each of the following parameters: DO, 10%; spe-
When methanol extraction is the chosen method
cific conductance, 3%; temperature, 3%; pH, 0.1
of sample preparation, the appropriate volume of
units; ORP/Eh, 10 mV; and (2) the final purge
analytical-grade methanol (high performance liq-
uid chromatography or spectrographic) is added
water volume exceeds the drawdown volume and
to the container in a laboratory setting. This task
the volume of water necessary to fill the sample
can be performed prior to or after sample collec-
transfer tubing. When more than one flow-through
tion (Hewitt 1999). If methanol is added to a soil
cell is used, the first one that groundwater passes
sample after it has been enclosed in a VOA vial,
through should contain the DO probe to avoid
this addition must be performed using a syringe
potential influences due to leaks or from small
by puncturing the septum with a 23 or smaller
bubbles of air being trapped in the system. Wells
gauge needle. For example, a Luer Lok needle (B-
that have slow recharge rates may either require a
D) attached to a 5.00-mL glass syringe (SGE) with
special pump capable of lower pumping rates (e.g.,
a Luer connector could be used. After introduc-
bladder or peristaltic pumps), or if recharge is
ing the methanol, the soil sample should be com-
lower than the slowest pumping rate, the well
pletely dispersed and the inner glass surfaces
should be purged dry and then sampled as soon
rinsed. Caution should be taken if aliquots are re-
as recharge allows.
moved after different extraction periods since grit
Water samples taken for laboratory analysis
on the Teflon-lined septum may prevent a
must be collected before the groundwater has
hermetic seal from forming when closing the
passed through a cell by either having a by-pass
VOA vial.
valve or disconnecting the tubing. Furthermore,
Once methanol has been placed in a container,
the transfer tubing should remain filled so as to
it should be opened only to add the subsamples
minimize contact with the atmosphere. Samples
and to remove aliquots for analysis. The ratio of
taken for VOC analysis should be collected first,
sample to methanol is based on a sample weight
followed by those taken for other constituents of
in grams that is equivalent to or less than the vol-
concern. Samples should be collected in a 40- to
ume (mL) of methanol (i.e., ≤ 1:1, grams of soil to
120-mL VOA vial that either already contains the
milliliters of methanol). Sample volume can be
appropriate amount of acid (sodium thiosulfate,
used instead of weight once the matrix density has
Na2S2O3, ascorbic acid, or 1:1 hydrochloric acid,
been established. The ratio used between these two
HCl) to establish a pH below 2, or to which this
constituents should allow for the formation of a
amount of acid is added immediately after filling
clear layer of methanol over the sample after thor-
the vial. The appropriate amount of acid needed
oughly mixing and allowing the suspended par-
to meet this pH requirement should be established
ticles to settle. When a sample that was placed into
during well purging. When filling the sample vial,
a VOA vial containing methanol fails to allow a
it should be initially tipped to allow the water to
clear supernatant layer to form, an additional vol-
flow gently down the side, then turned vertical so
ume of methanol can be added through the sep-
that the water surface forms a crown above the
tum after the samples weight is established. The
bottle's rim (top edge). By slightly overfilling the
difference in weight of the container, measured be-
collection bottle, little or no air is trapped when
fore and after the sample is introduced, is used to
the cap is screwed on. Once sealed, VOA vials con-
taining preserved samples should be stored at 4
establish the sample's wet weight. Samples im-
2C until prepared for analysis.
mersed in methanol should not be stored for more
than a couple days in VOA vials that have punc-
tured septa. When methanol is introduced through
the septum via a needle, the septum should be
PREPARATION FOR ANALYSIS
replaced if the sample is archived. Lastly, when
samples are immersed in methanol, both organic
Soil preparation
analytes and water (i.e., soil moisture) are ex-
The VOA vials or bottles used for sample prepa-
tracted from the sample. Because water is miscible
ration should already have its tared weight re-
in methanol, they form a single solution that for
corded to the nearest 0.01 g before a subsample is
all practical purposes is volumetrically additive.
transferred. Furthermore, the sample collection
Since an aliquot is removed from this solution, the
vial may also already contain a solution and stir-
dilution effect must be accounted for when calcu-
ring bar, depending on the anticipated concentra-
lating the sample's analyte concentration. Simi-
tions of analytes, method of analysis, or to inhibit
larly, this correction factor applies to surrogates if
biological activity.
5
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