Techniques and methods for the determination of haloacetic acids in
potable waterf
Edward T. Urbansky
United States Environmental Protection Agency (EPA), Office of Research and Development,
National Risk Management Research Laboratory, Water Supply and Water Resources
Division, 26 West Martin Luther King Drive, Cincinnati OH 45268, USA.
E-mail: urbansky.edward@epa.gov; Fax: +1 513 5697658; Tel: +1 513 569 7655
Received 13th April 2000, Accepted 23rd May 2000
Published on the Web 20th July 2000
Tutorial
Review
Haloethanoic (haloacetic) acids (HAAs) are formed as disinfection byproducts (DBFs) during the chlorination
of natural water to make it fit for consumption. Sundry analytical techniques have been applied in order to
determine the concentrations of the HAAs in potable water supplies: gas chromatography (GC-MS, GC-ECD);
capillary electrophoresis (CE); liquid chromatography (LC), including ion chromatography (1C); and
electrospray ionization mass spectrometry (ESI-MS). Detection limits required to analyze potable water samples
can be regularly achieved only by GC-ECD and ESI-MS. Without improvements in preconcentration or
detector sensitivity, CE and LC will not find application to potable water supplies. The predominant GC-ECD
methods use either diazomethane or acidified methanol to esterify (methylate) the carboxylic acid moiety. For
HAAS analytes, regulated under the EPA's Stage 1 DBF Rule, diazomethane is satisfactory. For HAA9 data
gathered under the Information Collection Rule, acidified methanol outperforms diazomethane, which suffers
from photo-promoted side reactions, especially for the brominated trihaloacetic acids. Although ESI-MS can
meet sensitivity and selectivity requirements, limited instrumentation availability means this technique will not
be widely used for the time being. However, ESI-MS can provide valuable confirmatory information when
coupled with GC-ECD in a research setting.
1 Introduction
Chlorination is the most common method for disinfecting
drinking water in the United States. During chlorination, active
(oxidizing) compounds (HOC1, NaOCl, C12) disable micro-
organisms present in the raw water. However, these com-
pounds also react with organic matter, producing a variety of
chlorine-containing byproducts. Bromide ion rapidly reacts
with HOC1 or C12 to give HOBr [eqns. (1) and (2)].
HOCl+Br-->BrCl+OH- ^ HOBr+Cr
-OH"
Cl2+Br-->BrCH-Cr ^~
(1)
(2)
In this way, bromine-containing oxidants are produced when
Ed Urbansky attended Allegheny
College in Meadville, PA, and
Purdue University in West Lafay-
ette, IN. He joined EPA's National
Risk Management Research
Laboratory in July 1997. Although
he is an inorganic chemist, much of
his work at EPA has dealt with the
analytical chemistry of disinfection
byproducts or perchlorate. He has
authored or coauthored more than
20 papers and edited a book,
Perchlorate in the Environment.
bromide-containing waters are chlorinated. Thus, brominated
and chlorinated organic compounds can result from chlorina-
tion. Raw (untreated) source water contains a mixture of
natural organic matter (NOM) from the decay and breakdown
of vegetation and animal matter as well as anthropogenic
organic matter, such as pesticides. Some of the organic matter
is soluble, but some of it is particulate. Regardless of its form or
origin, exposed organic matter can react with bromine- or
chlorine-based oxidizing agents to produce an array of
disinfection byproducts (DBFs).'
Two classes of compounds make up most of the identifiable
post-disinfection halogenated organic matter: the trihalo-
methanes, which account for ~20%, and the haloethanoic
acids, which account for ~13%.2 In the US, the EPA will
regulate the haloethanoic acids (haloacetic acids or HAAs)
under the Stage 1 Disinfection Byproducts (DBF) Rule
beginning in December 2001 ? Regulations regarding the
HAAs have been nicely summarized by Pontius and Diamond4
and a more detailed discussion is beyond the scope of this work.
The environmentally significant HAAs are given in Table 1.
Haloacetic acids are moderately strong and therefore
dissociated nearly completely (>99.9%) to the haloacetate
ions under typical drinking water conditions (pH > 6). The pATas
of mono-, di-, and trichloroacetic acids are 2.86, 1.3, and 0.66,
respectively.5 Nonetheless, the regulations are written in terms of
the parent acids rather than the haloacetate ions. Although the
HAAs represent a significant fraction of the halogenated organic
matter, they are polar, hydrophilic species that readily ionize.
This must be accounted for when deciding on an analytical
approach to their measurement in finished potable water.
—— — 2 Extraction and preconcentration
fThis is the work of a United States government employee engaged in
his official duties. As such it is in the public domain and exempt from Extraction of an analyte into an organic solvent affords certain
copyright. © US government. . - — . -
DOI: 10.1039/b002977g
benefits. Chief among these is that the analyte is concentrated
/. Environ. Monit., 2000, 2, 285-291 285
This journal is © The Royal Society of Chemistry 2000
-------
Table 1 HAAs to be regulated or undergoing information collection in the US
No.
