# Method 1631, Revision E: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry August 2002United States Office of Water Environmental Protection 4303 August 2002 Agency EPA-821-R-02-019



# Method 1631, Revision E: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence SpectrometryMethod 1631, Revision E



### Acknow ledgments
This Method was developed under the direction of W illiam A. Telliard and Maria Gom ez-Tay l or of the Engineering and Analy s is Division (EAD) within the U.S. Environm ental Protection Agency ' s (EPA' s ) Office of Science and Technology (OST). EPA acknow ledges contributions to this m e thod by Frontier Geosciences, Inc., Albion Environm ental, Battelle Marine Sciences Laboratory , STL-Canton, and Tekran Inc. Additional assistance in preparing the Method was provided by Dy nCorp Environm ental and Interface, Inc.



### Disclaimer

This Method has been reviewed and approved for pub lication by the Statistics and Analy tical Support Branch within EPA’s Engineering and Analy s is Di vision. Mention of trade nam es or comm e rcial products does not constitute endorsem ent or recom m e ndation for use.

Questions concerning this Method or its application should be addressed to: W.A. Telliard Statistics and Analy tical Support Branch (4303T) U.S. Environm ental Protection Agency Ariel Rios Building 1200 Pennsy l vania Avenue, N.W. Washington, DC 20460 Phone: 202/566–1061 Fax: 202/566–1053

iMethod 1631, Revision E



## Table of Contents

Introduction

.......................................................... iii 1.0 S cope and Application

............................................ 1 2

. 0 S u m m a ry o f M e t h o d

.............................................. 2 3

. 0 D e f i n i t i o n s

...................................................... 3 4.0 C ontamination and Interferences

.................................... 3 5

. 0 S a fe t y

......................................................... 6 6.0 A pparatus and Materials

........................................... 8 7.0 R eagents and Standards

......................................... 1 1 8.0 S ample Collection, Preservation, and Storage

......................... 1 3 9

. 0 Q u a l i t y C o n t r o l

................................................. 1 4 10.0 C alibration and Standardization

.................................... 2 2 11.0 P rocedure

..................................................... 2 5 12.0 D ata Analysis and Calculations

.................................... 2 7 13.0 M ethod Performance

............................................ 2 9 1 4

. 0 P o l l u t i o n P r e v e n t i o n

............................................. 2 9 15.0 W aste Management

............................................. 3 0 1 6

. 0 R e fe r e n c e s

.................................................... 3 0 1 7

. 0 G l o s s a ry

...................................................... 3 1 18.0 Tables and Figures

.............................................. 3 4

ii August 2002Method 1631, Revision E



### Introduction
Method 1631 (the "Method") supports technology -based and water quality -based m onitoring program s authorized under the Clean Water Act (CWA; the "Act"). CWA Sections 301 and 306 require EPA to publish effluent standards that restrict the direct discharge of pollutants to the nations waters, and CWA Sections 307(b) and (c) require EPA to prom ulgate nationally applicable pretreatem ent standards which restrict pollutant discharges into sewers flowing to publicly owned treatm e nt works (POTWs). The effluent lim itations guidelines are published at CFR parts 401- 503. CWA Section 303 requires each State to set a water quality standard for each body of water within its boundaries. A State water quality standard consists of a designated use or uses of a water body or a segm e nt of a water body , the water quality criteria that are necessary to protect the designated use or uses, and an antidegradation policy

. CWA Section 304(a) requires EPA to publish water quality criteria that reflect the latest scientific knowledge concerning the phy sical fate of pollutants, the effects of pollutants on ecological and hum an health, and the effect of pollutants on biological comm unity diversity , productivity , and stability

. These water quality standards serve two purposes: (1) they establish the water quality goals for a specific water body , and (2) th ey are the basis for establishing water quality -based treatm e nt controls and strategies bey ond the technol ogy -based controls required by CWA Sections 301(b) and 306. In 1987, am endm ents to the CWA required States to adopt num eric criteria for toxic pollutants (designated in Section 307(a) of the Act) based on EPASection 304(a) criteria or other scientific data, when the discharge or presence of those toxic polluta nts could reasonably be expected to interfere with designated uses. Method 1631 was specifically devel oped to provide reliable m easurem e nts of m e rcury at EPA WQC levels. In developing m e thods for determ ination of trace m e tals, EPA found that one of the greatest difficulties was precluding sam ple contam ination during collection, tr ansport, and analy s is. The degree of difficulty , however, is highly dependent on the m e tal and s ite-specific conditions. Method 1631 is designed to preclude contam ination in nearly all situations. It also contains procedures necessary to produce reliable results at the lowest WQC levels published by EPA. Inrecognition of the variety of situations to which this Method m a y be applied, and in recognition of continuing t echnological advances, Method 1631 is perform ance based. Alternative procedures m a y be u sed so long as those procedures are dem onstrated to y i eld reliable results. Requests for additional copies of this draft Method should be directed to:
U.S. EPA Sam p le Control Center 6101 Stevenson Avenue Alexandria, VA 22304-3540 703/461–2100

iiiMethod 1631, Revision E

Note: This Method is perform ance based. The laboratory is perm itted to om it steps or m odify procedures provided that all perform ance requirem e nts in this Method are m e t. The laboratory m

u st not om it or m odify any procedure defined by the term “shall” or “m ust” and m u st perform all quality control tests.

ivMethod 1631, Revision E

vMethod 1631, Revision E 

## Method 1631, Revision E Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry

1.0 S cope and Application
1.1 Method 1631, Revision E (the "Method") is for dete rm ination of m e rcury (Hg) in filtered and unfiltered water by oxidation, pur ge and trap, desorption, and cold-vapor atom ic fluorescence spectrom e try (CVAFS). This Method is for use inEPA' s data gathering and m onitoring program s associated with the Clean Water Act, the R esource Conservation and Recovery Act, the Com p rehensive Environm ental Response, Com p ensa tion and Liability Act, and the Safe Drinking Water Act. The Method is based on a contract or-developed procedure (Reference 16.1) and on peer-reviewed, published procedures for the de term ination of m e rcury in aqueous sam ples, ranging from sea water to sewage effluent (References 16.2–16.5). 

### 1.2 This Method is accom p anied by Method 1669: Sampling Ambient W a ter for Determination of Trace Metals at EPA Water Quality Criteria Levels (Sam pling Method). The Sam p ling Method guidance docum ent is recom m e nded to preclude contam ination during the sam pling process. 

### 1.3 This Method is for determ ination of Hg in the range of 0.5–100 ng/L. Application m a y be extended to higher levels by selection of a sm alle r sam ple size or by calibration of the analy tical sy stem across a higher range. For m easurem e nt of blank sam ples, the Method m a y be extended to a lower level by calibration to a lower calib ration point. Section 10.4 gives requirem e nts for extension of the calibration range. 

### 1.4 The ease of contam inating am bient water sam ples with m e rcury and interfering substances cannot be overem phasized. This Method includes s uggestions for im provem e nts in facilities and analy tical techniques that should m i nim i ze contam ination and m a xim i ze the ability of the laboratory to m a ke reliable trace m e tals determ ina tions. Certain sections of this Method contain suggestions and other sections contain requirem e nts to m i nim i ze contam ination. 

### 1.5 The detection lim it and m i nim u m level of quantitation in this Method usually are dependent on the level of interferences rather than instrum e nt lim itations. The m e thod detection lim it (MDL; 40 CFR 136, Appendix B) for Hg has been determ ined to be 0.2 ng/L when no interferences are present. The m i nim u m level of quantitation (ML) has been established as 0.5 ng/L. An MDL as low as 0.05 ng/L can be achieved for low Hg sam ples by using a larger sam ple volum e, a lower BrCl level (0.2% ) , and extra caution in sam ple handling. 

### 1.6 Clean and ultraclean—The term s "clean" and "ultr aclean" have been applied to the techniques needed to reduce or elim inate contam ination intrace m e tals determ inations. These term s are not used in this Method because they lack an exact definition. However, the inform ation provided in this Method is consistent with the summ a ry guidance on clean and ultraclean techniques (References 16.6-16.7). 

### 1.7 This Method follows the EPA Environm ental Methods Managem e nt Council' s "Guidelines and Form at for Methods to Be Proposed at 40 CFR, part 136 or part 141."

Method 1631, Revision E - August 2002 1Method 1631, Revision E


### 1.8 This Method is "perform ance based." The la boratory is perm itted to m odify the Method to overcom e interferences or lower the cost of m easurem e nts if all perform ance criteria are m e t. Section 9.1.2.1 gives the requirem e nts for establishing m e thod equivalency

. 

### 1.9 Any m odification of this Method, bey ond those e xpressly perm itted, shall be considered a m a jor m odification subject to application and approva l of alternate test procedures under 40 CFR 136.4 and 136.5. 

### 1.10 This Method should be used only by analy s ts e xperienced in the use of CVAFS techniques and who are trained thoroughly in the sam ple handling and instrum e nt techniques described in this Method. Each laboratory that uses this Method m u st dem onstrate the ability to generate acceptable results using the procedures in Section 9.2. 

### 1.11 This Method is accom p anied by a data veri fication and validation guidance docum ent, Guidance on the Documentation and Evaluation of Trace M e tals Data Collected for CW A Compliance M

onitoring (Reference 16.8), that can be used for veri fication and validation of the data obtained. 1.12 This Method uses either a bubbler or flow-inj ection sy stem for determ ination of m e rcury in water. Separate calibration, analy s is, and calculation procedures are provided for a bubbler sy stem (Sections 10.2, 11.2.1, and 12.2) and fo r a flow-injection sy stem (Sections 10.3, 11.2.2, and 12.3).



## 2.0 S ummary of Method
2.1 A 100- to 2000-m L sam ple is collected directly into a cleaned, pretested, fluoropoly m er or glass bottle using sam ple handling techniques designed for collection of m e rcury at trace levels (Reference 16.9). 

### 2.2 For dissolved Hg, the sam ple is filtered through a 0.45- 

### : m capsule filter prior to preservation. 

### 2.3 The sam ple is preserved by adding either pretest ed 12N hy drochloric acid (HCl) or brom ine m onochloride (BrCl) solution. If a sam ple will al so be used for the determ ination of m e thy l m e rcury , it should be preserved according to procedures in the m e thod that will be used for determ ination of m e thy l m e rcury
. 

### 2.4 Prior to analy s is, all Hg in a 100-m L sam ple aliquot is oxidized to Hg(II) with BrCl. 

### 2.5 After oxidation, the sam ple is sequentially reduced with NH 2 OH 

### @ HCl to destroy the free halogens, then reduced with stannous chloride (SnCl 2 ) to convert Hg(II) to volatile Hg(0). 

### 2.6 The Hg(0) is separated from solution either by purging with nitrogen, helium , or argon, or by vapor/liquid separation. The Hg(0) is collected onto a gold trap (Figures 1, 2, and 3). 

### 2.7 The Hg is therm a lly desorbed from the gold trap into an inert gas stream that carries the released Hg(0) to a second gold (analy tical) trap. The Hg is desorbed from the analy tical trap into a gas stream that carries the Hg into the cell of a cold-vapor atom ic fluorescence spectrom e ter (CVAFS) for detection (Figures 2 and 3). 

### 2.8 Quality is assured through calibration and testi ng of the oxidation, purging, and detection sy stem s.

2 Method 1631, Revision E - August 2002Method 1631, Revision E



## 3.0 D efinitions 3.1 Total m e rcury

— all BrCl-oxidizable m e rcury form s and species found in an unfiltered aqueous solution. This includes, but is not lim ited to, Hg(II), Hg(0), strongly organo-com p lexed Hg(II) com pounds, adsorbed particulate Hg, and sever al tested covalently bound organo-m e rcurials (e.g., CH 3 HgCl, (CH 3 ) 2 Hg, and C 6 H 5 HgOOCCH 3 ). The recovery of Hg bound within m i crobial cells m a y require the additional step of UV photo- oxidation. In this Method, total m e rcury and total recoverable m e rcury are sy nony m ous. 

### 3.2 Dissolved m e rcury

— all BrCl-oxidizable m e rcury form s and species found in the filtrate of an aqueous solution that has been filtered through a 0.45- 

### : m filter. 

### 3.3 Apparatus—Throughout this Method, the sam ple c ontainers, sam pling devices, instrum e ntation, and all other m a terials and devices used in sam ple collection, sam ple processing, and sam ple analy s is that com e in contact with the sam ple and therefore require careful cleaning will be referred to collectively as the Apparatus. 

