Page 373 - Tandem Techniques

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Consequently, an analytical method that will identify and measure the presence of nitro-diphenylamines
in an explosive would be very useful. LC/MS employing a thermospray interface is an obvious solution
to this problem. Via and Taylor [16] developed a method, using their SFC/MS tandem system, to
separate, identify and assay the amount of nitrated diphenyl-amines present in a nitrocellulose explosive
sample. The results from a test sample, containing the stabilizer and its derivatives, that was separated
by SFC and analyzed by the mass spectrometer are shown in Figure 9.20.

The reconstructed total ion current chromatogram of the separation is shown at the top of Figure 9.20. It
is seen that a good separation of the solutes of interest was obtained. It is also seen that the spectra for
2,4 dinitrotoluene and 2-nitrodiphenylamine are clean, and would allow the substance to be identified
with little or no ambiguity. The authors claimed that the sensitivity of the analytical procedure was
about 1 ng. However, according to Via and Taylor, in a private communication, Wilkes of the Vestec
Corp. claimed that satisfactory spectra could be obtained from samples present at the picogram level.
For example, 60 pg of 2-nitrodiphenylamine injected on the column could provide an identifiable mass
spectrum.

Cannavan, et al. [18] used the high sensitivity available from the thermospray interface LC/MS, in a
similar manner to the previous authors, to determine the amount of levamisole in animal tissues.
Levamisole [1 ]-(-)-2,3,5,6-tetrahydro-6-phenylimidazole(l, -b)thiazole, the laevorotatory isomer of
tetramisole, is an anthelmintic drug used to control gastrointestinal parasites in cattle pigs and sheep. As
in the assay of furazolidone in animal tissue, a somewhat complicated sample preparation procedure
was necessary. 3 g of the tissue sample was mixed with 2 g of anhydrous sodium sulfate, 9 ml of ethyl
acetate and 0.5 ml of 50%w/v caustic potash solution. and the mixture homogenized. To 6 ml of the
supernatant liquid, 6 ml of n-hexane was added, and the mixture passed through a Baker Bond CN
cartridge column. The column was washed with 5 ml of chloroform/n-hexane mixture (1+1) and air-
dried. The levamisol was eluted with two 5 ml aliquots of methanol, evaporated to dryness, and