Al
A2
A3
A4
A5
A6
Haloacetic acid
Chloroacetic
Dichloroacetic
Trichloroacetic
Bromoacetic
Dibromoacetic
Tribromoacetic
Chemical formula
C1CH,CO2H
C12CHCO>H
C13CCO2H
BrCH,CO2H
Br2CHCO2H
Br3CCO2H
CAS registry no.
[79-1 1-8]
[79-43-6]
[76-03-9]
[79-08-3]
[631-64-1]
[75-96-7]
Regulatory status
HAAS MCL"
DBPR1
DBPR1
DBPR1
DBPR1
DBPR1
n/a
HAA6 ICR*
Required
Required
Required .
Required
Required
Encouraged'
A7 Bromochloroacetic BrClCHCO2H [5589-96-3] n/a Required
AS Bromodichloroacetic BrCl2CCO2H [71133-14-7] n/a Encouraged'
A9 Dibromochloroacetic'' Br2ClCCO2H [7278-95-5] n/a Encouraged'
"HAA5 maximum contaminant level (MCL) is to be regulated as the sum of the concentrations of 5 HAAs (A1-A5), not to exceed 60 ug L~'
under the Stage 1 DBF Rule (DBPR1); n/a=DBPRl not applicable. The sum HAAS is expressed in ugL , rounded to 2 significant digits.
Dichloroacetic acid has a maximum contaminant level goal (MCLG) of zero and trichloroacetic acid has an MCLG of 300 ug L~'. Chlorina-
tion plants that use 4 quarterly values to compute an average and have HAA5<30ugL~' and THM4<4ugL~' are permitted to opt out of
further treatment studies. If a public water system (PWS) has an annual average ^80% of the MCL (48 ug L~'), it is required to create a disin-
fection profile under the Interim Enhanced Surface Water Treatment Rule [IESWTR, 40 CFR 9, 141, 142, Fed. Regist., 1998, 63 (241), 69478.]
DBPR1 takes effect December 2001 for surface water PWSs (serving > 10 000 persons and December 2003 for all remaining PWSs. *HAA6 =
HAAS+bromochloroacetic acid (A1-A5+A7) as specified in the Information Collection Rule (ICR). PWSs serving > 100000 persons must
comply with all parts of the ICR. THAA9 includes all 9 species. PWSs are encouraged—but not required—to monitor for A6, AS, and A9 indi-
vidually under the ICR. These species may be considered for regulation at some point in the future, but are not part of any proposed or pro-
mulgated rule for US PWSs at this time. ''A note on nomenclature. This compound is named correctly as dibromochloroacetic acid because the
order is alphabetical based on the halogen substituents not the prefix (di) telling the number; however, it is often encountered named incorrectly
as chlorodibromoacetic acid, especially in the drinking water/environmental chemistry literature.
by the extraction procedure. A second benefit is the elimination
of potential interferents that remain in the original aqueous
phase. In order to use liquid-liquid extraction for the HAAs,
the haloacetate ions must be protonated. Given that the pjfa of
C13CCO2H is 0.66, only 82% of the trichloroacetate is
protonated in 1.0 M acid (pH = 0), In order for liquid-liquid
extraction to be feasible, either high acidification or a favorable
solvent is required. To further promote partitioning into the
solvent, the analytes are often salted out using high
concentrations of an inert salt, such as sodium hydrogen
sulfate.
In addition to classical liquid-liquid extraction, newer
solid-phase extraction cartridges, microfibers, or membranes
are also available. Because of the need for preconcentration, a
considerable amount of effort has been expended on various
extraction methods. Individual approaches to extraction will
be addressed in the selections below based on which analytical
technique was subsequently used.
0 © (DO 9 ffl
Scheme 1 Resonance structures for diazomethane.
and uses diazomethane, which exists in the canonical forms
(resonance structures) shown in Scheme 1.
Diazomethane, CH2N2, is a powerful methylating agent,
able to esterify oxyacids under mild conditions without
catalysts and even with small amounts of water present in
the solution. The mechanism is shown in Scheme 2.
In practice, diazomethane is generated by the action of
hydroxide on JV-methyl-W-nitroso-p-toluenesulfonamide (Dia-
zald®, Aldrich, Milwaukee, WI, USA) or l-methyl-3-nitro-l-
3 Gas chromatography
Gas chromatography is the most common instrumental
technique used for drinking water analysis. Gas chromatography
may be coupled with either mass-selective detection or electron-
capture detection. GC-ECD is more sensitive than GC-MS by a
factor of about 1000, and it forms the basis for EPA's Methods
552s and 552.27 because of the low concentrations at which
haloacetates are found in potable water supplies. Methods 552
and 552.2 are both based on liquid-liquid extraction and GC-
ECD. Both use sulfuric acid to protonate the haloacetates in the
water sample and tert-butyl methyl ether (MTBE) to extract the
protonated analytes. The major difference between the two is the
esterification step. Fig. 1 shows a typical chromatogram of a
standard run according to Method 552.2.