### 3.4 Definitions of other term s used in this Method are given in the glossary (Section 17.0).



## 4.0 C ontamination and Interferences
4.1 Preventing sam ples from becom i ng contam inated during the sam pling and analy s is process constitutes one of the greatest difficulties encounter ed in trace m e tals determ inations. Over the last two decades, m a rine chem ists have com e to recognize that m u ch of the historical data on the concentrations of dissolved trace m e tals in seawater are erroneously high because the concentrations reflect contam ination from sam pli ng and analy s is rather than am bient levels. Therefore, it is im perative that extrem e care be taken to avoid contam ination when collecting and analy z ing sam ples for trace m e tals. 

### 4.2 Sam p les m a y becom e contam inated by num erous routes. Potential sources of trace m e tals contam ination during sam pling include: m e tallic or m e tal-containing labware (e.g., talc gloves that contain high levels of zinc), containers, sam pling equipm ent, reagents, and reagent water; im properly cleaned or stored equipm ent, labwar e, and reagents; and atm o spheric inputs such as dirt and dust. Even hum an contact can be a source of trace m e tals contam ination. For exam ple, it has been dem onstrated that dental work (e.g., m e rcury am algam fillings) in the m ouths of laboratory personnel can contam inate sam ples dir ectly exposed to exhalation (Reference 16.9). 

### 4.3 Contam ination Control
4.3.1 P hilosophy —The philosophy behind contam in ation control is to ensure that any object or substance that contacts the sam ple is m e tal free and free from any m a terial that m a y contain m e rcury
. 4.3.1.1 T he integrity of the results produced cannot be com p rom i sed by contam ination of sam ples. This Method and the Sam p ling Method give requirem e nts and suggestions for control of sam ple contam ination.

Method 1631, Revision E - August 2002 3Method 1631, Revision E

4.3.1.2 S ubstances in a sam ple cannot be allowed to contam inate the laboratory work area or instrum e ntation used for trace m e tals m easurem e nts. This Method gives requirem e nts and suggestions for protecting the laboratory

. 4.3.1.3 A lthough contam ination control is essen tial, personnel health and safety rem a in the highest priority

. The Sam p ling Me thod and Section 5 of this Method give suggestions and requirem e nts for personnel safety

. 4.3.2 A voiding contam ination—The best way to control contam ination is to com p letely avoid exposure of the sam ple to contam ina tion in the first place. Avoiding exposure m eans perform ing operations in an area known to be free from contam ination. Two of the m o st im portant factors in avoiding/reducing sam ple contam ination are (1) an awareness of potential sources of contam ination and (2) strict attention to work being done. Therefore, it is im perative that the procedures described in this Method be carried out by well-trained, experienced personnel.
4.3.3 U se a clean environm ent—The ideal environm ent for processing sam ples is a class-100 clean room

. If a clean room is not available, all sam ple preparation should be perform ed in a class-100 clean bench or a nonm etal glove box fed by m e rcury - and particle-free air or nitrogen. Digestion should be perform ed in a nonm etal fum e hood equipped with HEPA filtration and id eally situated in a clean room

. 4.3.4 M inim ize exposure—The Apparatus that will contact sam ples, blanks, or standard solutions should be opened or exposed only ina clean room , clean bench, or glove box so that exposure to an uncontrolled atm o sphe re is m i nim i zed. When not being used, the Apparatus should be covered with clean pl astic wrap, stored in the clean bench or in a plastic box or glove box, or bagged in cl ean zip-ty pe bags. Minim i zing the tim e between cleaning and use will also m i nim i ze contam ination.
4.3.5 C lean work surfaces—Before a given ba tch of sam ples is processed, all work surfaces in the hood, clean bench, or glove box in which the sam ples will be processed should be cleaned by wiping with a lint-free cloth or wipe soaked with reagent water.
4.3.6 W ear gloves—Sam p ling personnel m u st wear clean, non-talc gloves during all operations involving handling of the Appara tus, sam ples, and blanks. Only clean gloves m a y touch the Apparatus. If another obj ect or substance is touched, the glove(s) m

u st be changed before again handling the Apparatus. If it is even suspected that gloves have becom e contam inated, work m u st be halted, the contam inated gloves rem oved, and a new pair of clean gloves put on. Wearing m u ltiple lay e rs of clean gloves will allow the old pair to be quickly stripped with m i nim a l disruption to the work activity

. 4.3.7 U se m e tal-free Apparatus—All Apparatu s used for determ ination of m e rcury at am bient water quality criteria levels m u st be nonm etallic, free of m a terial that m a y contain m e tals, or both.
4.3.7.1 C onstruction m a terials—Only fluoropoly m er or glass containers m u st be used for collection of sam ples that will be analy zed for m e rcury because m e rcury vapors can diffuse in or out of other m a terials, leading to results that are biased low or high. Poly ethy lene and/or poly p ropy lene labware m a y be used for digestion and other purposes because the tim e of sam ple exposure to these m a terials is relatively short. All m a terials, regardl ess of construction, that will directly or

4 Method 1631, Revision E - August 2002Method 1631, Revision E indirectly contact the sam ple, m u st be known to be clean and free of Hg at the levels specified in this Method before proceeding.
4.3.7.2 S erialization—It is recomm e nded that serial num bers be indelibly m a rked or etched on each piece of reusable Apparatu s so that contam ination can be traced, and logbooks should be m a intained to track the sam ple from the container through the labware to introduction into the instrum e nt. It m a y be useful to dedicate separate sets of labware to different sam ple ty pes; e.g., receiving waters vs. effluents. However, the Apparatus used for processing blanks and standards m

u st be m i xed with the Apparatus used to process sam ples so that contam ination of all labware can be detected.
4.3.7.3 T he laboratory or cleaning facility is responsible for cleaning the Apparatus used by the sam pling team

. If there are any indications that the Apparatus is not clean when received by the sam pling team (e.g., ripped storage bags), an assessm ent of the likelihood of contam ination m u st be m a de. Sam p ling m u st not proceed if it is possible that the Apparatus is contam inat ed. If the Apparatus is contam inated, it m

u st be returned to the laboratory or cleaning facility for proper cleaning before any sam pling activity resum es. 4.3.8 A void sources of contam ination—Avoid c ontam ination by being aware of potential sources and routes of contam ination.
4.3.8.1 C ontam ination by carry over—Contam ination m a y occur when a sam ple containing a low concentration of m e rcury is processed imm e diately after a sam ple containing a relatively high concentration of m e rcury
. The Hg concentration at which the analy tical sy stem (purge, traps, detector) will carry greater than 0.5 ng/L of Hg into a succeeding bubbler or sy stem blank m u st be determ ined by analy z ing calibration solutions containing successively larger concentrations of Hg. This test m u st be run prior to first use of the analy tical sy stem and whenever a change is m a de that would increase the am ount of carry over. When a sam ple contains 1⁄2 or greater of this determ ined Hg concentration, a bubbler blank (bubbler sy stem ) or sy stem blank (flow injection sy stem ) m u st be analy zed to dem onstrate no carry over at the blank criteria level. For the bubbler sy stem , the blank m u st be run using the sam e bubbler and sam ple trap used to run the high concentrati on sam ple. Sam p les analy zed following a sam ple that has been determ ined to r esult in carry over m u st be reanaly zed. Sam p les that are known or suspected to contain the lowest concentration of m e rcury should be analy zed first follo wed by sam ples containing higher levels.
4.3.8.2 C ontam ination by sam ples—Significant laboratory or instrum e nt contam ination m a y result when untreated effluents, in-process waters, landfill leachates, and other undiluted sam ples containing concentrations of m e rcury greater than 100 ng/L are processed and analy zed. Sam p les known or suspected to contain Hg concentrations greater than 100 ng/L s hould be diluted prior to bringing them into the clean room or laboratory dedicated for processing trace m e tals sam ples.
4.3.8.3 C ontam ination by indirect contact—Apparatus that m a y not directly com e in contact with the sam ples m a y still be a source of contam ination. For exam ple, clean tubing placed in a dirty plastic bag m a y pick up contam ination from the bag and subsequently transfer the contam ination to the sam ple. It is im perative that every piece of the Apparatus that is directly or indirectly used in the collection, processing, and analy s is of water sam ples be thoroughly cleaned (Section 6.1.2). Method 1631, Revision E - August 2002 5Method 1631, Revision E

4.3.8.4 C ontam ination by airborne partic ulate m a tter—Less obvious substances capable of contam inating sam ples include airborne particles. Sam p les m a y be contam inated by airborne dust, dirt, particles, or vapors from unfiltered air supplies; nearby corroded or rusted pipes, wires, or other fixtures; or m e talcontaining paint. Whenever possible, sam ple processing and analy s is should occur as far as possible from sources of airborne contam ination.
4.3.8.5 C ontam ination from reagents— Contam ination can be introduced into sam ples from m e thod reagents used during processing and analy s is. Reagent blanks m u st be analy zed for contam ination prior to use (see Section 9.4.3). If reagent blanks are contam inated, a new batch of reagents m u st be prepared (see Section 9.4.3.2). 

### 4.4 Interferences
4.4.1 A t the tim e of prom ulgation of this Me thod, gold and iodide were known interferences. At a m e rcury concentration of 2.5 ng/L and at increasing iodide concentrations from 30 to 100 m g /L, test data have shown that m e rcury recovery will be reduced from 100 to 0 percent. At iodide concentrations greater than 3 m g /L, the sample should be prereduced with SnCl 2 (to rem ove the brown color) and additional or m o re concentrated SnCl 2 should be added. To preclude loss of Hg, the additional SnCl 2 should be added in a closed vessel or analy s is should proceed imm e diately

. If sam ples containing iodide concentrations greater than 30 m g /L are analy zed, it m a y be necessary to clean the analy tical sy stem with 4N HCl after the analy s is (Reference 16.10).
4.4.2 T he potential exists for destruction of the gold traps if free halogens are purged onto them , or if they are overheated (>500 °C). When the instructions in this Method are followed, neither of these outcom es is likely

. 4.4.3 W ater vapor m a y collect in the gold traps and subsequently condense in the fluorescence cell upon desorption, giving a false peak due to scattering of the excitation radiation. Condensation can be avoided by predry ing the gold trap. Traps that tend to absorb large quantities of water vapor should not be used.
4.4.4 T he fluorescent intensity is strongly dependent upon the presence of m o lecular species in the carrier gas that can cause "quenc hing" of the excited atom s. The dual am algam a tion technique elim inates quenching due to trace gases, but it rem a ins the laboratory ' s responsibility to ensure high purity inert carrier gas and a leak-free analy tical train. 

## 5.0 S afety
5.1 The toxicity or carcinogenicity of each chem ical used in this Method has not been precisely determ ined; however, each com pound should be treated as a potential health hazard. Exposure to these com pounds should be reduced to the lowest possible level.
5.1.1 C hronic m e rcury exposure m a y cause kidney dam a ge, m u scle trem ors, spasm s, personality changes, depression, irritability and nervousness. Organo-m e rcurials m a y cause perm anent brain dam a ge. Because of the toxicological and phy sical properties of Hg, pure standards should be handled onl y by highly trained personnel thoroughly fam iliar with handling and cautionary procedures and the associated risks.

6 Method 1631, Revision E - August 2002Method 1631, Revision E 5.1.2 I t is recom m e nded that the laboratory purch ase a dilute standard solution of the Hg in this Method. If prim ary solutions are prepared, they shall be prepared in a hood, and a NIOSH/MESA-approved toxic gas respirator shall be worn. 

### 5.2 This Method does not address all safety issues associated with its use. The laboratory is responsible for m a intaining a current file of OS HA regulations for safe handling of the chem icals specified in this Method. OSHA rules require thata reference file of m a terial safety data sheets (MSDSs) m u st be m a de available to all pe rsonnel involved in these analy ses (29 CFR 1917.28, Appendix E). It also is suggested that the laboratory perform personal hy giene m onitoring of each analy s t who uses this Method and that the results of this m onitoring be m a de available to the analy s t. Personal hy giene m onitoring should be perform ed using OSHA or NIOSH approved personal hy giene m onitoring m e thods. Additiona l inform ation on laboratory safety can be found in References 16.11-16.14. The references and bibliography included in Reference 16.14 are particularly com p rehensive in dealing withthe general subject of laboratory safety

. 

