United States
Environmental Protection
Agency
Environmental Monitoring and
Support Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S4-84-022 May 1984
4»EPA Project Summary
Two Methods for Analyzing
Trihalomethanes in Drinking
Water by Purge and Trap and
Liquid-Liquid Extraction
Techniques
Beverly J. Warner, Sam C. Cheng, Charles S. Friedman,
Sueann Mitrosky, Arthur D. Snyder, and Carl R. McFvlillin
The experimental design and the
results of an interlaboratory study of
two U.S. Environmental Protection
Agency (USEPA) methods to detect
trihalomethanes in drinking water are
described herein. In USEPA 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 contain-
ing a suitable sorbent. The trapped com-
pounds are subsequently thermally
desorbed onto the head of a gas chro-
matographic column. An electrolytic
conductivity detector is used to mea-
sure the compounds. In USEPA Method
501.2, trihalomethanes are extracted by
liquid/liquid extraction using n-pentane
(2 mL pentane per 10 mL water) and
subsequent direct analysis by gas
chromatography using an electron cap-
ture detector. For both methods, the six
concentrations (three Youden pairs) of
spiking solutions used in this study con-
tained 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 In-
terlaboratory 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 ac-
curacy and precision.
This Project Summary was developed
by USEPA's Environmental Monitoring
and Support Laboratory, Cincinnati, OH,
to announce key findings of the re-
search project that is fully documented
in two separate reports of the same title
(see Project Report ordering information
at back).
Introduction
The various analytical laboratories of
USEPA gather water quality data to provide
information on water resources, to assist
research activities, and to evaluate pollution
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 Sup-
port Laboratory — Cincinnati (EMSL-
Cincinnati), of USEPA, develops analytical
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methods and conducts quality assurance
programs for the water laboratories. EMSL-
Cincinnati's quality assurance program is
designed to maximize the reliability and legal
defensibility of all water quality information
collected by USEPA laboratories. The re-
sponsibility for these activities is assigned to
the Quality Assurance Branch (QAB) which
conducts interlaboratory tests of the
methods.
The methods evaluated in this report were
prepared by the EMSL-Cincinnati staff at the
request of the Office of Drinking Water, with
cooperation from its Technical Support Divi-
sion, and the Municipal Environmental Re-
search Laboratory — Cincinnati. Additional
comments and suggestions from the Health
Effects Research Laboratory — Cincinnati
are gratefully acknowledged.
Procedure
The interlaboratory study of the two
methods consisted of three distinct phases.
Phase I involved the analysis of the prestudy
samples by 20 participating laboratories. Two
samples were analyzed for each of the four
trihalomethanes, 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 prob-
lems associated with the study. Accuracy
was not as important as being familiar with
the methodology. 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 in Cincinnati, Ohio. Each sub-
contracting laboratory sent at least one
analyst to the meeting. This meeting, which
was held after the data from the prestudy
had been evaluated, was designed to ex-
amine the results of the prestudy and to
discuss any problems encountered in the
methodology.
Phase III of the interlaboratory study re-
quired the analysis of the study samples. For
both methods, 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 participating laboratories sup-
plied 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 which was conducted by Battelle
Memorial Laboratories, Columbus, Ohio,
under contract to USEPA.
Results and Discussion
Through statistical analyses of 960 ana-
lyzed values per methods, estimates of ac-
curacy and precision were made and
expressed as regression equations. Table 1
represents those regression equations for
Method 501.1 and Table 2 is for Method
501.2.
The accuracy is obtained by comparing
the mean recovery to the true values of con-
centrations. The accuracy expressed as per-
cent recovery for both water types ranges
from 92% to 108% for Method 501.1 and
from 98% to 103% for Method 501.2. The
accuracy of the methods based on percent
recovery is excellent. With Method 501.1,
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 preci-
sion associated with the measurement gen-
erated by a group of laboratories. For
Method 501.1, the percent relative standard
deviation (% BSD), ranges from 18% to
32%. The overall standard deviation is con-
sidered to be good. Over the range of 0.8
^g/L to 550 f^g/L, the best precision occurs
at the middle Youden pair which is near the
drinking water standards. For Method 501.2,
the % RSD ranges from 12% to 25% for
both water types for the middle and high
concentration levels (45 ppb to 174 ppb). The
% RSD ranges from 18% to 76% for the
lowest concentration levels (1.7 ppb to 7.2
ppb) in both water types. The overall stan-
dard deviation is very good except at the very
low concentration levels.
The single-analyst standard deviation in-
dicates the precision associated within a
single laboratory. The single-analyst percent
relative standard deviation (% RSD-SA) in
Method 501.1 ranged from 10% to 23%; this
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. For
Method 501.2, the % RSD-SA for both
water types ranges from 5% to 12% for the
middle and high concentrations. The lowest
concentration levels yield a range of 5% to
81%. The single-analyst standard deviation
is excellent except at the very low concen-
tration levels. A statistical comparison of the
effect of the type of water in Method 501.1
indicated no significant difference between
water types.