Because of their polar nature and acidity, haloacetic acids
cannot be injected directly onto a GC column. Accordingly, the
carboxylic acid functionality is typically esterified. Methylation
has dominated the determination of HAAs; however, a wide
variety of silylating and other derivatizing agents are also
available for acidic compounds.8 Method 552 was developed
specifically for HAAS (see Table 1 for HAAS identification)
10 15 20 25 30 35 40 4.5
Retention time/min
Fig. 1 GC-ECD chromatogram of a haloacetic acid standard prepared
in reagent water using EPA Method 552.2 on a J&W Scientific
(Folsom, CA, USA) DB-5.625 column. Concentrations: chloroacetic
(CAA) and dichloroacetic (DCAA) acids: 6.0 ug L~'; trichloroacetic
(TCAA) and dibromoacetic (DBAA) acids: 2.0 ug L"1; bromoacetic
(BAA), bromochloroacetic (BCAA), bromodichloroacetic (BDCAA),
and 2,2-dibromopropanoic (2,2-DCPA) acids: 4.0 ugL""1; dibromo-
chloroacetic acid (CDBAA): 1.0 ug L~'; tribromoacetic acid (TBAA):
20ugL"1. Internal standard is 1,2,3-trichloropropane. Resolution of
the peaks for dibromochloroacetic acid and the surrogate (2,3-
dibromopropanoic acid) is better than it appears to be in the
chromatogram (0.2 min difference in retention time). On the recom-
mended confirmation column (J&W Scientific DB-1701), the retention
time difference is nearly 1 min. (The figure is adapted from ref. 7.)
286 J. Environ. Monti., 2000, 2, 285-291
-------
RC-OH + e:CH2-N=N: RC-OMe <-»• ROOMe
-H*
O
RC-OMe
Schemes Mechanism for methylation of a carboxylic acid with
acidified methanol.
MTBE as the acids, the haloacetates are trapped on an am'on
exchange resin. They are then simultaneously eluted and
esterified with acidified methanol.17'18 EPA developed Method
552.1 based on this approach; however, on-column methyla-
tion is infrequently used today. Although Method 552.1 is still
approved for use, it has fallen out of favor due to its more
complicated sample preparation in addition to lower precision
and accuracy.19'20 For HAAS, Standard Method 6251 and
EPA Method 552.2 are used almost exclusively by the
American drinking water community—in large part because
they are EPA-approved methods for these DBFs.
In addition to acidified methanol and diazomethane,
dimethylsulfate [(H3CO)2SO2] has been used to methylate the
HAAs in natural waters.21 In that case, no extraction-
preconcentration step was used since the airspace was aspirated
for GC-MS; however, dimethylsulfate is quite toxic and
requires a level of care in handling. A few other derivatives
have also been prepared. HAA difluoroanilides were analyzed
by GC-MS with single-ion monitoring. Detection limits were
impressive (0.5-2 ug L~:), except for tribromoacetic acid
(100 ug L"').22'23 When this approach was applied to environ-
mental samples, detection limits for several analytes were of the
order of lOngL"1, but tribromoacetic acid was not evalu-
ated.24 Solid-phase extraction has also been used,25'26 but it has
not been incorporated into any EPA-approved method.
4 Capillary electrophoresis
Similar acidification and liquid-liquid extraction can be used
for capillary electrophoresis; however, CE normally uses an
aqueous running electrolyte. Consequently, two extractions
must be performed: the first, to preconcentrate; and the second,
to take the analytes back into an aqueous solution. Without
preconcentration, CE can only reach concentrations of ~ 1—
lOmgL"1.27 With a liquid-liquid extraction into MTBE,
detection limits in the 1-10 ugL"1 range are reported.26'28
Martinez et al used MTBE-extraction to preconcentrate then
evaporated to dryness and redissolved the residue in a
minimum of water.29 They reported detection limits near
lOOugL"' with 2,6-napthalenedicarboxylate as the running
electrolyte. Online preconcentration techniques were successful
with standard solutions, but not real samples, demonstrating
the profound influence of the matrix.30 Thus, it appears that
CE will require either solid-phase or liquid-liquid extraction
prior to analysis. Solid-phase extraction has been investigated
using a variety of media. Cross-linked styrene-divinylbenzene
gave the best detection limits, rivaling that of GC-ECD for
HAAS (<5 fig L"1). The method has not been tested on all of
the HAA9 analytes, however.31 Because capillary electropher-
ographs are infrequently found in most drinking water testing
laboratories, it is unlikely that this technique will make any
headway in the near future. Although CE is a mature analytical
technique with many advancements having taken place,32
methods for haloacetates are not yet adequately rugged or
reliable to meet the demands of trace-level quantitation of these
DBFs. Particularly problematic is the heavy reliance on indirect
spectrophotometric detection, which is unselective and insuffi-
ciently sensitive. On the other hand, CE may find a niche in
research laboratories, especially those that already have the
instrumentation.
