PERCENT RECOVERY

R = ((MS – (CA * WS))/SM) * 100, (10)

where

R = percent recovery

MS = analytically determined mercury mass in aliquot

CA = average concentration of unspiked sample

WS = mass of sample aliquot

SM = mass of spike added

Recoveries ranged from 75 to 176 percent with an 

average of 113 and a standard deviation of 31 for the 

clay substrate sample (table 3). For the organic substrate 

sample, only four samples could be evaluated for accuracy 

due to operational problems encountered. The identification codes were in question for six of the bombs; therefore, 

the mass of the sample aliquots were uncertain for those 

samples, and spike recoveries could not be positively 

calculated. Based on the four samples that were not in 

question, recoveries ranged from 77 to 90 percent with an 

average of 85 and a standard deviation of 6. The percent 

recoveries for the sand substrate ranged from 89 to 104 

percent, with an average of 97 and a standard deviation 

of 5.

Part 2. Method for the Oxidation 

and Analysis of Total Mercury in 

Suspended Solids

Scope and Application

This method is suitable for the determination of HgT 

in suspended solids isolated onto pre-baked quartz fiber filters (QFF). The minimum sample mass detectable is 0.059 

ng and the range can be extended to meet most samples by 

controlling the amount of water filtered through the QFF 

and through dilutions of the oxidized sample. All samples 

are reported in ng/L.

Method Summary

Particulate samples collected onto baked quartz fiber 

filters are oxidized with BrCl to convert all forms of Hg 

to Hg2+. After oxidation, the sample is pre-reduced with 

NH2OH*HCl to remove the free halogens, then reduced 

with SnCl2 to convert Hg2+ to Hg0. The Hg0 is purged, captured on a gold trap, then thermally desorbed and detected 

using a CVAFS. This method can be used to determine 

HgT concentrations in particulate samples with a MDL of 

0.059 ng of Hg on a filter. The amount of Hg on a filter is 

dependent on the solids load in the sample and volume of 

sample filtered.

Sample Collection and Preservation

To provide reliable concentrations for HgT in suspended solids, the WDML has developed a method to 

concentrate suspended solids from unfiltered water by 

either in-line filtration or by vacuum filtration. In either 

case, samples should be collected using clean hands/dirty 

hands sampling protocols (Olson and DeWild, 1999) to 

ensure sample integrity. Sample size is dependent on suspended particulate load and HgT concentration, but generally ranges from 0.5 to 1 liter. The suspended solids are 

retained on baked (prepared by heating to 550°C for four 

hours) QFF. To provide HgT concentrations for suspended 

solid samples in mass per unit volume (for example, 

ng/L), field crews must measure and record the volume of 

water filtered. Individual filters are placed into stackable 

Teflon petri dishes, double bagged in sealable plastic bags, 

and frozen. Samples are shipped to the lab on dry ice by 

overnight mail, and held frozen at a temperature of -15°C 

or less until processing. The WDML has not performed a 

Table 3. Percent recovery data for the clay substrate, 

organic substrate, and sand substrate solids samples. Each 

sample was spiked with 1 nanogram of mercury.

Percent 

Recovery 

Clay 

Substrate

Percent 

Recovery 

Organic 

Substrate

Percent 

Recovery 

Sand 

Substrate

118 99

91 93

132 97

144 98

79 89

176 104

102 88 95

99 77 92

111 84 98

75 90 101

Average 113 85 97

Standard deviation 31 6 5
holding time study; however, a frozen CRM certified for 

Hg is available through NIST and is stable for a duration 

of 9 years.

Method Detection Limit

Samples are reported in ng/L. The ng/L concentration can be converted to ng/g if the mass of particles per 

volume of water is also determined. The ng/L concentration can also be combined with the ng/L concentration 

of the corresponding filtered water sample to obtain an 

estimate of the whole water Hg concentration. In hydrologic systems that are low in suspended solids, the filtered 

and whole water Hg concentrations can be indistinguishable within the limits of detection. The ability to separate 

and concentrate the suspended solids increases the ability 

to accurately evaluate the difference between the filtered 

and whole waters. 

Suspended particulate loads vary considerably within 

hydrologic settings; therefore, varying amounts of sample 

water need to be filtered to obtain an appropriate amount 

of material for analysis. Using an MDL based on mass per 

filter allows a direct comparison of the amount of mercury 

in the oxidized sample solution to the consistent value of 

0.059 ng rather than a constantly changing MDL expressed 

in ng/L based on the volume of sample water filtered. The 

volume of water filtered varies from 0.050 L to 1.0 L, and 

this range provides a minimum sample reporting limit 

varying from 0.059 ng/L to 1.18 ng/L. 