### 5.3 Sam p les suspected to contain concentrations of Hg at μ g /L or higher levels are handled using essentially the sam e techniques em ploy ed in handling radioactive or infectious m a terials. Wellventilated, controlled access laboratories are required. Assistance in evaluating the health hazards of particular laboratory conditions m a y be obtai ned from certain consulting laboratories and from State Departm e nts of Health or Labor, m a ny of which have an industrial health service. Each laboratory m u st develop a safety program for handling Hg.
5.3.1 F acility —When sam ples known or suspected of containing high concentrations of m e rcury are handled, all operations (including rem oval of sam ples from sam ple containers, weighing, transferring, and m i xing) should be perform ed in a glove box dem onstrated to be leak-tight or in a fum e hood dem onstrated to have adequate airflow. Gross losses to the laboratory ventilation sy stem m u st not be allowed. Handling of the dilute solutions norm a lly used in analy ti cal and anim al work presents no inhalation hazards except in an accident.
5.3.2 P rotective equipm ent—Disposable plastic gloves, apron or lab coat, safety glasses or m ask, and a glove box or fum e hood adequate for radioactive work should be used. During analy tical operations that m a y give rise to aerosols or dusts, personnel should wear respirators equipped with activated carbon filters.
5.3.3 T raining—Workers m u st be trained in the proper m e thod of rem oving contam inated gloves and clothing without contacting the exterior surfaces.
5.3.4 P ersonal hy giene—Hands and forear m s should be washed thoroughly after each m a nipulation and before breaks (coffee, lunch, and shift).
5.3.5 C onfinem ent—Isolated work areas posted with signs, segregated glassware and tools, and plastic absorbent paper on bench tops will aid in confining contam ination.
5.3.6 E ffluent vapors—The effluent from the CVAFS should pass through either a column of activated charcoal or a trap containing gold or sulfur to am algam a te or react m e rcury vapors. 5.3.7 W aste handling—Good technique includes m i nim i zing contam inated waste. Plastic bag liners should be used in waste cans. Jan itors and other personnel m u st be trained in the safe handling of waste.
5.3.8 D econtam ination
Method 1631, Revision E - August 2002 7Method 1631, Revision E

5.3.8.1 D econtam ination of personnel—Use any m ild soap with plenty of scrubbing action.
5.3.8.2 G lassware, tools, and surfaces—Sulfur powder will react with Hg to produce m e rcuric sulfide, thereby elim inating the possible volatilization of Hg. Satisfactory cleaning m a y be accom p lished by dusting a surface lightly with sulfur powder, then washing with any detergent and water.
5.3.9 L aundry

— Clothing known to be contam inat ed should be collected in plastic bags. Persons that convey the bags and launder the clothing should be advised of the hazard and trained in proper handling. If the launderer knows of the potential problem , the clothing m a y be put into a washer without contact. The washer should be run through a cy cle before being used again for other clothing.
5.3.10 Wipe tests—A useful m e thod of determ ining cleanliness of work surfaces and tools is to wipe the surface with a piece of filter pape r. Extraction and analy s is by this Method can achieve a lim it of detection of less than 1 ng per wipe. Less than 0.1 

### : g per wipe indicates acceptable cleanliness; any t hing higher warrants further cleaning. More than 10 

### : g on a wipe constitutes an acute hazard and requires prom pt cleaning before further use of the equipm ent or work space, and indicates that unacceptable work practices have been em ploy ed.


## 6.0 A pparatus and Materials
Disclaimer: The mention of trade names or commercial products in this Method is for illustrative purposes only and does not constitute endorsement or recommendation for use by the Environmental Protection Agency. Equivalent performance may be achievable using apparatus, materials, or cleaning procedures other than those suggested here. The laboratory is responsible for demonstrating equivalent performance. 

### 6.1 Sam p ling equipm ent 6.1.1 S am ple collection bottles-fluoropoly m er or glass, 125- to 1000-m L , with fluoropoly m er or fluoropoly m er-lined cap.
6.1.2 C leaning
6.1.2.1 N ew bottles are cleaned by heating to 65–75 °C in 4 N HCl or concentrated HNO 3 for at least 48 h. The bottles are c ooled, rinsed three tim es with reagent water, and filled with reagent water containing 1% HCl. These bottles are capped and placed in a clean oven at 60-70° C overnight. After cooling, they are rinsed three m o re tim es with reagent wate r, filled with reagent water containing 0.4% (v/v) HCl, and placed in a m e rcury -free Class-100 clean bench until the outside surfaces are dry

. The bottles are tightly capped (with a wrench), doublebagged in new poly e thy l ene zip-ty pe bags until needed, and stored in wooden or plastic boxes until use. The bottles m a y be shipped to the sam pling site containing dilute HCl solution (e.g., 0.04% ), containing reagent water, or em pty

. 6.1.2.2 U sed bottles known not to have contai ned m e rcury at high (>100 ng/L) levels are cleaned as above, except for only 6–12 h in hot 4 N HCl.

8 Method 1631, Revision E - August 2002Method 1631, Revision E

6.1.2.3 B ottle blanks m u st be analy zed as described in Section 9.4.7. To verify the effectiveness of the cleaning procedures, bottle blanks m u st be dem onstrated to be free of m e rcury at the ML of this Method.
6.1.2.4 As an alternative to cleaning by the laboratory , bottles m a y be purchased from a com m e rcial supplier and each lot certified to be clean. Bottles from the lot m u st be tested as bottle blanks (Section 9.4.7) and dem onstrated to be free of m e rcury at the ML of this Method. If m e rcury is present above this level in any bottle, either the lot m u st be rejected or the bottles m u st be re-cleaned.
6.1.3 F iltration Apparatus
6.1.3.1 F ilter—0.45- 

### : m , 15-mm diam eter capsule filter (Gelm a n Supor 12175, or equivalent)
6.1.3.2 P eristaltic pum p—115-V a.c., 12-V d.c., internal battery , variable-speed, singlehead (Cole-Parm er, portable, "Masterflex L/S," Catalog No. 07570-10 drive with Quick Load pum p head, Catalog No. 07021-24, or equivalent).
6.1.3.3 T ubing—sty r ene/ethy lene/buty l ene/silicone (SEBS) resin for use with peristaltic pum p, approx 3/8-in ID by approxim a tely 3 ft (Cole-Parm er size 18, Catalog No. 06424-18, or approxim a tely 1/4-in OD, Cole-Parm e r size 17, Catalog No. 06424- 17, or equivalent). Tubing is cleaned by soaking in 5–10% HCl solution for 8–24 h, rinsing with reagent water in a clean bench in a clean room , and dry i ng in the clean bench by purging with m e tal-free air or nitrogen. After dry i ng, the tubing is double-bagged in clear poly e thy l ene bags, serialized with a unique num ber, and stored until use. 

### 6.2 Equipm ent for bottle and glassware cleaning
6.2.1 V at, 100–200 L, high-density poly e thy l ene (HDPE), half filled with 4 N HCl in reagent water. 6.2.2 P anel im m e rsion heater, 500-W, all-fluoropoly m er coated, 120 vac (Cole-Parm er H03053-04, or equivalent)
WARNING: Read instructions carefully!! The heater will maintain steady state, without temperature feedback control, of 60–75°C in a vat of the size described. However, the equilibrium temperature will be higher (up to boili ng) in a smaller vat. Also, the heater plate M U ST be maintained in a vertical position, comp letely submerged and away from the vat walls to avoid melting the vat or burning out!
6.2.3 L aboratory sink—in Class-100 clean area, with high-flow reagent water (Section 7.1) for rinsing.
6.2.4 C lean bench—Class-100, for dry i ng rinsed bottles.
6.2.5 O ven—stainless steel, in Class-100 clean area, capable of m a intaining ± 5°C in the 60–70°C tem p erature range. 

### 6.3 Cold vapor atom ic fluorescence spectrom e ter (CVA FS): The CVAFS sy stem used m a y either be purchased from a supplier, or built in the labor atory from comm e rcially available com ponents. Method 1631, Revision E - August 2002 9Method 1631, Revision E

6.3.1 C omm e rcially available CVAFS—Tekran(Toronto, ON) Series 2600 CVAFS, BrooksRand (Seattle, WA) Model III CVAFS, Leem an Labs Hy dra AF Gold plus CVAFS, or equivalent
6.3.2 C ustom

- built CVAFS (Reference 16.15). Figure 2 shows the schem atic diagram

. The sy stem consists of the following:
6.3.2.1 L ow-pressure 4-W m e rcury vapor lam p 6.3.2.2 F ar UV quartz flow-through fluorescence cell—12 m m x 12 mm x 45 mm , with a 10-m m path length (NSG Cells, or equivalent).
6.3.2.3 UV-visible photom ultiplier (PMT)—sensitive to < 230 nm

. This PMT is isolated from outside light with a 253.7-nm interference filter (Oriel Corp., Stam ford, CT, or equivalent).
6.3.2.4 P hotom eter and PMT power supply (Oriel Corp. or equivalent), to convert PMT output (nanoam p ) to m illivolts
6.3.2.5 B lack anodized alum inum optical block—holds fluorescence cell, PMT, and light source at perpendicular angles, and provides collim ation of incident and fluorescent beam s (Frontier Geosciences Inc., Seattle, WA, or equivalent).
6.3.2.6 F lowm eter—with needle valve capable of reproducibly keeping the carrier gas flow rate at 30 m L /m in 

### 6.4 Hg purging sy stem —Figure 2 shows the schem atic diagram for the purging sy stem

. The sy stem consists of the following:
6.4.1 F low m e ter/needle valve—capable of c ontrolling and m easuring gas flow rate to the purge vessel at 350 ± 50 m L /m in.
6.4.2 F luoropoly m er fittings—connections betweencom ponents and column s are m a de using 6.4-m m OD fluoropoly m er tubing and fluoropoly m er friction-fit or threaded tubing connectors. Connections between com pone nts requiring m obility are m a de with 3.2- m m OD fluoropoly m er tubing because of its greater flexibility

. 6.4.3 A cid fum e pretrap—10-cm long x 0.9-cm ID fluoropoly m er tube containing 2–3 g of reagent grade, nonindicating, 8–14 m esh s oda lim e chunks, packed between wads of silanized glass wool. This trap is cleaned of Hg by placing on the output of a clean cold vapor generator (bubble r) and purging for 1 h with N 2 at 350 m L /m in.
6.4.4 C old vapor generator (bubbler)—200-m L borosilicate glass (15 cm high x 5.0 cm diam eter) with standard taper 24/40 neck, fitted with a sparging stopper having a coarse glass frit that extends to within 0.2 cm of the bubbler bottom (Frontier Geosciences, Inc. or equivalent). 

### 6.5 The dual-trap Hg(0) preconcentrating sy stem 6.5.1 F igures 2 and 3 show the dual-trap am algam a tion sy stem (Reference 16.5).

10 Method 1631, Revision E - August 2002Method 1631, Revision E 6.5.2 G old-coated sand traps—10-cm long x 6.5-m m OD x 4-m m ID quartz tubing. The tube is filled with 3.4 cm of gold-coated 45/60 m esh quartz sand (Frontier Geosciences Inc., Seattle, WA, or equivalent). The ends are plugged with quartz wool.
6.5.2.1 T raps are fitted with 6.5-m m ID fluoropoly m er friction-fit sleeves for m a king connection to the sy stem

. When traps are not in use, fluoropoly m er end plugs are inserted in trap ends to elim inate contam ination.
6.5.2.2 A t least six traps are needed for effi cient operation, one as the "analy tical" trap, and the others to sequentially collect sam ples.
6.5.3 H eating of gold-coated sand traps—To deso rb Hg collected on a trap, heat for 3.0 m i n to 450–500 °C (a barely visible red glow when the room is darkened) with a coil consisting of 75 cm of 24-gauge Nichrom e wire at a potential of 10-14 vac. Potential is applied and finely adjusted with an autotransform e r. 6.5.4 T im ers—The heating interval is contro lled by a tim er-activated 120-V outlet (Gralab, or equivalent), into which the heating coil autotransform e r is plugged. Two tim ers are required, one each for the "sam ple" trap and the "analy tical" trap.
6.5.5 A ir blowers—After heating, traps are cooled by blowing air from a sm all squirrel-cage blower positioned im m e diately above the trap

. Two blowers are required, one each for the "sam ple" trap and the "analy tical" trap. 

