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EPA METHOD 557

DETERMINATION OF HALOACETIC ACIDS, BROMATE, AND DALAPON IN 

DRINKING WATER BY ION CHROMATOGRAPHY/ELECTROSPRAY IONIZATION 

TANDEM MASS SPECTROMETRY (IC/ESI-MS/MS)

RESEARCH SUMMARY

March 2009

by

A. D. Zaffiro and M. Zimmerman

Shaw Environmental, Inc.

Prepared for

D. J. Munch

Technical Support Center

Office of Ground Water and Drinking Water

U. S. Environmental Protection Agency

Cincinnati, Ohio 45268
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Table of Contents _____________________________________

Page

List of Tables ...................................................................................................................................3

List of Figures..................................................................................................................................3

List of Acronyms .............................................................................................................................4

1.0 Introduction and Background ..............................................................................................5

2.0 Chronology of the Method 557 Development Effort at EPA ..............................................7

3.0 Preservation..........................................................................................................................9

4.0 Standard Preparation Considerations and Storage Stability of Aqueous Standard

Solutions ............................................................................................................................10

4.1 Standard Preparation Considerations.....................................................................10

4.2 Stability of Aqueous Standards..............................................................................11

5.0 Second Source Verification ...............................................................................................13

6.0 Accelerated Storage Stability Studies................................................................................13

7.0 Chlorite and Chlorate P&A Study .....................................................................................15

8.0 EPA Method Performance Data.........................................................................................19

9.0 Second Laboratory Results................................................................................................20

10.0 References..........................................................................................................................24
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List of Tables _________________________________________

Table Title Page

1 Presentations and Manuscripts Associated with the Method 557 Development Project.....9

2 PDS Storage Stability Results............................................................................................12

3 Calibration Standard Storage Stability Results..................................................................12

4 Method Performance Quality Control Sample Results, 5-μg/L Standard .........................13

5 Accelerated Storage Stability Study in Reagent Water .....................................................14

6 Accelerated Storage Stability Study in Cincinnati Tap Water...........................................15

7 P&A Results at 5 μg/L in the Presence of 1 mg/L Chlorite, and 0.5 mg/L Chlorate ........15

8 Southern Nevada Water Authority IC/ESI-MS/MS Lowest Concentration MRLs...........21

9 Southern Nevada Water Authority Precision and Accuracy Results for Tap Water 

Fortified at 10 μg/L (n = 9)................................................................................................22

10 Southern Nevada Water Authority Precision and Accuracy Results for Reagent Water

Fortified at 10 μg/L (n = 9)................................................................................................22

11 Southern Nevada Water Authority Precision and Accuracy Results for Synthetic

Matrix Fortified at 10 μg/L (n = 9)....................................................................................22

List of Figures ________________________________________

Figure Title Page

1 Dionex AS24 column: synthetic sample matrix fortified at 5 μg/L plus chlorite 

(1 mg/L) and chlorate (0.5 mg/L) ......................................................................................17

2 Dionex AS24 column: conductivity trace, synthetic sample matrix plus chlorite 

(1 mg/L) and chlorate (0.5 mg/L) ......................................................................................18

3 Las Vegas tap water fortified at 10 μg/L and analyzed on the AS24 

column at the SNWA laboratory........................................................................................23
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List of Acronyms

ACS American Chemical Society

AS24 Analytical Separator 24

BCAA bromochloroacetic acid

BDCAA bromodichloroacetic acid

CDBAA chlorodibromoacetic acid

ClO2 chlorine dioxide

DBAA dibromoacetic acid

DCAA dichloroacetic acid

DL detection limit

EDA ethylenediamine

EPA U.S. Environmental 

Protection Agency 

ESI electrospray ionization

GC gas chromatography

HAA haloacetic acid

HAA5 five regulated haloacetic 

acids

HAA9 nine haloacetic acids

IC ion chromatography

IDC Initial Demonstration of 

Capability

L liter

LCMRL lowest-concentration, 

minimum reporting level

MBAA monobromoacetic acid

MCAA monochloroacetic acid

MCL maximum contaminant level

μg microgram

mg milligram

mL milliliter

MRL minimum reporting level

MRM multiple reaction monitoring

MS mass spectrometry

MS/MS tandem mass spectrometer

MtBE methyl-t-butyl ether

NERL National Exposure Research 

Laboratory

n number of observations

NH4Cl ammonium chloride

P&A precision and accuracy

PDS primary dilution standard

PI principal investigator

QC quality control

QCS quality control sample

RAA running annual average

RPD relative percent difference

RSD relative standard deviation

SNWA Southern Nevada Water 

Authority

SOP standard operating procedure

TBAA tribromoacetic acid

TCAA trichloroacetic acid

TSC Technical Support Center
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1.0 Introduction and Background

EPA developed Method 557 as an alternate test procedure for compliance monitoring of 

haloacetic acids (HAAs), dalapon, and bromate in drinking water. This introduction provides a 

brief background on the regulation of HAAs, a review of existing methods for their detection in 

drinking water, and discusses the developments that led EPA to propose this new approach. This 

section also explains the reason EPA included dalapon and bromate in the analyte list.

HAAs are formed during the disinfection of drinking water through a reaction of hypochlorous 

acid (or hypochlorite) with natural organic matter. Five haloacetic acids (HAA5) are currently 

regulated in drinking water by the U.S. Environmental Protection Agency (EPA) under the Stage 

II Disinfection Byproducts (DBP) Rule1 at a total maximum contaminant level (MCL) of 

60 micrograms per liter (μg/L). Included in this group are monochloroacetic acid (MCAA), 

monobromoacetic acid (MBAA), dichloroacetic acid (DCAA), dibromoacetic acid (DBAA), and 

trichloroacetic acid (TCAA). Unlike other regulations, the DBP rule sets a minimum reporting 

limit (MRL) for each of the HAA5 species.

Three EPA methods2

and two Standard Methods3 are currently approved under the Stage II DBP 

Rule for compliance monitoring of HAAs. Each method requires extraction of the HAAs into an 

organic solvent, and then methylation of the analytes using either diazomethane or acidic 

methanol. Extracts are analyzed by gas chromatography (GC) with electron capture detection. 

Because the methylation efficiencies are not complete for all analytes, each of the approved 

methods requires the processing of at least five calibration standards to prepare an internalstandard-based, procedural calibration curve. Quality control (QC) samples also require 

processing through the entire method.