The background levels in drinking water
were as high as 65 ppb for chloroform and
20 ppb for bromodichloromethane. The low
precision is probably due to subtracting a
large blank value at low concentration levels.
The comparison on the effect of water
types for Method 501.2 shows a statistically
significant difference for bromodichloro-
methane. However, a practical significant
difference does not exist.
Conclusions and
Recommendations
Method 501.1 is acceptable for the
analysis of trihalomethanes in drinking water.
The accuracy is excellent, while the overall
precision and single-analyst precision 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 compounds,
'especially bromoform. ' " • • ~
Special care must be taken in handling
samples and blanks to avoid contamination
from the laboratory atmosphere. It is recom-
mended that at least daily checks be made
for contamination by the use of appropriate
blanks.
Carry-over of the trihalomethane analytes
from the analysis of high concentration
samples to the next analysis was noted. It
is recommended that the purge device be
filled with distilled water and purged for 10
minutes after the analysis of samples sus-
pected of containing high concentrations of
trihalomethanes.
Method 501.2 is also recommended for the
analysis of trihalomethanes in drinking water.
The accuracy is excellent. The overall preci-
sion and single-analyst precision are very
good except at very low concentrations.
For analytical laboratories located at high
altitude, isooctane is the recommended ex-
traction solvent.
Extraction solvents must be checked for
contamination. Solvents such as n-hexane
and cyclohexane were reported to contain
impurities which have the same retention
time as chloroform and bromoform. Con-
tamination can come from impurities in the
solvent or from impurities absorbed from the
laboratory atmosphere. Analysis of blanks is
recommended on a daily basis.
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Table 1. Method 501. J Regression Equations for Accuracy and Precision
Water type
Range (\tglU
Distilled water
Single-analyst precision
Overall precision
Accuracy
Tap water
Single-analyst precision
Overall precision
Accuracy
Range (pg/L)
Chloroform
0.86-
SR =
S =
X =
SR =
S =
X =
0.26-
550
0. 10X +
0.20X +
0.92C +
o.nx +
0. 18X +
1.02C +
550
0.13
0.20
0.04
0.03
0.74
0.52
Bromodichloromethane
0.88-
SR =
S =
w
SR =
S =
X =
0.88-
550
0. 15X -
0.23X +
0.95C -
0. 15X +
0.22X +
1.02C +
550
0.05
0.15
0.04
0.18
0.38
0.08
Chlorodibromomethane
0.84-
SR =
S =
X =
SR =
S =
X =
0.84-
550
0. 16X + 0.06
0.26X + 0.35
0.99C - 0.08
0. 18X + 0. 13
0.27X + 0.07
1.04C - 0.16
550
Bromoform
4.8 - 550
SR =
S =
X =
SR =
5 =
X =
4.84-
0. 19X -
0.28X +
1.03C -
0.23X -
0.32X +
1.08C -
550
0.25
0.63
1.48
0.05
0.47
1.75
X = mean recovery.
C = true value for the concentration.
Table 2. Method 501.2 Regression Equations'for Accuracy and'Precision
Water type Chloroform Bromodichloromethane
Chlorodibromomethane
Bromoform
Distilled water
Single-analyst precision
Overall precision
Accuracy
Tap water
Single-analyst precision
Overall precision
Accuracy
SR =
S =
X =
SR =
S =
X =
0.06X + 0.76
0.17X + 0.65
1.01C + 0. 14
0.08X + 1.33
0.26X + 0.60
1.03X - 0.37
SR =
S =
S =
SR =
Q
X =
0.05X +
0. 17X +
0.98C +
0.07X +
0.23X +
1.01C +
0.07
0.31
0.02
0.67
0.86
0.51
SR
S
S
SR
S
X
= 0.07X +
= 0. 16X +
= 1.02C +
= 0.07X +
= 0. 13X +
= 1.00C -
0.09
0.47
0.07
0.30
0.50
0.05
SR
S
X
SR
S
X
= 0.07X +
= ft 15X +
= J.01C -
= 0.08X -
= ft 16X +
= 1.03C -
0.24
0.17
2.29
0.11
0.11
2.08
X = mean recovery.
C = true value for the concentration.
Beverly J. Warner, Sam C. Cheng, Charles S. Friedman, Sueann Mitrosky, Arthur
D. Snyder, and Carl R. McMillin are with Monsanto Research Corporation,
Dayton, OH 454O7.
Raymond Wesselman is the EPA Project Officer (see below).
The complete report consists of two volumes:
"EPA Method Study 23A, Method 501.1, Trihalomethanes by Purge and Trap"
(Order No. PB 84-169 994; Cost $13.OO, subject to change).
"EPA Method Study 23B, Method S01.2, Trihalomethanes by Liquid/Liquid
Extraction" (Order No. PB 84-168 806; Cost $13.OO, subject to change).
The above reports 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
U.S. GOVERNMENT PRINTING OFFICE; 1984 — 759-015/7679
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Environmental Protection
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