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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