To demonstrate that the WDML can accurately quantify HgT in particulate samples at or below environmentally important levels, an MDL study was performed. An 

MDL of 0.059 ng of HgT per filter was determined from 

multiple analyses of a CRM that was suspended in reagent 

water and filtered onto 10 separate QFFs (table 4). A mass 

of 0.0502 g of the CRM (MESS-2 marine sediment) was 

added to 2.0 L of reagent water. A subsample of the slurry 

was poured into a Hg clean Teflon bottle after thorough 

mixing. The remaining slurry was then mixed and filtered 

onto baked QFFs that were frozen until oxidation. Some 

of the filtrate was also collected into a clean Teflon bottle. 

The samples were analyzed over five days. The unfiltered 

and filtered water samples were analyzed during a single 

analysis run. For this study, the target volume per filter was 

100.0 mL. This volume was not accurately achieved for 

each filter; therefore, the analytically determined mass per 

filter was converted to a 100.0 mL equivalency to accurately determine a mass-based MDL. 

Reagents

Upon receipt at the laboratory or on the day of preparation, reagent containers should be labeled with the date 

received or made and the initials of the person preparing 

them.

A. Reagent water. Ultra-pure reagent grade water 

containing less than 0.1 ng/L Hg with a resistance 

greater than 18 MΩ-cm starting from a prepurified source (distilled, reverse osmosis, and others). 

The water is delivered through a 0.2 μm filter, as 

obtained from a Millipore Academic water-purification system or equivalent.

B. Hydrochloric acid. EM Science Omni Pure HCl 

(containing less than 5 ng/L Hg) or equivalent. 

C. Bromine monochloride. Dissolve 10.8 g of 

reagent grade KBr in a Hg clean Teflon or glass 

bottle containing 1L of concentrated HCl. Place a 

Teflon coated stir bar into the bottle and stir for one 

hour or until dissolved. Slowly add 15.2 g reagent 

grade KBrO3

 to the bottle while stirring. CAUTION: This needs to be done slowly and in a fume 

hood because large quantities of free halogens 

are produced. Addition of KBrO3

 to the solution 

Part 2. Method for the Oxidation and Analysis of HgT in Suspended Solids 9

Table 4. Results from multiple analyses of particulate 

MESS-2 CRM for detection limit assay

[all masses in ng per 100.0 mL of slurry]

Particulate CRM

0.201

.208

.177

.184

.164

.152

.141

.169

.176

.187

Average .176

Standard deviation .021

Percent relative standard deviation 11.9

Detection limit

(standard deviation x 2.821*) .059

*students T-value at the 99 percent confidence interval for n=10
10 Methods for the Preparation and Analysis of Solids and Suspended Solids for Methylmercury

should produce a color change from yellow to red 

to orange. Cap bottle loosely and stir for an additional hour. Prepare fresh monthly.

D. Stannous chloride. Add 30 g SnCl2

 to 50 mL 

concentrated HCl in a dark 2.5 L glass bottle. Add 

950 mL reagent water. Purge with Hg free N2 at 30 

mL/min during initial start up and during analysis. 

Prepare fresh monthly.

E. Hydroxylamine hydrochloride. Dissolve 30 g of 

NH2OH*HCl in a Teflon bottle containing 100 mL 

reagent water. Add 10 μL SnCl2 to the solution and 

purge with Hg free N2 at 300 mL/min for 1 hour. 

Prepare fresh every six months. 

F. Nitrogen. Grade 5.0 (ultra high purity) N2 that is 

passed through a gold bead trap attached to the 

outlet of the tank to remove any Hg. 

G. Argon. Grade 5.0 (ultra high purity) Ar that is 

passed through a gold bead trap attached to the 

outlet of the tank to remove any Hg. 

Standards

The stock and substock standards should be stored 

outside of the clean laboratory to prevent contamination of 

the entire lab. To clean a volumetric flask, fill to approximately 20 percent total volume with 50 percent HNO3, 

place the ground glass stopper on its side over the opening 

to prevent pressure buildup, and reflux on a hotplate for 

4 hours.

A. Stock standard (1x109

 ng/L (1000 mg/L)). Commercially available Hg standard verified against a 

NIST standard reference material. All subsequent 

standards are prepared using the stock standard. 

