hot methanol
txtraetio'"
(rng(\q:)
240
=
]1·
41
700
±
2082"
121 700
==
II 719'
630= 58"
JSO
±
2Y
270
±
37'
130
±
29
methanol
imm~io'"
(rntlkg)
140
==
15
26000:4~
&5
000
:!:
13 BY
530: 3J·
UO± 5"
240
±
U'
110:
5"
100± 57
3070
±
351
5900
±
1210
240
±
63
2
±
1
190:: 4J
2: 0
compounds
trichJorof:thylene
ci5-1.1«hloroethylene
trich~thylene
methylene
chloride
benu~
tolutM
chloroform
soil
type.
component
Kentuc~'
(clay)
louisiana (silry loam)
Florida
(~'.
fine tovery
fiDe
Ynd)
Table 1. Comparison of Three Methods formeasuring VOCs in Soils
purlZ~d-tr3p(mg/kg)
Table 2. Comparison
of
Ezt,.ctionMethods for LouisLanil SoUafter 1 Week o' AIr Stripping
compound
methylene
chloride
cis·1.t-dichloroethylene
trichloroethylene
puJ1'e-and-traP"
(mg/kg)
94±5O
86± 39
310
±
60
methanol
immersion"
(ma/kg)
150
±
43
390
±
122l
5400± 916'
hot
methanol
extraction-
{mglki)
J60
±
lIO
2110
±
1688'
5500
±
lOBI'
• AYffage of
three
soil
sample measurements.•
Significantly
high~
mean
than
pu~d-tnlp
at
95%In>el of confidence.
<
Significantly
high~
men! Ibn! purge-and-tr.lp
at
90\
level of confidence.
cores
wert
sealed
in
glass
jars
with
minimum headspece and
Slam!
at
4 °C
on arrival.
AI
the
start
of each experiment. the
sample
cere was
plugged and subdivided
10
obtain
three
5-g
subsampl~
Scbsamples
wert
mruded
dirtttIy
intoVOAvials
(Dynateeh.
Baton
Rouge.
1A)
and
mixed
with
5
mL
of
Wllter
containing internal standards and surrogales before capping.
Measurements
ofVOCs.
Contuninants
were
extr'ackd from
soilsamplesbymethodsofpurge-and-trap,
methanol
immersion.
and
hoi methanol extraction. Contaminant concentrations
were
txprtSsed as
microgr.ams
per
kilogram
of soil.
hrgH1Ui-Trap.
Samplealiquotswerepurgedusinga
Dynat–
ech
PTA-30
autosampler
and
aTekmar (Cincinnati.
OH) LSC2
purge-and-trap
device. Soil samples of 2
g
each
wert
purged
al
40·C. Thetrapwasdesorbed.andmeasurementwasperfonoed
with
aHewlett-PackardModel
5890/5971
GC/MS. usingand
EPA
method
8260.
1:;.'.13
All
quality
assurance
measures
given
in the
methodwere followed.
Methanollmmenitm.
FIVe milliliters of
purge-aod-trap
grade
methanolwas added
10
sample aliquots. The
vial
was
capped
as
prmousl)'described andvigorouslyshaken for
30
s
to
facilitate
wttting
ofthe soil surface.
A501tL
aliquot of
~
methanolwas
then
rtmO'Ved
and added 10 5
mL
ofwater
containing
internal
SWldards
and
surrogates.
The
waterwas
1heosubjected
to
~
and-trap
and
analyzed
for the concentrationof
chemicals
by
GC.
HotMetha1lOl
EztradUnt.
Hotmethanol extraction
was
per–
fonned
in
the
samemanner
as
methanol
immersion
ex~
that.
prior to
withdrawal
of
the'
aliquot
of
methanol
theVOA
vial
was
placed
in
a
40°C
ultrasonic
water bath for
30min. The
methanol
was
drawn
and
anal)'zed
as
described
above.
E:.rtrrutUm
Fol1owi7Il
Air
StriPPilll.
The
Louisiana sample
was
mixed in
a
j:3
rat io
with
calciumoxide
to prevent solidification
during
air
stripping. The sample
was
then placed
in
a Buchner
funnel with a vacuum
running
from the bottom of
the
funnel
through
a
flask.
Aml»entair
was
passed through
the
sample
using
a YaOJum of
450-675
mmHg
for
1
week. Occasional
mixing
of
the soil
was
perfonoed
throughout
this time.
The
soil sample
was
dividedinto
three
subsamples. and
each
subsample
was
then
subjected to
one of
the three
methods
as pm;ous!y
descnbecl..
AD
of the
above
extractions was perlonned
as
written
in
EPA!
SW-846 methodology.
Intemal
standards
were
added.
andsur–
rogate
recovery
was
within
the
limits
of the method
for
an
extractions.
All
quality
assurance procedures
wert
applied.
RESULTS
Measurement resultsfromthe
three
different
sites-Kentueky,
Louisiana.
and
Florida-are presented
in
Table 1. Trichloroeth–
ylene
was
the onlycontaminant detected in the
Kentucky
soil
(fable I),
with
a
purge-and-trap
recovery only
42%
as
compared
to
hoi methanol extraction. Both cis-l.l-dichloroethylene and
bichloroethene weredetected in the
Louisiana
soil.
Pura:e-and–
trap
recovery
of these'
two
contaminants
was
only
7.4
and
f.B\.
respeaive!y,
when
compared
10
hoimethanolextradion
method.
Four compounds
were
identified in the
Florida
soil: methylene
chJoride. beaeene,
toluene,
and chloroform.
with
purge-and-trap
recovery
38.0. 1.5.71.2.
and
1.5" respectively,
in
comparison
to
hot methanol extraction.
EBecr:
of
Air
StrippiDg.
ContaminantcoDCentntiODS for
air–
stripped
Louisiana
soil
art
presented
in
Table2. Purge-and-trap
detected
levels
of
~
chloride.
cis-Ll~ylene.
and
TeE at 58.
4.1,
and
5.6\.. rnpectively.
that of
hot
methanol
extraction. Comparisonoftht'se results
with
thoseinTable
1
for
Louisianasoilsindicales that
air
stripping
does
not
appear
to
atrect
the disbibution of contaminants between
the
accessible and
inaccessible phases.
(lZ1
Con6~.
J.
R:Young.
C.
L
!'II'ftil (/Clm.,iclI.I
M_"",~f
by
Gw;
01"""",
ItJfTOphy.
John
Wil~·
and
Sons:
"tv,
York. 1979.
(l3l l.Iub.
R.
J.:
F'«'sok.
Rl.
Pft'sitMr....
~IApp1~titnrJ
af(;;u
CJI~pity.
JohnWiif')· and
Sons:
Ne...'York. 1978.
DISCUSSION
Purge-and-trap is the EPA-recommended method (EPAlSYr'–
84&-S030A) for measurement of VOCs in soils. Under the
3432 AnaMlcal Chemisrrv. Vol
68.
No
19.
OCrober
1. 1996
