THE ANALYSIS OF TRIHALOMETHANES IN FINISHED
WATERS BY THE PURGE AND TRAP METHOD
Method 501.1
I/)
U. S. ENVIRONMENTAL PROTECTION AGENCY
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
CINCINNATI, OHIO 45268
November 6, 1979
QD142.
U55
1979
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Foreword
This method has been prepared by the staff of the Environmental
Monitoring and Support Laboratory - Cincinnati, at the request of the Office
of Drinking Water. Comments and suggestions offered by the Municipal
Environmental Research Laboratory, the Technical Support Division, ODW, and
the Health Effects Research Laboratory on the September 9, 1977, draft are
gratefully acknowledged.
The procedure represents the current state-of-the-art, but as time
progresses improvements are anticipated. Users are encouraged to identify
problems and assist in updating the method by contacting the Environmental
Protection Agency, Environmental Monitoring and Support Laboratory,
Cincinnati, Ohio, 45268.
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The Analysis of Trihalomethanes In Drinking
Water by the Purge and Trap Method
1. Scope
1.1 This method (1) Is applicable 1n the determination of four
tMhalomethanes, I.e. chloroform, dlchlorobromethane, dibromo-
chloromethane, and bromoform in finished drinking water, raw source
water, or drinking water In any stage of treatment. The concen-
tration of these four compounds is totaled to determine total
trihalomethanes (TTKM).
1.2 For compounds other than the above-mentioned trihalomethanes, or
for other sample sources, the analyst must demonstrate the useful-
ness of the method by collecting precision and accuracy data on
actual samples as described (2).
1.3 Although the actual detection limits are highly dependent upon the
gas chromatographic column and detector employed, the method can be
used over a concentration range of approximately 0.5 to 1500 micro-
grans per liter.
1.4 Well in excess of 100 different water supplies have been analyzed
using this method. Supplementary analyses using gas chromatography
mass spectrometry (GC/MS) have shown that there is no evidence of
interference in the determination of trihalomethanes (3). For this
reason, it 1s not necessary to analyze the raw source water as is
required with the Liquid/Liquid Extraction Method (4).
2. Summary
2.2 Trihalomethanes are extracted by an inert gas which is bubbled
through .the aqueous sample. The trihalomethanes, along with other
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If any trihalomethane is noted in the method blank in excess of 0.4
ug/1, ths analyst should change the purge gas source and regenerate
the molecular sieve ourge gas filter. Subtracting the blank values
is not recommended. The use of nqn-TFE plastic tubing, non-TFE
thread.sealants, or flow controllers with rubber components should
bo avoided since such materials generally.out-gas organic compounds
which will be concentrated.in the .trap during the purge operation.
Such out-gasing problems are common whenever new equipment is put
into service; as time progresses, minor out-gasing problems
generally cure themselves.
3.2 Several instances of accidental sample contamination have been
noted and attributed to diffusion of volatile organics through the
septum seal and into the sample during shipment and storage. The
sample blank is used as a monitor for this problem.
3.3 For compounds that are not efficiently purged, such as bromoform,
small variations in sample volume, purge time, purge flow rate, or
purge temperature can affect the analytical result. Therefore,
samples and standards must be analyzed under identical conditions.
3.4 Cross-contamination can occur whenever high-level and low-level
samples are sequentially analyzed. To reduce this likelihood, the
purging device and sample syringe should be rinsed twice between
samples with organic-free water. Whenever an unusually concen-
trated sample is encountered, it is highly recommended that it be
followed by a sample blank analysis to ensure that sample cross
contamination dees not occur. For samples containing large amounts
of water soluble materials, it may be necessary tc wash out the
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organic constituents which exhibit low water solubility and a vapor
pressure significantly^greater than water, are efficiently trans-
ferred from the aqueous phase to" the gaseous phase. These
compounds.are swept from the purging device and are trapped In a
short column containing a suitable* sorbent1." After a predetermined
-period of time, the trapped'components"are thermally desorbed and
bacicf lushed onto'the'head-of argas chromatographic column and
separated under programmed 'conditions/' Measurement Is accomplished
with a halogen 'specific detector such as" electrolytic conductivity
or-mlcrocbulometric tltratlon.