While these GC methods meet EPA’s regulatory need under the Stage II DBP Rule, advances in 

ion chromatography/mass spectrometry (IC/MS) created the potential for a direct-inject 

approach. A direct-inject method simplifies the analysis of HAAs by eliminating the extraction 

and derivatization steps and the associated procedural calibration. Several methods for HAA 

analysis based on the use of IC coupled with single-stage MS were reported in the literature; 

however, these methods did not demonstrate adequate sensitivity4 and lacked suitable selectivity 

to resolve matrix interferences.5 In addition, these early attempts were subject to interference, 

because the ion-exchange columns available at that time could not separate common anions 

(chloride, carbonate, sulfate, and nitrate), present in all drinking water sources, from HAAs.

In 2005, Dionex (Sunnyvale, California) collaborated with MDS/Sciex (Toronto, Canada) to 

evaluate the application of IC coupled with electrospray ionization (ESI)/tandem mass 

spectrometry (MS/MS) to HAA analysis. Method development projects conducted at the EPA 

Technical Support Center (TSC) laboratory in Cincinnati had already demonstrated the potential 

gains in selectivity and sensitivity via use of MS/MS as the detection technique for direct-inject, 

drinking water methods. To eliminate the problem caused by the matrix, Dionex developed an 

ion-exchange column with optimized selectivity to separate the common anions in drinking 

water from the HAA analytes. [Dionex Analytical Separator 24 (AS24), 150 mm x 2 mm i.d.]. 

The use of this column eliminated the key limitations inherent in previous attempts to analyze for 

HAAs in drinking water using a direct-inject approach: 1) suppression in the ESI interface 

resulting from the coelution of matrix components, and 2) fouling of the ESI source by these 
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matrix components. MS/MS provided the sensitivity required to achieve the promulgated MRLs 

for HAAs.

In addition to HAA5, the AS24 column separates dalapon (2,2-dichloropropionic acid), 

bromochloroacetic acid (BCAA), bromodichloroacetic acid (BDCAA), chlorodibromoacetic acid 

(CDBAA), and tribromoacetic acid (TBAA) from common anions; therefore, these compounds 

were evaluated for inclusion in the proposed IC/ESI-MS/MS method. (Note: the group of nine 

chlorine- and bromine-containing HAAs that includes HAA5, BCAA, BDCAA, CDBAA, and 

TBAA are commonly referred to as “HAA9” within the environmental community.) Dalapon is

regulated in drinking water6 and it is an analyte in the all of the current GC methods. Dalapon is 

amenable to analysis using IC, presumably, for the same reason it amenable to the GC technique: 

it is a small carboxylic acid with a similar structure and acidity (pKa) to HAAs. 

Bromate is regulated under the Stage II DBP Rule, and EPA has published a number of directinject IC methods for this compound; however, none of these methods utilizes MS or MS/MS 

detection. Dionex and MDS/Sciex recognized the potential to simultaneously analyze for HAAs 

and bromate by IC, and to take advantage of the selectivity offered by MS/MS. For these 

reasons, bromate was included in the initial evaluations along with HAA9 and dalapon. 

Dionex contacted EPA in late 2005 and proposed a collaborative effort to develop an EPA

method for the analysis of HAAs, dalapon, and bromate using the IC/ESI-MS/MS technique. 

EPA agreed and initiated in-house studies in early 2006. This document presents a history of the

method development effort over the last three years, documents important “lessons learned” and 

the results of associated studies, which are not included in the published method. Specific 

research objectives to validate the IC/ESI-MS/MS method are listed in the following bullets:

1. To establish single-laboratory, lowest-concentration, minimum reporting levels7

(LCMRLs) in reagent water 

2. To determine single-laboratory detection limits8 (DLs) in reagent water

3. To verify acceptable precision and accuracy (P&A) in reagent water, synthetic sample 

matrix (solution of common anions in reagent water), tap water from a ground water 

source, and tap water from a surface water source

4. To determine stability of aqueous standards (unlike the GC method, aqueous standards 

are necessary to efficiently perform the method, and their stability had not been 

previously documented for these analytes—with the exception of bromate)

5. To investigate potential interferences and limitations of the IC method, including an 

evaluation of the effect of the presence of chlorite and chlorate anions in drinking waters 

treated with chlorine dioxide (ClO2) 

EPA decided not to investigate preservation techniques because preservation for HAA9 and 

dalapon were validated during development of the GC methods. EPA decided, based on 

theoretical grounds, that the preservation agent prescribed in the GC methods is applicable to 

bromate. This argument is presented in Section 3 of this research summary.

The following graphic summarizes the target compounds evaluated during the method 

development effort, their regulatory limits, existing methods, and the preservation scheme 

specified in those methods:
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HAAs Other Analytes (Regulatory Limit)

HAA5 (MRL)

MCAA (2 μg/L) Bromate (MCL 10 μg/L, MRL 5 μg/L)

a Dalapon (2,2-dichloropropionic acid) (MCLb 20 μg/L)

MBAA (1 μg/L)

DCAA (1 μg/L)

TCAA (1 μg/L)

DBAA (1 μg/L)

HAA9/dalapon/bromate: 100 mg/L NH4Clc

Method 557 Preservation

HAA5 (MCL 60 μg/L RAAd)

HAA9 (Regulatory Limit)

Preservation, Existing Methods

BCAA (not regulated) 300.1 Bromate: EDAf 50 mg/L

e

BDCAA (not regulated) 552.1, 552.2, 552.3 HAA9/Dalapon: 100 mg/L NH4Cl

CDBAA (not regulated)

TBAA (not regulated)

a MRL = minimum reporting level; National Primary Drinking Water Regulations: Stage II DBP Rule.

b MCL = maximum contaminant level; National Primary Drinking Water Regulations: EPA 816-F-02-

013, July 2002

c NH4Cl = ammonium chloride.

d RAA = running annual average.

e U.S. EPA Office of Ground Water and Drinking Water (other approved bromate methods not listed).

f EDA = ethylenediamine.

2.0 Chronology of the Method 557 Development Effort at 

EPA

This section is a basic narrative describing the activities and major milestones during this 

three-year effort and provides a record of publications related to Method 557. Mr. Alan Zaffiro 

served as principal investigator (PI) for Shaw Environmental, Inc. Messrs. Barry Pepich and 

Mike Zimmerman were the Shaw program managers, and Mr. Dave Munch was the EPA project 

officer. Throughout the project, Shaw collaborated with Dionex. Doug Later, Dr. Richard Jack, 

Rida Al-Horr, and Rosanne Slingsby were the primary points of contact on the Dionex team. Dr. 