### 6.6 Recorder—Any m u lti-range m illivolt chart recorder or integrator with a range com p atible with the CVAFS is acceptable. By using a two-pen recorder with pen sensitivity offset by a factor of 10, the dy nam i c range of the sy stem is extended to 10 3

. 

### 6.7 Pipettors—All-plastic pneum atic fixed-volum e and variable pipettors in the range of 10 

### : L to 5.0 mL

. 

### 6.8 Analy tical balance capable of weighing to the nearest 0.01 g 

## 7.0 R eagents and Standards

Note : The quantities of reagents and the preparation pr ocedures in this section are for illustrative purposes. Equivalent performance may be ac hievable using quantities of reagents and procedures other than those suggested here. The laborato ry is responsible for demonstrating equivalent performance. 

### 7.1 Reagent water—18-M 

### S m i nim u m , ultrapure deionized water starting from a prepurified (distilled, reverse osm o sis, etc.) source. Water should be m onitored for Hg, especially after ion exchange beds are changed. 

### 7.2 Air—It is very im portant that the laboratory air be low in both particulate and gaseous m e rcury
. Ideally , m e rcury work should be conducted in a new laboratory with m e rcury -free paint on the walls. A source of air that is very low in Hg should be brought directly into the Class-100 clean bench air intake. If this is not possible, air com i ng into the clean bench can be cleaned for m e rcury by placing a gold-coated cloth prefilter over the intake. Gold-coated cloth filter: Soak 2 m 2 of cotton gauze in 500 m L of 2% gold chloride solution at pH 7. In a hood, add 100 m L of 30% NH 2 OH 

### @ HCl solution, and hom ogenize into the cloth with gloved hands. The m a terial will turn black as colloidal gold is precipitated. Allo w the m i xture to set for several hours, then rinse
Method 1631, Revision E - August 2002 11Method 1631, Revision E with copious am ounts of deionized water. Squeeze-dry the rinsed cloth, and spread flat on newspapers to air-dry

. When dry , fold and place over the intake prefilter of the lam inar flow hood.
CAUTION: Great care should be taken to avoid contaminating the laboratory with gold dust. This could cause interferences with the analysis if gold becomes incorporated into the samples or equipment. The gilding procedure should be done in a remote laboratory if at all possible. 

### 7.3 Hy drochloric acid—trace-m e tal purified reagent-grade HCl containing less than 5 pg/m L Hg. The HCl should be analy zed for Hg before use. 

### 7.4 Hy droxy lam ine hy drochloride—Dissolve 300 g of NH 2 OH 

### @ HCl in reagent water and bring to 1.0 L. This solution m a y be purified by the addition of 1.0 m L of SnCl 2 solution and purging overnight at 500 m L/m in with Hg-free N 2 . Flow injection sy stem s m a y require the use of less SnCl 2 for purification of this solution. 

### 7.5 Stannous chloride—Bring 200 g of SnCl 2 

### @ 2H 2 O and 100 m L concentrated HCl to 1.0 L with reagent water. Purge overnight with m e rcury -free N 2 at 500 m L/m in to rem ove all traces of Hg. Store tightly capped. 

### 7.6 Brom ine m onochloride (BrCl)—In a fum e hood, dissolve 27 g of reagent grade KBr in 2.5 L of low-Hg HCl. Place a clean m a gnetic stir bar in the bottle and stir for approxim a tely 1 h in the fum e hood. Slowly add 38 g reagent grade KBrO 3 to the acid while stirring. When all of the KBrO 3 has been added, the solution color should ch ange from y e llow to red to orange. Loosely cap the bottle, and allow to stir another hour before tightening the lid.
WARNING: This process generates copious quantities of free halogens (Cl 2 , Br 2 , BrCl), which are released from the bottle. Add the KBrO 3 slowly in a fume hood! 

### 7.7 Stock m e rcury standard—NIST-certified 10,000- ppm aqueous Hg solution (NIST-3133). This solution is stable at least until the NIST expiration date. 

### 7.8 Secondary Hg standard—Add approx 0.5 L of reag ent water and 5 m L of BrCl solution (Section 7.6) to a 1.00-L Class A volum etric flask. Add 0.100 m L of the stock m e rcury standard (Section 7.7) to the flask and dilute to 1.00 L with reagen t water. This solution contains 1.00 μ g /m L (1.00 ppm ) Hg. Transfer the solution to a fluoropoly m er bottle and cap tightly

. This solution is considered stable until the NIST expiration date. 

### 7.9 Working Hg Standard A—Dilute 1.00 m L of th e secondary Hg standard (Section 7.8) to 100 m L in a Class A volum etric flask with reagent water containing 0.5% by volum e BrCl solution (Section 7.6). This solution contains 10.0 ng/m L and should be replaced m onthly , or longer if extended stability is dem onstrated. 

### 7.10 Working Hg Standard B—Dilute 0.10 m L of th e secondary Hg standard (Section 7.8) to 1000 m L in a Class A volum etric flask with reagent water containing 0.5% by volum e BrCl solution (Section 7.6). This solution contains 0.10 ng/m L and should be replaced m onthly , or longer if extended stability is dem onstrated. 

### 7.11 Initial Precision and Recovery (IPR) and Ongoing Precision and Recovery (OPR) solutions—Using the working Hg standard A (Section 7.9), prepare IPR and OPR solutions at a

12 Method 1631, Revision E - August 2002Method 1631, Revision E

13 Method 1631, Revision E - August 2002 concentration of 5 ng/L Hg in reagent water. IPR/OPR solutions are prepared using the same amounts of reagents used for preparation of the calibration standards. 

### 7.12 Nitrogen—Grade 4.5 (standard laboratory grade) n itrogen that has been further purified by the removal of Hg using a gold-coated sand trap. 

### 7.13 Argon—Grade 5.0 (ultra high-purity, GC grade) argon that has been further purified by the removal of Hg using a gold-coated sand trap. 

## 8.0 Sample Collection, Preservation, and Storage 8.1 Before samples are collected, consideration should be given to the type of data required (i.e., dissolved or total), so that appropriate preservation and pretreatment steps can be taken. An excess of BrCl should be confirmed either visua lly (presence of a yellow color) or with starch iodide indicating paper, using a separate sample aliquot, prior to sample processing or direct analysis to ensure the sample has been properly preserved. 

### 8.2 Samples are collected into rigorously cleaned fluoropolymer bottles with fluoropolymer or fluoropolymer-lined caps. Glass bottles may be used if Hg is the only target analyte. It is critical that the bottles have tightly sealing caps to avoi d diffusion of atmospheric Hg through the threads (Reference 16.4). Polyethylene sample bottles must not be used (Reference 16.15). 

### 8.3 Collect samples using guidance provided in the Sampling Method (Reference 16.9). Procedures in the Sampling Method are based on rigorous protocols for collection of samples for mercury (References 16.4 and 16.15).
NOTE: Discrete samplers have been found to contami nate samples with Hg at the ng/L level. Therefore, great care should be exercised if this ty pe of sampler is used. It may be necessary for the sampling team to use other means of sample collection if samples are found to be contaminated using the discrete sampler. 

### 8.4 Sample filtration—For dissolved Hg, a sample is filtered through a 0.45- 

### : m capsule filter (Section 6.1.3.1) in a mercury-free clean area prior to preservation. If the sample is filtered, it must be accompanied by a blank that has been filtered under the same conditions. The Sampling Method describes sample filtration procedures. 

### 8.5 Preservation—Samples are preserved by adding either 5 mL/L of pretested 12N HCl or 5 mL/L BrCl solution to the sample bottle. If a sample will be used also for the determination of methyl mercury, it should be collected and preserved according to procedures in the method that will be used for determination of methyl mercury (e.g., HCl or H 2 SO 4 solution). Preserved samples are stable for up to 90 days of the date of collection. 8.5.1 Samples to be analyzed for total or disso lved Hg only may be shipped to the laboratory unpreserved and unrefrigerated if they are collected in fluoropolymer or glass bottles and capped tightly. Samples must be eith er preserved or analyzed within 48 hours of collection. If a sample is oxidized in the sample bottle, the time to preservation can be extended to 28 days. 8.5.2 Samples that are acid-preserved may lose Hg to coagulated organic materials in the water or condensed on the walls (Reference 16. 16). The best approach is to add BrCl directly to the sample bottle at least 24 hours before analysis. If other Hg species are to be analyzed, these aliquots must be removed prior to the addition of BrCl. If BrClMethod 1631, Revision E

14 Method 1631, Revision E - August 2002 cannot be added directly to the sample bo ttle, the bottle must be shaken vigorously prior to sub-sampling. 8.5.3 Handling of the samples in the laboratory should be undertaken in a mercury-free clean bench, after rinsing the outside of the bottles with reagent water and drying in the clean air hood.
NOTE: Because of the potential for contamination, it is recommended that filtration and preservation of samples be performed in the clean room in the laboratory. However, if ci rcumstances prevent overnight shipment of samples, samples should be filtered and preserved in a designated clean area in the field in accordance with the procedures given in Method 1669 (Reference 16.9). If filtered in the field, samples ideally should be filtered into the sample bottle. 

### 8.6 Storage—Sample bottles should be stored in clean(new) polyethylene bags until sample analysis. 8.7 Sample preservation, storage, and holding time requirements also are given at 40 CFR part 136.3(e) Table II. 

## 9.0 Quality Control
9.1 Each laboratory that uses this Method is requi red to operate a formal quality assurance program (Reference 16.17). The minimum requirements of th is program consist of an initial demonstration of laboratory capability, ongoing analysis of standards and blanks as a test of continued performance, and the analysis of matrix spik es (MS) and matrix spike duplicates (MSD) to assess precision and recovery. Laboratory performance is compared to established performance criteria to determine that the results of analyses meet the performance characteristics of the Method. 9.1.1 The laboratory shall make an initial dem onstration of the ability to generate acceptable accuracy and precision. This ability is established as described in Section 9.2. 9.1.2 In recognition of advances that are occurring in analytical technology, the laboratory is permitted certain options to improve results or lower the cost of measurements. These options include automation of the dual-amalgamation system, single-trap amalgamation (Reference 16.18), direct electronic data acquisition, calibration using gas-phase elemental Hg standards, use of the bubbler or flow-injection systems, or changes in the detector (i.e., CVAAS) when less sensitivity is acceptable or desired. Changes in the determinative technique, such as the use of colo rimetry, are not allowed. If an analytical technique other than the CVAFS technique specified in this Method is used, that technique must have a specificity for mercur y equal to or better than the specificity of the technique in this Method. 9.1.2.1 Each time this Method is modified, the la boratory is required to repeat the procedure in Section 9.2 to demonstrate that an MDL (40 CFR part 136, Appendix B) less than or equal to one-third the regulatory compliance limit or less than or equal to the MDL of this Method (Table 1), whichever is greater, can be achieved. If the change will affect calibration, the instrument must be recalibrated according to Section 10.
Note : If the compliance limit is greater than the con centration of Hg in the OPR/OPR (5 ng/L), the acceptance criteria for blanks and the concentrations of mercury spiked into qua lity control samples may be increased to support measurements at the compli ance limit. For example, if the compliance limit is 12Method 1631, Revision E

15 Method 1631, Revision E - August 2002 ng/L (National Toxics Rule, 40 CFR 131.36), the MDL must be less than or equal to 4 ng/L; concentrations of the calibration standards may be 5, 10, 20, 50 , and 100 ng/L; concentrations of the IPR/OPR samples may be 10 ng/L; spike concentra tions and acceptance criteria for MS/MSD samples would remain as specified in Section 9.3; and an appropriate blank acceptance criterion would be 5 ng/L. 9.1.2.2 The laboratory is required to maintain r ecords of modifications made to this Method. These records include the following, at a minimum:

9.1.2.2.1 The names, titles, addresses, and telephone numbers of the analyst(s) who performed the analyses and modification, and the quality control officer who witnessed and will verify the analyses and modification 9.1.2.2.2 A narrative stating the reason(s) for the modification(s) 9.1.2.2.3 Results from all quality control (QC) tests demonstrating the performance of the modified method, including the following: (a) Calibration (Section 10) (b) Initial precision and recovery (Section 9.2.2) (c) Analysis of blanks (Section 9.4) (d) Matrix spike/matrix spike duplicate analysis (Section 9.3) (e) Ongoing precision and recovery (Section 9.5) (f) Quality control sample (Section 9.6) (g) Method detection limit (Section 9.2.1) 9.1.2.2.4 Data that will allow an independent reviewer to validate each determination by tracking the instrument output to the final result. These data are to include the following: (a) Sample numbers and other identifiers (b) Processing dates (c) Analysis dates (d) Analysis sequence/run chronology (e) Sample weight or volume (f) Copies of logbooks, chart recorder, or other raw data output (g) Calculations linking raw data to the results reported 9.1.3 Analyses of MS and MSD samples are required to demonstrate the accuracy and precision and to monitor matrix interferences. Section 9.3 describes the procedure and QC criteria for spiking. 9.1.4 Analyses of blanks are required to dem onstrate acceptable levels of contamination. Section 9.4 describes the procedures and criteria for analyzing blanks. 9.1.5 The laboratory shall, on an ongoing basis, demonstrate through analysis of the ongoing precision and recovery (OPR) sample and the quality control sample (QCS) that the system is in control. Sections 9.5 and 9.6 describe these procedures, respectively. 9.1.6 The laboratory shall maintain records to define the quality of the data that are generated. Sections 9.3.7 and 9.5.3 descr ibe the development of accuracy statements. 9.1.7 Quality of the analyses is controlled by an analytical batch. An analytical batch is a set of samples oxidized with the same batch of reagents, and analyzed during the same 12- hour shift. A batch may be from 1 to as many as 20 samples. Each batch must be accompanied by 3 system blanks (Section 9.4.2 for the flow-injection system), aMethod 1631, Revision E

16 Method 1631, Revision E - August 2002 minimum of 3 bubbler blanks (Section 9.4.1 for the bubbler system), 1 OPR sample at the beginning and end of the batch (Section 9.5), a QCS (Section 9.6), and at least 3 method blanks (Section 9.4.4). In addition, there must be 1 MS and 1 MSD sample for every 10 samples (a frequency of 10%). A typical analytical sequence would be: (a) Three system blanks (Section 9.4.2) or a minimum of 3 bubbler blanks (Section 9.4.1) (b) A minimum of five, non-zero calibration standards (Section 10.2.2.1) (c) On-going precision and recovery (Section 9.5) (d) Quality control sample (Section 9.6) (e) Method blank (Section 9.4.4) (f) Seven samples (g) Method blank (Section 9.4.4) (h) Three samples (i) Matrix spike (Section 9.3) (j) Matrix spike duplicate (Section 9.3) (k) Four samples (l) Method blank (Section 9.4.4) (m) Six samples (n) Matrix spike (Section 9.3) (o) Matrix spike duplicate (Section 9.3) (p) Ongoing precision and recovery (Section 9.5) The above sequence includes calibration. If sy stem performance is verified at the end of the sequence using the OPR, analysis of samples and blanks may proceed without recalibration (i.e., the analytical sequence w ould be entered at Step (d) above), unless more than 12 hours has elapsed since verifica tion of system performance. If more than 12 hours has elapsed, the sequence would be initiated at Step (c) above. 9.2 Initial demonstration of laboratory capability 9.2.1 Method detection limit—To establish the ability to detect Hg, the laboratory shall achieve an MDL that is less than or equal to the MDL listed in Section 1.5 or one-third the regulatory compliance limit, whichever is greater. The MDL shall be determined according to the procedure at 40 CFR 136, Appendix B using the apparatus, reagents, and standards that will be used in the practi ce of this Method. This MDL shall be used for determination of laboratory capability onl y, and should be determined when a new operator begins work or whenever, in the judgment of the laboratory, a change in instrument hardware or operating conditions would dictate reevaluation of capability. 9.2.2 Initial precision and recovery (IPR)—To establish the ability to generate acceptable precision and recovery, the laboratory shall perform the following operations: 9.2.2.1 Analyze four replicates of the IPR solution (5 ng/L, Section 7.11) according to the procedure beginning in Section 11. 9.2.2.2 Using the results of the set of f our analyses, compute the average percent recovery (X), and the standard deviati on of the percent recovery (s) for Hg. 9.2.2.3 Compare s and X with the corres ponding limits for initial precision and recovery in Table 2. If s and X meet the accep tance criteria, system performance is acceptable and analysis of samples may begin. If, however, s exceeds theMethod 1631, Revision E

17 Method 1631, Revision E - August 2002 precision limit or X falls outside the acceptance range, system performance is unacceptable. Correct the problem and repeat the test (Section 9.2.2.1). 9.3 Matrix spike (MS) and matrix spike duplicat e (MSD)—To assess the performance of the Method on a given sample matrix, the laboratory must spike, in duplicate, a minimum of 10% (1 sample in 10) from a given sampling site or, if for compliance monitoring, from a given discharge. Therefore, an analytical batch of 20 samples would require two pairs of MS/MSD samples (four spiked samples total). 9.3.1 The concentration of the spike in the sample shall be determined as follows: 9.3.1.1 If, as in compliance monitoring, the c oncentration of Hg in the sample is being checked against a regulatory compliance lim it, the spiking level shall be at that limit or at 1–5 times the background concentration of the sample (as determined in Section 9.3.2), whichever is greater. 9.3.1.2 If the concentration of Hg in a sample is not being checked against a limit, the spike shall be at 1–5 times the background concentration or at 1-5 times the ML in Table 1, whichever is greater. 9.3.2 To determine the background concentration (B), analyze one sample aliquot from each set of 10 samples from each site or discharge according to the procedure in Section 11. If the expected background concentration is known from previous experience or other knowledge, the spiking level may be established a priori

. 9.3.2.1 If necessary, prepare a standard soluti on to produce an appropriate level in the sample (Section 9.3.1). 9.3.2.2 Spike two additional sample aliquots with identical amounts of the spiking solution and analyze these aliquots as described in Section 11.1.2 to determine the concentration after spiking (A). 9.3.3 Calculate the percent recovery (R) in each aliquot using the following equation:

9.3.4 Compare percent recovery (R) with the QC acceptance criteria in Table 2. 9.3.4.1 If results of the MS/MSD are similar and fail the acceptance criteria, and recovery for the OPR standard (Section 9.5) for the analytical batch is within the acceptance criteria in Table 2, an interfe rence is present and the results may not be reported or otherwise used for permitting or regulatory compliance purposes. If the interference can be attributed to sampling, the site or discharge should be resampled. If the interference can be a ttributed to a method deficiency, the laboratory must modify the method, repeat the test required in Section 9.1.2, and repeat analysis of the sample and MS/MSD. However, during the developmentMethod 1631, Revision E

18 Method 1631, Revision E - August 2002 of Method 1631, very few interferences have been noted in the determination of Hg using this Method. (See Section 4.4 for information on interferences.) 9.3.4.2 If the results of both the spike and the OPR test fall outside the acceptance criteria, the analytical system is judged to be not in control, and the results may not be reported or used for permitting or regulatory compliance purposes. The laboratory must identify and correct the problem and reanalyze all samples in the sample batch. 9.3.5 Relative percent difference (RPD)—Co mpute the RPD between the MS and MSD results according to the following equation using the concentrations found in the MS and MSD. Do not use the recoveries calcula ted in Section 9.3.3 for this calculation because the RPD is inflated when the background concentration is near the spike concentration.

9.3.6 The RPD for the MS/MSD pair must not exceed the acceptance criterion in Table 2. If the criterion is not met, the system is judged to be out of control. The problem must be identified and corrected, and the MS/MSD and corresponding samples reanalyzed. 9.3.7 As part of the QC program for the laboratory, method precision and recovery for samples should be assessed and records maintained. After analyzing five samples in which the recovery passes the test in Sec tion 9.3.4, compute the average percent recovery (R a ) and the standard deviation of the percent recovery (s r ). Express the accuracy assessment as a percent recovery interval from R a- 2s r to R a + 2s r . For example, if R a= 90% and s r = 10% for five analyses, the accuracy interval is expressed as 70–110%. Update the accuracy assessment regularly (e.g., after every five to ten new accuracy measurements). 9.4 Blanks—Blanks are critical to the reliable determin ation of Hg at low levels. The sections below give the minimum requirements for analysis of blanks. Analysis of additional blanks is recommended as necessary to pinpoint sources of contamination in, and external to, the laboratory. 9.4.1 Bubbler blanks—Bubbler blanks are analyzed to demonstrate that bubbler systems are free from contamination at levels that coul d affect data quality. At least three bubbler blanks must be run during calibrati on and with each analytical batch. 9.4.1.1 To analyze a bubbler blank, place a clean gold trap on the bubbler. Purge and analyze previously purged water using the procedure in Section 11, and determine the amount of Hg remaining in the system. 9.4.1.2 If the bubbler blank is found to contain more than 50 pg Hg, the system is out of control. The problem must be investigated and remedied, and the samples run on that bubbler must be reanalyzed. If the blanks from other bubblers contain less than 50 pg Hg, the data associated with those bubblers remain valid, provided that all other criteria in Section 9 also are met.Method 1631, Revision E

19 Method 1631, Revision E - August 2002 9.4.1.3 The mean result for all bubbler blanks (from bubblers passing the specification in Section 9.4.1.2) must be < 25 pg (0.25 ng/ L) Hg with a standard deviation (n-1) of <10 pg (0.10 ng/L). If the mean is < 25 pg, the average peak area or height is subtracted from all raw data before results are calculated (Section 12.2). 9.4.1.4 If Hg in the bubbler blank exceeds the acceptance criteria in Section 9.4.1.3, the system is out of control. The problem must be resolved and the system recalibrated. Usually, the bubbler blank is too high for one of the following reasons: (a) Bubblers need rigorous cleaning; (b) Soda-lime is contaminated; or (c) Carrier gas is contaminated. 9.4.2 System blanks— System blanks are analyzed to demonstrate that flow injection systems are free from contamination at levels that could affect data quality. Three system blanks must be run during calibration and with each analytical batch. 9.4.2.1 To analyze a system blank, analyze reagent water containing the same amount of reagents used to prepare the calibration standards. 9.4.2.2 If a system blank is found to contain 

### $ 0.50 ng/L Hg, the system is out of control. The problem must be investigated and remedied, and the system recalibrated. If the blanks contain < 0.50 ng/L Hg, the data associated with the blanks remain valid, provided that all other criteria in Section 9 also are met. 9.4.2.3 The mean result for the three system blanks must be <0.5 ng/L Hg with a standard deviation (n-1) <0.1 ng/L. If the mean exceeds these criteria, the system is out of control, and the problem must be resolved and the system recalibrated. If the mean is <0.5 ng/L, the average peak height or area is subtracted from all raw data before results are calculated (Section 12.3). 9.4.3 Reagent blanks—Reagent blanks are used to demonstrate that the reagents used to prepare samples for Hg analyses are free from contamination. The Hg concentration in reagent blanks is determined by analyzing the reagent solutions using either the bubbler or flow-injection system. For the bubbler system, reagent may be added directly to previously purged water in the bubbler. 9.4.3.1 Reagent blanks are required when the batch of reagents (bromine monochloride plus hydroxylamine hydrochloride) are prepared. The amount of Hg in a reagent blank containing 0.5% (v/v) BrCl solution (Section 7.6) and 0.2% (v/v) hydroxylamine hydrochloride solution (Sec tion 7.4) must be < 20 pg (0.2 ng/L). 9.4.3.2 The presence of more than 20 pg (0.2 ng/L) of Hg indicates a problem with the reagent solution. The purging of certain reagent solutions, such as SnCl 2 or NH 2 OH, with mercury-free nitrogen or argon can reduce Hg to acceptable levels. Because BrCl cannot be purified, a new batch must be prepared and tested if the BrCl is contaminated. 9.4.4 Method blanks— Method blanks are used to demonstrate that the analytical system is free from contamination that could otherwise compromise sample results. Method blanks are prepared and analyzed using sample containers, labware, reagents, and analytical procedures identical to those used to prepare and analyze the samples.Method 1631, Revision E

20 Method 1631, Revision E - August 2002 9.4.4.1 A minimum of three method blanks pe r analytical batch are required for both the bubbler and flow-injection systems. 9.4.4.2 If the result for any method blank containing the nominal amount of reagent used to prepare a sample (Section 11.1.1) is found to contain 

