## Methods of Analy s is by T he U.S. Geological Survey National W a ter Quality Laboratory

— Determination of Organic Plus Inorganic Mercur y

in F iltered and Unfiltered Natural W a ter w i th Cold Vapor–Atomic F l uorescence Spectrometry

W a ter-Resources Inv e stigations Report 01-4132



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

## Methods of Analy s is by t he U.S. Geological Survey National W a ter Quality Laboratory

— Determination of Organic Plus Inorganic Mercur y

in F iltered and Unfiltered Natural W a ter w i th Cold Vapor–Atomic F l uorescence Spectrometry

By John R. Garbarino and Donna L. Damrau

_______________________________________________________

U.S. GEOLOGICAL SURVEY

W a ter-Resources Inv e stigations Report 01-4132

D env er , C o l o r ado 2001

### U. S. Depar t ment of the I n ter i or Gale A

. Norton, Secretary

U. S. Geol ogi cal Sur v ey Charles G. Gr oat, Di r ector

T he us e of tr ade, pr oduc t, or f i r m nam es in this r epor t is f o r des c r iptive pur pos es only and does not im ply endor s e m ent by the U.S. G o ver n m ent.

F o r additional inf o r m ation w r ite to: Copies of this r epor t c an be pur c has ed f r om :

Chief

, National W a ter Q uality Labor ator y U.S. G eologic a l Sur v ey U.S. G eologic a l Sur v ey Br anc h of Inf o r m ation Ser v ic es Box 25046, Mail Stop 407 Box 25286 F eder al Center F eder al Center Denver , CO 80225- 0046 Denver , CO 80225- 0286

## CONTENTS

Abst ract 1 I n troduction 1 Analy tical method 2 1. Application 2 2. Summary of method 2 3. Sample collection and storag e 3 4. Quality -control samples, sampling methods, sample -collection equipment, and cl eani n g procedures 3 5. Contamination and interferences 4 6. Apparatus and instrumentation 5 7. Reag ents and calibration standards 5 8. Sample preparation 6 9. Analy tical procedure 7 10. Calculations 7 11. Reporting of results 7 Discussion of results 8 Conclusions 14 R e ferences ci t e d 15

FIGU R ES

1-3. B o x plots showing : 1. Re sults f o r

a

se r i e s of solutions ba se d on a Na tiona l I n stitute of Sta nda r d s and Technolog y standard re ference material preserve d with acid dichromate or hy drochloric acid 9
2. Results for U.S. Geolog ical Survey st andard reference wat e r sam p l e s Hg 24 and Hg 26 and two dilutions of a B a ker I n stra-Analy z e d standard preserved in a c i d dic h r o ma te 11

3. The effects of using arg on instead of nitrog en as the purg e g a s in cold vapor–atomic fluorescence spectrometry 12

4. Graph showing linear reg r ession analy s is of r e sults f o r

sa mple solutions ba se d on two r e f e r e nc e sta nda r d s ( e x p e r ime nta l ) a nd Na tiona l I n stitute of Standards and Technol og y standard reference material (theoretical) 13

TA B L ES

1. Method detection limit and analy tical precision for the determination of mercury by cold vapor

– at om i c fl uorescence spect rom e t r y 3 2. Ty pical instrument operating conditions 7 3. Ave r a g e pe r c e n t spike r e c ove r i e s f o r

me r c ur y

in r e a g e n t- wa te r , f ilte r e d a nd unfiltered surface-water, and filtered and unfiltere d g r ound-water matrices 14

Contents III

### CONVERSION FA CTORS

Mu ltip ly B y T o o b t a i n Le ngt h

m i crom eter (μm ) 3.94 x 10 -5 inch

m illim eter (m m ) 3.94 x 10 -2 inch

nanom eter (nm ) 3.94 x 10 -8 inch Mass g r am (g ) 3.53 x 10 -2 ounce, av oirdupois

m illig ram (m g ) 3.53 x 10 -5 ounce, av oirdupois
nanog ram (ng ) 3.53 x 10 -1 1 ounce, av oirdupois Vol u m e liter (L ) 2.64 x 10 -1 g a llon

m i croliter (μL ) 2.64 x 10 -7 g a llon

m illiliter (m L ) 2.64 x 10 -4 g a llon P ressure k ilopascal (k Pa) 1.45 x 10 -1 pounds per square inch

De g r e e s Ce lsius ( o C) may be converted to deg r ees F a hrenheit ( o F ) by using the following equation:

o F = 9/5 ( o C) + 32.

A BBRE V I A T E D W A TE R-QUA L ITY UNITS

mg /L millig r a ms pe r lite r μg /L mic r o g r a m s pe r lite r μg /mL mic r o g r a m pe r millilite r ng /L na nog r a ms pe r lite r mL /min millilite r s pe r minute L /min lite r s pe r minute

Contents IV

### A BBREVI A T I O NS A ND A CRONYM S

AS TM Am eri can S o ci et y for Test i n g and Mat e ri al s C A S R N C h em i cal Abst ract S e rvi ce R e g i st ry Num b er CV–AAS cold vapor–atomic absorption spectrometry CV–AF S cold vapor–atomic fluorescence spectrometry HCl hy drochloric acid M Mola r ( m ole s pe r lite r ) L T –MDL long -term me thod detection level MDL ( s) method de tection limit(s) MRL method reporting level HNO 3 nitr ic a c i d N Nor m a l ( a c i d e quiva le nts pe r lite r ) NI ST National I n stitute of Standards and Technolog y NWQL Na tiona l Wa te r Qua lity L a bor a t or y s second sp. g r

. S p eci fi c g r avi t y S R M st andard reference m a t e ri al S R W S (s) U.S

. Geol og i cal S u rvey st andard reference wat e r sam p l e (s) USEPA U.S. Environmental Protection Ag ency US GS U.S

. Geolog ical S u rvey
< le ss tha n ± plus or minus



### GLOSSA RY

MDL — The method detection limit (MDL ) is defi ned as the minimum concentration of an el em ent t h at can be m easured and report e d wi t h 99-percent confi d ence t h at t h e el em ent

c onc e n tr a tion is g r e a t e r tha n ze r o a nd is de te r mine d f

r o m a n a l y s is of a

sa mple in a g i ve n ma tr ix that contains the element of interest (U.S. Environmental Protection Ag ency , 2000).