5 Liquid chromatography
Like capillary electrophoresis, ion chromatography (1C) suffers
from interferences from other anions due to its unselective
mode of detection (conductivity). At concentrations of
25 ug L~', haloacetate standards were shown to be amenable
to 1C, and reported detection limits (based on 1-4 ugL"1
spikes) were <1 ugL"1 for all analytes except tribromoace-
J. Environ. Monit., 2000, 2, 285-291 287
-------
1.4
1.2
T 1.0
CO
-5-0.8
0.6
0.4
0.2
0.0
VI
10 15 20 25
Retention time/min
30 35
40
Fig. 2 Ion chromatogram of a haloacetic acid standard prepared in
reagent water using a Dionex (Sunnyvale, CA, USA) DX500 system
with AG11 and ASH columns and suppressed conductivity
detection. Concentrations: chloroacetic (MCAA), dichloroacetic
(DCAA), trichloroacetic (TCAA), bromoacetic (MBAA), dibromoa-
cetic (DBAA), and bromochloroacetic (BCAA) acids: l.OugL"1;
bromodichloroacetic (BDCAA) and dibromochloroacetic (DBCAA)
acids: 3.13 ug L~*; tribromoacetic acid: 4.17 ug L"1. Reprinted from
ref. 30 with permission. See ref. 30 for gradient program and other
details.
tate. However, at more realistic concentrations of 2—
10 ug L~' and in actual water samples, matrix interference
became severe despite a preconcentrating extraction into
MTBE. Even in reagent water, 1C was limited in its ability to
separate the analytes from background anions; see chromato-
gram in Fig. 2.33 Even with preconcentration, realistic
concentrations for tap water could not be determined by
1C, with the best detection limits too high by a factor of at
least 4.34 Attempts to find alternate detectors, such as
polymer-modified microelectrodes, have led to small increases
in sensitivity, but the detection limits are not low enough
without about 50-fold preconcentration.35 High performance
liquid chromatographic methods have also been attempted,
but their detection limits are at least 10 000 times greater than
that of GC-ECD and they have no hope of application to
potable water analysis at this time.36'37
6 Electrospray ionization mass spectrometry
This technique has two important advantages in that it is
both sensitive and selective. When coupled with liquid
chromatography, ESI-MS can achieve detection limits of
<70ngL~', and it has been applied to several real
matrices.38 Sample preparation requires a single extraction
step (the same as GC-ECD) and minimal sample volume.
Selectivity improvements have been made using reagents
(perfluorinated alkylcarboxylates) that form stable associa-
tion complexes with the analytes; these complex anions are
detectable by ESI-MS.39 The disadvantage of ESI-MS is the
cost of the instrumentation and its lack of availability in
most testing laboratories. However, for research labora-
tories, ESI-MS can be an ideal complement to GC-ECD for
confirmatory analyses.
7 Preservation and fixation
Not all samples require this kind of pretreatment, and it is not
intrinsically necessary for the fundamental mechanism of the
analytical procedure itself. Nevertheless, improperly preserved
and fixed samples can lead to meaningless analytical data.
Initially defining clear objectives for the use of data is essential
to choosing appropriate means to preserve and fix these
analytes in solution. Real samples nearly always require some
type of preservation and fixation. It is not always possible to
immediately analyze a sample of potable water; consequently,
effort should be made to preserve the sample. Consider how
analyte concentration may change: volatility loss, chemical
reaction (loss or gain), biodegradation loss. It is therefore
important to preserve analytes from loss and fix their
concentrations at the time of sampling.