2.3 Confirmatory analyses are performed using dissimilar columns, or by
mass spectrometry (5).
2.4 Aqueous standards and unknowns are extracted and analyzed under
identical conditions In order to compensate for extraction losses.
2.5 The total analysis time, assuming the absence of other organo-
halides, 1s approximately 35 minutes per sample.
3. Interferences
3.1 Impurities contained in the purge gas and organic compounds, out-
gasing from the plumbing ahead of the trap usually account for the
majority of contamination problems. The presence of such inter-
ferences are easily monitored as a part of the quality control
program. Sample blanks are normally run between each set of
samples. When a positive trihalomethane response is noted in the
sample blank, the analyst .should analyze a method blank. Method
blanks are run by charging the purging.device with organic-free
.water and analyzing 1n the normal manner.
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purging device with a soap solution, rinse with distilled water, and
then dry In a 105°C oven between analyses.
3.5 Qualitative nils-identifications are a problem 1n using gas chromato-
graphic analysis. Whenever samples whose qualitative nature 1s
unknown are analyzed, the following precautionary measures should be
incorporated Into the' analysis.
3.5.1 Perform duplicate analyses using the two recommended columns
(4.2.1 and 4.2.2} which provide different retention order and
retention times for the trlhalomethanes and other organo-
halldes.
3.5.2 Whenever possible, use GC/MS techniques which provide
unequivocal qualitative Identifications (5).
4. Apparatus
4.1 The purge and trap equipment consists of three separate pieces of
apparatus: the purging device, trap, and desorber. Construction
details for a purging device and an easily automated trap-desorber
hybrid which has proven to be exceptionally efficient and
reproducible are shown in Figures 1 through 4 and described in'4,1.1
through 4.1.3. An earlier acceptable version of the above-mentioned
equipment is described 1n (1).
4.1.1 Purging Device - Construction details are given in Figure 1
for an all-glass 5 ml purging device. The glass frit
Installed at the base of the sample chamber allows finely
divided gas bubbles to pass through the sample while the
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sample is restrained above the frit. Gaseous volumes above
the sample are kept to a minimum to eliminate dead volume
effects, yet allowing sufficient .space for most foams to
disperse. The inlet and exit ports are constructed from
heavy-walled 1/4-inch .glass tubi-ng sp-that Jeak-free
removable connect ions^carj. be made .using "finger-tight"
compression fittings containing Teflon ferrules. The
removable foam trap is used,to..control Camples that foam.
4/1.2 Trapping Device - The trap (Figure_2\.\s a short gas
chromatographic column which at <35°C .retards the flow of
the compounds of interest while venting the purge gas and,
depending on which sorbent is used, much of the water vapor.
The trap should be constructed with a low thermal mass so
that it can be heated to 180°C in less than 1 minute for
efficient desorption, then rapidly cooled to room tempera-
ture for recycling. Variations in the trap ID, wall
thickness, sorfrents, sorbent packing order, and sorbent mass
couTd adverse!/ affect the trapping and desorption efficien-
cies for compounds-discussed in this text. For this reason,
it is important to faithfully reproduce the trap configu-
rations recomme'nded in figure 2. Traps containing Tenax
only, or combinations of Tenax'and other sorbents are
acceptable for this analysis.
4,1.3 Desorber assembly -Details for the desorber are shown in
Figures 3, and 4. With the 6-port valve in the Purge Sorb
position (Figure 3), the effluent from the purging device
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passes through the trap where the flew rate of the organlcs
1s retarded. The GC carrier gas also passes through the
6-port valve and 1s returned to the GC. With the 6-port
valve 1n the Purge-Sorb position,, the operation of the GC 1s
1n no way Impaired; therefore, routine liquid Injection
analyses can be performed using the gas chromatograph.
After the sample.has been purged, the 6-port valve 1s turned
to the desorb position (Figure 4}.,. In this configuration,
the trap 1s coupled In series with the gas chromatographic
column allowing the carrier gas to backflush the trapped
materials Into the analytical column. Just as the valve 1s
actuated, the power 1s turned on to the resistance wire
wrapped around the trap. The power 1s supplied by an
electronic temperature controller. Using this device, the
trap 1s rapidly heated to 180°C and then maintained at
180°C with minimal temperature overshoot. The trapped
compounds are released as a "plug" to the gas chromatograph.