Contents V

## Methods of Analy s is by the U. S. Geological Survey National Water Quality Laboratory

— Determination of Organic Plus Inorganic Mercury in Filtered and Unfiltered Natural Water w i th Cold Vapor – Atomic Fluorescence Spectrometry

By J ohn R. G a r bar ino and Donna L. Dam r au

A b st ract An analy tical method using cold vapor– at om i c fl uorescence spect rom e t r y

was developed by the U.S. Geolog ical Survey in 2001 for the determination of org a nic plus inor g a nic me r c ur y

in f ilte r e d a nd unf ilte r e d natural water. This method was developed to

e limina t e the use of a c i d dic h r o ma te pr e s e r va tive a nd to pr ovide c a p a b ility to

m easure am bi ent m e rcury concent r at i ons i n
na tur a l wa te r

. Dissolve d me r c ur y

inc l ude s a ll

ox idiza b le me r c ur y

spe c i e s pr e s e n t in na tur a l water that has been filtered throug h a 0.45- mic r o me te r por e size c a p sule f ilte r

. Whole

wat e r recoverabl e m e rc ury includes dissolved

m e rcury speci es and m e rcury speci es
a d sor b e d to pa r tic ula t e ma tte r in unf ilte r e d

na tur a l wa te r

. Me r c ur y

speci es can i n cl ude

e l e m e n ta l me r c ur y , me r c ur y

( I I ) , me r c ur y

( I I ) complex e s, various alky l- and pheny lmercury compounds, and other forms of mercury

. I n this method, samples are col l ect ed and processed accordi n g t o st andard U.S. Geolog ical Survey protocols. Samples are preserved onsite w ith 6N hy drochloricacid in a ratio of 1 to 100 in a borosilicateg l ass bottle with fluor opoly m er-lined cap. Mercury speci es are ox i d i z ed t o m e rcury (I I ) by using bromine monochloride; ex cess
ox ida tion r e a g e n t is ne utr a lize d with hy drox y l amine hy drochloride. Elemental mercury produced after adding stannous

c h lor i de is pur g e d f r o m the solution with ultr a pur e a r g on g a s into a c e ll in whic h the

me r c ur y

c onc e n tr a tion is measured by atomic fluorescence emission at 253.7 nanometers. The analy tical response is linear up to 125 na nog r a ms pe r lite r ( n g / L ) of me r c ur y , a nd the short-term method detection limit is about 5 ng /L . The a n a l y tic a l va r i a b ility a t 50 ng /L is about 10 percent.
This report descri bes the method and compares the use of hy drochloric acid to acid di chrom a t e as a fi el d preservative. Ambient mercury concentrations in hy drochloric acidpreserved samples stored in borosilicate-g l ass bottles with fluoropoly m er-lined caps are shown to be stable for at least 30 day s

. Mercury concent r at i ons are st abl e for at l e ast 5 months after bromine monochloride is

a dde d to the sa mple bottle s in the la bor a t or y

. The l ong -t erm averag e percent recoveri es at 20, 45, and 75 ng /L in r eag ent water, filtered and unfiltered g r ound wate r, and filtered and unfiltered surface water rang e from 89 to 108, 96 to 103, and 94 to 98 percent, respectively

. INTRODUCTION

The am bi ent concent r at i on for di ssol v ed and whole-water rec overable mercury is g e ne r a lly a t the pa r t s- pe r

- t r illion le ve l ( n a nog r a ms- p e r

- lite r , ng /L ) f o r

na tur a l- wa te r
sa mple s. Me a s ur e m e n t a t this c onc e n tr a tion le ve l is impor ta nt because mercury bi oaccum u l a t e s i n l i v i n g org a ni sm s. The previous method (F ishman and F r iedman, 1989, p. 289–291) that used cold vapor–

a t omic a b sor p tion spe c t r o me tr y

( C V

–AAS ) was not capable of measuring such low concentrations. Cold vapor–atomic fl uorescence spect rom e t r y

(C V

–AFS ) is capabl e of m easuri n g 5 ng /L mercury directly
, without sample preconcentration. B y

Introduction 1eliminating sample prec oncentration, analy s is throug hput is increased while maintaining the

c a p a b ility to de te r mine me r c ur y concentrations at levels ty pic a lly r e g u la te d by

wa te r

- qua lity sta nda r d s. The me r c ur y concentration, org a nic pl us inorg a nic species, is de te r mine d in f ilte r e d a nd unf ilte r e d

na tur a l- wa te r sa mple s by using a br omina ting dig e stion pr oc e dur e tha t minimize s i n t e rferences. S a m p l e s are preserved wi t h hy drochloric acid instead of acid dichromate solution, which has previously been used. Thi s chang e was necessary because shi p m e nt of samples preserve d with dic h r o ma te solution is restricted, and the cost of disposing of chromium waste is ex pensive. I n addition, hy drochloric acid samp le preservation has been shown as effect i v e as sam p l e preservation with acid dichromate solution.
This report describes a method for de te r mining me r c ur y

in na tur a l- wa te r samples. I t was developed by the U.S. Geolog ical Survey (USGS) for use in the Na tiona l Wa te r Qua lity L a bor a t or y

( N WQL )

. I t is rapid, more effi ci ent , and can det ect lowe r c onc e n tr a tion le ve ls c o mpa r e d to previous USGS methods (F ishman and F r iedman, 1989, p. 289–291). This method supplements other met hods of the USGS for the de te r mina tion of me r c ur y

tha t a r e described by F i shman and F r iedman (1989) and by F i shman (1993). The new method was implemented at NW QL in April 2001.
This report provi des a detailed description of all aspects of the method, including the instrumentation, the reag ents, the a n a l y tic a l pr oc e dur e , a nd the qua lity

control procedures. Me rcury concentration is

r e por te d by NWQL in mic r o g r a m s pe r lite r inste a d of na nog r a ms pe r lite r , the concentration unit used throug hout this report, because of current (2001) limitations in the data base.

AN AL Y T I C AL M E T H O D Inorganic Constituents and Method, Lab, and Parameter Codes

Const i t u ent M e t h o d Lab code P a rameter and met hod code Mercury
, w a ter filtered, org a nic + inorg a nic,  g/ L I

- 2464- 0 1 2 7 0 7 7 1 8 9 0 C Mercury
, w a ter unfiltered, org a nic + inorg a nic,  g/ L I

- 4464- 0 1 2 7 0 8 7 1 9 0 0 D

1. A pplicat ion

This method is used to determine concentrations of org a nic plus inorg a nic

me r c ur y

in f ilte r e d a nd unf ilte r e d na tur a lwater samples. B r omine monochloride is

use d to ox idize e l e m e n ta l me r c ur y , me r c ur y complex e s, various alky l- and pheny lmercury compounds, and other forms of mercury

. The upper limit of the linear concentration rang e is 125 ng /L mercury

. The short-term method detection limit (MDL
, see Glossary ) is 5 ng /L mercury (table 1).

