Page 206 - Tandem Techniques

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The mass spectrometer was a Riber AQX 156 quadrupole filter having a mass range of 0-300. Electron
impact ionization was employed with energies of 70 eV, and the mass spectrometer ion source was
maintained at about 100°C. An example of the total ion current chromatogram of a crude silane sample
is shown in figure 5.17. It is seen that there are a number of low level contaminants in the crude
material, and by the use of single ion monitoring, very small traces of contaminants can easily be
identified. The chromatogram obtained by single ion monitoring at a m/z value of 76 discloses the
presence of arsine at a level of 4 ppb in the original sample.

GC/MS has been used by Goldberg et al. [16] to assay trans-resveratol in wines. Trans-resveratol
(3,5,4'-trihydroxystilbene) has potent antifungal properties and appears to be synthesized by vines, in
response to fungal infection. Its incorporation in Japanese herbal medications has roused an interest in
its use in fungal, inflammatory and lipid disorders. The trans-resveratol was extracted from the wine
onto a bed of C18 reversed phase that had be preconditioned with ethyl acetate, followed by 96%
ethanol, and then 10% ethanol in water. The solid phase extraction cartridge was then dried and the
absorbed trans-resveratol extracted by ethyl acetate. The ethyl acetate extract was used directly for
analysis.

The GC/MS comprised a Hewlett-Packard Model 5890 gas chromatograph and the Hewlett-Packard
Model 5970 quadrupole MS detector. The column (DB-5) was 30 m long, 250 mm I.D. and carried a
film of stationary phase, 0.25 mm thick. 1 ml aliquots of the ethyl acetate extract were injected; the
column was held at 150°C for 6 min; then heated to 290°C at 20°C/min and held at 290°c for 2 min;
then heated to 305°C at 25°C/min and finally held at 305°C for 5 min. The authors demonstrated that
solid phase extraction, followed by GC/MS analysis using single ion monitoring, could be readily used
for determining trans-resveratol in wines. Furthermore, although a little lengthy, the extraction
procedure appeared to be generally useful for the analysis of other trace materials in aqueous solutions.