Normally, packed columns with theoretical efficiencies near
500 plates/foot under programmed temperature conditions can
accept such desorb Injections without altering peak
geometry. Substituting a non-controlled power supply, such
as a manually-operated variable transformer, will provide
nonreprodudble retention times and poor quantitative data
unless Injection Procedure (8.9.2) Is used.
4.1.4 Several Purge and Trap Devices are now commercially
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available. It 1s recommended that the following be taken
into consideration If a unit Is to be purchased:
a. Be sure that the unit Is completely compatible with the
gas chromatograph to be used for the analysis.
b. Use a-5-ml-purging device similar to that shown 1n Figure
V.
c:n Be sure-'the'"tenax portion of the trap meets or exceeds
• the dimensions shown 1ri Figure 2.
d:-With'the exception of s'ample' Introduction, select a unit
that has as many of the purge trap functions automated as
possible.
4.2 - Gas chromatograph - The chroraatograph must be temperature program-
mable and equipped with-a hall'de specific detector.
4.2.1 Column I Is an-unusually efficient column which provides
outstanding separations for a wide variety of organic
compounds. Because of Its ability to resolve trihalo-
methanes from other organodilorlne compounds, column I
should be used as* the primary analytical column (see Table 1
for retention data uslrtg this column).
4.2.1.1 Column I parameters: Dimensions - 8 feet long x
O.V Inch ID stainless steel or glass tubing.
Packing - IX SP-100Q on Carbopack-B (60/80} mesh.
Carrier Gas - helium at 40 ml/minute. Temperature
program sequence: 45°C Isothermal for 3 minutes,
program at S°C/minute to 220°C then hold for 15
minutes or until all compounds have eluted.
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NOTE: It has been found that during handling,
packing, and programming, active sites are
exposed on the Carbopack-B packing. This
results In tailing peak geometry and poor
resolution of many constituents. To correct
this, pack the first 5 on of the column with
3% SP-1000 on Chromosorb-W 60/80 followed by
the Carbopack-B packing. Condition the pre-
coluinn and the Carbopack columns with carrier
gas flow at 220°C overnight. Pneumatic
shocks and rough treatment of packed columns
will cause excessive fracturing of the
Carbopack. If pressure 1n excess of 60 ps1
Is required to obtain 40 ml/minute carrier
flow, then the column should be repacked.
4.2.7.2 Acceptable column equivalent to Column I:
Dimensions - 8 feet long x 0.1 Inch ID stainless
steel or glass tubing. Packing - 0.22 Carb'owax
1500 on Carbopack-C (80/100) mesh. Carrier Gas -
helium at 40 ml/minute. Temperature program
sequence - 60°C Isothermal for 3 minutes, program
at 8°C/ minute to 160°C, then hold for 2
minutes or until all compounds have eluted.
NOTE: It has been found that during handling,
packing, and programming, active sites are
exposed on the Carbopack-C packing. This
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results in poor resolution of constituents
and poor peak geometry. To correct this,
place a 1 ft. 0.125 in. 00 x 0.1 1n. ID
stainless steel column packed with 3%
Carbowax 1500 on Chromosorb-W 60/80 mesh in
series before the Carbopack-C column.
Condition the precolumn and the Carbopack
columns with carrier gas flow at 190°C
overnight. The two columns may be retained
1n series for routine analyses. Trihalo-
methane retention times are listed 1n Table 1.
4.2.2 Column II provides unique organohalide-trihalomethane
separations when compared to those obtained from Column I
(see Figures 5 and 6). However, since the resolution
between various compounds 1s generally not as good as those
with Column I, it Is recommended that Column II be used as a
qualitative confirmatory column for unknown samples when
GC/N5 confirmation is not possible.
4.2.2.1 Column II parameters: Dimensions - 6 feet long x
0.1 Inch ID stainless steel or glass. Packing -
n-octane on Porisil-C (100/120 mesh). Carrier Gas
- helium at 40 cc/minute. Temperature program
sequence - 50°C Isothermal for 3 minutes, program
at 6°/m1nute to 170°C, then hold for 4 minutes
or until all compounds have eluted. Trihalomethane
retention times are listed in Table 1.