### $ 0.50 ng/L (50 pg) Hg, the system is out of control. Mercury in the analytical system must be reduced until a method blank is free from contamination at the 0.50 ng/L level. Samples associated with a contaminated method blank must be reanalyzed. 9.4.4.3 Because method blanks are analyzed us ing procedures identical to those used to analyze samples, any sample requiring an increased amount of reagent must be accompanied by at least one method blank that includes an identical amount of reagent. 9.4.5 Field blanks–Field blanks are used to demonstrate that samples have not been contaminated by the sample collection and transport activities. 9.4.5.1 Analyze the field blank(s) shipped with each set of samples (samples collected from the same site at the same time, to a maximum of 10 samples). Analyze the blank immediately before analyzing the samples in the batch. 9.4.5.2 If Hg or any potentially interfering s ubstance is found in the field blank at a concentration equal to or greater than the ML (Table 1), or greater than one-fifth the level in the associated sample, whic hever is greater, results for associated samples may be the result of contaminati on and may not be reported or otherwise used for regulatory compliance purposes. 9.4.5.3 Alternatively, if sufficient multiple field blanks (a minimum of three) are collected, and the average concentration (of the multiple field blanks) plus two standard deviations is equal to or gr eater than the regulatory compliance limit or equal to or greater than one-half of the level in the associated sample, results for associated samples may be the result of contamination and may not be reported or otherwise used for regulatory compliance purposes. 9.4.5.4 If contamination of the field blanks and associated samples is known or suspected, the laboratory should communicat e this to the sampling team so that the source of contamination can be identified and corrective measures taken before the next sampling event. 9.4.6 Equipment blanks—Before any sampling equipment is used at a given site, the laboratory or cleaning facility is required to generate equipment blanks on all sampling equipment that will be used to demonstrate that the sampling equipment is free from contamination. 9.4.6.1 Equipment blanks are generated in th e laboratory or at the equipment cleaning facility by processing reagent water through the sampling devices using the same procedures that are used in the field (see Sampling Method). Therefore, the "clean hands/dirty hands" technique used during field sampling should be followed when preparing equipment blanks at the laboratory or cleaning facility for low level mercury measurements. If grab samples are to be collected using any ancillary equipment, e.g., an extension pole or a dipper, an equipment blankMethod 1631, Revision E

21 Method 1631, Revision E - August 2002 is generated by submersing this equipmen t into the reagent water and analyzing the resulting reagent water collected. 9.4.6.2 The equipment blank must be analyzed using the procedures in this Method. If mercury or any potentially interfering subs tance is detected in the blank at or above the level specified for the field blank (Section 9.4.5), the source of contamination or interference must be identified, and the problem corrected. The equipment must be demonstrated to be free from mercury and interferences before the equipment may be used in the field. 9.4.7 Bottle blanks— Bottles must be subjected to conditions of use to verify the effectiveness of the cleaning procedures. A representative set of sample bottles (Section 6.1.2) should be filled with reagen t water acidified to pH <2 and allowed to stand for a minimum of 24 h. At least 5% of the bottles from a given lot should be tested, and the time that the bottles are allo wed to stand should be as close as possible to the actual time that the sample will be in contact with the bottle. After standing, the water must be analyzed for any signs of contamination. If a bottle shows contamination at or above the level specified for the field blank (Section 9.4.5), the problem must be identified, the cleaning procedures corrected or cleaning solutions changed, and all affected bottles re-cleaned. 9.5 Ongoing precision and recovery (OPR)—To demonstrate that the analytical system is within the performance criteria of this Method and that acceptable precision and recovery is being maintained within each analytical batch, the laboratory shall perform the following operations: 9.5.1 Analyze the OPR solution (5 ng/L, Section 7. 11) prior to the analysis of each analytical batch according to the procedure beginning in Section 11. An OPR also must be analyzed at the end of an analytical sequence or at the end of each 12-hour shift. 9.5.2 Compare the recovery with the limits fo r ongoing precision and recovery in Table 2. If the recovery is in the range specified, the anal ytical system is in control and analysis of samples and blanks may proceed. If, however, the concentration is not in the specified range, the analytical process is not in control. Correct the problem and repeat the ongoing precision and recovery test. All reported results must be associated with an OPR that meets the Table 2 performance criteria at the beginning and end of each batch. 9.5.3 The laboratory should add results that pass the specification in Section 9.5.2 to IPR and previous OPR data and update QC charts to form a graphic representation of continued laboratory performance. The laboratory also should develop a statement of laboratory data quality by calculating the average percent recovery (R a ) and the standard deviation of the percent recovery (s r ). Express the accuracy as a recovery interval from R a– 2s r to R a+ 2s r . For example, if R a= 95% and s r = 5%, the accuracy is 85–105%. 

### 9.6 Quality control sample (QCS) – The laboratory must obtain a QCS from a source different from the Hg used to produce the standards used rou tinely in this Method (Sections 7.7–7.10). The QCS should be analyzed as an independent check of system performance. 

### 9.7 Depending on specific program requirements, the laboratory may be required to analyze field duplicates and field spikes collected to assess the precision and accuracy of the sampling, sample transportation, and storage techniques. The relative percent difference (RPD) between field duplicates should be less than 20%. If the RPD of the field duplicates exceeds 20%, the laboratory should communicate this to the sampling team so that the source of error can be identified and corrective measures take n before the next sampling event.Method 1631, Revision E

22 Method 1631, Revision E - August 2002 

## 10.0 Calibration and Standardization
10.1 Calibration and standardizati on— Separate calibration procedures are provided for a bubbler system (Section 10.2) and flow-injection system (Section 10.3). Both systems are calibrated using standards traceable to NIST Standard Re ference Materials. If system performance is verified at the end of an analytical batch using the OPR, analysis of samples and blanks may proceed without recalibration, unless more than 12 hours has elapsed since verification of system performance. 10.2 Bubbler system calibration 10.2.1 Establish the operating conditions necessary to purge Hg from the bubbler and to desorb Hg from the traps in a sharp peak. Further details for operation of the purgeand-trap, desorption, and analysis systems are given in Sections 11.2.1 and 11.2.2. 10.2.2 The calibration must contain a minimum of five non-zero points and the results of analysis of three bubbler blanks. The lowest calibration point must be at the Minimum Level (ML).
NOTE : The purge efficiency of the bubbler system is 100% and is independent of volume at the volumes used in this Method. Calibration of th is system is typically performed using units of mass. For purposes of working in concentrati on, the volume is assumed to be 100 mL. 10.2.2.1 Standards are analyzed by the addition of aliquots of Hg working standard A (Section 7.9) and Hg working standard B (Section 7.10) directly into the bubblers. Add 0.50 mL of working standard B and 0.5 mL SnCl 2 to the bubbler. Swirl to produce a standard containing 50 pg of Hg (0.5 ng/L). Purge under the optimum operating conditions (Section 10. 2.1). Sequentially follow with the addition of aliquots of 0.05, 0.25, 0.50 and 1.0 mL of working standard A to produce standards of 500, 2500, 5000, and 10,000 pg Hg (5.0, 25.0, 50.0 and 100.0 ng/L).
NOTE : If calibration to the higher levels results in carryover (Section 4.3.8.1), calibrate the system across a narrower range (Section 10.4) 10.2.2.2 Analyze the standards beginning with the lowest concentration and proceeding to the highest. Tabulate the height or area for each peak. 10.2.2.3 Prepare and analyze a minimum of 3 bubbler blanks. If multiple bubblers are used, there must be 1 bubbler blank per bubbler (to a maximum of 4 bubblers). Calculate the mean peak area or height for the bubbler blanks. 10.2.2.4 For each calibration point, subtract the mean peak height or area of the bubbler blanks from the peak height or area for each standard. Calculate the calibration factor (CF x ) for Hg in each of the five standards using the mean bubbler-blanksubtracted peak height or area and the following equation:Method 1631, Revision E

23 Method 1631, Revision E - August 2002 10.2.2.5 Calculate the mean calibration factor (CF m ), the standard deviation of the calibration factor (SD; n-1), and the re lative standard deviation (RSD) of the calibration factor, where RSD = 100 x SD/CF m . 10.2.2.6 If RSD 

### # 15%, calculate the recovery for the lowest standard using CF m . If the RSD 

### # 15% and the recovery of the lowest standard is in the range of 75-125%, the calibration is acceptable and CF m may be used to calculate the concentration of Hg in samples. If RSD > 15% or if the recovery of the lowest standard is not in the range of 75-125%, recalibrate the analytical system and repeat the test. 10.2.2.7 Calculate the concentration of Hg inthe bubbler blanks (Section 10.2.2.1) using CF m . The bubbler blanks must meet the criteria in Section 9.4.1; otherwise, mercury in the system must be reducedand the calibration repeated until the bubbler blanks meet the criteria. 10.3 Flow-injection system calibration 10.3.1 Establish the operating conditions necessary to purge Hg from the gas-liquid separator and dryer tube and desorb Hg from the trap s in a sharp peak. Further details for operating the analytical system are given in Section 11.2.1. 10.3.2 The calibration must contain a minimum of 5 non-zero points and the results of analysis of 3 system blanks. The lowest calibration point must be at the minimum level (ML). 10.3.2.1 Place 25-30 mL of reagent water and 250 μL of concentrated BrCl solution (Section 7.6) in each of 5 calibrated 50-mL autosampler vials. Prepare the 0.5 ng/L calibration standard by adding 250 μL of working standard B (Section 7.10) to the vial. Dilute to the mark with r eagent water. Sequentially follow with the addition of aliquots of 25, 125, 250 and 500 μL of working standard A (Section 7.9) to produce standards of 5.0, 25.0, 50.0 and 100.0 ng/L, respectively. Cap the vials and invert once to mix. 10.3.2.2 Immediately prior to analysis, remove the caps and add 125 μL of NH 2 OH solution (Section 7.4). Re-cap, invert once to mix, and allow to stand until the yellow color disappears. Remove all caps and place vials into the analysis rack. 10.3.2.3 Analyze the standards beginning with the lowest concentration and proceeding to the highest. Tabulate the height or area for the Hg peak. 10.3.2.4 Prepare and analyze a minimum of 3 system blanks and tabulate the peak heights or areas. Calculate the mean peak area or height for the system blanks. 10.3.2.5 For each calibration point, subtract the mean peak height or area of the system blanks (Section 9.4.2) from the peak height or area for each standard. CalculateMethod 1631, Revision E

24 Method 1631, Revision E - August 2002 the calibration factor (CF x ) for Hg in each of the five standards using the mean reagent-blank-subtracted peak height or area and the following equation:

10.3.2.6 Calculate the mean calibration factor (CF m ), the standard deviation of the calibration factor (SD; n-1), and the re lative standard deviation (RSD) of the calibration factor, where RSD = 100 x SD/CF m . 10.3.2.7 If RSD 

### # 15%, calculate the recovery for the lowest standard (0.5 ng/L) using CF m . If the RSD 

### # 15% and the recovery of the lowest standard is in the range of 75-125%, the calibration is acceptable and CF m may be used to calculate the concentration of Hg in samples, blanks, and OPRs. If RSD > 15% or if the recovery of the lowest standard is not in the range of 75-125%, recalibrate the analytical system and repeat the test. 10.3.2.8 Calculate the concentration of Hg inthe system blanks (Section 9.4.2) using CF m . The system blanks must meet the criteria in Section 9.4.2; otherwise, mercury in the system must be reduced and the ca libration repeated until the system blanks meet the criteria. 10.4 Calibration to a range other than 0.5 to 100 ng/L—This Method may be calibrated to a range other than 0.5 to 100 ng/L, provided that the following requirements are met: (a) There must be a minimum of five non-zero calibration points. (b) The difference between successive calibration points must be no greater than a factor of 10 and no less than a factor of 2 and should be approximately evenly spaced on a logarithmic scale over the calibration range. (c) The relative standard deviation (RSD) of the calibration factors for all calibration points must be less than 15%. (d) The calibration factor for any calibration point at a concentration greater than 100 ng/L must be within ±15% of the average calibration factor for the points at or below 100 ng/L. (e) The calibration factor for any point <0.5 ng/L must be within 25% of the average calibration factor for all points. (f) If calibration is to a higher range and this Method is used for regulatory compliance, the ML must be less than one-third the regulatory compliance limit 

## 11.0 Procedure

NOTE: The following procedures for analysis of samples are provided as guidelines. Laboratories may find it necessary to optimize the procedures, such as drying time or potential applied to the Nichrome wires, for the laboratory's specific instrument set-up.Method 1631, Revision E

