United States
Environmental Protection
Agency
Environmental Monitoring and Support
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S4-84/020 Aug. 1986
Project Summary
EPA Method Study 23A, Method
501.1, Trihalomethanes by
Purge and Trap
Beverly J. Warner, Sam C. Cheng, Charles S. Friedman, Sueann Mitrosky,
Arthur D. Snyder, and Carl R. McMillin
The experimental design and the
results of an interlaboratory study for an
analytical method to detect trihalo-
methanes in water are described herein.
In EPA Method 501.1, trihalomethanes
are extracted by an inert gas which is
bubbled through the aqueous sample.
The vapors are then trapped on a short
column containing a suitable sorbent.
The trapped compounds are subse-
quently thermally desorbed onto the
head of a gas chromatographic column.
An electrolytic conductivity detector is
used to measure the compounds. The
spiking solutions contained chloroform,
bromodichloromethane, chlorodibromo-
methane, and bromoform at six concen-
trations. Two water types, distilled and
drinking water, were supplied by the
individual analytical laboratories. Statis-
tical analyses and conclusions are based
on analytical data obtained by twenty
collaborating laboratories.
Participating laboratories were select-
ed based upon technical evaluation of
proposals and upon the analytical re-
sults of prestudy samples. The data
obtained from the interlaboratory study
were analyzed employing a series of
•computer programs known as the Inter-
laboratory Method Validation Study
(IMVS) system, which was designed to
implement ASTM procedure D2777.
The statistical analyses included tests
for the rejection of outliers, estimation
of mean recovery (accuracy), estimation
of single-analyst and overall precision,
and tests for the effects of water type
on accuracy and precision.
This Project Summary was developed
by EPA's Environmental Monitoring and
Support Laboratory. Cincinnati. OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The analytical laboratories of the U.S.
Environmental Protection Agency (EPA)
gather water quality data to provide
information on water resources, to assist
research activities, and to evaluate pollu-
tion abatement activities. The success of
these pollution control activities depends
upon the reliability of the data provided by
the laboratories, particularly when legal
action is involved.
The Environmental Monitoring and
Support Laboratory-Cincinnati (EMSL-
Ci), of the EPA develops analytical meth-
ods and conducts quality assurance pro-
grams for the water laboratories. The
quality assurance program of EMSL is
designed to maximize the reliability and
legal defensibility of all water quality
information collected by EPA laboratories.
The responsibility for these activities is
assigned to the Quality Assurance Branch
(QAB). One of these activities istoconduct
interlaboratory tests of the methods. This
study reports the results of the validation
effort on Method 501.1 (Study 23A).
The method evaluated in the full report
was prepared by the EMSL-Cincinnati
staff at the request of the Office of
Drinking Water, with cooperation from
the Technical Support Division, Office of
Drinking Water and the Municipal Environ-
mental Research Laboratory. Additional
comments and suggestions from the
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Health Effects Research Laboratory are
gratefully acknowledged.
Procedure
The interlaboratory study of EPA Meth-
od 501.1 consisted of three distinct
phases. Phase I involved the analysis of
the prestudy samples by twenty partici-
pating laboratories. Two samples were
analyzed for each of the four trihalometh-
anes, one in organic-free water and one
in drinking water. Both waters were
supplied by the individual participating
laboratories. The objective of Phase I was
to become familiar with the methodology
employed and to identify any potential
problems associated with the analytical
methodology. Accuracy was not as im-
portant as being familiar with the meth-
odology. A short report, including the data
obtained and any potential problems
encountered, was received at the comple-
tion of Phase I from each subcontracting
laboratory.
Phase II consisted of a prestudy con-
ference held at the U.S. EPA, Cincinnati,
Ohio. Each subcontracting laboratory sent
at least one participant to the meeting.
The analyst, or principal analyst if more
than one analyst was involved, attended
this meeting. This meeting, which was
held after the data from the prestudy had
been evaluated, was designed to examine
the results of the prestudy and to discuss
any problems encountered in the meth-
odology.
Phase III of the interlaboratory study
required the analysis of the study sam-
ples. In the case of Method 501.1, the
analysis of the four trihalomethanes in
both distilled water and drinking water
was required at each of sixconcentrations
(three Youden pairs). Again, the partici-
pating laboratories supplied the required
water samples for these analyses. In
addition, the participating laboratories
analyzed their distilled and tap water
blanks. Each participating laboratory then
issued a report containing all data ob-
tained, copies of all chromatograms, and
any comments.