Before preparing other standards, ensure the 

expiration date of the stock standard has not been 

exceeded. 

B. Substock standard (1x106

 ng/L (1000 μg/L)). 

Dispense approximately 50 mL of reagent grade 

water and 5 mL of BrCl into a 100 mL Hg clean 

class A volumetric flask. Pipette 100 μL of the 

stock standard into the flask and bring to volume 

with reagent water.

C. Working standard (1000 ng/L). Dispense approximately 500 mL of reagent grade water and 5 mL 

of BrCl into a 1.0 L Hg clean class A volumetric 

flask. Pipette 1.0 mL of the substock standard into 

the flask and bring to volume with reagent water. 

Prepare fresh every six months.

D. Analytical standards. Analytical standards range 

from 1 ng/L to 40 ng/L, and the standards should 

span the expected concentrations of the samples to 

be analyzed. Dispense approximately 500 mL of 

reagent grade water and 5 mL of BrCl into a 1.0 L 

Hg clean class A volumetric flask. Pipette a volume 

of working standard into the flask that yields the 

desired concentration of the analytical standard and 

bring to volume with reagent water. For a 1 ng/L 

analytical standard, 1.0 mL of the working standard 

would be added. The analytical standard must be 

compared to the previous analytical standard and 

agree within ± five percent. Prepare fresh every six 

months.

Quality-Control Sample

The QCS will be prepared from a commercially 

available Hg standard. The standard will be of a different 

source or lot than the standard used to prepare the analytical standards. The QCS is used throughout analysis to 

verify statistical control.

A. Quality-control stock standard (1x1010 ng/L 

(10,000 mg/L)). Prepared from NIST standard reference material 3133. All subsequent quality-control standards and samples are prepared using this 

stock standard. Before preparing other standards, 

ensure the expiration date of the stock standard has 

not been exceeded.

B. Quality-control substock standard (1x107

 ng/L 

(10,000 μg/L)). Dispense approximately 50 mL of 

reagent grade water and 5 mL of BrCl into a 100 

mL Hg clean class A volumetric flask. Pipette 100 

μL of the quality-control stock standard into the 

flask and bring to volume with reagent water. 

C. Quality-control working standard (1000 ng/L). 

Dispense approximately 500 mL of reagent grade 

water and 5 mL of BrCl into a 1.0 L Hg clean class 

A volumetric flask. Pipette 100 μL of the qualitycontrol substock standard into the flask and bring 

to volume with reagent water. Prepare fresh every 

six months.
D. Quality-control samples. Concentrations for QCS 

should represent the concentrations of the environmental samples being analyzed. A 5 ng/L, 10 ng/L, 

and 30 ng/L QCS are used to represent the range of 

samples encountered. The 5 ng/L and 10 ng/L QCS 

would be used for lower concentrations, and the 

10 ng/L and 30 ng/L QCS would be used for higher 

concentrations. Dispense approximately 500 mL of 

reagent grade water and 5 mL BrCl into a 1.0 L Hg 

clean class A volumetric flask. Pipette the appropriate amount of quality-control working standard 

into the flask to yield the desired QCS concentration and dilute to volume with reagent water. For 

a 5 ng/L QCS, add 5 mL of the quality-control 

working standard. The new QCS must be verified 

against the previous QCS and agree within ± five 

percent. A new QCS should be made fresh every 

six months.

Sample Preparation

Filters to be analyzed for HgT are thawed and placed 

into a 125-mL wide-mouth Hg clean Teflon bottles using 

a Teflon forceps. The Teflon petri dishes are rinsed three 

times with 5 percent BrCl into the sample bottle then the 

volume is brought up to 100.0 mL with the same 5 percent 

BrCl that was used for rinsing the petri dishes. The petri 

dish ID’s are recorded and matched to the sample bottle ID 

that will now be used to track the sample through analysis. A method blank and a CRM are included with every 

ten samples, and a minimum of three blanks are included 

in each preparation batch. The preparation batch is all 

the samples that were prepared that day. A method blank 

includes a baked QFF and 100.0 mL of the 5 percent BrCl. 

A CRM is prepared by adding a measured mass of CRM to 

a 125 mL wide mouth Hg clean Teflon bottle and adding 

100.0 mL of the 5 percent BrCl. The samples are capped 

tightly, double bagged and placed into an oven at 50°C for 

five days.