After disinfection, residual oxidizing agents remain behind
(e.g., HOBr, C1O~). Residual disinfectants continue to provide
protection from pathogens as water navigates the distribution
system on its way to homes.! However, this additional contact
time allows additional reaction and thus additional DBF
formation. When a sample of water is taken for analysis, the
residual oxidants must be scavenged (quenched) to prevent
further reaction with organic matter. Active chlorine residuals
in potable water are limited by EPA to no more than 1 mg L~'
Cl2 (14 uM). Even at this low concentration, further halogena-
tion of organic matter is possible, e.g.,
C1CH2CO2H-»C12CHCO2H-»C13CCO2H. In bromide-con-
taining waters, bromine atoms can also be incorporated
through formation of species such as BrCl and HOBr. In
Method 552.2," ammonium ion is added (as NH4C1) to
convert hypochlorite or dichlorine to chloramine (NH2C1) so as
to minimize additional DBF formation or conversion to more-
halogenated forms. Other reducing agents, such as ascorbic
acid, have also been used.9'40 Because dihalo- and trihaloace-
tates represent oxidized species, care must be taken not to add a
reagent capable of reducing these analytes. For instance 30 uM
sulfite has been demonstrated to destroy the haloacetonitrile
analogs of some HAAs, specifically CC13CSN and
CHBr2C=N.41 No such effect was observed for the HAAs
when ~ 1.4 HIM sulfite was added either immediately before
analysis or after holding 7 or 14 days in Method 552.2." Some
sulfite is rapidly consumed by the chloramine and some is
subject to reaction with dissolved oxygen, accounting for about
~ 10-50% of the reducing capacity of the sulfite. Thus, excess
sulfite was present throughout the holding times tested.
Many chemical reactions can be speculated; however,
minimal investigation has taken place to indicate which
reactions are responsible for the loss of these analytes. For
example, hydrolysis-decarboxylation of trihaloacetic acids to
give H2CO3/CO2 and CHX3 (the corresponding haloform) are
known. Other hydrolyses may also be possible. For example,
nucleophilic attack by water at the trichloromethyl group could
convert trihaloacetates to ethanedioate (oxalate), which
actually has been detected by GC-MS after NOM is
chlorinated.1 To minimize hydrolyses, acidification with
sulfuric acid is normally prescribed. Any nucleophilic species
(not just water) may in fact be able to substitute for a chloride
or bromide; thus, exposure to nucleophiles should be
minimized. Although chloramine and ammonia (from excess
ammonium cation) are somewhat nucleophilic,42 this does not
appear to pose a problem in Method 552.2.">43
Biodegradation is also a potential problem that has been
reported.44 When all residual oxidant is quenched, microbial
fAlthough a more detailed explanation is beyond the scope of this
work, it is worth noting that sewage and potable water lines are often
run near each other. When breaks or leaks occur, positive pressure
normally forces water out of a supply line, thereby preventing
contamination. However, if supply pressure drops below ~ 140 kPa
(~20 Ib in~2), sewage-tainted water can seep into a supply line,
establishing a cross-connection. Residual disinfectant minimizes the
health impacts of cross-connections by inactivating microbes that
infiltrate the supply line.
288 J. Environ. Monit., 2000, 2, 285-291
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activity may Yead to analyte loss. Method 552.2 calls for the
addition of 0.27 M copper(n) sulfate, which could act as an
antimicrobial agent (2.0 g CuSCVSt^O per 30 mL sample).
However, Method 552.2 does not use the cupric cation for this
purpose. To minimize volatilization, Method 552.2 requires
samples to be collected in vials without airspace. Loss to the air
was adjudged to be a more serious problem than biodegrada-
tion. Nonetheless, when an EPA-approved method is not
required, this reagent can be added at the time of collection,
especially when biological activity is suspected to present a
problem. Refrigeration is recommended in all cases (and
required by Method 552.2) since volatilization and microbial
growth decrease with decreasing temperature.
Not only are stored samples subject to changes in analyte
concentration, but standards themselves can be affected.
Unsurprisingly, when the carboxylic acids are prepared as
methanolic solutions, spontaneous esterification occurs.45 To
avoid this phenomenon, HAA9 standards are prepared in
MTBE rather than methanol.
In addition to analyte loss by chemical means, physical losses
are also possible. Besides volatilization loss (as noted above),
analytes may be adsorbed to the container wall or absorbed
into the container structure. For this reason, glass vials and
PTFE-lined caps are required in all versions of EPA Method
552. Because the samples are acidified, the neutral acids (rather
than the anions) will be present at sufficient concentrations that
they could migrate into some materials, especially low grade
plastics. Likewise, a poor choice of container can lead to the
introduction of contaminants that overlap with the analyte
peaks in the chromatogram or otherwise skew results.
In general, preservation and fixation require balancing the
objectives of the research project with possible interferences or
adverse effects. An investigator involved in HAA research must
be aware that adding or omitting reagents or practices may lead
to unexpected and undesirable consequences. Vigilance and
scrupulous evaluation of data cannot be overemphasized.
8 Quality assurance
Once the effort has been expended to analyze a sample, we
would like to have some assurance that the correct answer has
been obtained. To this end, a number of actions can be taken to
ensure that the data are of high quality. Those actions most
commonly taken by practitioners in the field using GC-ECD
will be summarized here.§ Use of high quality reagent
chemicals, appropriate glassware and measuring devices, and
good laboratory technique are important in any experiment.
There are five actions commonly taken: (1) adding a surrogate
to test the analyst, (2) adding an internal standard to test the
instrument, (3) analyzing several replicates to ensure precision,
(4) running calibration check standards to ensure accuracy, (5)
analyzing spiked samples to ensure the matrix does not
interfere (method ruggedness).
