Enhanced Preservation of
Volatile Organic Compounds
in Soil with Sodium Bisulfate
ALAN D. HEWITT
servative was based on its low toxicity, compati-
INTRODUCTION
bility with field operations, and its success in a
Most soil samples collected during site investi-
study of VOC stability in aqueous matrices
gations for establishing the presence and concen-
(Maskarinec 1990). The 28-day storage period was
tration of volatile compounds (VOCs) are sent to
selected based on the success of an earlier study
off-site laboratories for analysis. To allow for some
(Hewitt 1995) and efforts to establish longer prov-
flexibility between sampling and analysis opera-
en holding times for VOCs in preserved aqueous
tions, the U.S. Environmental Protection Agency
matrices.*
(U.S. EPA 1986) has recommended that samples
Here, spiked soil samples were stored in sealed
be stored at 4C, and held no more than 14 days.
glass ampoules, and analyzed after transfer to
This practice continues although it is well-recog-
volatile organic analysis (VOA) vials containing
nized that soils can remain biologically active un-
water. Once VOA vials were capped, the ampoules
der these conditions. While several efforts have
were broken, dispersing the contents in prepara-
been made to demonstrate the magnitude of this
tion for static headspace gas chromatography
potential problem (Jackson et al. 1991, Maskari-
(HS/GC) analysis. Using this protocol, we never
nec et al. 1992 King 1993), only recently have stud-
exposed the spiked soils to the atmosphere, al-
ies been designed to eliminate confounding of
lowing biodegradation and chemical preservation
biodegradation and volatilization losses (Hewitt
studies to be performed independent of volatil-
1994, Hewitt 1995a,b, Turriff 1995). These efforts
ization. This experimental procedure is consistent
are the first to assess only the biological influence
with practice of retaining soil samples in either
on VOCs in soil samples held at 4C.
vaportight glass bottles while they await labora-
Our approach has been to seal treated samples
tory subsampling and analysis (this practice is
in glass ampoules before exposing them to vari-
not recommended by the author [Hewitt et al.
ous holding and storage conditions (Hewitt 1994,
1995]), or in VOA vials for low level purge and
Hewitt 1995 a,b). Here we assess the concentra-
trap gas chromatography mass spectrometry
tion stability of 24 (see Table 1) of the 56 analytes
(PT/GC/MS) analysis as recommended in Method
currently identified by the Environmental Protec-
5035, a method scheduled for inclusion in the pro-
tion Agency as hazardous VOCs (U.S. EPA 1986,
posed third update of the SW-846, U.S. EPA (1986).
SW-846, Methods 8240/8260), and gasoline. Ex-
periments look at both the effect of chemical pres-
EXPERIMENTAL SECTION
ervation and temperature on analyte concentra-
tion in soil samples held over a 28-day storage
The silty-sand topsoil used in this study was
period under conditions that eliminated volatil-
obtained locally from between 5 and 10 cm below
ization losses. The preservative chosen was sodi-
the ground surface just before the start of this
um bisulfate (NaHSO4). A sufficient quantity of
this salt was used so that pH 2 or less was ob-
tained, once the soil sample was made into an
* Personal communication with David Bottrell, U.S.
aqueous slurry. The selection of this chemical pre-
Department of Energy, Washington, D.C., 1995.
Previous Page
