○
○
○
○
○
○
○
○
○
○
○
○
○
○
○
○
7
formation of a void at the front of the column. This, in turn, will effect the
retention times of the compounds eluting from the GPC column and ulti-
mately result in the possibility of some target compounds being uncollected.
Therefore, toavoid large amounts of acetonebeing applied to the column, it is
critical that all extracts be reduced to as small a volume as possible prior to
reconstitution in dichloromethane.
PolarContaminants andCo-Extractants: Adsorbent SPETubes
BothFlorisil
®
and silica adsorbents have beenused since the 1960s for chro-
matographic cleanup and fractionation of environmental samples, especially
thosecontainingchlorinatedpesticides.Florisil
®
isamagnesiumsilicate,while
silica ismanufactured from a sodium silicate sol. Originally tested and used
inmanually-packed, largeopen-columncleanupprocedures, theseadsorbents
were found to be useful in retaining polar contaminants from soil and waste
samples that had been extractedwith organic solvents such as hexane. They
are ideal for retaining co-extractants, such as phenols, that may interfere
with GC analysis of pesticides, PCBs, and chlorinated hydrocarbons. Large
Florisil
®
tubes also were used to fractionate pesticide groups based on small
differences in polarity, by eluting with increasing percentages of polar sol-
vents such as ethyl ether.
1
Testing based on this method is a standard QA
procedure for pesticide-grade Florisil
®
adsorbent. All grades of these bulk
adsorbents shouldbeheat-activatedat 130°C for 16hours, stored ina sealed
glasscontainer, andcooled to room temperaturebeforebeingmanuallypacked
into glass tubes.
2
To increase laboratory efficiency and reduce the amount of solvents used for
these processes, the US EPA has allowed the use of pre-packed SPE tubes
containingFlorisil
®
or silicapacking. These small tubesare convenient touse,
require less solvent, and still are effective. Theywill cleanup small volumes of
pesticide-containing or chlorinated hydrocarbon-containing samples. They
oftenareusedafterGPC cleanup, as recommended inSW846. Details on the
appropriate use and preparation of these cartridges is contained in SW 846
Method 3620B, 3630C, and in the CLP Pesticides Statement of Work (SOW).
3
It is very important to evaluate each lot of tubes to ensure minimal back-
ground from the device itself, and to verify that the packing is at maximum
activity level to maintain the expected retention capacity. These tubes are
available with stainless steel or Teflon
®
frits to reduce interferences from ph-
thalates,whichmaybeextracted from typicalpolyethylene fritmaterials.Using
adsorbent beds of 1g or more and slower gravity elution of the samples will
minimize premature breakthrough or channeling and ensure maximum re-
coveries in each recovered fraction.
To increase laboratory
efficiency and reduce the
amount of solvents used for
extract cleanup, theUSEPA
has allowed the use of pre-
packedSPE tubes containing
Florisil
®
or silicapacking.
Refer to page 19 for SPE
ordering information. For
additional questions on the
use of Florisil
®
SPE, refer to
the appropriateEPAMethod,
requestApplicationsNote
#59562 fromRestek, or call
Technical Service at 800-356-
1688 or 814-353-1300, ext. 4.
○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
References
1.
J. of AOAC
, Ch. 24, 208, Vol. 49, Nov.1 (1966), p. 223
2. “Test Methods for Evaluating Solid Waste Physical/Chemical Methods (US EPA SW 846) Final
Update III,” December 1996. Available from theUS government, Mail Stop: SSOP,Washington, DC,
20402-9328.
3. USEPAContractLaboratoryProgram,
Statement ofWork forOrganicAnalysis0LM04.0
,ExhibitD
Pesticides/Aroclors.
References not available fromRestek.