Houssain El Aribi was the technical lead at MDS/Sciex. Dr. Aribi was the first to demonstrate 

the technique in the MDS/Sciex application laboratory (Concord, Ontario, Canada). Throughout 

the project, Dionex provided Shaw with prototype versions of the AS24 column. Shaw 

evaluated an “alpha” and a “beta” version of this column before collecting the final method

performance data using a production version of the AS24 column.

EPA performed much of the initial project activity using a Dionex ICS 3000 ion chromatograph

interfaced to an MDS/Sciex API 3200 ESI-MS/MS located in the National Exposure Research 

Laboratory (NERL) in Cincinnati. (Note that Dr. Aribi performed the original work using an API 

4000 MS/MS.) Eventually, problems with response drift using the MDS/Sciex MS/MS platform 

forced EPA to seek an alternate MS/MS system. Although the problems with response drift 

using the MDS/Sciex MS/MS platform could not be resolved, the method was demonstrated in a 

second laboratory using an MDS/Sciex system. Shaw believes the drift problems experienced at 

EPA were caused by the zero-air generator. 
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Dionex provided an alpha version of the AS24 column in May 2006. However, after testing the 

alpha column at the Dionex applications laboratory, Dr. Al-Horr concluded that the resin did not 

possess enough capacity to accommodate high ionic strength matrices. Dionex optimized the ion 

exchange resin, adding additional capacity, and delivered a beta version of the AS24 column to 

EPA in February 2007. EPA utilized the beta column to optimize method parameters, design a 

suitable aqueous standard preparation technique, and to evaluate the storage stability of the 

method analytes in aqueous standards and tap water samples.

Because of the problems with response drift related to use of+ the MDS/Sciex MS/MS, EPA

moved the Dionex ICS-3000 ion chromatograph from the NERL to the TSC laboratory in 

September 2007. The ion chromatograph was interfaced to the Waters Quattro Premier XE 

MS/MS system, which was already resident in the TSC laboratory.

On February 11, 2008, the AS24 production column was installed, and Shaw began the process 

of collecting the method performance data that appears in the published method. As observed 

when using the API 3200 MS/MS system, MCAA response was low relative to the other 

analytes. To ensure that the Waters system was not compromised in any way, annual service 

was performed, including cleaning the source, cleaning the T-wave assembly, and servicing the 

scroll pump. A Waters service engineer performed the cleaning procedure. MCAA response 

improved marginally, and—as with the API 3200—the low response for MCAA was addressed 

by use of longer relative dwell times and by optimizing the resolution. Accurate mass 

calibration, as discussed in Section 10.2 of the method, is necessary to ensure adequate signal-tonoise response for this analyte. 

Collection of the method performance data was completed on May 17, 2008. During these 

experiments, two problems of note occurred. On April 24, 2008, after an extended lapse in

project activity, peak tailing appeared in the ion chromatograms. Replacing the precolumn 

immediately restored column performance; that is, peak profiles were again symmetrical. 

Because tailing peaks limit the analyst’s ability to set divert windows for matrix elimination, this 

corrective action measure is included in Section 4 of the method. Later, a loss of signal 

(~50 percent area response) in the third Multiple Reaction Monitoring (MRM) function of the 

chromatogram (the retention time window in which the trihaloacetic acids elute) occurred during 

the first few runs of an analytical sequence. The signal loss coincided with high background 

conductivity during the third MRM function as measured by the conductivity detector. In this 

region of the chromatogram, the hydroxide concentration in the gradient is 60 millimolar (mM). 

The problem was resolved by flushing the column with 60 mM hydroxide prior to beginning a 

sequence. Apparently, ions collect on the column while the system is idle and the hydroxide 

concentration in the gradient is held at the standby level of 7 mM. Users are cautioned about this 

potential problem in Section 4 and in the procedure section (Sect. 11) of the method.

An additional experiment to evaluate the affect of the presence of chlorite and chlorate in 

drinking water on precision, accuracy, and band broadening was conducted on May 23, 2008. 

The findings are discussed in Section 4 of the method; however, the method does not include the 

supporting data. These are presented in this document (Sect. 6).
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Shaw made oral presentations on the method development effort at the American Chemical 

Society (ACS) National meeting in 2007 and the National Environmental Monitoring 

Conference in August 2007, and presented a poster at the Water Quality Technical Conference 

(WQTC, American Water Works Association) in November 2008. Shaw submitted manuscripts, 

which EPA management approved, for the ACS and WQTC proceedings. Table 1 lists these 

documents and their document numbers.

On August 15, 2008, Dave Munch sent a formal letter to Southern Nevada Water Authority 

(SNWA) inviting them to participate in the method development project by conducting a second 

laboratory validation. Alan Zaffiro sent a draft copy of the method (TSC-3-0371) to SNWA on 

August 8, 2008, and followed with LCMRL guidance on September 4, 2008. SNWA completed 

the second laboratory validation in early November 2008. Mr. Zaffiro compiled the results, 

which are presented in Section 9 of this report.

TABLE 1. PRESENTATIONS AND MANUSCRIPTS ASSOCIATED WITH THE 

METHOD 557 DEVELOPMENT PROJECT

Location Document No.a Document Description

ACSb National meeting, March 2007 TSC-3-0111 PowerPoint presentation

ACS National meeting, March 2007 TSC-3-0042 Manuscript for proceedings

NEMCc 2007, Cambridge, MA TSC-3-0220 PowerPoint presentation

WQTC,d November 2008 TSC-3-0374 Manuscript for proceedings

WQTC, November 2008 TSC-3-0390 Poster

a TSC = Technical Support Center.

b ACS = American Chemical Society.

c NEMC = National Environmental Monitoring Conference.

d WQTC = Water Quality Technical Conference (American Water Works Association, Denver, CO).

