United States
Environmental Protection
Agency
Environmental Monitoring and Support
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S4-84/021 June 1986
&EPA Project Summary
EPA Method Study 23B, Method
501.2, Trihalomethanes by
Liquid/Liquid Extraction
Beverly J.Warner, Sam C. Cheng, Julie M. Finke, Charles S. Friedman, Sueann
Mitrosky, Arthur D. Snyder, and Carl R. McMillin
The experimental design and results
of an interlaboratory study for an ana-
lytical method to detect trihalometh-
anes in water are described herein. In
EPA Method 501.2, trihalomethanes
are extracted by liquid/liquid extraction
using n-pentane (2 ml pentane/10 ml
water) and subsequent direct analysis
by gas chromatography using an elec-
tron capture detector. The six con-
centrations (three Youden pairs) of
spiking solutions used in this study
contained chloroform, bromodichloro-
methane, chlorodibromomethane, and
bromoform. The two water types, dis-
tilled and drinking water, were supplied
by the individual analytical laboratories.
Statistical analyses and conclusions are
based on analytical data obtained by
twenty collaborating laboratories.
Participating laboratories were se-
lected based upon technical evaluation
of proposals and upon the analytical
results 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), estima-
tion of single-analyst and overall preci-
sion, 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 pol-
lution abatement activities. The success
of these pollution control activities de-
pends 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 methods
and conducts quality assurance programs
for the water laboratories. The quality
assurance program of EMSL is designed
to maximize the reliability and legal
defensibility of all water quality informa-
tion collected by EPA laboratories. The
responsibility for these activities of EMSL
is assigned to the Quality Assurance
Branch (QAB). One of these activities is to
conduct interlaboratory tests of the
methods. This study reports the results of
the interlaboratory study on Method
501.2 (Study 23B).
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 Envi-
ronmental Research Laboratory. Addi-
tional comments and suggestions from
the Health Effects Research Laboratory
are gratefully acknowledged.
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Procedure
The interlaboratory study of EPA Meth-
od 501.2 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 trihalo-
methanes, 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 method-
ology. A short report, including the data
obtained and any potential problems
encountered, was received from each
subcontracting laboratory at the comple-
tion of Phase I.
Phase II consisted of a prestudy con-
ference held at 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 was involved, attended this
meeting. This meeting, which was held
after the data from the prestudy had been
evaluated, was designed to examine the
resul ts of the p rest udyandto discuss any
problems encountered in the method-
ology.
Phase III of the interlaboratory study
required the analysis of the study sam-
ples. In the case of Method 501.2, the
analysis of the four trihalomethanes in
both distilled water and drinking water
was required at each of six concentrations
(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
the concentration. The accuracy, ex-
pressed as percent recovery, ranges from
98% to 103% in both water types. The
accuracy of the method based on percent
recovery is excellent.
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 1 2% to 25% for both
water types for the middle and high
concentration levels (45 ppb to 174 ppb).
The percent relative standard deviation
ranges from 18% to 76% for the lowest
concentration levels (1.7 ppb to 7.2 ppb)
in both water types. The overall standard
deviation is very good except at the very
low concentration levels.
The single-analyst standard deviation
indicates the precision associated within
a single laboratory. The percent relative
standard deviation for single analyst (%
RSD-SA) for both water types ranges
from 5% to 1 2% for the middle and high
concentrations. The lowest concentration
levels yield a range of 5% to 81%. The
single analyst standard deviation is excel-
lent except at the very low concentration
levels.
Method 501.2 performed satisfactorily
in the hands of twenty laboratories, who
used various instruments and varied
conditions.
The background levels in drinking water
were ashighas65 ppb for chloroform and
20 ppb for bromodichloromethane. It is
concluded that the low precision is prob-
ablydue to subtract ing a large blank value
at low concentration levels.
The comparison on the effect of water
types shows a statistically significant
difference for bromodichloromethane.
However, a practical significant difference
does not exist.
Conclusions and
Recommendations
Method 501.2 is recommended for the
analysis of trihalomethanes in drinking
water. The accuracy is excellent. The
overall precision and single-analyst preci-
sion are very good except at very low
concentrations.
For analytical laboratories located at
high altitude, isooctane is the recom-
mended extraction solvent.
Extraction solvents must be checked
for contamination. Solvents such as n-
hexaneand cyclohexane were reported to
contain impurities which have the same
retention time as chloroform and bromo-
form. Contamination can come from
impurities in the solvent or from impur-
ities being absorbed from the laboratory
atmosphere. Analysis of blanks is recom-
mended on a daily basis.
Table 1. Regression Equations lor Accuracy and Precision for Compounds
Water Type
Distilled Water
Single-analyst precision
Overall precision
Accuracy
Tap Water
Single-analyst precision
Overall precision
Accuracy
Chloroform
SR
S
X
SR
S
X
= 0.06X
= 0.17X
= 1.01C
= 0.08 X
= 0.'26X
= 1.03X
+ 0.76
+ 0.65
+ 0. 14
+ 7.33
+ 0.60
- 0.37
Bromodichloromethane
SR
S
S
SR
S
X
= 0.05X + 0.07
= 0.77X + 0.31
= 0.98C + 0.02
= 0.07X + 0.67
= 0.23X + 0.86
= 1.01C + 0.51
Chlorodibromomethane
SR
S
S
SR
S
X
= 0.07X
= 0.76X
= ;.02C
= 0.07X
= 0. 13X
= 1.00C
+ 0.09
+ 0.47
+ 0.07
+ 0.30
+ 0.50
- 0.05
SR
S
X
SR
S
X
Bromoform
= 0.07 X +
= 0./5X +
= 1.01C -
= 0.08X -
= 0.1 6X +
= 1.03C -
0.24
0.17
2.29
0.11
0.11
2.08
X = mean recovery.
C = true value for the concentration.
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Beverly J- Warner. Sam C. Cheng, Julie M. Finke, Charles S. Friedman, Sueann
Mitrosky. ArthurD. Snyder, andCarlR. 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 23B, Method 501.2, Trihalo-
methanes by Liquid/Liquid Extraction," (Order No. PB 84-168 806; 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:
Enviromnetal Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center (or Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA/600/S4-84/021
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