Appendix A to Part 136 -- Methods for Organic Chemical Analysis of
Municipal and Industrial Wastewater
METHOD 601 -- PURGEABLE HALOCARBONS
1. Scope and Application
1.1 This method covers the determination
of 29 purgeable halocarbons.
The following parameters may be determined by this method:
------------------------------------------------------------------------
STORET
Parameter No. CAS No.
------------------------------------------------------------------------
Bromodichloromethane........................... 32101 75-27-4
Bromoform...................................... 32104 75-25-2
Bromomethane................................... 34413 74-83-9
Carbon tetrachloride........................... 32102 56-23-5
Chlorobenzene.................................. 34301 108-90-7
Chloroethane................................... 34311 75-00-3
2-Chloroethylvinyl ether....................... 34576 100-75-8
Chloroform..................................... 32106 67-66-3
Chloromethane.................................. 34418 74-87-3
Dibromochloromethane........................... 32105 124-48-1
1,2-Dichlorobenzene............................ 34536 95-50-1
1,3-Dichlorobenzene............................ 34566 541-73-1
1,4-Dichlorobenzene............................ 34571 106-46-7
Dichlorodifluoromethane........................ 34668 75-71-8
1,1-Dichloroethane............................. 34496 75-34-3
1,2-Dichloroethane............................. 34531 107-06-2
1,1-Dichloroethane............................. 34501 75-35-4
trans-1,2-Dichloroethene....................... 34546 156-60-5
1,2-Dichloropropane............................ 34541 78-87-5
cis-1,3-Dichloropropene........................ 34704 10061-01-5
trans-1,3-Dichloropropene...................... 34699 10061-02-6
Methylene chloride............................. 34423 75-09-2
1,1,2,2-Tetrachloroethane...................... 34516 79-34-5
Tetrachloroethene.............................. 34475 127-18-4
1,1,1-Trichloroethane.......................... 34506 71-55-6
1,1,2-Trichloroethane.......................... 34511 79-00-5
Tetrachloroethene.............................. 39180 79-01-6
Trichlorofluoromethane......................... 34488 75-69-4
Vinyl chloride................................. 39715 75-01-4
------------------------------------------------------------------------
1.2 This is a purge and trap gas
chromatographic (GC) method applicable to the determination of the compounds
listed above in municipal and industrial discharges as provided under 40 CFR
136.1. When this method is used to analyze unfamiliar samples for any or all of
the compounds above, compound identifications should be supported by at least
one additional qualitative technique. This method describes analytical
conditions for a second gas chromatographic column that can be used to confirm
measurements made with the primary column. Method 624 provides gas
chromatograph/mass spectrometer (GC/MS) conditions appropriate for the
qualitative and quantitative confirmation of results for most of the parameters
listed above.
1.3 The method detection limit (MDL,
defined in Section 12.1)1 for each parameter is listed in Table 1.
The MDL for a specific wastewater may differ from those listed, depending upon
the nature of interferences in the sample matrix.
1.4 Any modification of this method,
beyond those expressly permitted, shall be considered as a major modification
subject to application and approval of alternate test procedures under 40 CFR
136.4 and 136.5.
1.5 This method is restricted to use by or
under the supervision of analysts experienced in the operation of a purge and
trap system and a gas chromatograph and in the interpretation of gas
chromatograms. Each analyst must demonstrate the ability to generate acceptable
results with this method using the procedure described in Section 8.2.
2. Summary of Method
2.1 An inert gas is bubbled through a 5-mL
water sample contained in a specially-designed purging chamber at ambient
temperature. The halocarbons are efficiently transferred from the aqueous phase
to the vapor phase. The vapor is swept through a sorbent trap where the
halocarbons are trapped. After purging is completed, the trap is heated and
backflushed with the inert gas to desorb the halocarbons onto a gas
chromatographic column. The gas chromatograph is temperature programmed to
separate the halocarbons which are then detected with a halide-specific
detector.2,3
2.2 The method provides an optional gas
chromatographic column that may be helpful in resolving the compounds of
interest from interferences that may occur.