2. Summary of Method

Concentrations of or g a nic plus inorg a nic

me r c ur y

in f ilte r e d a nd unf ilte r e d na tur a l- wa te r
sa mple s a r e de te r mine d by using CV–AF S

. The method is based on U.S. Environmental

Determination of O r ganic Plus Inorgani c Mer c ur y

in Filter ed and U n filter ed N a tur a l Water w i th C o ld Vapor -A tomic Fluor escence Spectr o metr y 2Protection Ag ency (1999) Method 1631 but does not use g o ld amalg a mation for mercury preconcentration. B y eliminating the preconcentration procedure, the MDL is at least a factor of 10 g r eater, y e t the method provides the determina tion of mercury at

am bi ent concent r at i ons. Mercury speci es i n a
na tur a l- wa te r sa mple a r e ox idize d to me r c ur y ( I I ) inside the bor osilic a t e

- g l a ss sa mple bottle by using bromine monochloride; ex cess
ox idant is neutraliz ed with hy drox y l amine hy drochloride. Mercury (I I ) is reduced to elemental mercury by using stannous chloride, and is purg e d from the solution with ultr a pur e a r g on g a s into a c e ll in whic h the

me r c ur y

c onc e n tr a tion is measured by atomic fluorescence emission at 253.7 nanometers (nm )

.

T a b l e 1. Method detec tion lim it and analy t ic al pr ec is ion f o r the deter m i nation of m e r c ur y by c o ld vapor
– atom ic f l uor es c enc e s pec tr om etr y
[n g / L
, n a n o g r am s p e r liter; MDL
, m e th o d d e tectio n lim it]

Element Mean, ng/L Standard dev i ation, ng/L tstatistic D e gr ees of freedom MD L, ng/L

M e rcury 1 1 2 2

. 4 9 2 2 4 5

3. Sample C o llect ion and St orage

Sa mple

- c olle c tion pr otocol must follow either the procedure outlined for trace elements in Horowitz and others (1994) or for mercury in Olson and DeW ild (1999). The le ve l of c onta mina ti on related to field collection and processing for either protocol, however, must be established by using an equipment blank. F iltered and unfiltered

na tur a l- wa te r sa mple s a r e pr e s e r ve d with hy drochloric acid to a pH less than 2. S a m p l e s are st ored i n cl ean borosi l i cat e-g l ass sample bottles with fluor opoly m er-lined caps. B o ttle s a r e pr e p a r e d by r i nsing onc e with 10 percent (by volume) mercury -free nitric

a c i d a nd thr e e time s with de ionize d wa te r before ai r-dry i n g on a l a m i n ar-fl ow cl ean be nc h. The sa mple bottle must be r i nse d with

a

por tion of the f ilte r e d or unf ilte r e d na tur a l water prior to filling th e bottle with about 200 mL of sa mple . Eve r y

sa mple must be preserved with 2 mL of 6N hy drochloric acid (HCl); more acid mig ht be required to lower the pH to 2 in some ma tr ic e s . I t is impor ta nt that field personnel us e 6N HCl prepackag ed in poly p ropy lene vials that can be obtained f r o m the USGS Oc a l a Wa te r Qua lity a nd Research L a boratory in F l orida (part number 06910) because the quality control is

c ontinua lly monitor e d. Ambient mercury concentrations are stable for 1 month in preserved samples. Nevertheless, samples should be shipped to the laboratory for anal y s i s as qui ckl y as possi bl e.

4. Qualit y - Cont rol Samples, Sampling Methods, Sample-Collection Equipment, and Cleaning Procedures

4.1 Quality

- c ontrol sample s. Colle c tion of

qua lity

- c ontr o l ( Q C) sa mple s is a r e quir e d component of sample collection for waterqua lity studie s . QC sa mple s a r e c o lle c t e d, usually onsite, to iden tify
, quantify
, and doc ume n t bia s a nd va r i a b ility in da ta tha t result from collecting
, processing , shipping
, and handling of samples by field and laboratory personnel. The ty pe, number, and distribution of QC samp le s a r e de te r mine d by the de sig n a nd da ta

- qua lity r e quir e me nts of the study . Detailed di scussion of the ty pes
a nd pur pose s of qua lity

- c ontr o l sa mple s is provided in W ilde and others (1999).
The primary purpose of a blank sample is to ide n tif y

pote n tia l sour c e s of sa mple contamination and to a ssess the mag n itude of mercury contamination. F i eld blanks are col l e ct ed and processe d onsite in the sa me

A n aly t ical Method 3manner and by using the same equipment as f o r

the e nvir onme n ta l sa mple s. The f i e l d blank is an aliquot of blank water that is processed sequent i a l l y t h roug h each component of the sampling sy stem. The source water needed for blank samples must be produced and certifie d by a laboratory to have mercury concentr ations that do not

ex ceed a specified method detection limit. I norg a nic-free blank water must be used for all equipment field bl anks (Horowitz and others, 1994, p. 22).

Re plic a t e sa mple s a l so ma y be collected. The primary purpose of replicate

sa mple s is to qua ntif y

the va r i a b ility in a ll or part of the sampling and analy s is process. R e pl i cat es, envi ronm ent a l sam p l e s col l ect ed in duplic a t e , tr iplic a t e , or hig h e r multiple s, a r e consi d ered i d ent i cal i n com posi t i on and are

a n a l y z e d f

o r

the sa me c h e mic a l c onstitue n ts.

4.2 Sampling methods . Use methods tha t a llow c o lle c tion of wa te r sa mple s tha t accurately represent the water-quality characteristics of the surface water or g r ound water at a g i ven time or location. Detailed descriptions of sampling methods used by the US GS for obt ai ni ng surface-wat e r sam p l e s, g r ound-water samples, a nd sample-processing procedures (splitting
, f iltration, and shipping ) are provided by W ilde and others (1999).

4.3 Sample-collection equipment. Use

sa mple

- c olle c tion e quipme n t a nd a u toma tic samplers that are free of tubing , g a skets, and other components made of metal or that mig ht sorb m e rcury from t h e wat e r. The best

ma te r i a l f o r

sa mple

- c o llection and processing equipment is any ty pe of fluorocarbon poly m er.