3.0 Preservation

At the direction of the EPA project officer, Dave Munch, Shaw excerpted the preservation 

requirements from the GC method (EPA method 552.3). However, bromate is not an analyte in 

the GC method, and because storage stability was not revisited during development of 

Method 557, preservation of this anion with NH4Cl is untested. To investigate the efficacy of 

NH4Cl to preserve bromate, Dave Munch, Barry Pepich, and Alan Zaffiro met with Mr. Dan 

Hautman, EPA TSC, who is an IC expert. Mr. Hautman provided the following explanation, 

which enabled EPA to predict, on theoretical grounds, that NH4Cl would effectively preserve 

bromate:

Using the Method 552.3 approach, chloramines are formed by the reaction of hypochlorite with the ammonium ion, effectively arresting the chlorine-mediated formation of 

HAAs and dalapon. The combined chlorine residual prevents microbiological 

degradation during storage.9

 The question is whether NH4Cl would also effectively 

preserve bromate. Guidance for the preservation of bromate is found in EPA 

Method 300.1. Method 300.1 specifies EDA as the preservative for this anion. The 

mechanism is analogous to HAA preservation using NH4Cl—the formation of 

bromamines to prevent formation of bromate from bromite during storage. EDA also 

complexes iron, a function important for the preservation of chlorite in Method 300.1. 

Because chlorite is not an analyte in the IC method and, like EDA, NH4Cl will form 
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bromamines, NH4Cl would be an acceptable preservation agent for bromate when 

bromate is analyzed by use of the IC method.

At the request of Dave Munch, this explanation does not appear in Method 557. However, a note 

stating that the preservation scheme is identical to the GC method is included in Section 8 of the 

method.

4.0 Standard Preparation Considerations and Storage 

Stability of Aqueous Standard Solutions

This section discusses the parameters that led to the guidance for standard preparation in Method

557, and presents results that support the recommendations for the safe storage time of standard 

solutions. Shaw and Dionex realized that the availability of stable aqueous standards would be 

necessary for the efficient conduct of a direct-inject approach for the analysis of the method 

analytes. Dionex and Shaw proposed the preparation of an analyte PDS at a concentration of 1.0 

μg/mL in reagent water, and the preparation of aqueous calibration solutions from this PDS by 

dilution with reagent water containing 100 mg/L NH4Cl. The internal standard PDS was 

prepared at the same concentration as the analyte PDS (i.e., 1.0 μg/mL), so that its stability could 

be inferred from the evaluations of the analyte PDS. Standard solutions were stored at 4 °C in 

glass vials with polytetrafluoroethylene-lined silicone septa. Tables in Section 7 of the method 

present example recipes for the preparation of PDS and calibration solutions. 

4.1

The HAA method analytes are available as solutions in MtBE. For Method 552, some vendors 

offer dalapon combined with the HAAs in the MtBE solution. Dalapon is also available as a 

single-analyte solution in methanol. Bromate is available as certified aqueous solutions 

(generally at 1000 μg/mL). Supelco offers three of the internal standards: MCAA[2-

13C], 

MBAA[1-

13C], and DCAA[2-13C] as single-analyte solutions in MtBE at a concentration of 

1000 μg/mL. Dionex now offers all four internal standards as single-analyte solutions in MtBE 

at a concentration of 1000 μg/mL. The Dionex standards were not available until after Shaw 

completed the laboratory phase of the project. However, SNWA used them during the second

laboratory validation studies. Shaw used the three Supelco internal standards, and prepared 

TCAA[2-

13C] from custom-synthesized neat material (Isotec, a member of the Sigma-Aldrich 

Group (

Standard Preparation Considerations 

www.sigma-aldrich.com/isotec). Section 7 of the method lists current sources for the 

analytes and internal standards, and the guidance for standard preparation in that section is based 

on these currently available sources. 

Because MtBE has limited water solubility (~5 percent), the method cautions users not to add

more than 0.5 percent by volume when fortifying an aqueous matrix. Shaw and Dionex chose 

this limit somewhat arbitrarily to build in a wide safety margin. The research team did not 

formally study the application of larger volumes; however, observations of the dispersion of 

MtBE in water when added via syringe injection suggest that such precaution is advised. Large 

volumes of MtBE tend to bubble quickly toward the surface rather than immediately mix with 

water. MtBE disperses into small bubbles that quickly dissolve when smaller volumes are 

injected by syringe well under the surface.
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4.2 Stability of Aqueous Standards

To evaluate the stability of the aqueous PDS, stored PDS solutions were analyzed periodically 

against PDS solutions freshly prepared from the solvent-based stock standards. To evaluate the 

stability of the calibration standards, stored calibration standard solutions were analyzed 

periodically against freshly prepared calibration standards. Both the stored and the fresh 

calibration standards were prepared using a common PDS solution. In order to make a 

defensible assessment of storage stability, stored solutions were subjected to normal use. That is, 

PDS solutions were often removed from the refrigerator and brought to room temperature for the 

purpose of preparing dilutions or fortifying samples, and calibration standards were often 

removed from storage to fill autosampler vials for analytical sequences.

 

Aqueous PDS solutions of the method analytes at 1.0 μg/mL (1000 μg/L) were evaluated after 

35 and 77 days of storage prior to collecting the method performance data. This work was 

conducted in the NERL laboratory using the API 3200 MS/MS system. These initial evaluations 

of PDS storage stability are presented in Table 2. Based on these results, Shaw and Dionex 

concluded that aqueous standards are stable for extended periods, and that it was safe to adopt 

the proposed aqueous standard preparation approach. During the collection of the method 

performance data, an aqueous PDS was evaluated for stability after 82 days of storage to confirm 

the earlier findings. These later results are also presented in Table 2.

The stability of aqueous calibration standards was evaluated at concentrations of 2.0 and 

5.0 μg/L. These results are presented in Table 3.

Based on the results of these studies and discussion with the EPA project officer, Dave Munch, 

the estimated safe storage time included in Section 7 of Method 557 for PDS solutions (internal 

standard PDS and analyte PDS) is 60 days, and 14 days for calibration standards. However, the 

method recommends that users determine safe storage times independently in their own 

laboratories.
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TABLE 2. PDS STORAGE STABILITY RESULTSa

Storage Time: 35 Days 77 Days 82 Days

Analysis Date: 7/03/2007 5/25/2007 5/14/2008

%Rb %RSDcn=3 %R RPDd % R

%RSD

n=3

MCAA 98.5 4.0 100 3.0 109 2.5

MBAA 98.5 1.2 96.5 2.3 100 1.0

Bromate 99.8 3.8 90.8 1.8 113 9.9

Dalapon 102 2.7 89.9 3.3 75.1 10

DCAA 100 0.61 96.4 1.2 100 5.2

BCAA 98.9 0.48 101 3.6 105 10

DBAA 100 1.2 106 2.8 102 14

TCAA 99.7 0.46 97.4 0.82 100 2.4

BDCAA 96.7 1.8 100 0.60 105 5.5

CDBAA 98.0 14 97.2 7.4 99.2 0.81

TBAA 96.7 1.1 83.8 6.2 91.4 3.4

a MCAA = monochloroacetic acid; MBAA = monobromoacetic acid; DCAA = dichloroacetic acid; BCAA = 

bromochloroacetic acid; DBAA = dibromoacetic acid; TCAA = trichloroacetic acid; BDCAA = 

bromodichloroacetic acid; CDBAA = chlorodibromoacetic acid; TBAA = tribromoacetic acid.

b %R = percent recovery.

c %RSD = percent relative standard deviation.

d RPD = relative percent deviation.