Sample Analysis

After oxidation, the samples are cooled, mixed, 

and 50 mL of sample is poured into a 60-mL Teflon 

vial containing 50 μL of NH2

OH*HCl. The samples are 

analyzed according to USEPA Method 1631, Revision E 

(U.S. Environmental Protection Agency, 2002) utilizing 

an automated flow injection system. An analytical batch 

consists of 12 samples and is bracketed by the appropriate 

high level and low level QCS. All samples must fall within 

the calibration range. If they do not, they must be diluted 

appropriately. A sample can consist of a method blank, a 

CRM, or an environmental sample. 

Data Quality Objectives

DQOs have been established to evaluate statistical 

control over the analytical system during the analysis.

A. Correlation coefficient. The correlation coefficient of the standard curve using a simple linear 

regression forcing zero must be 0.995 or greater. If 

the standard curve does not meet the objective, the 

system is deemed out of control, and sample analysis cannot proceed. The issue must be resolved, and 

an acceptable standard curve needs to be generated 

before analyzing samples.

B. Quality-control samples. The analytically determined QCS concentrations must have a percent 

recovery of 90 to 110 percent as compared to the 

actual concentration. If either QCS fails to meet 

criteria, the samples that were bracketed must be 

reanalyzed until they are bracketed by acceptable 

QCS or until volume is exhausted. If no sample 

volume remains and either bracketing QCS does 

not meet the DQO, then the batch must be flagged 

with a QA flag indicating QCS failure.

RQCS = (CA/CT) * 100, (11)

where

RQCS = percent recovery for the QCS

CA = Analytically determined concentration of the 

QCS, in ng/L

CT = Theoretical concentration of the QCS, in ng/L

Analytical Equipment

A. Regulator capable of supplying 30 psi of pressure.

B. Detector. The detector is a commercially available 

Model 2600 CVAFS mercury detector from Tekran 

equipped with a mass flow controller capable of 

measuring 30 mL/min and an auxiliary flow meter 

capable of measuring 300 mL/min.

C. Autosampler. The Model 2630 automatic sample 

changer from Tekran holds 4 racks of 12 60-mL 

autosampler vials and contains a rinse station.

Part 2. Method for the Oxidation and Analysis of HgT in Suspended Solids 11
12 Methods for the Preparation and Analysis of Solids and Suspended Solids for Methylmercury

D. Peristaltic pump. The Model 2610 peristaltic 

pump from Tekran flushes the rinse station and 

pumps sample, reagents, and rinse water to the 

gas/liquid separator. The pump also removes waste 

from the gas/liquid separator and overflow from the 

rinse station.

E. Gold-coated glass bead trap. The gold-coated 

glass bead trap is constructed of a 7-mm O.D. 

quartz tube, 10 cm long and with a constriction 3 

cm from the outlet end. A plug of quartz wool is 

placed into the inlet end, about 0.7 g (filling about 

3.5 cm in the tube) of gold-coated glass beads are 

added, and the inlet end is plugged with another 

piece of quartz wool. After the traps are packed, 

another constriction is added at the inlet end. 

Female fittings for gold traps are made from small 

pieces of 6-mm I.D. monobarb Teflon tubing. 

F. Soda lime trap. The soda lime trap is supplied 

with the Tekran Model 2600 CVAFS mercury 

detector. The trap is filled with 4-8 mesh soda 

lime. The soda lime trap captures moisture and free 

halogens that are generated by purging the sample. 

The soda lime trap removes these constituents 

before they can reach the gold trap. Moisture will 

create interferences with the Hg detector and free 

halogens will destroy the gold trap.

G. Rinse water reservoir. 5-L Teflon carboy filled 

with reagent water and acidified to 1 percent with 

HCl. 

H. Stannous chloride reservoir. SnCl2

 solution is 

placed into a dark 2.5-L glass bottle and slowly 

purged with N2 throughout the analysis.

Data Analysis

The following formulas are used to determine the 

amount of Hg in ng/L from the original sample. 