4.4 Cleaning procedures. F o llow the pr oc e dur e s outline d in e ithe r Hor o witz a nd others (1994) or Olse n and DeW ild (1999). 5. C ont aminat ion and Int e rf erences

Conta mina tion must be avoided because of the inherently low mercury concentration found in natural water. The analy s t and field personnel need to be attentive to potential sources of contamination. Sampling equipment must be clean ed, and samples need to be collected as described by Horowitz and others (1994) or by Olson and DeW ild (1999). Every sample mu st be preserved with 2 mL of 6N HCl that can be obtained from the USGS Oc a l a Wa te r Qua lity a nd Re se a r c h L a boratory in F l orida. Samples mig ht becom e cont am i n at ed duri n g anal y s i s by carry over from a previous sample that had unusually hig h mercur y

concentration. Conta mina tion f r o m a i r borne sources can be minimize d by pla c i ng the a u tosa mple r inside a plastic enclosure pressuriz e d with mercury

free nitrog en.
Gold, silver, and iodi de inte r f e r e with the determination of me rcury by this method. Ele m e n ta l me r c ur y

is a m a l g a ma te d by g o ld or silver. The recovery of 2.5 ng /L of mercury in the presence of 5 to 100 mg /L iodide rang es from 100 to 0 percent (U.S. Environmental Protection Ag ency , 1996; B l oom, 1995). After analy z ing a sample that contains g r eater than 30 mg /L iodide, it may be necessary t o cl ean t h e anal y t i cal sy st em with 4N HCl (U.S. E nvironmental Protection Ag ency , 1999; B l oom, 1995). Most forms of mercury are ox idiz ed by the bromine monochloride solution; however, the recovery of mercury bound within microbial cells mig ht r e quir e a dditiona l ultr a v iole t photoox idation (U.S. Environmental Protection Ag ency , 1999). B u ildup of condensation in the vapor g e nerator or f l uor e s c e n c e c e ll will de g r a d e the a n a l y tic a l sig n al. Condensation can be eliminated by wrapping heating tape around the vapor g e nerator and by using a dry i ng tube in front

Determination of O r ganic Plus Inorgani c Mer c ur y

in Filter ed and U n filter ed N a tur a l Water w i th C o ld Vapor -A tomic Fluor escence Spectr o metr y 4of the fluorescence cell. The dry i ng tube should be replaced after about 1 y ear of operation. Ultrapure arg on (99.998 percent) must be use d f

o r

the pur g e g a s to minimize the possibility of f

l uor e s c e n t que nc hing by impur itie s.

6. A pparatus and Instrumentation

6.1 Labware. Use cl ean Ty pe A g l ass volumetric flasks to pr epare al l sol u t i ons. Store mercurystock solutions in borosilicateg l ass bottles with fluoropoly m er-lined caps. The accuracy of al l pi pet s and vol um et ri c flasks should be reg u larly verified g r a v ime tr ic a lly or by using a n a u toma tic volume-calibrating spect rophotometer sy stem before preparing standard solutions.

6.2 Instrumentation . Several

c o mme r c ia l a u toma te d CV–AF S sy ste m s a r e avai l a bl e. These sy st em s are com posed of a spe c t r o me te r , me r c ur y

- vapor g e nerator,

a

u tosa mple r , a nd c o mpute r . The ma jor components of the spectrometer are a mercury line source, a quartz flow-throug h fluorescence cell, and a photometer. The mercury

- vapor g e nerator is composed of

se ve r a l pe r i sta ltic pumps a nd a se r i e s of

c o mpute r c ontr o lle d, time

- a c t ua te d sole noid val v es t h at i n t r oduce sam p l e and reag ent s , a g a s-liquid separator, and a membrane dry e r tube tha t r e move s moistur e . The a u tosa mple r and computer automate sample introduction, data acquisition, and quantitation.

7. R eagent s and C a librat i on Standards

All solutions used in this method must be verified to have me r c ur y

- c onta mina n t concentration, after the prescribed dilution, that is le ss tha n the MDL

. ASTM Ty pe I r e a g e n t wat e r (Am e ri can S o ci et y for Test i n g and Materials, 2000) must alway s be used to prepare solutions. Heating each compound used in this method, with the ex ception of the hy drated stannous chloride, in a muffle furnace at 250  C for 8 hours will volatiliz e
me r c ur y

impur itie s. All solutions must be stor e d in de sig n a t e d bor osilic a t e

- g l a ss bottle s with fluoropoly m er-lined caps. All calibration standards are stable for 1 month.

7.1 Argon gas is used as the purg e (carrier) g a s. I t s purity must be at least 99.998 percent.

7.2 Nitrogen gas i s used as t h e sheat h g a s. I t s purity must be at least 99.998 percent

.
7.3 Hydroxylamine hydrochloride (NH 2 OH
· HC l ) C h em i cal Abst ract S e rvi c e Reg i stry Number (CASRN) 5470-11-1.

7.4 Potassium bromate (KBrO 3 ) CASRN 7758-01-2.

7.5 Potassium bromide (KBr) C A S R N 7758-02-3.

7.6 Stannous chloride (SnCl 2 · 2H 2 O) CASRN 10025-69-1.

7.7 Nitric ac id solution , 0.4 percent (by volume). Add 4 mL of concentrated nitric aci d [ HNO 3 , 16 M, specific g r avity (sp. g r .) 1.41] to 500 mL of water in a 1-L volumetric flask. B r ing to volume with water. This solution is use d to r i nse be twe e n sa mple anal y s es.

7.8 Hydroxylamine hydrochloride (N H

2 OH
· HCl) solution , 15 percent (by weig ht). Dissolve 30 g of NH 2 OH
· HCl in a 200-mL volumetric flask that contains about 10 mL of water. B r ing to volume with water. Solution must be prepared weekly

.

A n aly t ical Method 57.9 Bromine monochloride ( B rCl) solution. This solution is use d to ox idize

me r c ur y

spe c i e s in a sa mple to me r c ur y

( I I )

. Dissolve 10.8 g of KB r in 1 L of concentrated hy drochloric acid (HCl, 12 M, sp. g r . 1.19) in a borosilicate-g l ass bottle. Place a clean

ma g n e tic stir ba r in the bottle a nd stir f

o r (NOTE: This process produces copious qua ntitie s of f

r e e ha log e ns, suc h a s Cl 2 , B r 2 , B r Cl.) W h en all of the KB rO 3 has been added, the color of the solution should chang e from y e llow to red to orang e . L oosely cap the bottle, and stir another hour before tig htening

.
7.10 Stannous chloride ( SnCl 2 ) solution , 2 percent (weig h t-to-volume ratio). This solution is used to reduce mercury (I I ) to elemental mercury

. Dissolve 20 g of SnCl 2 · 2H 2 O into a 1-L volumetric flask that contains 200 mL of water. Slowly add 30 mL concentrated HCl, mix , and bring to volume with wa te r

. Allow solution to e quilibr a te 1 hour before use. Solution must be prepared daily

.
7.11 Pri m ary mercury st ock sol u t i o n , 10,000 mg /L . National I n s titute of Standards and Technolog y (NI S T) standard reference material (SRM) 3133. This reference material is sta b le until the NI ST e x pir a tion da te

.
7.12 Secondary mercury stock solution
, 1.00 mg /L . Pipet 100 L of primary standard solution into a 1-L volumetric flask, and 5 mL of B r Cl solution, and bring to volume with water. Solution is stable for 1 y ear.