TABLE 3. CALIBRATION STANDARD STORAGE STABILITY RESULTSa

Storage Time: 10 Days 22 Days

Analysis Date: 4/17/2008 4/29/2008

Concentration: 5 μg/L 2 μg/L

% Difference %RSDb n=3 % Difference %RSD n=3

MCAA -4.0 1.9 -0.74 4.5

MBAA -0.10 0.68 -5.2 2.3

Bromate 6.3 8.6 -0.68 13

Dalapon -1.7 4.7 3.6 7.2

DCAA -2.0 7.0 3.4 9.0

BCAA -4.3 2.1 -2.4 6.6

DBAA -9.9 12 -4.9 11

TCAA -1.4 1.5 1.8 0.31

BDCAA -4.4 2.2 -0.85 11

CDBAA 1.3 5.1 5.4 4.8

TBAA 1.3 4.4 -2.0 3.3

a MCAA = monochloroacetic acid; MBAA = monobromoacetic acid; DCAA = dichloroacetic acid; BCAA = 

bromochloroacetic acid; DBAA = dibromoacetic acid; TCAA = trichloroacetic acid; BDCAA = 

bromodichloroacetic acid; CDBAA = chlorodibromoacetic acid; TBAA = tribromoacetic acid.

b %RSD = percent relative standard deviation.
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5.0 Second Source Verification

The QCS results obtained during method development are presented in Table 4. The PDS 

prepared from the second source stocks was diluted to 5 μg/L, analyzed in triplicate, and 

quantitated from an initial calibration constructed using calibration standards prepared from the 

primary source stocks.

TABLE 4. METHOD PERFORMANCE QUALITY CONTROL SAMPLE RESULTS, 

5.0-μg/L STANDARD

Analytea Primary Source Second Source Analysis Date % Recovery RSD,b % (n=3)

MCAA Restek Ultra Scientific 2/20/2008 105 4.1

MBAA Restek Ultra Scientific 2/20/2008 98.5 1.3

Bromate Ultra Scientific AccuStandard 2/20/2008 97.2 1.7

Dalapon Ultra Scientific AccuStandard 5/14/2008 96.5 3.0

DCAA Restek Ultra Scientific 2/20/2008 107 1.2

BCAA Restek Ultra Scientific 2/20/2008 105 1.5

DBAA Restek Ultra Scientific 2/20/2008 113 1.5

TCAA Restek Ultra Scientific 2/20/2008 106 0.27

BDCAA Restek Ultra Scientific 2/20/2008 89.7 0.94

CDBAA Restek Ultra Scientific 2/20/2008 87.3 1.9

TBAA Restek Ultra Scientific 2/20/2008 84.4 3.8

a MCAA = monochloroacetic acid; MBAA = monobromoacetic acid; DCAA = dichloroacetic acid; BCAA = 

bromochloroacetic acid; DBAA = dibromoacetic acid; TCAA = trichloroacetic acid; BDCAA = 

bromodichloroacetic acid; CDBAA = chlorodibromoacetic acid; TBAA = tribromoacetic acid.

b RSD = relative standard deviation.

6.0 Accelerated Storage Stability Studies

The storage stability studies described in this section provided critical information on the 

performance of the proposed method. Based on these results, the research team realized that a 

refrigerated autosampler would be required to successfully implement the direct-inject approach. 

This requirement appears in Section 6 in Method 557, and the justification is discussed in 

Section 4 of the method.

Dalapon, CDBAA, and TBAA exhibited anomalous behavior during the initial attempts to 

conduct P&A studies. The group suspected that aqueous solutions of the method analytes were 

degrading in the warm autosampler. The autosampler sample tray reached temperatures of 25 °

to 28 °C during operation as measured using a digital thermometer. 

The storage stability studies were designed to study the effects of storing aqueous solutions of 

standards and samples under controlled conditions. Two matrices were evaluated: 1) reagent 

water, and 2) Cincinnati tap water. For the first matrix, three standards (10 μg/L) prepared in 

reagent water and three standards (10 μg/L) prepared in reagent water and preserved with NH4Cl

were incubated at 40 °C for 40 hours. These six samples represented the “accelerated storage 
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conditions” for the reagent water matrix. Three standards prepared in reagent water and stored at 

4 °C served as the controls for the reagent water set. For the drinking water matrix, six split 

aliquots of Cincinnati tap water were fortified at 10 μg/L and preserved with NH4Cl. Three were 

incubated at 40 °C for 48 hours. These three samples represented the “accelerated storage 

condition” for the tap-water matrix. The other three were stored at 4 °C. These samples 

represented the control condition for the tap-water matrix.

Standards prepared in reagent water and stored at 4 °C served as the calibration standards for 

both matrices. The heated samples were cooled to 4 °C prior to analysis. Internal standards 

were added just prior to loading the samples into the autosampler and the analysis was started 

immediately. That is, the residency time in the warm autosampler was limited to only a few 

minutes. These later steps were necessary to eliminate the variable associated with storage of the 

internal standards and the samples in a warm environment. To cancel the effects of instrument 

drift, calibration standards, experimental conditions and controls were alternated during the 

analytical sequence.

Table 5 presents the results of the accelerated storage stability studies in reagent water. The 

analytes highlighted in bold/italic exhibited significant losses. Note that the decomposition is 

more extensive in the presence of the preservative—right-hand column. This finding indicates 

that the decomposition is accelerated at lower pH or via another mechanism involving NH4Cl. 

Table 6 presents the results of the accelerated storage stability studies in drinking water. As 

expected from previous studies published in association with the GC method,9 all of the targets 

are stable when stored at 4 °C in the presence of the preservative—first column in the table. 