25 Method 1631, Revision E - August 2002 11.1 Sample Preparation 11.1.1 Pour a 100-mL aliquot from a thoroughly shaken, acidified sample, into a 125-mL fluoropolymer bottle. If BrCl was not added as a preservative (Section 8.5), add the amount of BrCl solution (Section 7.6) given below, cap the bottle, and digest at room temperature for a 12 h minimum. 11.1.1.1 For clear water and filtered samples, add 0.5 mL of BrCl; for brown water and turbid samples, add 1.0 mL of BrCl. If the yellow color disappears because of consumption by organic matter or sulfid es, more BrCl should be added until a permanent (12-h) yellow color is obtained. 11.1.1.2 Some highly organic matrices, such as sewage effluent, will require high levels of BrCl (e.g., 5 mL/100 mL of sample) and longer oxidation times, or elevated temperatures (e.g., place sealed bottles in oven at 50 °C for 6 h). The oxidation must be continued until it is complete. Complete oxidation can be determined by either observation of a permanent yellow color remaining in the sample or the use of starch iodide indicating paper to test for residual free oxidizer. The sample also may be diluted to reduce the amount of BrCl required, provided that the resulting level of mercury is sufficient for reliable determination. 11.1.2 Matrix spikes and matrix spike duplicates—For every 10 or fewer samples, pour 2 additional 100-mL aliquots from a selected sample (see Section 9.3), spike at the level specified in Section 9.3, and process in th e same manner as the samples. There must be a minimum of 2 MS/MSD pairs for each analytical batch of 20 samples. 11.2 Hg reduction and purging—Separa te procedures are provided for the bubbler system (Section 11.2.1) and flow-injection (Section 11.2.2). 11.2.1 Hg reduction and purging for the bubbler system 11.2.1.1 Add 0.2-0.25 mL of NH 2 OH solution to the BrCl-oxidized sample in the 125-mL sample bottle. Cap the bottle and swirl the sample. The yellow color will disappear, indicating the destruction of the BrCl. Allow the sample to react for 5 min with periodic swirling to be sure that no traces of halogens remain.
NOTE: Purging of free halogens onto the gold trap will result in damage to the trap and low or irreproducible results. 11.2.1.2 Connect a fresh trap to the bubbler, pour the reduced sample into the bubbler, add 0.5 mL of SnCl 2 solution, and purge the sample onto a gold trap with N 2 at 350 ± 50 mL/min for 20 min. 11.2.1.3 When analyzing Hg samples, the recovery is quantitative, and organic interferents are destroyed. Thus, sta ndards, bubbler blanks, and small amounts of high-level samples may be run directly inpreviously purged water. After very high samples (Section 4.3.8.1), a small degree of carryover (<0.01%) may occur. Bubblers that contain such samples must be demonstrated to be clean prior to proceeding with low level samples. Samples run immediately following a sample that has been determined to result in carryover must be reanalyzed using a bubbler that is demonstrated to be clean as per Section 4.3.8.1. 11.2.2 Hg reduction and purging for the flow-injection systemMethod 1631, Revision E

26 Method 1631, Revision E - August 2002 11.2.2.1 Add 0.2-0.25 mL of NH 2 OH solution (Section 7.4) to the BrCl-oxidized sample in the 125-mL sample bottle or in the autosampler tube (the amount of NH 2 OH required will be approximately 30 percen t of the BrCl volume). Cap the bottle and swirl the sample. The yellow color will disappear, indicating the destruction of the BrCl. Allow the sample to react for 5 minutes with periodic swirling to be sure that no traces of halogens remain.
NOTE: Purging of free halogens onto the gold trap will result in damage to the trap and low or irreproducible results. 11.2.2.2 Pour the sample solution into an auto sampler vial and place the vial in the rack. 11.2.2.3 Carryover may occur after analysis of a sample containing a high level of mercury. Samples run immediately following a sample that has been determined to result in carryover (Section 4.3.8.1) must be reanalyzed using a system demonstrated to be clean as per Section 4.3.8.1.

11.3 Desorption of Hg from the gold trap 11.3.1 Remove the sample trap from the bubbler, place the Nichrome wire coil around the trap and connect the trap into the analyzer train between the incoming Hg-free argon and the second gold-coated (analytical) sand trap (Figure 2). 11.3.2 Pass argon through the sample and analytical traps at a flow rate of approximately 30 mL/min for approximately 2 min to drive off condensed water vapor. 11.3.3 Apply power to the coil around the sample tr ap for 3 minutes to thermally desorb the Hg (as Hg(0)) from the sample tr ap onto the analytical trap. 11.3.4 After the 3-min desorption time, turn off the power to the Nichrome coil, and cool the sample trap using the cooling fan. 11.3.5 Turn on the chart recorder or other data acquisition device to start data collection, and apply power to the Nichrome wire coil around the analytical trap. Heat the analytical trap for 3 min (1 min beyond the point at which the peak returns to baseline). 11.3.6 Stop data collection, turn off the power to the Nichrome coil, and cool the analytical trap to room temperature using the cooling fan. 11.3.7 Place the next sample trap in line and proceed with analysis of the next sample.
NOTE: Do not heat a sample trap while the analy tical trap is still warm; otherwise, the analyte may be lost by passing through the analytical trap.
11.4 Peaks generated using this tec hnique should be very sharp and almost symmetrical. Mercury elutes at approximately 1 minute and has a width at half-height of about 5 seconds. 11.4.1 Broad or asymmetrical peaks indicate a problem with the desorption train, such as improper gas flow rate, water vapor on the tr ap(s), or an analytical trap damaged by chemical fumes or overheating.Method 1631, Revision E

27 Method 1631, Revision E - August 2002 11.4.2 Damage to an analytical trap is also indicated by a sharp peak, followed by a small, broad peak. 11.4.3 If the analytical trap has been damaged, the trap and the fluoropolymer tubing downstream from it should be discarded because of the possibility of gold migration onto downstream surfaces. 11.4.4 Gold-coated sand traps should be tracked by unique identifiers so that any trap producing poor results can be quickly recognized and discarded. 

## 12.0 Data Analysis and Calculations
12.1 Separate procedures are provided for calculation of sample results using the bubbler system (Section 12.2) and the flow-injection system (Section 12.3), and for method blanks (Section 12.4). 12.2 Calculations for the bubbler system 12.2.1 Calculate the mean peak height or area for Hg in the bubbler blanks measured during system calibration or with the analytical batch (A BB ; n = 3 minimum). 12.2.2 Calculate the concentration of Hg in ng/L (parts-per-trillion; ppt) in each sample according to the following equation:



### 12.3 Calculations for the flow-injection system 12.3.1 Calculate the mean peak height or area for Hg in the system blanks measured during system calibration or with each analytical batch (A SB ; n = 3) 12.3.2 Calculate the concentration of Hg inng/L in each sample according to the following equation:

12.4 Calculations for concentration of Hg in me thod blanks, field blanks, and reagent blanks.Method 1631, Revision E

28 Method 1631, Revision E - August 2002 12.4.1 Calculate the concentration of Hg in the method blanks (C MB ), field blanks (C FB ), or reagent blanks (C RB ) in ng/L, using the equation in Section 12.2.2 (if bubbler system is used) or Section 12.3.2 (if flow injection system is used) and substituting the peak height or area resulting from the method blank, field blank, or reagent blank for A s . 12.4.2 Determine the mean concentration of Hg in the method blanks associated with the analytical batch (a minimum of three). If a sample requires additional reagent(s) (e.g., BrCl), a corresponding method blank containing an identical amount of reagent must be analyzed (Section 9.4.4.3). The concentration of Hg in the corresponding method blank may be subtracted from the concentration of Hg in the sample per Section 12.5.2. 

### 12.5 Reporting 12.5.1 Report results for Hg at or above the ML, in ng/L, to three significant figures. Report results for Hg in samples below the ML as <0 .5 ng/L, or as required by the regulatory authority or in the permit. Report results for Hg in reagent blanks and field blanks at or above the ML, in ng/L, to three significant figures. Report results for Hg in reagent blanks, method blanks, or fiel d blanks below the ML but at or above the MDL to two significant figures. Report results for Hg not detected in reagent blanks, method blanks, or field blanks as <0.2 ng/L, or as re quired by the regulatory authority or in the permit. 12.5.2 Report results for Hg in samples, method bl anks and field blanks separately. In addition to reporting results for the samples and blank(s) separately, the concentration of Hg in the method blanks or field blanks associated with the sample may be subtracted from the results for that sample, or must be subtracted if requested or required by a regulatory authority or in a permit. 12.5.3 Results from tests performed with an analyti cal system that is not in control must not be reported or otherwise used for permitting or regulatory compliance purposes, but do not relieve a discharger or permittee of reporting timely results.



## 13.0 Method Performance 13.1 This Method was tested in 12 laboratories using reagent water, freshwater, marine water and effluent (Reference 16.19). The quality control accep tance criteria listed in Table 2 were verified by data gathered in the interlaboratory st udy, and the method detection limit (MDL) given in Section 1.5 was verified in all 12 laboratories. In addition, the techniques in this Method have been compared with other techniques for low-leve l mercury determination in water in a variety of studies, including ICES-5 (Reference 16.20) and the International Mercury Speciation Intercomparison Exercise (Reference 16.21). 

### 13.2 Precision and recovery data for reagent water, freshwater, marine water, and secondary effluent are given in Table 3.Method 1631, Revision E

29 Method 1631, Revision E - August 2002 

## 14.0 Pollution Prevention
14.1 Pollution prevention encompasses any technique that reduces or eliminates the quantity or toxicity of waste at the point of generation. Many opportunities for pollution prevention exist in laboratory operation. EPA has established a pref erred hierarchy of environmental management techniques that places pollution prevention as the ma nagement option of first choice. Whenever feasible, laboratory personnel should use pollution prevention techniques to address waste generation. When it is not feasible to redu ce wastes at the source, the Agency recommends recycling as the next best option. The acids u sed in this Method should be reused as practicable by purifying by electrochemical techniques. The only other chemicals used in this Method are the neat materials used in preparing standards. These standards are used in extremely small amounts and pose little threat to the environment when managed properly. Standards should be prepared in volumes consistent with laboratory use to minimize the disposal of excess volumes of expired standards. 

### 14.2 For information about pollution prevention that may be applied to laboratories and research institutions, consult Less is Better: Laboratory Chemical Management for Waste Reduction , available from the American Chemical Society' s Department of Governmental Relations and Science Policy, 1155 16th Street NW, Washington DC 20036, 202/872–4477. 

## 15.0 Waste Management
15.1 The laboratory is responsible for complying w ith all Federal, State, and local regulations governing waste management, particularly hazardous waste identification rules and land disposal restrictions, and for protecting the air, water, and land by minimizing and controlling all releases from fume hoods and bench operations. Complia nce with all sewage discharge permits and regulations is also required. An ove rview of requirements can be found in Environmental Management Guide for Small Laboratories (EPA 233-B-98-001). 

### 15.2 Acids, samples at pH <2, and BrCl solutions must be neutralized before being disposed of, or must be handled as hazardous waste. 

### 15.3 For further information on waste management, consult The Waste Management Manual for Laboratory Personnel and Less is Better: Laboratory Chemical Management for Waste Reduction , both available from the American Chemical Society's Department of Government Relations and Science Policy, 1155 16t h Street NW, Washington, DC 20036. 

## 16.0 References
16.1 Bloom, Nicolas, Draft “Total Mercury in Aqueous Media,” Frontier Geosciences, Inc., September 7, 1994. 

### 16.2 Fitzgerald, W.F.; Gill, G.A. "Sub-Nanogram De termination of Mercury by Two-Stage Gold Amalgamation and Gas Phase Detection Applied to Atmospheric Analysis," Anal. Chem. 1979, 15 , 1714. 

### 16.3 Bloom, N.S; Crecelius, E.A. "Determination of Mercury in Sea water at Subnanogram per Liter Levels," Mar. Chem. 1983, 14 , 49. 

### 16.4 Gill, G.A.; Fitzgerald, W.F. "Mercury Sampling of Open Ocean Waters at the Picogram Level," Deep Sea Res 1985, 32 , 287.Method 1631, Revision E

30 Method 1631, Revision E - August 2002 

### 16.5 Bloom, N.S.; Fitzgerald, W.F. "Determination of Volatile Mercury Species at the Picogram Level by Low-Temperature Gas Chromatography with Cold-Vapor Atomic Fluorescence Detection," Anal. Chim. Acta. 1988, 208 , 151. 

### 16.6 Guidance on Establishing Trace Metal Clean Rooms in Existing Facilities, U.S. EPA, Office of Water, Office of Science and Technology, E ngineering and Analysis Division (4303), 401 M Street SW, Washington, DC 20460, January 1996, EPA 821-B-96-001. 