7.13 Tertiary mercury stock solution
, 2.0 g / L

. Pipet 2.0 mL of secondary stock solution into a 1-L volumetric flask, and 5 mL of B r Cl solution, and bring to volume with water. Solution is stable for 1 month. 7.14 Calibration standard 1 , 0 ng /L . Add 1 mL of B r Cl solution to a 200-mL volumetric flask and bring to volume with water.

7.15 Calibration standard 2 , 5.0 ng /L

. Add 0.5 mL of the ter tiary mercury stock solution and 1 mL of B r Cl solution to a 200- mL volumetric flask and bring to volume with water.

7.16 Calibration standard 3 , 10.0 ng /L

. Add 1.0 mL of the ter tiary mercury stock solution and 1 mL of B r Cl solution to a 200- mL volumetric flask and bring to volume with water.

7.17 Calibration standard 4 , 25.0 ng /L

. Add 2.5 mL of the ter tiary mercury stock solution and 1 mL of B r Cl solution to a 200- mL volumetric flask and bring to volume with water.

7.18 Calibration standard 5 , 50.0 ng /L

. Add 5.0 mL of the ter tiary mercury stock solution and 1 mL of B r Cl solution to a 200- mL volumetric flask and bring to volume with water.

7.19 Calibration standard 6 , 100.0 ng /L . Add 10.0 mL of the tertiary mercury stock solution and 1 mL of B r Cl solution to a 200-mL volumetric flask and bring to volume with wa te r

. 8. Sample Preparat ion

Sa mple s a nd c a libr a tion solutions a r e processed i d ent i cal l y . Mercury speci es are
ox idiz ed to mercury (I I ) by adding 1 mL of B r Cl solution (see section 7.9) to 200 mL of f i e l d- a c i dif i e d, f ilte r e d or unf ilte r e d, na tur a lwa te r sa mple . The sa mple is dig e ste d f

o r

a t least 12 hours at room temperature prior to

Determination of O r ganic Plus Inorgani c Mer c ur y

in Filter ed and U n filter ed N a tur a l Water w i th C o ld Vapor -A tomic Fluor escence Spectr o metr y 6anal y s i s . I f t h e y e l l o w col o r di sappears, add

mor e B r Cl solution to f u lly dig e st the sa mple

. The sa mple is c o mple te ly dig e ste d whe n the y e llow color persists for at least 12 hours. Record the total volume of B r Cl solution added so that the fina l me r c ur y

c onc e n tr a tion can be adjusted for dilution. Mercury bound within mic r obia l c e lls a l so mig ht r e quir e ultraviolet photoox idation (U.S. Environmental Protection Ag ency , 1999). Some hig h ly org a nic matrices mig ht require long e r ox ida tion time s a t a n e l e v a t e d te mpe r a t ur e

. The sa mple bottle s c a n be pl aced i n an oven set at 50  C for 6 hours when el evat ed t e m p erat ure i s requi red. Nevertheless, samples s hould be analy z ed as quickly as possible after the ox idation procedure.

J u st prior to analy s is, 10 mL of B r Clox idize d sa mple is pipe td into a n a u tosa mple r borosilicate-g l ass test tube. Adding 40 L of hy drox y l amine hy drochloride solution (see section 7.8) neutraliz es ex cess B r Cl. Allow about 5 minutes for the reaction to reach completion. The disappearance of the y e llow col o r i ndi cat es t h at al l t h e BrC l has been dest roy e d and no t r aces of hal o g e ns rem a i n.

9. A n aly t ical Procedure
The analy tical pro cedure for the method is f u lly a

u toma te d. Af te r c a libr a tion standards and unknown sa mples have been pr oc e sse d by using the pr oc e dur e outline d in sect i on 8, t h ey are l o aded i n t o t h e aut o sam p l e r. The sy st em i n t r oduces a g i ven volume of sample and SnCl 2 solution ( s e e section 7.10) with a se ries of peristaltic pumps and solenoid valves . The mercury (I I ) present i s reduced t o el em ent a l m e rcury t h at i s purg e d from t h e react or i n t o t h e fl uorescence cel l wi t h arg on g a s. The mercury concentration is de te r mine d by rel a t i n g t h e si g n al peak area for t h e sam p l e s t o t h e peak area for t h e cal i b rat i on st andards. Re f e r

to the NWQL Sta nda r d Ope r a ting Procedure I M 0348.0 (D.L . Damrau, U.S. Geolog ical Survey , written commun., 2001), Z e llweg er Analy tics I n c. (1996; 1997), and W e ndt (1997) for details of the operation and

ma inte na nc e of the instr u me nta tion use d in this method. Ty pical operating conditions are liste d in ta ble 2.

Ta b l e 2 . T y pic a l ins t r u m ent oper ating c onditions

[k P a , k ilo p a scal; lb s/in 2 , p o u n d s p e r sq u a re in ch ; m L /m in
, m illiliters p e r m i n u t e; L / m i n , liters p e r m i n u t e; s, seco n d ]

P a r a m e t e r S e t t i n g Mercury

- v a por generator flow rates

300 m L /m in

2.75 L / m i n A r g on a t 276 k P a ( 40 lbs /in 2 ) P u rg e (carrier) g a s - - - - - - - - - - - - - N itr og e n a t 276 k P a ( 40 lbs /in 2 ) Dry e r g a s - - - - - - - - - - - - - - - - - - - She a t h g a s - - - - - - - - - - - - - - - - - - 250 m L /m in Mercury

- v a por generator timing
18 s 170 s Sam p le d e lay - - - - - - - - - - - - - - - - - - W a sh p e rio d - - - - - - - - - - - - - - - - - - L o ad p e rio d - - - - - - - - - - - - - - - - - - - 4 5 s Spe c t rom e te r 1,000 6.50 Ra tio Calib ratio n ran g e- - - - - - - - - - - - - - - - Fin e g a in - - - - - - - - - - - - - - -- - - - - - Mo d e sw itch - - - - - - - - - - - - - - - - - - In teg r atio n tim e - - - - - - - - - - - - - - - - 0

. 2 5 s

10. C a lculat ions

No cal cul a t i ons are requi red ex cept whe n sa mple s a r e dilute d a nd dilution f a c t or s are appl i e d.