Part of the process requires knowing what the final objectives
for the data are. Is a false positive or a false negative of greater
concern? False positives are uncommon with most chromato-
graphic methods. However, suppose that no peaks are seen in a
chromatogram. Does that mean that the analytes were not
present? Even the best analyst will forget a step occasionally.
Or a reagent will deteriorate. Every step in a method is a place
for something to go wrong. To detect such problems, a
surrogate analyte is often added. The surrogate is added to all
real samples at the beginning of the procedure. Surrogates must
have several properties. (1) They must not interfere with the
determination of the actual analytes. Overlapping chromato-
graphic peaks is one such interference. (2) A surrogate's
§These actions apply to many analytical methods and reflect standard
practices of quality assurance in environmental chemistry.
concentration must be at least as difficult to determine as that
of the actual analytes. For example, a surrogate that is much
easier to methylate than the HAAs cannot test the effectiveness
of the methylation step. (3) Surrogates must not be present in
real samples. Common surrogates for HAA determination
include fluorinated carboxylic acids, which neither occur
naturally nor result from the disinfection process. If the
performance of the surrogate is acceptable, the analyst can
have reasonable confidence that every step of the procedure
was successful.^
Haloalkanes, such.as 1,2,3-trichloropropane or 1,2-dibro-
mopropane, are used as internal standards (dissolved into the
MTBE extraction solvent). They verify that the instrument is
functioning properly (i.e., correct injection volume, retention
time, and detector response). If the internal standard peak is as
expected, but the surrogate peak is missing, we can infer that
either the extraction or the methylation failed. If the internal
standard and surrogate peaks are half of what would be
expected, a clogged needle may be to blame. If the internal
standard retention time shifts, the column may be deteriorat-
ing.
One of the ways to deal with random errors is to analyze
replicate samples. In practice, large numbers of samples taken
for many studies preclude each being run 3-5 times due to cost
and time limitations. Nevertheless, it is common to include
duplicates at a convenient ratio, such as 1 every 5 or 10
samples. Experienced analysts will establish criteria for
duplicate analyses based on careful studies with many
replicates. For Method 552.2, duplicate analyses will usually
agree within 20%. The precision needed will vary with the
intended use of the data. Measuring a 30% change in
concentration will require greater precision than demonstrating
that an analyte is undetectable.
Accurate measurement is of obvious importance. It is worth
noting that there can be no assurance of accuracy without
adequate precision, especially when the number of replicate
measurements is small. Ensuring accuracy begins with calibra-
tion of the instrument, including running sufficient standards
over the linear dynamic range. This begins with establishing
minimum acceptable values for the correlation coefficient (e.g.,
r2>0.95), standard error of the slope, value of the ^-intercept
(and its standard error), in other words, a set of quality control
criteria. When calibration data fall outside this range, the
calibration must be repeated. For a chromatographic method,
the y-intercept of a calibration curve should be statistically
indistinct from zero (no analyte should mean no peak). To
ensure that the overall method response remains constant for
the analytes, calibration check standards near the expected
concentrations should be periodically run, such as every 5-10
samples. The blank or zero-concentration point is usually
deionized water for this method; it should have no measurable
peaks at the methylated analyte retention times. Although a
full discussion is beyond the scope of this work, peak shape and
signal-to-noise ratio should be incorporated into considera-
tions of data quality, especially near the limit of detection.
Integrating a noisy signal can result in poor precision, and
baseline noise can lead to unsatisfactorily high limits of
detection.
Fortifying (spiking) a known amount of analyte into a
sample and measuring the recovery is a way to see if the matrix
interferes. For example, if a sample is found to contain
10 ng L~' tribromoacetic acid, we might spike it with 7 ug L~'
more. Ideally, we should measure a concentration of 17 ug L~'
in the spiked sample. Suppose we detect 15 ug L~' in the spiked
sample. There are two ways to calculate the recovery [eqns. (4)
and (5)]. Eqn. (4) is prescribed by EPA Method 552.2.
fin direct injection 1C, the same species can serve as surrogate and
internal standard because there is only one step. In this case, it is not
normally thought of as a surrogate.