3. Interferences
3.1 Impurities in the purge gas and
organic compounds outgassing from the plumbing ahead of the trap account for the
majority of contamination problems. The analytical system must be demonstrated
to be free from contamination under the conditions of the analysis by running
laboratory reagent blanks as described in Section 8.1.3. The use of non-Teflon
plastic tubing, non-Teflon thread sealants, or flow controllers with rubber
components in the purge and trap system should be avoided.
3.2 Samples can be contaminated by
diffusion of volatile organics (particularly fluorocarbons and methylene
chloride) through the septum seal ilto the sample during shipment and storage. A
field reagent blank prepared from reagent water and carried through the sampling
and handling protocol can serve as a check on such contamination.
3.3 Contamination by carry-over can occur
whenever high level and low level samples are sequentially analyzed. To reduce
carry-over, the purging device and sample syringe must be rinsed with reagent
water between sample analyses. Whenever an unusually concentrated sample is
encountered, it should be followed by an analysis of reagent water to check for
cross contamination. For samples containing large amounts of water-soluble
materials, suspended solids, high boiling compounds or high organohalide levels,
it may be necessary to wash out the purging device with a detergent solution,
rinse it with distilled water, and then dry it in a 105°C oven between analyses.
The trap and other parts of the system are also subject to contamination;
therefore, frequent bakeout and purging of the entire system may be required.
4. Safety
4.1 The toxicity or carcinogenicity of
each reagent used in this method has not been precisely defined; however, each
chemical compound should be treated as a potential health hazard. From this
viewpoint, exposure to these chemicals must be reduced to the lowest possible
level by whatever means available. The laboratory is responsible for maintaining
a current awareness file of OSHA regulations regarding the safe handling of the
chemicals specified in this method. A reference file of material data handling
sheets should also be made available to all personnel involved in the chemical
analysis. Additional references to laboratory safety are available and have been
identified4-6 for the information of the analyst.
4.2 The following parameters covered by
this method have been tentatively classified as known or suspected, human or
mammalian carcinogens: carbon tetrachloride, chloroform, 1,4-dichlorobenzene,
and vinyl chloride. Primary standards of these toxic compounds should be
prepared in a hood. A NIOSH/MESA approved toxic gas respirator should be worn
when the analyst handles high concentrations of these toxic compounds.
5. Apparatus and Materials
5.1 Sampling equipment, for discrete
sampling.
5.1.1 Vial -- 25-mL capacity or larger,
equipped with a screw cap with a hole in the center (Pierce #13075 or
equivalent). Detergent wash, rinse with tap and distilled water, and dry at 105
°C before use.
5.1.2 Septum -- Teflon-faced silicone
(Pierce #12722 or equivalent). Detergent wash, rinse with tap and distilled
water, and dry at 105 °C for 1 h before use.
5.2 Purge and trap system -- The purge and
trap system consists of three separate pieces of equipment: a purging device,
trap, and desorber. Several complete systems are now commercially available.
5.2.1 The purging device must be designed
to accept 5-mL samples with a water column at least 3 cm deep. The gaseous head
space between the water column and the trap must have a total volume of less
than 15 mL. The purge gas must pass through the water column as finely divided
bubbles with a diameter of less than 3 mm at the origin. The purge gas must be
introduced no more than 5 mm from the base of the water column. The purging
device illustrated in Figure 1 meets these design criteria.
5.2.2 The trap must be at least 25 cm long
and have an inside diameter of at least 0.105 in. The trap must be packed to
contain the following minimum lengths of adsorbents: 1.0 cm of methyl silicone
coated packing (Section 6.3.3), 7.7 cm of 2,6-diphenylene oxide polymer (Section
6.3.2), 7.7 cm of silica gel (Section 6.3.4), 7.7 cm of coconut charcoal
(Section 6.3.1). If it is not necessary to analyze for dichlorodifluoromethane,
the charcoal can be eliminated, and the polymer section lengthened to 15 cm. The
minimum specifications for the trap are illustrated in Figure 2.
5.2.3 The desorber must be capable of
rapidly heating the trap to 180 °C. The polymer section of the trap should not
be heated higher than 180 °C and the remaining sections should not exceed 200
°C. The desorber illustrated in Figure 2 meets these design criteria.
5.2.4 The purge and trap system may be
assembled as a separate unit or be coupled to a gas chromatograph as illustrated
in Figures 3 and 4.