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4.3 Sampling containers - 40 ml screw cap vials sealed with Teflon
faced silicone septa.
Vials and caps - Pierce #13075 or equivalent.
Septa - Pierce #12722 or equivalent.
4.4 Syringes - 5-ml glass hypodermic with luerlok tip (2 each).
4.5 Micro syringes - 10, 100 ul.
4.6 Micro syringe - 25 pi with a 2" x 0.006" ID needle-Hamilton #702N,
or equivalent.
4.7 2-way syringe valve with luer ends (3 each) Hamilton #86570-1FM1,
or equivalent.
4.8 Standard storage containers - 15 ml amber screw-cap septum bottles
with Teflon faced silicone septa.
Bottles and Caps - Pierce #19830, or equivalent.
Septa - Pierce #12716, or equivalent.
5. Reagents and Materials
5.1 Porous polymer packing 60/80 mesh chromatographic grade Tenax GC
(2,6-diphenylene oxide).
5.2 Three percent OV-1 Chromosorb-W 60/80 mesh.
5.3 l.OX SP-1000 on Carbopack-B (60/80 mesh) available from Supelco.
5.4 n-Octane on Porasil-C (100/120 mesh) available from Waters
Associates.
5.5 Three percent SP-1000 on Chromosorb-W (60/80 mesh).
5.6 Free and combined chlorine reducing agent - crystalline sodium
thiosulfate, ACS Reagent Grade or sodium sulfite, ACS Reagent Grade.
5.7 Activated carbon - Filtrasorb-200, available from Calgon
Corporation, Pittsburgh, PA, or equivalent.
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5.8 Organic-free water is defined as water free of interference when
employed in the purge and trap analysis.
5.8.1 Organic-free water is generated by passing tap water through
a carbon filter bed containing about 1 Ih. of activated
carbon. Change the activated carbon bed whenever the
concentration of any trihalomethane exceeds 0.4 ug/1.
•5.8.2 A Millipore Super-Q Water System or its equivalent nay be
used to generate organic-free water.
5.8.3 Organic-free water may also be prepared by boiling water for
15 minutes. Subsequently, while maintaining the temperature
at 90°C, bubble a contami.nant-fr.ee inert, gas through the
water for one hour. While still hat, transfer the water to
a narrow-mouth screw-cap bottle with a Teflon seal.
5.8.4 Test organic free water each day it is used by analyzing
according to Section 8.
5.9 Standards3
5.9.1 Bromoform - 96% - available from Aldrich Chemical Company.
5.9.2' Bromodichl,orometha.ne 9756. - available from.Aldrich Chemical
Company.
5.9.3 Chlorodibromomethane - available from Columbia Chemical
Inc., Columbia, S.C.
5.9.4 Chloroform - 99% - available from Aldrich Chemical Company.
aAs a precautionary measure, all standards must be checked for purity by
boiling point determinations or GC/MS assays (5).
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5.10 Standard Stock Solutions
5.10.1 Place about 9.8 ml of methyl alcohol into a ground glass
stoppered 10 ml volumetric flask.
5.10.2 Allow the flask to stand unstoppered about 10 minutes or
until all alcohol wetted surfaces have dried.
5.10.3 Weigh the flask to the nearest 0.1 mg.
5.10.4 Using-a 100 ul syringe, immediately add 2 drops of the
reference standard to the flask, then reweigh. Be sure
that the 2 drops fall directly into the alcohol without
contacting the neck of the flask.
5.10.5 Dilute to volume, stopper, then mix by inverting the flask
several times.
5.10.6 Transfer the solution to a dated and labeled 15 ml screw
cap bottle with a Teflon cap liner.
NOTE: Because of the toxieity of trihalomethanes, it is
necessary to prepare primary dilutions in a hood.
It is further recommended that a NIOSH/MESA approved
toxic gas respirator be used'when the analyst
handles high concentrations of such materials.
5.10.7 Calculate the concentration in micrograms per microliter
from the net gain in weight.
5.10.8 Store the solution at 4°C.
NOTE: All standard solutions prepared in methyl alcohol
are stable up to 4 weeks when stored under these
conditions; They should be discarded after that
time has elapsed.
