creased beyond 14 days. Increasing holding times
ples prepared for HS/GC analysis, which failed
would not only be beneficial to site investigations
to prevent the loss of Ben and Tol. The reason for
not including this experiment is that an artifact was
performed in remote locations where turn-around
detected. Close inspection of the treated soil
limits are hard to achieve, but may also allow some
subsamples established that some had not been
samples to be archived.
completely dispersed at the start of the storage
period. These subsamples, which contained
clumps of wetted soil trapped in partially broken
CONCLUSION
ampoules, showed losses of Ben and Tol, while
there were no detectable losses of these two
Chemical preservation can maintain stable con-
analytes in subsamples where dispersion was com-
centrations of Ben and Tol in soil subsamples that
plete. Because of this artifact the experiment was
exhibited biodegradation of these two compounds
when held for 14 days at 4C. Concentrations of
repeated, taking special care to completely disperse
the soil in the acidified water. The results of this
TDCE and TCE were stable with and without pres-
second experiment found that there were no
ervation. The two methods of chemical preserva-
changes in any of the analyte concentrations
tion used--immersion in MeOH and acidification
greater than 10% (Table 4). Thus, depending on
with NaHSO4--are compatible with subsamples
the soil texture and composition, field subsamples
collected and handled for both PT/GC/MS and
may require vortex or sonication mixing. In addi-
HS/GC analysis. Prior to performing chemical
tion, more than 3 mL of water may be necessary
preservation studies, the range where biodegra-
when preparing for low-level PT/GC/MS. Also,
dation is uninhibited by analyte concentration
since the buffering capacity of soils varies widely,
must be established.
the amount of NaHSO4 necessary to achieve a pH
of 2 should be evaluated on a case-by-case basis.
Lastly, when high levels of calcium carbonate are
present in the soil acidification may not be feasible.
LITERATURE CITED
The selection of subsample preservation by ei-
ther acidification or immersion in MeOH depends
Hewitt, A.D. (1994a) Comparison of sampling
on the VOC concentrations expected and the
methods for trichloroethylene in vadose zone soils.
method of analysis. The two methods of analysis
Journal of the Association of Official Analytical Chem-
used here were HS/GC and PT/GC/MS. The
ists, 77: 458463
former is very compatible with on-site operations,
Hewitt, A.D. (1994b) Losses of trichloroethylene
while the latter is often required for fixed (off-site)
for soil during sample collection, storage and labo-
laboratories involved with government-regulated
ratory handling. USA Cold Regions Research and
site investigations. Acidification with NaHSO4 is
Engineering Laboratory, Special Report 94-8.
compatible with low levels of VOC (<1 g/g),
Hewitt, A.D. (1994c) Concentration stability of
while immersion in MeOH is preferable with high
four volatile organic compounds in soil subsam-
levels (>1 g/g).
ples. USA Cold Regions Research and Engineer-
ing Laboratory, Special Report 94-6.
By using chemical preservation with sample
Hewitt, A.D. (1994d) Vapor-fortified QA/QC soil
collection protocols that minimize volatilization
subsamples for the analysis of volatile organic
losses during storage and analysis, environmental-
compounds. American Environmental Laboratory,
ly representative analyte concentrations are more
March.
apt to remain stable for 14 days (Hewitt et al., in
Hewitt, A.D. (1994e) Preparation of spiked soils
press). Some small VOC losses may occur inde-
by vapor fortification for volatile organic com-
pendent of acidification since Teflon (the septum
cap liner) is believed to sorb VOCs (Leggett and
pound analysis. Journal of the Association of Official
Parker 1994). Another advantage that could be
Analytical Chemists, 77(3): 735737.
gained by using chemical preservation is that re-
Hewitt, A.D., P.H. Miyares, D.C. Leggett and T.F.
frigeration would not be as critical. Relaxing this
Jenkins (1992) Comparison of analytical methods
requirement would lower the cost of both on-site
for determination of volatile organic compounds
operations and shipping. Furthermore, the results
in soils. Environmental Science and Technology, 26:
(Tables 5 and 6) show that the concentration sta-
19321938.
bility obtained by either acidification or immer-
Hewitt, A.D., T.F. Jenkins and C.L. Grant (in press)
sion in MeOH may permit holding times to be in-
Collection, handling and storage: The keys to im-
7
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