5.3 Gas chromatograph -- An analytical
system complete with a temperature programmable gas chromatograph suitable for
on-column injection and all required accessories including syringes, analytical
columns, gases, detector, and strip-chart recorder. A data system is recommended
for measuring peak areas.
5.3.1 Column 1 -- 8 ft long × 0.1 in. ID
stainless steel or glass, packed with 1% SP-1000 on Carbopack B (60/80 mesh) or
equivalent. This column was used to develop the method performance statements in
Section 12. Guidelines for the use of alternate column packings are provided in
Section 10.1.
5.3.2 Column 2 -- 6 ft long × 0.1 in. ID
stainless steel or glass, packed with chemically bonded n-octane on Porasil-C
(100/120 mesh) or equivalent.
5.3.3 Detector -- Electrolytic
conductivity or microcoulometric detector. These types of detectors have proven
effective in the analysis of wastewaters for the parameters listed in the scope
(Section 1.1). The electrolytic conductivity detector was used to develop the
method performance statements in Section 12. Guidelines for the use of alternate
detectors are provided in Section 10.1.
5.4 Syringes -- 5-mL glass hypodermic with
Luerlok tip (two each), if applicable to the purging device.
5.5 Micro syringes -- 25-μL, 0.006 in. ID
needle.
5.6 Syringe valve -- 2-way, with Luer ends
(three each).
5.7 Syringe -- 5-mL, gas-tight with
shut-off valve.
5.8 Bottle -- 15-mL, screw-cap, with
Teflon cap liner.
5.9 Balance -- Analytical, capable of
accurately weighing 0.0001 g.
6. Reagents
6.1 Reagent water -- Reagent water is
defined as a water in which an interferent is not observed at the MDL of the
parameters of interest.
6.1.1 Reagent water can be generated by
passing tap water through a carbon filter bed containing about 1 lb of activated
carbon (Filtrasorb-300, Calgon Corp., or equivalent).
6.1.2 A water purification system
(Millipore Super-Q or equivalent) may be used to generate reagent water.
6.1.3 Reagent water may also be prepared
by boiling water for 15 min. Subsequently, while maintaining the temperature at
90°C, bubble a contaminant-free inert gas through the water for 1 h.
While still hot, transfer the water to a narrow mouth screw-cap bottle and seal
with a Teflon-lined septum and cap.
6.2 Sodium thiosulfate -- (ACS) Granular.
6.3 Trap Materials:
6.3.1 Coconut charcoal -- 6/10 mesh sieved
to 26 mesh, Barnabey Cheney, CA-580-26 lot # M-2649 or equivalent.
6.3.2 2,6-Diphenylene oxide polymer --
Tenax, (60/80 mesh), chromatographic grade or equivalent.
6.3.3 Methyl silicone packing -- 3% OV-1
on Chromosorb-W (60/80 mesh) or equivalent.
6.3.4 Silica gel -- 35/60 mesh, Davison,
grade-15 or equivalent.
6.4 Methanol -- Pesticide quality or
equivalent.
6.5 Stock standard solutions -- Stock
standard solutions may be prepared from pure standard materials or purchased as
certified solutions. Prepare stock standard solutions in methanol using assayed
liquids or gases as appropriate. Because of the toxicity of some of the
organohalides, primary dilutions of these materials should be prepared in a
hood. A NIOSH/MESA approved toxic gas respirator should be used when the analyst
handles high concentrations of such materials.
6.5.1 Place about 9.8 mL of methanol into
a 10-mL ground glass stoppered volumetric flask. Allow the flask to stand,
unstoppered, for about 10 min or until all alcohol wetted surfaces have dried.
Weigh the flask to the learest 0.1 mg.
6.5.2 Add the assayed reference material:
6.5.2.1 Liquid -- Using a 100 μL syringe,
immediately add two or more drops of assayed reference material to the flask,
then reweigh. Be sure that the drops fall directly into the alcohol without
contacting the neck of the flask.
6.5.2.2 Gases -- To prepare standards for
any of the six halocarbons that boil below 30°C (bromomethane, chloroethane,
chloromethane, dichlorodifluoromethane, trichlorofluoromethane, vinyl chloride),
fill a 5-mL valved gas-tight syringe with the reference standard to the 5.0-mL
mark. Lower the needle to 5 mm above the methanol meniscus. Slowly introduce the
reference standard above the surface of the liquid (the heavy gas will rapidly
dissolve into the methanol).