11. R e port i ng R esult s
Mercury concent r at i on is reported by NWQL in mic r o g r a m s pe r lite r ( g / L ) i n st ead of nanog rams per liter (ng / L ) because of the current (2001) limitations of the data base. The number of sig n ificant fig u res reported are liste d a s f o llows:

 I f the me r c ur y

c onc e n tr a tion is le ss than the long -term method de te c tion le ve l ( L T–MDL ) , the n the

A n aly t ical Method 7r e sult is r e por te d a s le ss tha n ( < ) the method reporting level (MRL ), in mic r o g r a m s pe r lite r

. Sa mple s between the L T –MDL and MRL will be “ E ” c ode d to indic a t e a n estimated concentration.

 I f the me r c ur y

c onc e n tr a tion is g r eat er t h an or equal t o t h e MDL
, but less than 0.100 g / L
, the n the

r e sult is r e por te d to the ne a r e s t 0.001 g/ L

.

 I f the me r c ur y

c onc e n tr a tion is
g r eater than 0.100 g / L
, the n the

r e sult is r e por te d to the ne a r e s t 0.01 g/ L

. DISCUSSION OF RESULTS

The CV–AF S mercury method was de ve lope d to e limina t e the use of the a c i d dichromate preservative and to provide a method that is capable of measuring ambient

me r c ur y

c onc e n tr a tions in na tur a l wa te r

. A U.S. Department of Tr ansportation reg u lation on the shipme nt of na tur a l- wa te r sa mple s preserved with acid dichromate requires packag ing and shipment protocols that are

ex pensive. I n addition, it is ex pensive to dispose of samples that contain hig h concent r at i ons of chrom i u m because i t i s a pr ior ity polluta nt . Several U.S. Environmental Protection Ag ency (USEPA) methods [ f or ex ample, Method 1631 (U.S. Environmental Protection Ag ency , 1999] , use hy drochloric acid (HCl) as a preservative. A

wa te r sa mple pr e s e r ve d with HCl pa sse s a ll required corrosion tests and can be shipped without ex pensive packag ing

.
A f ilte r e d or unf ilte r e d na tur a l- wa te r sample is stored in a 250-mL borosilicateg l ass bottle with a fluoropoly m er-lined cap after adding 2 mL of 6N HCl to about 200 mL water (water level at the shoulder of the bottle )

. Mor e a c i d must be a dde d to sa mple s that have hig h alkalinity to ensure that the pH is le ss tha n 2. I f mor e tha n 2 mL of HCl is used, the total volume of acid should be listed on the Analy tical Services Request form so that adjustments for dilution can be applied. I t is important that sa m p l e s are preserved wi t h HC l speci f i cal l y packag ed and t e st ed for such use. Poly propy lene vials that contain HCl preservative can be obtained from the USGS Oc a l a Wa te r Qua lity a nd Re se a r c h L a bor a t or y (part number 06910). The HCl preserves the

me r c ur y

c onc e n tr a tion in wa te r sa mple s f o r

a t le a s t 30 da y s ; the r e la tiv e standard deviation of

the r e sults wa s le ss tha n 10 pe r c e n t f o r

a solution that had 10 ng /L mercury and that

wa s a n a l y z e d two to thr e e time s a we e k f

o r

1 month. No sig n ificant difference was found between the HCl and the previously used (prior to April 2001) acid dichromate preservat i v es. The averag e concent r at i on for a sample that had 10 ng /L mercury preserved with HCl a nd tha t wa s a n a l y z e d r e pe titive l y for 90 day s was not sig n ificantly different at the 95-percent confiden ce level (p=0.20) than the a v e r a g e c onc e n tr a tion f o r

a

simila r solution preserved with acid dichromate. Results obtained for solutions that had 5, 10, 25, 50, and 100 ng /L mercury (fig

. 1) showed that the variation, as a function of mercury concentration, was similar for both preservation ag ents.

Me r c ur y

spe c i e s in na tur a l wa te r c a n take various forms, including elemental

me r c ur y , me r c ur y

c o mp lex e s, plus various alky l- and pheny l-mercury compounds. Ox idation of such species to mercury (I I ) by using B r Cl ma ke s it possible to de te r mine concentrations of org a nic plus inorg a nic

m e rcury and al so serves as a preservat i v e t o inc r e a s e sa mple

- holding time s. Ex pe r ime nts have indicated that samples are stable for up to 3 months after the addition of B r Cl. The percent-relative standard deviation for a sample that had 10 ng /L me r c ur y

tha t wa s
a n a l y z e d mor e tha n 24 time s f o r

3 months

Determination of O r ganic Plus Inorgani c Mer c ur y

in Filter ed and U n filter ed N a tur a l Water w i th C o ld Vapor -A tomic Fluor escence Spectr o metr y 85 1 0 2 5 5 0 100 0 20 40 60 80 10 0 12 0 14 0
HC lEXPERIMENTALMERCURYCONCENTRATION,INNANOGRAMSPERLITER

M E RC U R Y S T AN D A R D RE F E R E NC E M A T E R I A L 0 20 40 60 80 10 0 12 0 14 0
A c id d i ch r o m a t e

P e rcen tile 90 th 75 th 50 th 25 th 10 th

 = 1 s t an d 99 th p e rcen tile

= Mean E X P L ANAT ION

Figur e 1

. Res u lts f o r a s e r i es of s o lutions bas ed on a National Ins t itute of Standar ds and T e c hnology

s t andar d r e f e r enc e m a ter i al pr es er ved w i th ac id dic h r o m a te or hy dr oc hlor ic ac id ( HCl)

. Standar d

r e f e r enc e m a ter i al c onc entr a tion is in nanogr am s per liter

.

D i scussion of R esults 9was about 15 percent, an acceptable level of

va r i a b ility c onside r ing the c onc e n tr a tion le ve l and daily deviations in instrument performance and calibration standards. The bias and variability of the method was tested by using standard reference

ma te r i a l s f r o m se ve r a l di fferent sources. The method performance is validated throug h the repetitive analy s is of reag ent-water, g r oundwat e r, and surface-wat e r m a t r i ces spi k ed at t h ree di fferent m e rcur y

concentrations. C o m p ari s on of t h e anal y t i cal perform ance bet w een t h e new C V

–AF S method and the previously used CV

–AAS (prior to April 2001) is not feasible because the method

r e por ting le ve l f o r

the CV

–AAS is only about 100 ng /L . This reporting level is about 20 time s g r e a t e r tha n the MDL f o r

the ne w CV

– AF S method, and 100 ng /L corresponds to the upper calibration limit. Onsite samples collected before April 2001 were preserved with acid dichromate, thus making direct comparisons problematic. F u rthermore, during a ty pical y ear, more than 90 percent of the r e sults f o r

sa mple s a n a l y z e d by CV

–AAS for dissolved and whole-water recoverable mercury were less than or equal to 100 ng /L