However, dalapon, CDBAA, and TBAA (shown in bold/italic) decompose when heated, but not 

as much as observed in reagent water (Table 5). This may be the result of the higher pH of 

drinking water—8.1 for this matrix—compared with 5.8 for procedural standards prepared in 

reagent water. However, the stability of aqueous standards is equally important for the 

successful application of the method as the stability of field samples.

TABLE 5. ACCELERATED STORAGE STABILITY STUDY IN REAGENT WATER

Analyte

Reagent Water, 40 °C, 40 Hours

 

Reagent Water + Ammonium Chloride,

 

 

%Ra %RSDb (n=3) %R %RSD (n=3)

Bromate 105 9.6 113 4.8

MBAA 93.4 1.8 92.2 0.89

MCAA 95.4 1.4 94.8 7.4

Dalapon 93.0 4.6 45.5 2.0

DCAA 99.1 0.79 102 0.98

BCAA 95.1 9.3 102 4.6

DBAA 100 7.3 111 4.1

TCAA 98.2 0.69 99.1 0.63

BDCAA 96.8 3.7 95.3 3.2

CDBAA 82.0 3.3 68.3 2.4

TBAA 33.4 15 26.9 4.4

a %R = percent recovery.

b %RSD = percent relative standard deviation.
Page 15

TABLE 6. ACCELERATED STORAGE STABILITY STUDY IN CINCINNATI TAP 

WATER (CT)

Analyte

CT + Ammonium Chloride, 4 °C, 48 Hours

pH = 8.1

CT + NH4Cl 40 °C, 48 Hours

pH = 8.1

%Ra %RSDb (n=3) %R %RSD (n=3)

Bromate 92.1 5.1 90.9 1.8

MBAA 93.2 3.6 93.5 1.3

MCAA 94.1 2.7 95.8 3.1

Dalapon 87.9 15 82.9 9.4

DCAA 95.9 2.9 97.5 2.2

BCAA 90.2 3.9 90.5 4.3

DBAA 84.6 6.0 86.9 4.0

TCAA 95.3 2.0 95.6 2.7

BDCAA 95.0 1.2 91.6 5.2

CDBAA 101 2.3 86.7 2.6

TBAA 100 2.0 44.9 4.5

a %R = percent recovery.

b %RSD = percent relative standard deviation.

7.0 Chlorite and Chlorate P&A Study

Early in the history of the project, Dave Munch raised the question of potential interference 

caused by chlorite and chlorate anions, which may be present in drinking water disinfected with 

ClO2. On May 21, 2008, Shaw conducted a P&A study using synthetic matrix fortified at 5 μg/L

with the method analytes, 1 mg/L chlorite, and 0.5 mg/L chlorate. These are the MCLs for these 

two species. Figure 1 shows the location of the chlorite (m/z 67/51) and chlorate (m/z 83/67) 

anions relative to Method 557 analytes. Figure 2 is the conductivity trace corresponding to the 

chromatogram in Figure 1 showing the location of the chlorite and chlorate anions relative to the 

common anions in the synthetic sample matrix. The results of the P&A study are presented in 

Table 7.

TABLE 7. P&A RESULTS at 5 μg/L IN THE PRESENCE OF 1 mg/L CHLORITE, 

AND 0.5 mg/L CHLORATE

Analyte Recovery, % %RSDa n=8

MCAA 102 8.9

MBAA 104 1.4

Bromate 101 7.4

Dalapon 94.9 6.3

DCAA 99.0 5.1

BCAA 97.8 6.7

DBAA 92.6 8.7

TCAA 163 to 119 101 2.1

BDCAA 101 4.9

CDBAA 97.8 5.4

TBAA 107 1.5

a %RSD = relative standard deviation.
Page 16

As evidenced in Figure 1, chlorite co-elutes with MCAA. MCAA peak shape is severely 

degraded in the presence of chlorite and synthetic matrix. The median area response for MCAA 

in the eight fortified synthetic matrix (P&A samples) is 678 compared with a median of 3080 for 

the five procedural calibration standards analyzed during the May 21, 2008, sequence. The 

internal standard areas in the eight P&A samples failed the method’s QC criteria. Despite the 

peak shape and low area response, the percent recovery and percent relative standard deviation 

(RSD) for MCAA (Table 7) are well within QC limits. Evidently, the labeled internal standard 

(MCAA[2-

13C]) exactly compensates for the detrimental effects of the chlorite anion. However, 

the MRL for MCAA may be compromised if chlorite is present in the samples.

Chlorite interference is discussed in Section 4 of the method. Finished water treated with ClO2

could be analyzed using Method 552; however, the user must perform the method modification 

procedures (Sect. 9.4). Shaw introduced this option because chlorite may be present at much 

lower concentrations than examined during the P&A experiment described in this section. In 

addition, these P&A experiments constitute a “worst-case” scenario, because the synthetic matrix 

was used in conjunction with chlorite. The effect of chlorite on method performance was not 

evaluated in drinking water matrices.
Page 17

Figure 1. Dionex AS24 column: synthetic sample matrix fortified at 5 μg/L plus chlorite (1 mg/L) and chlorate 

(0.5 mg/L).
Page 18

Figure 2. Dionex AS24 column: conductivity trace, synthetic sample matrix plus chlorite (1 mg/L) and chlorate 

(0.5 mg/L).
~4812647.doc — Page 19

8.0 EPA Method Performance Data

The method performance data are described in Section 13 of Method 557 and the results are 

presented in tabular form in Section 17. These data were collected using a Dionex ICS-3000 IC 

and a Waters Quattro Premier XE ESI-MS/MS system under the conditions listed in Section 17

of the method. The method performance data include DLs and LCMRLs. Single laboratory 

P&A results are presented for four water matrices: reagent water, synthetic sample matrix, 

chlorinated (finished) ground water, and chlorinated (finished) surface water. Dr. Glynda Smith,

of Shaw, validated these results and verified transcription to the method tables as documented in 

the method validation memo dated September 24, 2008 (TSC-3-0387).

During method development, MCAA exhibited low response relative to the other method 

analytes when using the m/z 93/35 transition. Because a significant percentage of the precursor 

ion (m/z 93) is transmitted through the collision cell, an alternate transition (m/z 93/93) was 

investigated in an attempt to improve the DL for this analyte. However, the calculated DL for 

the alternate transition, 0.18 μg/L, is approximately the same as the primary transition. For this 

reason, the results collected for MCAA using the m/z 93/93 transition were not included in the 

method. However, LCMRL, P&A, and DL results for MCAA using the 93/93 transition are 

summarized in the raw data packages. In general, similar performance was observed for MCAA 

using the 93/93 transition with no evidence of adverse matrix effects.