The final step in the study was to
conduct a statistical analysis of all data
obtained. This analysis was conducted by
Battelle Memorial Laboratories, Colum-
bus, Ohio, under contract with the U.S.
EPA.
Results and Discussion
Through statistical analyses of 960
analyzed values, estimates of accuracy
and precision were made and expressed
as regression equations, shown in Table
1.
The accuracy is obtained by comparing
the mean recovery to the true values of
concentrations. The accuracy, expressed
as percent recovery, ranges from 92% to
108% in both water types. The accuracy
of the method based on percent recovery
is excellent. A slight high bias is seen in
the tap water, but it is not statistically
significant. The probable cause of this
slight bias is background in the tap water.
The overall standard deviation of the
analytical results is an indication of the
precision associated with the measure-
ment generated by a group of laboratories.
The percent relative standard deviation
(% RSD), ranges from 18% to 32%. The
overall standard deviation is considered
to be good. Over the range of 0.8 A/g/L to
550 A/g/L, the best precision occurs at the
middle Youden pair, which is near the
drinking water standards.
The single-analyst standard deviation
indicates the precision associated within
a single laboratory. The percent relative
standard deviation for single analyst (%
RSD-SA) ranged from 10% to 23%; this
Table 1. Regression Equations for Accuracy and Precision for Compounds 1 -4
also is considered to be good. Again,
slightly higher values (not statistically
significant) are reported for the tap water,
and the probable cause is background in
the tap water.
A statistical comparison of the effect of
the type of water was performed. It
indicated no significant difference be-
tween water types.
Conclusions and
Recommendations
Method 501.1 is acceptable for the
analysis of trihalomethanes in drinking
water. The accuracy is excellent, and the
overall precision and single-analyst preci-
sion are considered good.
Care must be taken to eliminate any hot
metallic (active) sites in both the gas
chromatograph and the detector. These
sites can cause breakdown of the com-
pounds, especially bromoform.
Special care must be taken in handling
samples and blanks to avoid contamina-
tion from the laboratory atmosphere. It is
recommended that at least daily checks
for contamination be made by the use of
appropriate blanks.
Carry-over of the trihalomethane ana-
lytes from the analysis of high concentra-
tion samples to the next analysis was
noted. It is recommended that the purge
device be filled with distilled water and
purged for ten minutes after the analysis
of samples suspected of containing high
concentrations of trihalomethanes.
Water Type
Chloroform
Bromodichloromethane
Chlorodibromomethane
Bromoform
Range f/jg/L)
0.86 - 550
0.88 - 550
0.84 - 550
4.8 - 550
Distilled water
Single-analyst precision
0 verall precision
Accuracy
Tap Water
Single-analyst precision
Overall precision
Accuracy
Range (ug/Lf
SR
S
X
SR
S
X
= 0.10X
= 0.20X
= 0.92C
+ 0. 13
+ 0.20
+ 0.04
= 0. 1 1X + 0.03
= 0.1 8X + 0.74
= 1.02C + 0.52
0.26 - 550
SR
S
X
SR
S
X
= 0.1 5X - 0.05
= 0.23X + 0.15
= 0.95C - 0.04
= 0.1 5X + 0. 18
= 0.22X + 0.38
= 1.02C + 0.08
0.88 - 550
SR
S
X
SR
S
X
= 0.16X +
= 0.26X +
= 0.99C -
0.06
0.35
0.08
= 0.1 8X + 0. 13
= 0.27X + 0.07
= 1.04C - 0.16
0.84 - 550
SR
S
X
SR
S
X
= 0.1 9X
= 0.28X
= 1.03C
- 0.25
+ 0.63
- 1.48
= 0.23X - 0.05
= 0.32X + 0.47
= 1.08C - 1.75
4.84 - 550
X = mean recovery.
C - true value for the concentration.
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Beverly J. Warner. Sam C. Cheng, CharlesS. Friedman. SueannMitrosky. Arthur
D. Snyder, and Carl R. McMillin are with Monsanto Research Corporation,
Dayton. OH 45407.
Raymond Wesselman is the EPA Project Officer (see below).
The complete report, entitled "EPA Method Study 23A. Method 501.1. Trihalo-
methanes by Purge and Trap. "(Order No. PB84-169 994; Cost: $ 16.95. subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA/600/S4-84/020
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