### 16.7 Trace Metal Cleanroom, prepared by Research Triangle Institute for U.S. Environmental Protection Agency, 26 W. Martin Luther King Dr., Cincinnati, OH 45268, RTI/6302/04-02 F. 

### 16.8 Guidance on the Documentation and Evaluation of Trace Metals Data Collected for Clean Water Act Compliance Monitoring, U.S. Environmental Protection Agency, Office of Water, Office of Science and Technology, Engineering and An alysis Division (4303), 401 M Street SW, Washington, DC 20460, July 1996, EPA 821-B-96-004. 

### 16.9 Method 1669, "Method for Sampling Ambient Wate r for Determination of Metals at EPA Ambient Criteria Levels," U.S. Environmental Protection Agency, Office of Water, Office of Science and Technology, Engineering and An alysis Division (4303), 401 M Street SW, Washington, DC 20460, April 1995 with January 1996 revisions. 

### 16.10 Correspondence from Nicolas Bloom, Frontier Geo sciences, Inc. to Dale Rushneck, Interface, Inc., December 31, 1998. 

### 16.11 "Working with Carcinogens," Department of H ealth, Education, and Welfare, Public Health Service. Centers for Disease Control. NIOSH Publication 77-206, Aug. 1977, NTIS PB-277256. 

### 16.12 "OSHA Safety and Health Standards, General Industry," OSHA 2206, 29 CFR 1910. 

### 16.13 "Safety in Academic Chemistry Laboratories," ACS Committee on Chemical Safety, 1979. 

### 16.14 "Standard Methods for the Examination of Water and Wastewater," 18th ed. and later revisions, American Public Health Association, 1015 15th Street NW, Washington, DC 20005. 1-35: Section 1090 (Safety), 1992. 

### 16.15 Bloom, N.S. "Trace Metals & Ultra-Clean Sample Handling," Environ. Lab. 1995, 7 , 20. 

### 16.16 Bloom, N.S. "Influence of Analytical Conditions on the Observed 'Reactive Mercury,' Concentrations in Natural Fresh Waters," In Mercury as a Global Pollutant ; Huckabee, J. and Watras, C.J., Eds.; Lewis Publishers, Ann Arbor, MI: 1994. 

### 16.17 "Handbook of Analytical Quality Control in Water and Wastewater Laboratories," U.S. Environmental Protection Agency. Environmental Monitoring Systems Laboratory, Cincinnati, OH 45268, EPA-600/4-79-019, March 1979. 

### 16.18 Liang, L.; Bloom, N.S. "Determination of Total Mercury by Single-Stage Gold Amalgamation with Cold Vapor Atom Spectrometric Detection," J. Anal. Atomic Spectrom. 1993, 8 , 591. 

### 16.19 "Results of the EPA Method 1631 Validation Study ," February, 1998. Available from the EPA Sample Control Center, 6101 Stevenson Avenue, Alexandria, VA, 22304; 703/461-2100.Method 1631, Revision E

31 Method 1631, Revision E - August 2002 

### 16.20 Cossa, D.; Couran, P. "An International Interc omparison Exercise for Total Mercury in Sea Water," App. Organomet. Chem. 1990, 4 , 49. 

### 16.21 Bloom, N.S.; Horvat, M.; Watras, C.J. "Results of the International Mercury Speciation Intercomparison Exercise," Wat. Air. Soil Pollut. , 1995, 80, 1257. 

## 17.0 Glossary The definitions and purposes below are specific to th is Method, but have been conformed to common usage as much as possible. 

### 17.1 Ambient Water—Waters in the natural environment (e.g., rivers, lakes, streams, and other receiving waters), as opposed to effluent discharges. 

### 17.2 Analytical Batch —A batch of up to 20 samples that are oxidized with the same batch of reagents and analyzed during the same 12-hour shift. Each analytical batch must also include at least three bubbler blanks, an OPR, and a QCS. In addition, MS/MSD samples must be prepared at a frequency of 10% per analytical batch (one MS/MSD for every 10 samples). 

### 17.3 Bottle Blank —The bottle blank is used to demonstrate that the bottle is free from contamination prior to use. Reagent water known to be free of me rcury at the MDL of this Method is added to a bottle, acidified to pH <2 with BrCl or HCl, and allowed to stand for a minimum of 24 hours. The time that the bottle is allowed to stand s hould be as close as possible to the actual time that the sample will be in contact with the bottle. After standing, the water is analyzed. 

### 17.4 Bubbler Blank —For this Method, the bubbler blank is specific to the bubbler system and is used to determine that the analytical system is free fro m contamination. After analysis of a standard, blank, or sample, the solution in the bubbler is purged and analyzed. A minimum of three bubbler blanks is required for system calibration. 

### 17.5 Equipment Blank —Reagent water that has been pr ocessed through the sampling device at a laboratory or other equipment cleaning facility prior to shipment of the sampling equipment to the sampling site. The equipment blank is used to demonstrate that the sampling equipment is free from contamination prior to use. Where appropriate, the "clean hands/dirty hands" technique used during field sampling should be followed when preparing equipment blanks at the laboratory or cleaning facility. 

### 17.6 Field Blank —Reagent water that has been transported to the sampling site and exposed to the same equipment and operations as a sample at the sampling site. The field blank is used to demonstrate that the sample has not been cont aminated by the sampling and sample transport systems. 

### 17.7 Intercomparison Study—An exercise in which samples are prepared and split by a reference laboratory, then analyzed by one or more testi ng laboratories and the reference laboratory. The intercomparison, with a reputable laboratory as th e reference laboratory, serves as the best test of the precision and accuracy of the analyses at natural environmental levels.Method 1631, Revision E

32 Method 1631, Revision E - August 2002 

### 17.8 Matrix Spike (MS) and Matrix Spike Duplicate (MSD) —Aliquots of an environmental sample to which known quantities of the analyte(s) of inte rest is added in the laboratory. The MS and MSD are analyzed exactly like a sample. Thei r purpose is to quantify the bias and precision caused by the sample matrix. The background concen trations of the analytes in the sample matrix must be determined in a separate aliquot and the measured values in the MS and MSD corrected for these background concentrations. 

### 17.9 May—This action, activity, or procedural step is allowed but not required. 

### 17.10 May not—This action, activity, or procedural step is prohibited. 

### 17.11 Method blank — Method blanks are used to determine the concentration of mercury in the analytical system during sample preparation and analysis, and consist of a volume of reagent water that is carried through the entire sample preparation and analysis. Method blanks are prepared by placing reagent water in a sample bottle and analyzing the water using reagents and procedures identical to those used to prepare and analyze the corresponding samples. A minimum of three method blanks is required with each analytical batch. 

### 17.12 Minimum Level (ML) —The lowest level at which the entire analytical system must give a recognizable signal and acceptable calibration point fo r the analyte. It is equivalent to the concentration of the lowest calibration standard, assuming that all method-specified sample weights, volumes, and cleanup procedures have been employed. The ML is calculated by multiplying the MDL by 3.18 and rounding the result to the number nearest to (1, 2, or 5) x 10 n , where n is an integer (See Section 1.5). 

### 17.13 Must—This action, activity, or procedural step is required. 

### 17.14 Quality Control Sample (QCS) —A sample containing Hg at known concentrations. The QCS is obtained from a source external to the laboratory, or is prepared from a source of standards different from the source of calibration standard s. It is used as an independent check of instrument calibration. 17.15 Reagent blank —Reagent blanks are used to determine the concentration of mercury in the reagents (BrCl, NH 2 OH 

### @ HCl, and SnCl 2 ) that are used to prepare a nd analyze the samples. In this Method, reagent blanks are required when each new batch of reagents is prepared. 

### 17.16 Reagent Water—Water demonstrated to be free of mercury at the MDL of this Method. It is prepared from 18 M 

### S ultrapure deionized water starting from a prepurified source. Reagent water is used to wash bottles, as trip and field blanks, and in the preparation of standards and reagents. 

### 17.17 Regulatory Compliance Limit—A limit on the concentration or amount of a pollutant or contaminant specified in a nationwide standard , in a permit, or otherwise established by a regulatory authority. 

### 17.18 Shall—This action, activity, or procedure is required. 

### 17.19 Should —This action, activity, or procedure is suggested, but not required.Method 1631, Revision E

33 Method 1631, Revision E - August 2002 

### 17.20 Stock Solution — A solution containing an analyte that is prepared from a reference material traceable to NIST, or a source that will attest to the purity and authenticity of the reference material. 

### 17.21 System Blank — For this Method, the system blank is specific for the flow-injection system and is used to determine contamination in the analytical system and in the reagents used to prepare the calibration standards. A minimum of three system blanks is required during system calibration. 

### 17.22 Ultraclean Handling — A series of established procedures designed to ensure that samples are not contaminated during sample collection, storage, or analysis.Method 1631, Revision E

34 Method 1631, Revision E - August 2002 

## 18.0 Tables and Figures

Table 1 Lowest Ambient Water Quality Criterion for Mercury and the Method Detection Limit and Minimum Level of Quantitation for EPA Method 1631

Metal Lowest Ambient Water Quality Criterion (1) Method Detection Limit (MDL) and Minimum Level (ML) MDL (2) ML (3) Mercury (Hg) 1.3 ng/L 0.2 ng/L 0.5 ng/L

1. Lowest water quality criterion for the GreatLakes System (Table 4, 40 CFR 132.6). The lowest Nationwide criterion is 12 ng/L (40 CFR 131.36). 2. Method detection limit (40 CFR 136, Appendix B) 3. Minimum level of quantitation (see Glossary)

Table 2

Quality Control Acceptance Criteria for Performance Tests in EPA Method 1631

Acceptance Criteria Section Limit (%) Initial Precision and Recovery (IPR) 9.2.2 Precision (RSD) 9.2.2.3 21 Recovery (X) 9.2.2.3 79-121 Ongoing Precision and Recovery (OPR) 9.5.2 77-123 Matrix Spike/Matrix Spike Duplicate (MS/MSD) 9.3 Recovery 9.3.4 71-125 Relative Percent Difference (RPD) 9.3.5 24Method 1631, Revision E

35 Method 1631, Revision E - August 2002 Table 3 Precision and Recovery for Reagent Water, Fresh Water, Marine Water, and Effluent Water Using Method 1631

Matrix *Mean Recovery (%) *Precision (% RSD)
Reagent Water 98.0 5.6 Fresh Water (Filtered) 90.4 8.3 Marine Water (Filtered) 92.3 4.7 Marine Water (Unfiltered) 88.9 5.0 Secondary Effluent (Filtered) 90.7 3.0 Secondary Effluent (Unfiltered) 92.8 4.5

* Mean percent recoveries and RSDs are based on expected Hg concentrations.Method 1631, Revision E

36 Method 1631, Revision E - August 2002 

### Figure 1. Schematic Diagram of Bubbler SetupMethod 1631, Revision E

37 Method 1631, Revision E - August 2002 

### Figure 2. Schematic Diagram of the Bubbler, Purge and Trap, Cold Vapor Atomic Fluorescence Spectrometer (CVAFS) SystemMethod 1631, Revision E

38 Method 1631, Revision E - August 2002WasteReducingAgentLiquid Sample HandlingGas / LiquidSeparatorSystemController(PC)AnalyticalCartridgeV24-wayV13-wayDetectorCarrier(Argon)Detector Carrier Flow(Mass Flow Controller)SeparatorFlow(BallFlowmeter)HEATER-AAF DETECTORData Acquisition/Control UnitFAN-ADual Stage Gold PreconcentratorKey:Main Pump Speed ControlDI waterAutosamplerAuto-Sampler PortFAN-BSoda LimeScrubberHEATER-BSamplingCartridgeWash Station Pump ControlV1VENTV2LOADSeparatorFlow(Argon orNitrogen)Hi-ResolutionA/D InputLiquid SamplePhase SeparatorCarrier GasControl LineDI WaterReducing AgentLiquid WasteArgon CarrierPP3P2PWash StationVent VentSampleRackSampleProbeWashPump(2 channel)Main PeristalticPumpMFC450 ml/m80ml/mCarrierGas InLiquidWasteLiquidSampleInLoadedCarrierOutP1



### Figure 3. Schematic Diagram of the Flow -Injection, Cold Vapor Atomic Fluorescence Spectrometer (CVAFS) System