. The accuracy of C V

–AFS was tested by using two USGS standard reference water

sa mple s ( S RWS) . Ca lib ration standards were prepared from NI ST SRM-3133 in acid di chrom a t e because al l avai l a bl e reference

wa te r sa mple s we r e pr e s e r ve d in the sa me preservative. The SRW S s were diluted by a fact or of 10 because t h e m o st probabl e m ean
me r c ur y

c onc e n tr a tion f o r

a ll a v a ila ble S R W S s ex ceeded t h e cal i b rat i on rang e. Additiona l me r c ur y

solu tions preserved in acid dichromate were prepared at 10 and 50 ng /L from B a ker I n stra-Analy z e d 1,000-
g /mL sta nda r d soluti on to provide another reference check. These four reference solutions we r e a n a l y z e d r e pe titive l y f

o r

2 months a f te r c a libr a ting the instr u me nt with NI ST standards preserved with acid dic h r o ma te . Re sults f o r

the dilute d SRWSs

com p ared favorabl y wi t h ex pect ed concentrations (fig

. 2). The ex perimental results of 38±2 (n=21) and 71±3 ng /L (n=19) correspond to the theoretical means of 420 and 700 ng /L , respectively
, after being adjusted for dilution. The results for the 10- and 50-ng /L solutions prepared from the B a ker I n stra-Analy z e d standard were accept a bl e at 10±2 and 55±3 ng / L
, respect i v el y

. Either nitrog en or arg on g a s has been used in analy tical methods for mercury to pur g e e l e m e n ta l me r c ur y

f

r o m the r e a c tor cell. Ex perimental resu lts (fig

. 3) show that the r e is little dif f e r e nc e be twe e n the two g a se s when m e rcury concent r at i ons ex ceed 10 ng / L

. The use of arg on g a s si g n i f i cant l y i n creases t h e preci si on at 10 ng / L , because t h e
se nsitivity of the me a s ur e m e n t is inc r e a s e d by about a factor of 2 over nitrog en g a s. Thus, the use of arg on g a s is necessary for measuring ambient mercury concentrations. The accuracy and variability of using arg on was established by analy z ing reference standards prepared from two different sources

r e pe titive l y f

o r

1 month. Me r c ur y

solutions preserved in HCl were prepared from B a ker I n stra-Analy z e d 1,000- g /mL (25 and 75
ng /L ) and Spex CertiPrep 10- g /mL (10 and 50 ng /L ) standard solutions. Ex perimental

c onc e n tr a tions we r e de te r mine d f

o r

the s e solutions r e la tive to NI ST c a libr a tion standards. L i near reg r ession analy s is (fig

. 4) of

r e sults shows a sig n if ic a n t c o r r e la tion bet w een t h e ex peri m e nt al (Baker and S p ex ) solutions a nd the the o r e tic a l c onc e n tr a tions (slope=0.925, correlation coefficient=0.9992). The va r i a b ility r a ng e d f

r o m 5 to 15 pe r c e n t and was a function of concentration. I n addition, the stability of the preservation and instrumentation is suppor ted by the data that

were accum u l a t e d for a m ont h.

Determination of O r ganic Plus Inorgani c Mer c ur y

in Filter ed and U n filter ed N a tur a l Water w i th C o ld Vapor -A tomic Fluor escence Spectr o metr y 10H g 24 H g 2 6 10 50 0 20 40 60 80 10 0

1: 10 D i l u t i o n M e a n

= 420 n g / L

Ba k e r Ba k e r 1: 10 D i l u t i o n Me a n =7 0 0 n g / LEXPERIMENTALMERCURYCONCENTRATION,INNANOGRAMSPERLITER

M E RC UR Y S T A N DA RD RE F E RE N C E M A T E R I AL

E X P L ANAT ION

P e rcen tile 90 th 75 th 50 th 25 th 10 th

 = 1 s t an d 99 th p e rcen tile

= Mean

Figur e 2

. Res u lts f o r U.S. G eologic a l Sur v ey s t andar d r e f e r enc e w a ter s a m p les Hg24 and Hg26 and tw o dilutions of a Bak e r Ins t r a

- A naly z ed s t andar d pr es er ved in ac id dic h r o m a te. Mer c ur y c onc entr a tions f o r s t andar d r e f e r enc e m a ter i als ar e in nanogr am s per liter ( ng/L)

.

D i scussion of R esults 110 20 40 60 80 100 120 140 Ni t r o g e n

5 1 0 2 5 5 0 100 0 20 40 60 80 100 120 140
Ar g o nEXPERIMENTALMERCURYCONCENTRATION,INNANOGRAMSPER LITER

TH E O R E TI C A L M E R C U R Y C O N C E N TR AT I O N , I N NA N O G R AM S P E R L I T E R

P e rcen tile 90 th 75 th 50 th 25 th 10 th

 = 1 s t an d 99 th p e rcen tile

= Mean E X P L ANAT ION

Figur e 3

. T he ef f e c t s of us ing ar gon ins t ead of nitr ogen as the pur ge gas in c o ld vapor –atom ic f l uor es c enc e s pec tr om etr y

.

Determination of O r ganic Plus Inorgani c Mer c ur y

in Filter ed and U n filter ed N a tur a l Water w i th C o ld Vapor -A tomic Fluor escence Spectr o metr y 120 2 0 4 0 6 0 8 0 20 40 60 80

Sl o p e : 0. 9 2 5 Y-i n ter cep t: 3. 3 C o r r e l a t i o n c o e f f i ci e n t : 0. 9992EXPERIMENTALMERCURYCONCENTRATION,INNANOGRAMSPER LITER

T H E O RE T I C A L M E RC UR Y CO N C E N T R A T I O N , I N NA NO G R AM S P E R L I T E R 0

Figur e 4

. Linear r egr es s i on analy s is of r e s u lts f o r s a m p le s o lutions bas ed on tw o r e f e r enc e
s t andar ds ( e x per im ental) and National Ins t itute of Standar ds and T e c hnology s t andar d r e f e r enc e
m a ter i al ( t heor etic al)

. Er r o r bar s c o r r e s pond to the s t andar d deviation.