J. Environ. Monit., 2000, 2, 285-291 289
-------
Table 2. Summary of analytical techniques useful for HAA determination in potable water
Technique Characteristic
GC-ECD
GC-MS
CE
1C
Sensitive (LOD< 1 ug L~')
Moderately selective
High preparation; extraction and esterification required
Long instrumental analysis time (>55 min)
Moderately insensitive (LODas 100 ugL"1, too high for potable water)
Higher sensitivity reported for 2,4-difluoroanilide derivatives
Selective based on mlz
High preparation; extraction and esterification required
Moderately insensitive for tested analytes (LODaj 100 ug L~', too high for potable water)
High sensitivity reported for some analytes with appropriate preparation
Moderate preparation; double extraction required
Fast instrumental analysis time (< 10 min)
Moderately sensitive (LOD« 1 ug L~' in deionized water, but 10-100 x higher in real water samples); double extraction required
Matrix-dependent sensitivity; not very rugged
Moderately fast instrumental analysis time (<40min)
ESI-MS Sensitive (LOD =S 1 ug IT')
Selective, especially when complexation is used
Minimal sample preparation, only one extraction required
Fast instrumental analysis time (<10min)
"Abbreviations: GC = gas chromatography; ECD = electron capture detection, MS = mass spectrometry, CE=capillary electrophoresis, IC=ion
chromatography, ESI=electrospray ionization, LOD=(lower) limit of detection.
Recoveries of ±20% are common when calculated using
eqn. (4); the allowed variability is ±3%, so this recovery would
be acceptable using Method 552.2.
recovery (1) =
measured change due to spike
known value of spike
(4a)
Acknowledgements
The assistance of Jennifer Heffron, Raymond A. Hauck, and
Betty L. Merriman in gathering materials for this article is
noted. Mention of specific brand names or products should not
be construed as endorsement by the US government.
recovery (1) =
-=71%
recovery (2) =
measured concentration in spiked sample
calculated concentration in spiked sample
recovery (2) =
(4b)
(5a)
(5b)
The term quality assurance has become an anathema in many
circles, but at its basic level it means making sure the analytical
measurement is in fact the right answer. It is the responsibility
of the analyst to choose appropriate QA criteria to meet the
overall objectives of the investigation.
9 Conclusions
For the present, the most widespread technique for HAA
determination is GC-ECD. Characteristics of the available
techniques are summarized in Table 2. Although diazomethane
can be used satisfactorily to methylate the carboxylic acid
moiety for HAAS, acidified methanol gives better results for
HAA9 analytes. LC methods are not sufficiently robust at this
time to meet drinking water needs. Instrument cost and
availability prevent ESI-MS from becoming more prominent
even though it meets sensitivity and selectivity requirements.
Because all EPA-approved methods for compliance monitoring
are based on GC-ECD and this technique meets both
sensitivity and selectivity needs, it can be expected to dominate
drinking water analysis in the US for the forseeable future.
Sample preservation and fixation are complicated and must be
attended to if usable data are to be obtained.
References
1 S. D. Richardson, in Encyclopedia of Environmental Analysis and
Remediation, ed. R. A. Meyers, Wiley, New York, 1998, vol. 3,
pp.1398-1421.
2 H. Weinberg, Anal. Chem., 1999, 71, 801A.
3 US Environmental Protection Agency, Fed. Regist., 1998,63(241),
69390.
4 F. W. Pontius and W. R. Diamond, J. Am. Water Works Assoc.,
1999, 91, 16.
5 D. C. Harris, Quantitative Chemical Analysis, Freeman, New
York, 2nd edn., 1987, Appendix G.
6 J. W. Hodgeson, 3. Collins and R. E. Barth, Method 552.
Determination of Haloacetic Acids and Dalapon in Drinking Water
by Liquid-Liquid Extraction, Derivatizalion, and Gas Chromato-
graphy with Electron Capture Detection, In Methods for the
Determination of Organic Compounds in Drinking Water, Supple-
ment 7, U.S. Environmental Protection Agency, Cincinnati, OH,
July 1990, EPA/600/4-90/200.
7 3. W. Hodgeson, D. J. Munch, J. W. Munch and A. M. Pawlecki,
Method 552.2. Determination of Haloacetic Acids and Dalapon in
Drinking Water by Liquid-Liquid Extraction, Derivatizalion, and
Gas Chromatography with Electron Capture Detection, Rev. 1.0. In
Methods for the Determination of Organic Compounds in Drinking
Water, Supplement III, U.S. Environmental Protection Agency,
Cincinnati, OH, Aug. 1995, EPA/600/R-95/131.
8 K. Blau and J. Halket, Handbook of Derivatives for Chromato-
graphy, Wiley, Chichester, 2nd edn., 1993, passim.
9 E. T. Urbansky, D. M. Freeman and F. J. Rubio, J. Environ.
Monit., 2000, 2, 253.
10 U.S. Environmental Protection Agency, Fed. Regist., 1996, 61(94),
24354.
11 A. M. Pawlecki-Vonderheide, D. J. Munch and J. W. Munch,
J. Chromatogr. Sci., 1997, 35, 293.
12 M. J. LaGuardia, Proc. Water Qual. Technol. Con/, Am. Water
Works Assoc., 1997, 256.
13 F. J. Rubio, E. T. Urbansky and M. L. Magnuson, J. Environ.
Monit., 2000, 2, 248.
