Page 212 - Tandem Techniques

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Aggarwal et al. [20] employed a GC/MS tandem system to determine the amount of tellurium in urine
by isotopic dilution. AS-101 [ammonium trichloro(dioxoethylene-O,O')tellurate (IV)] was the first
tellurium-containing compound to be shown to have immuno-modulating properties with little toxicity,
consequently its assay in biological fluids was of considerable interest. The process was also quite
complicated and can be briefly summarized as follows.

A sample of urine was spiked with a Te enriched standard solution and digested with concentrated
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nitric acid. The dried residue was redissolved in deionized water, centrifuged and adjusted to pH 3.0
with ammonium hydroxide solution. The mixture was then buffered with acetate buffer, treated with a
20 mM solution of lithium bis(trifluoroethyl)dithiocarbamate, vortexed for a few minutes, and the
chelate extracted with toluene. The extract was evaporated to dryness in a stream of argon and the
dissolved residue, treated in ether solution with (4-fluorophenyl)magnesium bromide. The excess
Grignard reagent was destroyed with isopropyl alcohol followed by nitric acid. The chelate was
extracted with toluene, evaporated to dryness and taken up in methylene dichloride, a sample of which
was placed on the GC column. The chromatograph used was a Varian 3700, with an SE-30 bonded
phase fused silica capillary column, 10 m long, 320 µm I.D., carrying a stationary phase film 0.25 µm
thick. On-column injection was employed and the column was programmed from 100°C to 300°C at 15
°C/min. The mass spectrometer was the Finnigan MAT Model 8230, and employed with electron
impact ionization.

Molecular ion peaks from the sample were generated at m/z values of 312, 313, 314, 315, 316, 318 and
320 which corresponded respectively to derivatives from the isotopes, Te, 123 Te, 124 Te, Te, 126 Te,
125
122
120
128 Te and 130 Te. The position of the Te(FC H )2 peak from the Te, used in the isotopic enrichment,
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6 4
was at 310. The method was found to be quite sensitive, and concentrations of the tellurium drug
ranging from 100-500 ng/ml in urine could be easily determined.
Veillon and Patterson [21] used a similar technique to determine chromium in urine, employing a
volatile chelate formed with