D i scussion of R esults 13The percentag e recovery of results for various concentrations of me r c ur y

spike d into reag ent water, filtere d and unfiltered surface water, and filtere d and unfiltered g r ound water was used to valid ate the method. Data were acquired during 7 nonconsecutive day s

. No mor e tha n two se ts of data were acquired i n 1 day

. The rang e of averag e percent

r e c ove r y

f

o r

a ll f ilte r e d a nd unf ilte r e d matrices at 20, 45, and 75 ng /L was 89 to108, 96 to 103, and 94 to 98 percent, respectively ( t a b le 3) . The va r i a b ility in the r e c ove r y

of 20 ng /L , a concentrati on about four times the short-term MDL
, was about twice that of hig h er spike concentrations. I n addition, the

va r i a b ility in r e c ove r i e s a t 20 ng /L f o r

the unfiltered matrices was about twice those for corresponding filtered ma trices. There was little dif f e r e nc e , howe v e r , in va r i a b ility f

o r f ilte r e d a nd unf ilte r e d ma tr ic e s f o r

spike concentrations of 45 and 75 ng /L . Sorption to pa r tic ula t e ma tte r mig ht c ontr i bute to the inc r e a s e in va r i a b ility f

o r

the 20- ng /L

me r c ur y

spike in unf ilte r e d ma tr ic e s

.

T a b l e 3. Aver age per c ent s p ik e r e c o ver i es f o r m e r c ur y in r eagent- w ater , f ilter ed and unf ilter ed s u r f ac ew a ter

, and f ilter ed and unf ilter ed gr ound- w a ter m a tr ic es
[A v e rag e is b a sed o n 9 to 1 1 rep licates acq u i red o n 7 n o n c o n secu tiv e d a y s ; n g / L
, n a n o g r am s p e r liter; %, p e rcen t;
± , p l us o r m i nus; f ilter e d
, sur f ace o r gr o und w a ter p r o cessed thr o ugh a 0

. 4 5

- m i cr o m eter m e m b r a ne]

M e r c ur y s p ik e c onc e n tr a t ion, ng/L 2 0 4 5 7 5 Ma t r i x A v erag e
reco v e ry , % A v erag e
reco v e ry , % A v erag e
reco v e ry , % R eag en t w a t e r - - - - - - - - - - - - - - - - 94±11 100±6 98±8

Su rf ace w a ter, f iltered - - - - - - - - - - - 89±8 100±9 96±6

Su rf ace w a ter, u n f iltered - - - - - - - - - 108±20 101±10 95±8

Gro u n d w a ter, f iltered - - - - - - - - - - - 9 1 ± 1 3 9 6 ± 6 9 5 ± 9

Grou n d w a ter, u n f iltered - - - - - - - - - 102±20 103±10 94±7

CONCLUS IONS
The new cold vapor

– a t omic fl uorescence spect rom e t r i c (C V

–AFS ) method for the determination of inorg a nic plus or g a nic me r c ur y

spe c i e s in f ilte r e d a nd unf ilte r e d na tur a l wa te r ha s se ve r a l advant ag es when com p ared t o t h e previ ousl y used (prior to April 2001) cold vapor

– a t omic absorption spectrometric method. Primary advantag es are impr oved method detection limit a nd e limina tion of a

c o r r o sive preservat i v e. The C V

–AF S method has a short-term method det ection limit of 5 ng /L without using g o ld amalg a mation for mercury preconcentration. W ithout mercury preconcentration, analy s is throug hput is inc r e a s e d while ma inta ining the c a p a b ility of de te r mining me r c ur y

a t c onc e n tr a tions ty

pic a lly r e g u la te d by wa te r

- qua lity sta nda r d s. Mercury samples ar e preserved with hy drochloric acid (HCl) instead of acid dichromate. Althoug h acid dichromate has been used ex tensively to preserve mercury samples, shipping and disposal reg u lations have made continued use too ex pensive. Ex periments sug g e st that there is no sig n ificant difference, however, between the

Determination of O r ganic Plus Inorgani c Mer c ur y

in Filter ed and U n filter ed N a tur a l Water w i th C o ld Vapor -A tomic Fluor escence Spectr o metr y 14averag e m e rcury concent r at i on i n a wat e r sample preserved with HCl and one preserved with acid dichromate. Ambient mercury

c onc e n tr a tions in sa mple s pr e s e r ve d with HCl in bor osilic a t e

- g l a ss bottle s with f l uor opoly m er-lined caps have been shown to be stable for at least 30 day s . Ox idation of inorg a nic and org a nic mercury species with bromine monochloride makes it possible to de te r mine tota l r e c ove r a ble me r c ur y

a nd

e x te nds the sa mple

- holding time to 3 months.
The bias and variability of the method were established usin g st andard reference materials and spike recovery results. C o m p ari s on of t h e anal y t i cal perform ance bet w een C V

–AF S and the previously used method were not feasible because of the siz a ble disparity in method detection limits. The concentration of the upper calibration standard used by the new method corresponds to the detection limit of the old method. R e sul t s for US GS st andard reference wat e r
sam p l e s were accept a bl e wi t h respect t o t h e most probable concentration. Other solutions that have vary ing me rcury concentrations were prepared from cert i f i e d st andards from two different sources. L i near reg r ession of the r e sults f o r

the s e solutions we r e sig n if ic a n tly c o r r e la te d ( c or r e la tion coefficient=0.9992) with standard solutions traceable to National I n stitute of Standards and Technolog y material s. The analy tical

va r i a b ility is e x pe c t e d to e x te nd f r o m 15 to 5 percent wi t h i n creasi n g concent r at i on bounded by the calibration rang e. The averag e percent recovery of 20, 45, and 75 ng /L of mercury in r eag ent

- wat e r, surfacewater, and g r ound-wa ter matrices was determined during 7 nonconsecutive day s

. The a v e r a g e pe r c e n t r e c ove r i e s f o r

a ll f ilte r e d and unfiltered matrices rang ed from 89 to108 (20 ng /L ), 96 to 103 (45 ng /L ), and 94 to 98 pe r c e n t ( 75 ng /L )

. The va r i a b ility f

o r

the recovery of the 20-ng /L spike, a concentration about four times the method detection limit, was about twice that of hig h er spike concentrations. I n addition, the variability in pe r c e n ta g e r e c ove r i e s f o r

unf ilte r e d ma tr ic e s
wa s twic e tha t f o r

ma tc hing f ilte r e d ma tr ic e s , possibly because of sorption to particulate

ma tte r

. Ana l y tic a l r e sults f r o m the ne w CV

– AF S method will most likely impact inte r p r e ta tion of long

- t erm trends observed in water-quality studies invol ving mercury

. The method detection limit of 5 ng /L is about a f a c t or of 20 time s lowe r tha n the pr e v iously used method. More than 90 percent of the mercury concentrations reported with the previous analy tical method during a ty pical y ear were less than or equal to 100 ng /L prior to April 2001. I m plementation of the CV

– AF S method will likely provide more definitive results because its analy tical rang e
ex tends well below 100 ng /L

.
RE FE RE NCE S CITE D

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