Throughout the project, TCAA could not be measured using the primary transition, m/z 161/117. 

A co-eluting contaminant originating in the system interfered with this transition. For this 

reason, the method performance data were collected using m/z 163/119 for TCAA. All attempts 

to eliminate the interference were unsuccessful, including a tetraborate flush of the column, 

replacing the eluent generator cartridge, and replacing the AS24 column.

As recognized by Dionex during development of the AS24 column resin, the presence of high 

concentrations of common anions in the sample matrix causes peak shapes to widen and 

retention times to shift slightly toward lower values. During the project, much more band 

broadening was observed in synthetic matrix (especially for MCAA, MBAA, and bromate) than 

was observed in the three tap waters examined (Ft. Mitchell, Cincinnati, and Las Vegas). These 

observations indicate that synthetic matrix is “worst case” and most users will not notice a 

significant difference between peak profiles in reagent water and tap water. These observations 

resulted in the recommendation in Section 4 of the method that matrix ion concentrations not 

exceed 320 mg/L chloride, 250 mg/L sulfate, 150 mg/L bicarbonate and 20 mg/L nitrate. These 

are the concentrations of matrix ions in the synthetic matrix. The figures in the method clearly 

illustrate the effect of high ionic strength on peak width when approaching these concentrations. 

The analyst is instructed to verify performance in synthetic matrix during the Initial 

Demonstration of Capability (IDC), and verify elution/divert windows on a daily basis in 

synthetic matrix fortified with the method analytes (M557, Sect. 10.2.5), to ensure that divert 

windows are properly set to compensate for the effects of high-ionic-strength matrices.
~4812647.doc — Page 20

9.0 Second Laboratory Results

Method 557 was independently validated by Ms. Rebecca Colgate at the Chemistry Division, 

Water Quality Laboratory, SNWA, Henderson, Nevada 89015. Her contact information is as 

follows:

R. J. Colgate, Scientist II

Rebecca.Colgate@lvvwd.com

702-856-3527

SNWA used a Dionex ICS-3000 IC coupled to an MDS/Sciex API-4000 ESI-MS/MS. They 

obtained the method internal standards as solutions in MtBE from Dionex. A chromatography 

vendor supplied the HAA method analytes as a certified mixed standard in MtBE.

Ms. Colgate completed the IDC, performed an LCMRL study for the HAA9 targets, and 

conducted a P&A study on Las Vegas tap water. The LCMRL results are presented in Table 8,

along with the LCMRL results that Shaw obtained at the TSC laboratories in Cincinnati. SNWA 

conducted P&A studies in three matrices: tap water (Table 9), reagent water (Table 10), and 

synthetic sample matrix (Table 11). An extracted ion chromatogram of a Las Vegas tap-water 

sample fortified at 10 μg/L during the P&A study is presented in Figure 3. Note the peak tailing 

evident in this chromatogram, which Shaw did not generally observe. Shaw experienced tailing 

peaks at one point during collection of the method performance data; however, changing the 

precolumn resolved this problem.

While conducting the LCMRL analyses, SNWA limited the calibration range in violation of the 

standard operating procedure (SOP) requirements. SNWA calibrated up to 5.0 μg/L during the 

LCMRL study, but used a calibration range of 0.50 to 30 μg/L during the IDC and during the 

tap-water P&A study. The Shaw LCMRL SOP (QA-011) was sent to them; however, this 

requirement was not specifically called out in the associated e-mail, or by telephone.

SNWA sent spreadsheets with the raw data results and the calculated study results. Alan Zaffiro 

reviewed and summarized the QC results associated with the second laboratory studies. The QC 

result summaries were added to the spreadsheets provided by SNWA. During the analytical 

sequences for all the second laboratory studies referenced above, the internal standard areas, 

continuing calibration checks, and laboratory reagent blanks met the QC acceptance criteria 

specified in Section 9 of the method. There were no outliers.
~4812647.doc — Page 21

TABLE 8. SOUTHERN NEVADA WATER AUTHORITY IC/ESI-MS/MS LOWEST 

CONCENTRATION MRLsa

Analyte LCMRLb Fortification 

Levels (μg/L)c - Shaw

LCMRL Fortification 

Levels (μg/L) – SNWA

Shaw 

LCMRL 

(μg/L)

SNWA 

LCMRL 

(μg/L)