 CONCENTRATION OF OXIDIZED SOLUTION

COx = PA/S, (12)

where

COx = concentration of oxidized solution, in ng/L

PA = peak area

S = slope of calibration line

MASS OF Hg IN METHOD BLANK

MFB = COx * VB, (13)

where

MF B = mass of Hg in method blank, in ng

COx = concentration of oxidized solution, in ng/L, as 

determined in Equation 11

VB = volume of sample originally in bottle, in L

MASS OF Hg ON FILTER

MF = (COx * VB) – MFB –AVE, (14)

where

MF = mass of Hg on filter, in ng

COx = concentration of oxidized solution, in ng/L, 

 as determined in Equation 11

VB = volume of sample originally in bottle, in L

MFB–AVE = average mass of Hg in all method blanks, 

 in ng

ng/L CONCENTRATION OF SUSPENDED SOLIDS 

SAMPLE

CP = MF /VF, (15)

where

CP = concentration of sample, in ng/L

MF = mass of Hg on filter, in ng

VF = volume of water that passed through filter, in L

Acceptance Criteria

Included with the preparation batch of environmental 

samples are method blanks and CRM samples. Each of 

these samples provides quality-control information used to 

evaluate the acceptability of the analytical runs. Typically, 

multiple analytical runs are necessary to analyze the entire 

preparation batch.

A. Method blanks. A method blank is included in 

every 10 samples, with a minimum of three blanks 

per preparation batch. These method blanks are 

used to evaluate gross contamination and to correct 

for background levels of Hg due to the reagents 

used during the oxidation and analytical steps. Values obtained from these blanks are used to calculate a BDL for the preparation batch. The DQO for 

BDL is 0.059 ng.
BDL = 3 * σ, (16)

where

BDL = Batch detection limit

σ = Standard deviation of the method blanks for 

the preparation batch, in ng

B. Certified Reference Material. A CRM is included 

with every 10 samples. The CRMs are used to 

evaluate the efficiency of the oxidation and the 

accuracy of the analytical run. DQOs for CRMs are 

80 to 120 percent recovery.

Method Performance

To evaluate method performance, two artificial 

water samples were created by adding different CRMs, 

0.20814 g IAEA-405 polluted marine sediment and 

0.0502 g MESS-2 marine sediment, to 2.0 L reagent water. 

IAEA-405 (certified concentration of 810 ng/g) represents environmental samples at higher concentrations, and 

MESS-2 (certified concentration of 92 ng/g) represents 

environmental samples at lower concentrations. Each of 

these artificial waters was filtered onto baked QFF filters 

to mimic environmental sample processing. Aliquots of the 

unfiltered samples were collected and analyzed to determine the beginning concentration of the solutions. Filtrate 

was also collected during sample processing and analyzed 

to determine how much mercury from the CRM dissolved 

in the reagent water.

Precision was evaluated by examining the percent 

relative standard deviation of the concentrations obtained 

from all analyses of the particulate filters for each concentration range. The percent relative standard deviation 

for the MESS-2 was 11.9 and for the IAEA-405 was 5.6 

(tables 5 and 6). Percent relative standard deviations were 

calculated using the formula:

PERCENT RELATIVE STANDARD DEVIATION

% RSD = (CSTDEV /CAVE) * 100, (17)

where

% RSD = percent relative standard deviation

CSTDEV = standard deviation of all samples

CAVE = average concentration of all samples

Accuracy was evaluated by calculating the theoretical and actual percent recovery of the CRM from each 

filter. The actual percent recovery utilized the analytically 

determined concentration for the unfiltered slurry, and 

the theoretical percent recovery used the mathematically 

derived concentration for the slurry based on the mass of 

the CRM added, the volume of water the CRM was added 

to, and the certified value for the CRM. Actual percent 

recoveries were calculated using the formula:

ACTUAL PERCENT RECOVERY

R = (CP /(CUa – CF)) * 100, (18)

where

R = percent recovery

CP = analytically determined concentration of 

 particulate sample

CUa = analytically determined concentration of 

 unfiltered slurry

CF = analytically determined concentration of filtrate

Theoretical percent recoveries were calculated using 

the formula:

THEORETICAL PERCENT RECOVERY

R = (CP /(CUt – CF)) * 100, (19)

where

R = percent recovery

CP = analytically determined concentration of 

 particulate sample

CUt = theoretical concentration of unfiltered slurry

CF = analytically determined concentration of filtrate

Table 5. Results for the analysis of MESS-2 CRM solution 

Particulate 

Hg

(ng/L)

Actual 

Percent 

Recovery

Theoretical

Percent 

Recovery

2.01 149 114

2.08 155 118

1.77 132 101

1.84 137 105

1.64 122 93

1.52 113 87

1.41 104 80

1.69 126 96

1.76 131 100

1.87 139 106

Average 1.76 131 100

Standard deviation 0.21 15 12

Percent relative 

standard deviation 11.9

Part 2. Method for the Oxidation and Analysis of HgT in Suspended Solids 13
14 Methods for the Preparation and Analysis of Solids and Suspended Solids for Methylmercury