6.5.3 Reweigh, dilute to volume, stopper,
then mix by inverting the flask several times. Calculate the concentration in
μg/μL from the net gain in weight. When compound purity is assayed to be 96% or
greater, the weight can be used without correction to calculate the
concentration of the stock standard. Commercially prepared stock standards can
be used at any concentration if they are certified by the malufacturer or by an
independent source.
6.5.4 Transfer the stock standard solution
into a Teflon-sealed screw-cap bottle. Store, with minimal headspace, at −10 to
−20 °C and protect from light.
6.5.5 Prepare fresh standards weekly for
the six gases and 2-chloroethylvinyl ether. All other standards must be replaced
after one month, or sooner if comparison with check standards indicates a
problem.
6.6 Secondary dilution standards -- Using
stock standard solutions, prepare secondary dilution standards in methanol that
contain the compounds of interest, either singly or mixed together. The
secondary dilution standards should be prepared at concentrations such that the
aqueous calibration standards prepared in Section 7.3.1 or 7.4.1 will bracket
the working range of the analytical system. Secondary dilution standards should
be stored with minimal headspace and should be checked frequently for signs of
degradation or evaporation, especially just prior to preparing calibration
standards from them.
6.7 Quality control check sample
concentrate -- See Section 8.2.1.
7. Calibration
7.1 Assemble a purge and trap system that
meets the specifications in Section 5.2. Condition the trap overnight at 180 °C
by backflushing with an inert gas flow of at least 20 mL/min. Condition the trap
for 10 min once daily prior to use.
7.2 Connect the purge and trap system to a
gas chromatograph. The gas chromatograph must be operated using temperature and
flow rate conditions equivalent to those given in Table 1. Calibrate the purge
and trap-gas chromatographic system using either the external standard technique
(Section 7.3) or the internal standard technique (Section 7.4).
7.3 External standard calibration
procedure:
7.3.1 Prepare calibration standards at a
miminum of three concentration levels for each parameter by carefully adding
20.0 μL of one or more secondary dilution standards to 100, 500, or 1000 μL of
reagent water. A 25-μL syringe with a 0.006 in. ID needle should be used for
this operation. One of the external standards should be at a concentration near,
but above, the MDL (Table 1) and the other concentrations should correspond to
the expected range of concentrations found in real samples or should define the
working range of the detector. These aqueous standards can be stored up to 24 h,
if held in sealed vials with zero headspace as described in Section 9.2. If not
so stored, they must be discarded after 1 h.
7.3.2 Analyze each calibration standard
according to Section 10, and tabulate peak height or area responses versus the
concentration in the standard. The results can be used to prepare a calibration
curve for each compound. Alternatively, if the ratio of response to
concentration (calibration factor) is a constant over the working range (<10%
relative standard deviation, RSD), linearity through the origin can be assumed
and the average ratio or calibration factor can be used in place of a
calibration curve.
7.4 Internal standard calibration
procedure -- To use this approach, the analyst must select one or more internal
standards that are similar in analytical behavior to the compounds of interest.
The analyst must further demonstrate that the measurement of the internal
standard is not affected by method or matrix interferences. Because of these
limitations, no internal standard can be suggested that is applicable to all
samples. The compounds recommended for use as surrogate spikes in Section 8.7
have been used successfully as internal standards, because of their generally
unique retention times.
7.4.1 Prepare calibration standards at a
minimum of three concentration levels for each parameter of interest as
described in Section 7.3.1.
7.4.2 Prepare a spiking solution
containing each of the internal standards using the procedures described in
Sections 6.5 and 6.6. It is recommended that the secondary dilution standard be
prepared at a concentration of 15 μg/mL of each internal standard compound. The
addition of 10 μL of this standard to 5.0 mL of sample or calibration standard
would be equivalent to 30 μg/L.
7.4.3 Analyze each calibration standard
according to Section 10, adding 10 μL of internal standard spiking solution
directly to the syringe (Section 10.4). Tabulate peak height or area responses
against concentration for each compound and internal standard, and calculate
response factors (RF) for each compound using Equation 1.