d

Monochloroacetic 

acid

0.10, 0.25, 0.375, 0.50, 

0.75, 1.0, 1.25, 1.5, 1.75, 

2.0

0.025, 0.05, 0.10, 0.20, 

0.50, 1.0, 2.0, 5.0 0.58 0.27

Monobromoacetic 

acid

0.050, 0.10, 0.25, 0.375, 

0.50, 0.75, 1.0, 1.25, 1.5, 

1.75, 2.0

0.025, 0.05, 0.10, 0.20, 

0.50, 1.0, 2.0, 5.0 0.19 0.12

Bromate

0.025, 0.050, 0.10, 0.25, 

0.375, 0.50, 0.75, 1.0, 1.25, 

1.5, 1.75, 2.0

Not analyzed 0.042 Not analyzed

Dalapon 0.25, 0.375, 0.50, 0.75, 1.0, 

1.25, 1.5, 1.75, 2.0 Not analyzed 0.41 Not analyzed

Dichloroacetic acid

0.025, 0.050, 0.10, 0.25, 

0.375, 0.50, 0.75, 1.0, 1.25, 

1.5, 1.75, 2.0

0.025, 0.05, 0.10, 0.20, 

0.50, 1.0, 2.0, 5.0 0.13 0.052

Bromochloroacetic 

acid

0.10, 0.25, 0.375, 0.50, 

0.75, 1.0, 1.25, 1.5, 1.75, 

2.0

0.025, 0.05, 0.10, 0.20, 

0.50, 1.0, 2.0, 5.0 0.16 0.050

Dibromoacetic acid

0.025, 0.050, 0.10, 0.25, 

0.375, 0.50, 0.75, 1.0, 1.25, 

1.5, 1.75, 2.0

0.010, 0.025, 0.05, 0.10, 

0.20, 0.50, 1.0, 2.0, 5.0 0.062 0.043

Trichloroacetic acid

0.10, 0.25, 0.375, 0.50, 

0.75, 1.0, 1.25, 1.5, 1.75, 

2.0

0.025, 0.05, 0.10, 0.20, 

0.50, 1.0, 2.0, 5.0 0.25 0.22

Bromodichloroacetic 

acid

0.050, 0.10, 0.25, 0.375, 

0.50, 0.75, 1.0, 1.25, 1.5, 

1.75, 2.0

0.025, 0.05, 0.10, 0.20, 

0.50, 1.0, 2.0, 5.0 0.19 0.067

Chlorodibromoacetic 

acid

0.050, 0.10, 0.25, 0.375, 

0.50, 0.75, 1.0, 1.25, 1.5, 

1.75, 2.0

0.025, 0.05, 0.10, 0.20, 

0.50, 1.0, 2.0, 5.0 0.080 0.062

Tribromoacetic acid

0.10, 0.25, 0.375, 0.50, 

0.75, 1.0, 1.25, 1.5, 1.75, 

2.0

0.010, 0.025, 0.05, 0.10, 

0.20, 0.50, 1.0, 2.0, 5.0 0.27 0.025

a IC/ESI = ion chromatography/electrospray ionization; MRL = minimum reporting level.

b LCMRL = lowest-concentration, minimum reporting level. c μg/L = micrograms per liter.

d Calibration range: low to 5.0 μg/L; this is a violation of standard operating procedure requirement to 

calibrate in the normal range. SNWA used a 0.5- to 30-μg/L calibration range for the initialdemonstration-of-capability and precision-and-accuracy studies.
~4812647.doc — Page 22

TABLE 9. SOUTHERN NEVADA WATER AUTHORITY (SNWA) PRECISION AND ACCURACY RESULTS FOR TAP 

WATER FORTIFIED AT 10 μg/La (n = 9)b

MCAA MBAA DCAA BCAA DBAA TCAA BDCAA CDBAA TBAA

Mean, unfortified samplec 2.3 0.86 16 9.7 4.5 11 4.7 2.5 0.39

Relative standard deviation (%) 4.8 6.6 1.9 5.1 2.4 1.8 2.2 2.3 3.3

Mean % recovery 106 105 101 91.5 100 105 111 114 111

a μg/L = micrograms per liter.

b Surface water physical parameters: pH = 7.79; hardness = 310 milligrams/liter (mg/L) (as CaCO3); free chlorine = 1.85 mg/L. These values 

are taken from the SNWA RMWTF Finished Water Inorganics report (September 2008). c Recoveries corrected for native levels in the unfortified matrix. 

TABLE 10. SOUTHERN NEVADA WATER AUTHORITY (SNWA) PRECISION AND ACCURACY RESULTS FOR 

REAGENT WATER FORTIFIED AT 10 μg/La (n = 9)

MCAA MBAA DCAA BCAA DBAA TCAA BDCAA CDBAA TBAA

Relative standard deviation (%) 4.8 1.7 1.7 7.1 9.3 4.8 6.9 5.8 7.1

Mean % recovery 96.2 108 100 101 103 102 102 102 110

a μg/L = micrograms per liter.

TABLE 11. SOUTHERN NEVADA WATER AUTHORITY (SNWA) PRECISION AND ACCURACY RESULTS FOR 

SYNTHETIC MATRIX FORTIFIED AT 10 μg/La (n = 9)

MCAA MBAA DCAA BCAA DBAA TCAA BDCAA CDBAA TBAA

Relative standard deviation (%) 4.0 2.5 2.7 3.1 3.3 2.7 2.3 2.9 4.4

Mean % recovery 99.7 104 99.7 94.0 99.8 101 88.3 92.4 99.5

a μg/L = micrograms per liter.
~4812647.doc — Page 23

Figure 3. Las Vegas tap water fortified at 10 micrograms per liter (μg/L) and analyzed on the AS24 column at the 

SNWA laboratory. Peak identification: 1) MCAA and MCAA[2-

13C], 2) MBAA and MBAA[1-13C], 

3) dalapon, 4) DCAA and DCAA[2-

13C], 5) BCAA, 6) DBAA, 7) TCAA and TCAA[2-13C], 8) BDCAA, 

9) CDBAA, 10) TBAA.
~4812647.doc — Page 24

10.0 References

1. U.S. Environmental Protection Agency. January 2006. National Primary Drinking 

Water Regulations: Stage 2 Disinfectants and Disinfection Byproducts Rule; Final Rule. 

40 CFR Parts 9, 141, and 142.

2. U.S. Environmental Protection Agency Office of Ground Water and Drinking Water. 

EPA Methods 552.1, 552.2, and 552.3

3. American Public Health Association, the American Water Works Association, and the

Water Environment Federation. Standard Methods 6251 B and 6251 B-94. Updated 

annually. 

4. Barron, L., and Paull, B. Simultaneous Determination of Trace Oxyhalides and 

Haloacetic Acids Using Suppressed Ion Chromatography-Electrospray Mass 

Spectrometry. Talanta 69 (2006) 621-630.

5. Barron, L., and Paull, B. Using Ion Chromatography to Monitor Haloacetic Acids in 

Drinking Water: A Review of Current Technologies. J. of Chromatography A, 1046 

(2004) 1-9.

6. U.S. Environmental Protection Agency. July 2002. National Primary Drinking Water 

Regulations: List of Contaminants and their Maximum Concentration Levels (MCLs), 

EPA 816-F-02-013, [www.epa.gov/safewater/mcl.html#mcls]

7. Winslow, S. D.; Pepich, B. V.; Martin, J. J.; Hallberg, G. R.; Munch D. J.; Frebis, C. P.; 

Hedrick, E. J.; and Krop, R. A. Statistical Procedures for Determination and Verification 

of Minimum Reporting Levels for Drinking Water Methods. Environ. Sci. Technol. 

2006; 40, 281-288.

8. Glaser, J. A.; Foerst, D. L.; McKee, G. D.; Quave, S. A.; and Budde, W. L. Trace 

Analyses for Wastewaters. Environ. Sci. Technol. 1981; 15, 1426-1435.

9. Pepich, B. V.; Domino, M. M.; Munch, D. J.; and Fair, P. S. Validating Sample 

Preservation Techniques and Holding Times for the Approved Compliance Monitoring 

Methods for Haloacetic Acids under the U.S. EPA’s Stage 1 D/DBP Rule. Wat. Res., 38 

(2004) 895-902.