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5.11 Aqueous Calibration Standard Precautions
5.11.1 In order to.prepare accurate aqueous standard solutions,
the following precautions must be observed.
.a. Do ..not inject more-than 20 ul of alcoholic standards
into 100 .ml of organic-free water.
b.. Use a 25 ul Hamilton 702N microsyringe or equivalent.
(Variations in needle-geometry will, adversely affect
the .-ability to deliver reproducible volumes of methan-
olic standards into water.)
c. Rapidly inject the alcoholic standard into the expanded
area of the filled volumetric flask. Remove the needle
as fast as possible after.injection.
d. Mix aqueous standards by inverting the flask three
times only.
e. Discard the .contents contained in the neck of the
fjask. Fill the sample syringe from the standard
solution contained in the expanded area of the flask as
directed in Section 8.5.
f. Never use pipets to dilute or transfer samples or
aqueous standards..
g. Aqueous standards when stored with a headspace are not
stable and.should be discarded after one hour.
h. Aqueous standards can be stored according to Sections
6o4 and 8.6.
5-. 11.2 Prepare, from the standard stock solutions, secondary
dilution mixtures.in methyl alcohol so that a 20 ul
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injection Into 100 ml of organic-free water will generate a
calibration standard which produces a response close (+10%)
to that of the sample (See 9.1).
5.11.3 Purge and analyze the aqueous calibration standards in the
same manner as the samples..
5.11.4 Othe*- calibration procedures (3).which.require the delivery
of less than 20 u! of a methanol.ic standard into a 5.0 ml
volume of water already contained in the sample syringe are
acceptable only if the-inathanolic standard is delivered by
the solvent flush technique (6),
5.12 Quality Check Standard (2.0 yg/1)
5.12.1 From the standard stock solutions, prepare a secondary
dilution in methyl alcohol containing 10 ng/yl of each
trihalomethane (See Section 5.10.8 Note).
5.12.2 Daily, inject 20.0 ul of this mixture into 100.0 ml of
organic-free water and analyze according to Section 8.
6. Sample Collection and Handling
5.1 The sample containers should have a total volume of at least 25 ml.
6.1.1 Narrow mouth screw cap bottles with the TFE fluorocarbon
face silicon septa cap liners are strongly recommended.
6.2 Sample Bottle Preparation
6.2.1 Wash all sample bottles and TFE seals in detergent. Rinse
with tap water and finally with distilled water.
6.2.2 Allow the bottles and seals to air dry at room temperature,
then place in a 105°C oven for one hour, then allow to
cool in an area known to be free of organics.
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NOTE: Do not heat the TFE seals for extended periods of
time (>1 Iiour) bacause the silicone layer slowly
degrades at 105°C.
6.2.3 When cool,-seal the bottles using the TFE seals that will
be used for-.sealIng the samples,
6.3 Sample:Stabilization - A chemical reducing agenc (Section 5.6) Is
added-to., the sample-, iir order "to. arrest the formation of trihalo-
methanes after"sampler collection (3, 7). Do not add the reducing
agent to samples whenjdata on maximum trlhalomethane formation is
desired. If chemical-stabilization'is employed, the reagent is
also added to the blanks. The-chemical agent (2.5 to 3 mg/40 ml)
.is added to the empty sample bottles just prior to shipping to the
sampling-'site.
6.4 Sample Collection
6.4.1 Collect all samples in duplicate.
6.4.2 Fill the.sample bottles in-such a manner that no air
bubbles pass through the sample as the bottle is filled.
6.4.3 Seal the bottles so that no air bubbles are entrapped in it.
6.4.4 Maintain the hermetic seal on the sample bottle until
analysis.
6.4.5 Sampling from a water tap.
6.4.5.1 Turn on water and allow the system to flush until
the temperature of the water has stabilized.
Adjust the flow to about 500 ml/minute and collect
duplicate samples from the flowing stream.
6.4.5 Sampling from -an open body of water.
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6.4.6.1 F111 a 1-quart wide-mouth bottle with sample from a
representative area. Carefully fill duplicate
sample bottles from the 1-quart bottle as noted In
6.4.2.
6.4.7 If a chemical reducing agent has been added to the sample
bottles, fill with sample just to overflowing, seal the
bottle, and shake vigorously for 1 minute.