For the MESS-2 solution, the analytically determined 

concentration of the unfiltered slurry was 1.89 ng/L, 

the theoretical concentration of the unfiltered slurry was 

2.30 ng/L, and the analytically determined filtrate concentration was 0.54 ng/L. Actual recoveries ranged from 

104 to 155 percent, with an average of 131 and a standard 

deviation of 15 (table 5). The theoretical recoveries ranged 

from 80 to 118 percent, with an average of 101 and a 

standard deviation of 11. For the IAEA-405 solution, the 

analytically determined concentration of the unfiltered 

slurry was 78.0 ng/L, the theoretical concentration of the 

unfiltered slurry was 84.3 ng/L and the analytically determined concentration of the filtrate was 3.58 ng/L. Actual 

recoveries ranged from 94 to 111 percent, with an average 

of 104 and a standard deviation of 6 (table 6). Theoretical 

recoveries ranged from 87 to 103 percent, with an average 

of 96 and a standard deviation of 5.

Summary

This document describes the methods used by the 

Wisconsin District Mercury Lab to analyze solids and 

suspended solids for total mercury concentration. Because 

the procedures used to process and analyze solids and suspended solids differ, two distinct analytical performance 

studies were conducted and the results are presented. 

The method detection limit established for the solids 

procedure as outlined in this report is 0.3 ng total mercury 

in a digestion bomb, which was acceptable because it is 

substantially below the levels commonly encountered in 

natural samples from a wide range of environments. The 

mass of sample digested varies, which gives a minimum 

sample reporting limit ranging from 0.6 ng/g to 6 ng/g. 

The method precision, calculated as the percent relative 

standard deviation, ranged from 10.0 to 12.8 percent. The 

accuracy of the procedure, which was determined from 

recovery tests for spiked samples, ranged from 85 to 113 

percent and was acceptable. 

The second method documented in this report is for 

sample preparation and analysis of suspended solids on 

baked quartz fiber filter. Two artificial raw water samples 

were created by suspending two different certified reference materials (IAEA-405 and MESS-2) in reagent water 

and filtering them to create suspended solids samples. 

The method detection limit was established by analyses 

of multiple filters of the MESS-2, and a limit of 0.059 ng 

was achieved. Based on the range of water filtered, the 

minimum sample reporting limit varies from 0.059 ng/L to 

1.18 ng/L. Precision was evaluated by calculating percent 

relative standard deviation from analyses of replicate filters. Percent relative standard deviations were 5.6 and 11.9 

for the IAEA-405 and MESS-2 certified reference materials, respectively. Accuracy was evaluated from percent 

recovery of total mercury on the filters from their target 

value. Target values were determined by subtracting the 

analytically determined concentration of the filtrate from 

the theoretical raw water sample concentration as well as 

the analytically determined raw water sample concentrations. Recoveries ranged from 94 to 155 percent, with an 

overall mean and standard deviation of 118 percent and 

18, respectively, for the analytically determined concentrations. For the theoretical concentrations, the recoveries 

ranged from 80 to 118 percent, with an overall mean of 99 

percent and a standard deviation of 9.

Table 6. Results for the analysis of IAEA-405 CRM solution 

Particulate 

Hg

(ng/L)

Actual 

Percent 

Recovery

Theoretical 

Percent 

Recovery

76.3 103 95

71.6 96 89

70.3 94 87

79.2 106 98

75.4 101 93

80.8 109 100

82.9 111 103

80.0 108 99

80.3 108 99

Average 77.4 104 96

Standard deviation 4.3 6 5

Percent relative 

standard deviation 5.6
References

Biester, H., Gosar, M., and Covelli, S., 2000, Mercury 

speciation in sediment affected by dumped mining 

residues in the drainage area of the Idrija Mercury Mine, 

Slovenia: Environmental Science and Technology, v. 34, 

p. 3330–3336.

DeWild, J.F, Olson, M.L., and Olund, S.D., 2002, Determination of Methyl Mercury by Aqueous Phase Ethylation, 

Followed by Gas Chromatographic Separation with 

Cold Vapor Atomic Fluorescence Detection: U.S. Geological Survey Open-File Report 01–445, 14 p.

DeWild, J.F., Olund, S.D., Olson, M.L., and Tate, M.T., 

2004, Methods for the Preparation and Analysis of 

Solids and Suspended Solids for Methylmercury: U.S. 

Geological Survey Techniques and Methods book 5, 

chap. A7, 13 p.

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