RESULTS AND DISCUSSION - SR95_260011

Figure 1. Gasoline-contaminated soil stored at 22C

Table 4. Set 2, trial 2. Mean and standard deviations of triplicate analyte concentrations of spiking solution (g)

SR95_26
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held at 100C for an additional 3.5 min. The third

ples that had been treated with NaHSO4. This

set of analytes used a GC program consisting of

issue will be addressed later. Of almost equal mag-

holding at 40C for 1 min., then increasing to 150C

nitude, n-BB was some 65% lower than expected.

in 6.1 min., and holding at 150C for an additional

This compound, which had the poorest solubility,

3.39 min. For gasoline the following GC program

also has the greatest octanolwater partition (o/w)

was used: holding at 40C for 1 min., and then

coefficient (Table 1). Correspondingly, the other

increasing to 220C in 8 min. Using these parame-

analytes with large o/ w coefficients also showed

ters we resolved all of the analytes in the sets 1

poor spike concentration recovery from the soil

through 3 with the exception of E-Ben and p-Xyl

(set 1). Examples of HS chromatogram for the

One apparent trend when using this treatment

gasoline treated soil sample (set 4) are shown in

process and analysis by HS/GC is that, as the o/w

Figures 1 through 3. These chromatograms show

partition coefficients increase, so does the discrep-

that several aromatic compounds in gasoline could

ancy between the spiking solution and initial soil

be readily identified.

sample concentrations. An additional observation

Analyte concentrations were established relative

relative to the spiking solution concentrations was

to aqueous headspace standards prepared by

adding small (<10 L) quantities of a methanol

Table 3. Set 1, trial 1. Mean and standard deviations of

(MeOH) stock solution to auto sampler vials

triplicate analyte concentrations of spiking solution (g)

containing 15 mL of type 1 water (Hewitt et al.

and of analyte concentrations (g/g) for preserved and

1992). For the analytes in sets 1 through 3 indi-

unpreserved samples stored at 22 and 4C.

vidual integrated peak areas or peak heights

Treatment aliquot

Treatment aliquot

were used, while the entire chromatogram was

integrated for gasoline (set 4).

RESULTS AND DISCUSSION

Storage period

The concentration estimates of the individ-

ual analytes or of gasoline in the spiking solu-

A. 22C--unpreserved (g/g)

tion, and in the preserved and unpreserved

soil samples throughout the 28-day holding

period, appear in Tables 3 through 7. The rel-

ative standard deviations (RSD) of the ana-

lyte concentrations obtained for the three

aqueous aliquots representing the spiking so-

lution, and those of the soil samples analyzed

on day 0 ranged from less than 1% to 30%.

B. 4C--unpreserved (g/g)

The worst case was for n-butyl benzene (n-

BB), which has a solubility of only 11.8 mg/L,

and correspondingly resulted in the lowest

treatment concentration. With the exception

of this compound, the RSDs were less than

14% and averaged less than 5%, thus demon-

strating that the treatment procedure was

C. 22C--preserved with NaHSO4 (g/g)

Inspection of the initial concentrations for

both the unpreserved and preserved soil sam-

ples shows that they often varied from the

spiking solution. The range in percentage rel-

ative differences extended from less than 1%

to 68%, with concentrations both greater and

less than that of the spiking solution (Tables

37). The worst case was for styrene in the

preserved soil samples. The dramatic loss of

* ND = not detected, less than 0.02 g of VOC/g.

this compound was unique to only those sam-

† Same set used for day 0 values for unpreserved samples.

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