6.4.8 Sealing practice for septum seal screw cap bottles.
6.4.8.1 Open the bottle and fill to overflowing, place on
a level surface, position the TFE side of the
septum seal upon the convex sample meniscus and
seal the bottle by screwing the cap on tightly.
6.4.8.2 Invert the sample and lightly tap the cap on a
solid surface. The absence of entrapped air
Indicates a successful-seal. If bubbles are
present, open the bottle, add a few additional
drops of sample and reseal the bottle as above.
6.4.9 Blanks
6.4.9.1 Prepare blanks 1n duplicate at the laboratory by
filling and sealing sample bottles with organic-
free water just prior to shipping the sample
bottles to the sampling site.
6.4.9.2 If the sample 1s to be stabilized, add an
Identical amount of stabilization reagent to the
blanks.
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S.4.9-.3 Ship the blanks to and from the sampling site
along with the sample bottles.
6.4.9.4 Store the blanks and the samples collected at a
given site (sample, set) together. A sample set 1s
defined as all .the samples collected at a given
site .(I.e.-, at a water tretment plant, the
duplicate raw source waters, the duplicate
f 1n1 shed .waters, and the duplicate .blank samples
comprise the sample set).
6.5. When samples have been collected according to Section 6, no measur-
able loss of trlhalomethanes .has been detected over extended
periods of storage time (3). It Is recommended that all samples be
analyzed within 14 days of collection.
7. Conditioning Traps
7.1 Condition newly p.acked traps overnight at 180°C with an Inert gas
flow of at least 20 ml/rain.
7.1.1 Vent the trap effluent to the room, not to the analytical
column.
7.2 Prior to dally use, condition traps 10 minutes while backflushing
at 180°C. It may be beneficial to routinely condition traps
overnight while backflushing at 180°C.
7.2.1 The trap may be vented to the analytical column; however,
after conditioning, the column must be programmed prior to
use.
8. Extraction and Analysis
8.1 Adjust the purge gas (nitrogen or helium) flow rate to 40 ml/min.
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8.2 Attach the trap Inlet to the purging device. Turn the valve to the
purge-sorb position (Figure 3).
8.3 Open the syringe valve located on the purging device sample Intro-
duction needle.
8.4 Remove the plungers from two 5 ml syringes and attach a closed
syringe valve to each.
8.5 Open the sample bottle and carefully pour the sample Into one of
the syringe barrels until 1t overflows. Replace the syringe
plunger and compress the sample. Open the syringe valve and vent
any residual air while adjusting the sample volume to 5.0 ml.
Close the valve.
8.6 Fill the second syringe In an Identical manner from the same sample
bottle. This second syringe 1s reserved for a duplicate analysis,
1f necessary (See Section 9.3 and 9.4).
8.7 Attach the syringe-valve assembly to the syringe valve on the
purging device.
8.8 Open the syringe valve and Inject the sample Into the purging
chamber. Close both valves. Purge the sample for 11.0 + .05
alnutes.
8.9 After the !l-m1nute purge time, attach the trap to the.chromato-
graph (turn the valve to the desorb position) and Introduce the
trapped materials to the GC column by rapidly heating the trap to
180°C while backflushlng the trap with an Inert gas between 20
and 60 ml/m1n for 4 minutes.
8.9.1 If the trap can be rapidly heated to 180°C and maintained
at this temperature, the GC analysis can begin as the
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sample is desorbed, i.e., the column is at the initial
45°C operating temperature. The equipment described in
Figure 4 will perform accordingly.
8.9.2 With other types of equipment (see Section 4.1.4 and
Reference.!) where the trap is not rapidly heated or is not
heated in a reproducible manner, it may be necessary to
transfer the contents of the trap into the analytical
column at <30°C where it is once again trapped. Once the
transfer is complete (4 minutes), the column is rapidly
heated to the initial operating temperature for analysis.
8.9.3 If injection procedure 8.9.1 is used and the early eluting
peaks in the resulting chromatogram have poor geometry or
variable retention times, then Section 8.9.2 should be used.
