DeactivationProcedure
Prior to analysis byGC, it is critical tobothderivatize the organo
tin chlorides andprocess the sample extracts using some type of
sorbent cleanup.Although several techniques are available, the
followingprocedureworkswell for all compounds in anymatrix.
(Note: Thismethoduses a commercially availableGrignard
reagent. Because this reagent ismoisture-sensitive, keep
exposure to the atmosphere to aminimumbyhandling the
solution in a syringe.) The goal of this reaction is todisplace all
chlorides on the tin and replace themwith ann-hexyl group.
For thismethod, it is very important to remove asmuchof the
potential contaminants as possible. If these compounds arenot
extracted, theywill cause considerable interference, especially in
soil or biotamatrices.Theprimary interference is causedby
sulfur-containing compounds.Theseoccur in a relativelyhigh
concentration in comparisonwith theorgano tin compounds. The
large-capacity cleanupdescribedbelowwill remove thesenon-
target compounds. For your convenience, SPE tubes designed for
thissampleextract cleanupareavailable fromRestek (cat.#24049).
SampleAnalysis
Once the organo tin chlorides have been extracted and
derivatized to tetraalkyl tin compounds and the extracts are
cleanedusing the listedprocedure, theGC analysis is relatively
simple.The flamephotometricdetector (FPD)must beoperated
under fuel-rich conditions for efficient conversionof the alkyl tin
compounds to tinhydrides. Theonlymodificationneeded is the
installationof a 610nmwavelength filter in theFPD to collect
themolecular emission for tinhydride. This filter canbe
obtained fromOrielCorporation, Stratford, CT, (203) 377-8282
(cat.#53925) or other optics supply companies.
Figures 1 and2 show a simultaneous analysis using two capillary
columns of differing selectivity.This provides both aprimary
and a confirmation analysis from a single injection.The com-
pounds are injected at 500pgon-column.
Using the procedure detailed in thisApplicationsNote, a
commercial laboratory
5
was able toobtain the data shown in
Table I.The results easilymeet themethoddetection limit
requirements of 50ng/L. Shouldyour laboratoryneed tomeet a
1ng/Ldetection limit, somemodificationof themethodwill be
necessary. The simplest and least expensiveway tomeet a lower
detection limitwouldbe to switch fromusing anFPD to a
PulsedFPD (PFPD) detector. This detector cangive a sensitivity
enhancement of 10 to100 times over a standardFPD. Figure 3
shows the chromatogramobtained from an injectionof anorgano
tin calibration standardwith5pgon-column for each compound.
A comparisonof this chromatogram toFigures 1 and2 reveals
that a similar signal-to-noise ratio canbe obtainedwith100
times less analyte. This demonstrates an increase in sensitivity
(or lower reporting limits) of roughly100 times using thePFPD
and thepreparationmethodoutlined above.
Thismethod is adaptable tomost commercial laboratories and
uses commonglassware and equipment. If this is your first time
using thismethod, youwill not need topurchase a specialized
instrument because thePFPDdetector provides the sensitivity to
meet even the lowest of proposeddetection limits. The use of
equipment such as tandemmass spectrometers (MS/MS/MS) or
microwave inducedplasmadetectors (MIPorAED) areno
longer necessary. Both are expensive and requiremuchmore
operator skill. Finally, Restek is available toprovide additional
trainingon this andothermethods to eliminate the need for
literature andvendor research—please contact us formore
information.
References
1.
Special Report on Environmental Endocrine Disruption: An Effects
Assessment and Analysis
, EPA/630/R-96/012, Feb. 1997.
2. Unger, M.A, MacIntyre,W.G., Greaves, J., andHuggett, R.J.,
Chemosphere
, 15 (4), pp 461-70, 1986.
3.
Sampling and Analytical Methods of the National Status and
Trends Program
, National Benthic Surveillance andMusselWatch
Projects, 1984-1992, Vol. IV, NOAATechnical Memorandum, NOS
ORCA 71.
4. Jaima Conference, Tokyo, Japan. Nov. 1998.
5. ITS Environmental, 55 South Park Drive, Colchester, VT 05446.
SampleExtractDerivatizationandCleanup:
1.
Add0.8mLof 2Mn-hexylmagnesiumbromide.
2.
Place vial onwrist shaker for 30min., or agitate by
hand.
3.
Place vial in ice bath, and addHCl todissolve the
precipitate.
4.
Pipet off the hexane layer and transfer toKD
concentrator.
5.
Concentrate extract to approximately1mL.
6.
Add extract to16gm/5gmFlorisil
®
/silica-gel SPE
tube. (Restek cat.#24049).Mayuseprep-scale
chromatographycolumn.
7.
Elutewith100mLhexane, collecting eluent inKD
concentrator.
8.
Spike internal standard as appropriate.
9.
Concentrate extract to1.0mL.
Prior to final volumeadjustment, internal standards canbeadded.
Tetra-n-propyl tin is the recommended internal standard.All
standardsused in thismethodare solutionsof organo tinchlorides.
Calibration standardsmust beeither derivatizedby the same
procedure, or theycanbepurchasedasneat-derivatizedmaterial
fromRestek. (Contact our analytical referencematerialsgroupat
814-353-1300or800-356-1688.)TropoloneandGrignard reagents
areavailable fromAldrich. Sincealkyl tincompounds areknown
toexhibit ligandexchange, the samples and standards shouldbe
kept inacool (4°C), darkplaceuntil used. If properly stored, the
chemical standards shouldbe stable for sixmonths; but if left at
room temperature, peaks fromadditional organo tincompounds
maybeobserved in thechromatogram.Thesepeaks arecausedby
compounds exchangingalkyl groups. If this isobserved, replace
the standards.Theuseof at least one surrogatecompound, suchas
tripentyl tinchloride, is suggested toallow for extraction recovery
calculations.
RestekCorporation
(800) 356-1688