14 Y..Xie, D. A. Reckhow and D. C. Springborg, J. Am. Water
Works Assoc., 1998, 90, 131.
15 M. J. LaGuardia, Proc. Water Qual. Technol. Con/, Part I, Am.
Water Works Assoc., 1996, 167.
290 J. Environ. Monit., 2000, 2, 285-291
-------
16 Standard Methods for the Examination of Water and Wastewaler,
ed. A. D. Eaton, L. S. Clesceri and A. E. Greenberg, American
Public Health Association/American Water Works Association/
Water Environment Federation, Washington, DC, 19th edn.,
1995, Method 6251, pp. 6-67-6-76.
17 J. W. Hodgeson and D. Becker, Method 552.1. Determination of
Haloacetic Acids and Dalapon in Drinking Water by Ion-Exchange
Liquid-Solid Extraction and Gas Chromatography with an Electron
Capture Detector, Rev. 1, In Methods for the Determination of
Organic Compounds in Drinking Water, Supplement II,
U.S. Environmental Protection Agency, Cincinnati, OH, Aug.
1992, EPA/600/R-92/129.
18 D. Benanou, F. Acobas and P. Sztajnbok, Water Res., 1998, 32,
2798.
19 H. L. Shorney and S. J. Randtke, Proc. Water Qual. Technol.
Conf., Part 1, Am. Water Works Assoc., 1995, 453.
20 S. Seckinger, C. R. Ashe and J. F. Occhialini, Proc. Water Qual.
Technol. Conf., Am. Water Works Assoc., 1997, 9/A.
21 P. Neitzel, W. Walther and W. Nestler, Fresenius' J. Anal. Chem.,
1998, 361, 318.
22 H. Ozawa and T. Tsukioka, Analyst, 1990, 115, 1343.
23 H. Ozawa, /. Chromatogr., A, 1993, 644, 375.
24 B. F. Scott and M. Alaee, Water Qual. Res. J. Can., 1998,33, 279.
25 L. J. Yoo, Y. Shen and S. Fitzsimmons, Proc. Water Qual.
Technol. Conf., Am. Water Works Assoc., 1991, 913.
26 L. J. Yoo, Y. Shen, S. Fitzsimmons and M. Rigby, Proc. Water
Qual. Technol. Conf., Part 2, Am. Water Works Assoc., 1993,1335.
27 Y. Xie and J. P. Romano, Proc. Water Qual. Technol. Conf., Am.
Water Works Assoc., 1997, 5A6/1.
28 Y. Xie, H. Zhou and J. P. Romano, Abstracts of papers
(Environmental Division), 217th American Chemical Society
Meeting, Anaheim, CA, USA, 1999, abstract 092.
29 D. Martinez, J. Farre, F. Borrull, M. Calull, J. Ruann and
A. Colom, J. Chromatogr., A, 1998, 808, 229.
30 D. Martinez, F. Borrull and M. Calull, /. Chromatogr., A, 1999,
835, 187.
31 D. Martinez, F. Borrull and M. Calull, /. Chromatogr., A, 1998,
827, 105.
32 D. Martinez, F. Borrull and M. Calull, TrA C, Trends Anal. Chem.,
1999, 18, 282.
33 V. Lopez-Avila, Y. Liu and C. Charan, J. AOAC Int., 1999, 82,
689.
34 C. Sarzanini, M. C. Bruzzoniti and E. Mentasti, J. Chromatogr., A,
1999, 850, 197.
35 P. Akhtar, C. O. Too and G. G. Wallace, Anal. Chim. Ada, 1997,
341, 141.
36 R. Vichot and K. G. Furton, J. Liq. Chromalogr., 1994J17, 4405.
37 H. Carrero and J. F. Rusling, Talanla, 1999, 48, 711.
38 S. Hashimoto and A. Otsuki, J. High Resolul. Chromatogr., 1998,
21, 55.
39 M. L. Magnuson and C. A. Kelty, Anal. Chem., 2000, 72, 2308.
40 Y. Takahashi and M. Morita, Kankyo Kagaku, 1997, 7, 495.
41 J.-P. Croue and D. A. Reckhow, Environ. Sci. Techno!., 1989, 23,
1412.
42 E. J. Pedersen III, E. T. Urbansky, B. Y. Marinas and
D. W. Margerum, Environ. Sci. Technol., 1999, 33, 4239.
43 E. E. Chang, Y.-W. Ko, P.-C. Chiang and C.-F. Wang, Environ.
Sci. Res., 1996, 51, 409.
44 A. L. Weightman, A. J. Weightman and J. H. Slater, World
J. Microbiol. Biotechnoi, 1992, 8, 512.
45 Y. Xie, D. A. Reckhow and R. V. Rajan, Environ. Sci. Technol,
1993, 27, 1232.
J. Environ. Monit., 2000, 2, 285-291 291
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