8.10 After the extracted sample is introduced into the gas chromato-
graph, empty the gas purging device using the sample introduction
syringe, followed by two 5-ml flushes of organic-free water. When
the purging device is emptied, leave the syringe valve open
allowing the purge gas to vent through the sample introduction
needle.
8.11 Analyze each sample and sample blank from the sample set in an
identical manner (see" Section 6.4.9.4) on the same day,
8.12 Prepare calibration standards from the standard stock solutions
(Section 5.10) in organic-free water that are close to the unknown
.in trihalomethane composition and concentration (Section 9.1). The
concentrations should be such that only 20 ul or less of the
secondary dilution need be added to 100 ml of organic-free water to
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produce a standard at the same level as the unknown.
8.13 As an alternative to Section 8.12, prepare a calibration curve for
each trihalomethane containing at least 3 points, two of which must
bracket the unknown.
9. Analytical QualUy Control
9.1 Analyze the 2 ug/1 check sample daily-before any samples are
analyzed. Instrument status .checks and lower limit of detection
estimations based upon response factor calculations at five times
the noise level are obtained
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In organic-free water as described in Section 5.11.
9.4 Randomly select and analyze 10% of all samples in duplicate.
9.4.1 Analyze all samples In duplicate which appear to deviate
more than 30% from any established norm.
9.5 Maintain an up-to-date log on the accuracy and precision data
collected in Sections 9.3 and 9.4. If results are significantly
different'than thosd cited in Section 1*1.1, the analyst should
check out the entire analyses scheme to determine why the
laboratory's precision and accuracy limits are greater.
9.6- Quarterly, spike an EMSL-Cincinnati trihalcmethane quality control
sample into organic-free water and analyze.
9.6.1 The results of the EMSL trlhalomethane quality control
sample should agree within 20% of the true value for each
trihalomethane. If they do not then the analyst must check
each step in the standard generation procedure to solve the
problem (Section 5.9, 5.10, and 5.11).
9.7 Maintain a record of the retention times for each trihalomethane
using data gathered from spiked samples and standards.
9.7.1 Daily calculate the average retention time for each-
trihalomethane and the variance encountered for the
analyses.
9.7.2 If individual trihalomethane retention time varies by more
than 10% over an eight hour period or'does not fall with
10% of an established norm, the system is "out of
control." The source of retention data variantion must be
corrected before acceptable data can be generated.
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10. Calculations
10.1 Locate each trihalomethane in the sample chromatogram by comparing
the retention time of the suspect peak to the data gathered In
9.7.1. The retention time of the suspect peak must fall within the
limits established in 9:7.1 for single column identification.
10.2 Calculate- the concentration of the samples by comparing the peak
height or peak areas of the* samples to tha standard peak height
(8.12). Round off the data to the nearest ug/1 or two significant
figures.
*
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11. Accuracy and Precision
11.1 One liter of organic-free water was spiked with the trihalomethanes
and used to fill septum seal vials which were stored under ambient
conditions. Tha spiked samples were randomly analyzed over a
2-week period of time. The single laboratory data listed in Table
II- reflect the errors dua to- tha analytical procedure and storage.
-------
REFERENCES
1. Bellar, T.A., J.J. Lichtenberg, Determining Volatile Organics at the
Microgram per Litre Levels by Gas Chrcmatography, Journal AWWA., 66, 739
(December 1974).
2. "Handbook for Analytical Quality Control 1n Water and Wastewater
Laboratories," Analytical Quality Control Laboratory, National
Environmental .Research Center, Cincinnati, Ohio, June 1972.
3,, Brass, H.J., et al., "National Organic Monitoring Survey: Sampling and
Purgeable Organic Compounds,, Drinking Water Quality Through Source
Protection," R. B. Pojasek, Editor, Ann Arbor Science, p. 398, 1977.
4, "The Analysis of Trlhalomethanes 1n Finished Water by the Liquid/Liquid
Extraction Method, Method 501.2* Environmental Monitoring and Support
Laboratory, Environmental Research Center, Cincinnati, Ohio,-45268, May
15, 1979.
5. Budde, W.L. and J.W. Elchelberger, "Organics Analysis Using Gas
Chromatography-Mass Spectrometry," Ann Arbor Science, Ann Arbor,
Michigan, 1979.
