ANALYSIS - SR99

removed and prepared for analysis after seven and

Table 2. Average and standard deviations (n = 3)

12 days of additional storage (Table 1).

of analyte concentrations (mg/kg) for soil

In addition, aliquots of MeOH were removed

samples inside open and covered vials exposed

after various storage periods from the solutions

to VOC vapor fortification for two days.

used to determine the spike concentration and

from the D0 samples that had been prepared for

Vial covering

the first empty VOA vial experiment. The purpose

Translucent

of reanalyzing these samples was to assess analyte

Compound

Open

White Teflon*

Teflon†

concentration stability in MeOH held in VOA vi-

als, with and without punctured septa. The solu-

tions used to determine the spike concentration

had intact septa, while the D0 samples had septa

that had been punctured once.

ANALYSIS

All of the samples were analyzed by equilibrium

Tol

7.49

6.37(85%)

0.18 (2.4%)

headspace (HS) analysis. Soil samples that were

0.20

0.04

0.06

analyzed directly were allowed to reach room tem-

PCE

3.37

3.22 (96%)

0.25 (7.4%)

perature and then were vigorously hand-shaken

0.05

0.14

0.01

for two minutes prior to automated HS analysis.

E-Ben

2.97

2.32 (78%)

0.10 (3.4%)

Samples prepared by MeOH extraction typically

0.09

0.032

0.01

sat for at least 24 hours, before a 0.100- to 0.500-

p-Xyl

2.96

2.41 (81%)

0.10 (3.4%)

mL aliquot was transferred to a 22-mL VOA vial

0.16

0.04

0.01

containing 10 mL of organic-free water, capped,

o-Xyl

1.85

1.43 (77%)

0.09 (4.9%)

and then hand-shaken before automated HS analy-

0.07

0.02

0.01

sis. Automated HS analysis was performed using

an auto sampler (Tekmar 7000) coupled to a GC

*White Teflon sheeting, elastic, approx. 0.02-mm thickness.

(SRI, model 8610-0058) with sequential photoion-

†Translucent Teflon sheeting, nonelastic, approx. 0.05-mm

ization, flame ionization detectors. The instrumen-

thickness.

**Percent of soil VOC concentration found in Teflon (sheet)

tal setting used was consistent with those reported

covered vials vs. open vials.

elsewhere (e.g., Hewitt 1998b).

Concentration estimates were established rela-

VOCs, but at a much slower rate. The disparity in

tive to working standards. Working standards

performance of these two formulations of Teflon

were prepared by spiking analysis vials that con-

sheeting is also apparent in Table 3, which shows

tained the same amount of organic-free water and

the recoveries of spiked analyte concentrations

MeOH as the samples to be analyzed, with small

volumes (less than 10 L) of a MeOH stock stan-

from soils stored in covered core barrel liners.

VOCs escaped from the bulk soil samples

dard. The stock standards were prepared on a

wrapped with the white, elastic version of Teflon

weight basis, then volumetrically diluted with

sheeting much faster than those covered with the

MeOH, as necessary. Samples prepared by MeOH

translucent, nonelastic version. Table 3 also shows

extraction were corrected for the increase in ex-

that aluminum foil or the addition of a thin metal

traction solution volume, caused by soil moisture.

plate as a lid over the end of the core barrel liner

Sample prepared for direct HS/GC analysis were

prior to wrapping with the translucent Teflon

reported on a moist weight basis.

sheeting, failed to prevent rapid and continuous

losses of VOCs.

Although these laboratory experiments and oth-

RESULTS

ers (Hewitt and Lukash 1996) have shown that this

approach to transporting and storing samples for

The first experiment (Table 2) showed that the

VOC analysis is suspect, an additional experiment

white, elastic version of Teflon was rapidly pen-

was performed using contaminated field samples.

etrated by all nine VOCs tested. The translucent,

Effects established with spiked samples can be

nonelastic formulation was also permeated by

Index

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