8
8
MeOH
MeOH
Tetraglyme
Tetraglyme
PPG
PPG
c
6
6
c
b b
b b
4
4
c
c
a
b
a
b
b b
a
a
2
2
b
a
aa
a/b a/b
a
a
0
0
0
10
20
30
0
10
20
30
Time (days)
Time (days)
g. E-Ben.
h. p-Xyl.
8
MeOH
Tetraglyme
PPG
6
c
b b
4
c
a
b b
a
2
a
aa
a
0
0
10
20
30
Time (days)
i. o-Xyl.
Figure 3 (cont'd). Mean analyte concentrations determined for each extractant and extraction period for the CR-B
vapor-fortified soil with MeOH, tetraglyme, and PPG. Soils designated with different letters are significantly differ-
ent at the 95% confidence level.
of this soil was repeated. The results of this addi-
the highest analyte concentrations for eight of the
tional experiment confirmed those shown in Fig-
nine VOCs tested. H-HS gave the highest recov-
ure 3.
ery for TDCE, the most volatile analyte. Howev-
In contrast, after the initial extraction period,
er, recoveries tended to decline relative to MeOH
tetraglyme failed to show an increase in analyte
extraction with increasing analyte boiling point,
concentration for TDCE, CDEC, Ben, TCE, and
to the extent that it obtained the lowest recovery
PCE, but did for the other four analytes. PPG only
among the six methods for E-Ben, p-Xyl, and o-
showed an increasing analyte concentration for
Xyl. Tetraglyme and Aq-NaCl sat'd-HS gave sim-
TDCE after the initial extraction period. In all cas-
ilar recoveries that were significantly below MeOH
es, MeOH extraction showed the highest yields
and Aq-NaHSO4-HS but above PPG solvent ex-
among the three solvents throughout this experi-
traction.
ment.
Table 7 also shows the results of the statistical
DISCUSSION
analysis of the six sample preparation (extraction)
and analyses performed on samples within a
When developing analytical methods for envi-
2-hour period. Under these conditions, MeOH
ronmental samples, one of the most important
extraction and Aq-NaHSO4-HS usually produced
things that we must consider is method robust-
14
Previous Page