6. White, L.D., et al., "Convenient Optimized Method for the Analysis of
Selected Solvent Vapors in the Industrial Atmosphere," AIHA Journal,
Vol. 31, p. 225, 1970.
7. Kopfler, F.C., et al. "GC/MS Determination of Volatlles for the National
Organlcs Reconnaissance Survey (NORS) or Drinking Water, Identification
and Analysis of Organic Pollutants in Water," L. H. Keith, Editor, Ann
Arbor Science, p. 87, 1976.
-------
TABLE I
Retention Data for Trihalooiethanes
Trlhalomethane
Chloroform
Bromodl cfiloroiaettfane
Chiorodibromomethane
(Dlbromoch1oromethane)
Bromofonn
Retention Time Minutes
-Acceptable
Alternative to
Column I
1* SP1000
Carbopack B
10.7
13.7
16.5
Column I
0.4X Carbowa
Carbopack C
8.2
10.8
13.2
19.2
15.7
•Column II
n-Octane
Porasll-C
12.2
14.7
16.6
19.2
-------
TABLE II
Single Laboratory
Accuracy and Precision for Trihalomethanes
Chloroform
Spike
yg/1
1.2
12.
119
Number
Samples
12
8
11
Mean
yg/i
1.2
11.
105
Precision
Standard
Deviation
0.14
0.16
7.9
Accuracy
X Recovery
100
92
88
1.6
16.
160
2.0
20.
196.
2.3
23.
231.
12
8
11
12
8
11
12
8
11
Brorcod i ch 1 oromet h lane
1.5
15.
145.
Chlorodibromomethane
1.9
19.
185.
Bromoform
2.3
23.
223
0.05
0.39
10.2
0.09
0.70
10.6
0.16
1.38
16.3
94
94
91
95
95
94
100
100
97
-------
OPTIONAL
FOAM TRAP
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/
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13X MOLECULAR
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GAS FILTER
PURGE GAS
FLOW CONTROL
IP
-------
PACKING PROCEDURE
CONSTRUCTION
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FIGURE 2 TRAP
-------
CARRIER GAS FLOW CONTROL
PRESSURE REGULATOR
LIQUID INJECTION PORTS
\
PURGE GAS
FLOW CONTROL \
13X MOLECULAR
SIEVE FILTER
COLUMN OVEN
CONFIRMATORY COLUMN
TO DETECTOR
ANALYTICAL COLUMN
OPTIONAL 4-PORT COLUMN
SELECTION VALVE
TRAP INLET (TENTAX tND)
6-PORT VALVE / RESISTANCE WIRE
HEATER CONTROL
NOTE: ALL LINES BETWEEN
TRAP AND GC
SHOULD BE HEATED
PURGING DEVICE TO 80° C
FIGURE 3 PURGE-TRAP SYSTEM (PURGE-SORB MODE)
-------
CARRIER GAS FLOW CONTROL
LIQUID INJECTION PORTS
PRESSURE REGULATOR
PURGE GAS v
FLOW CONTROL X
\3X MOLECULAR
SIEVE FILTER
COLUMN OVEN
CONFIRMATORY COLUMN
TO DETECTOR
ANALYTICAL COLUMN
OPTIONAL 4-PORT COLUMN
SELECTION VALVE
TRAP INLET (TENAX END)
6-PORT VALVE / RESISTANCE WIRE
HEATER CONTROL
NOTE: ALL LINES BETWEEN
TRAP AND GC
SHOULD BE HEATED
TO 80°C
PURGING DEVICE
FIGURE 4 PURGE-TRAP SYSTEM (DESORB MODE)
-------
COlUMNt 0.5% CARBOWAX 1500 ON CARSOPACK-C
PlIOORAMt AO'C.S MINUTft SVMINUYl !O I»0»C
OIIICTOR: atCIROlY'lC CONOUCflVITV
RETENTION TIME MINUTES
FIOIIRF 1 CHROMATQGRAM OF ORGANOHALIDES
-------
COtUMN n-OCIANI ON
MOOIAMi SO*jC.) MIMUIII 4VMINUII TO t/O'C
oiifctoi fiiciioiTiic coNouctivirr
14 16
RETENTION TIME MINUICS
)l
FIGURE 6 CHROMATOGRAM OF ORGANOHALIDES
------- |