GLC determination of acetohexamide and hydroxyhexamide in biological fluids

Electron-capture gas chromatography of plasma sulphonylureas after extractive methylation

Conditions for the extractive alkylation of eight sulphonylurea hypoglycemic drugs have been evaluated. Extractive methylation of the compounds was achieved within 90 min using tetrabutylammonium as counter-ion (0.1 M at pH = 6.9) with 5% methyl iodide in dichloro-methane as organic phase. Mass spectral analysis showed derivatives methylated at the sulphonamide nitrogen. A higher pH or use of tetrapentylammonium as counter-ion caused hydrolysis of the sulphonylureas. The derivatives showed a high electron-capture response with minimum concentrations detectable in the range 1-4 x 10(-16) moles sec-1. Therapeutic plasma concentrations of glipzide and tolbutamide were determined by direct extractive methylation of the compounds from the plasma sample. The glipizide derivative was determined by electron-capture gas chromatography down to about 20 ng/ml in a 0.5-ml plasma sample. The relative standard deviation at the 0.2 microgram/ml level of glipizide was 6% (n = 6). The corresponding figure in the determination of tolbutamide at the 10 microgram/ml level was 3% (n = 10).

Mass spectrometry of N-methylsulfonylureas. A re-examination

Some confusion has arisen in the literature regarding the electron impact mass spectrum of N-methyltolbutamide. The situation is complicated by the thermal lability of this compound which causes the formation of the corresponding N-methylsulfonamide. We present here spectral data at relatively low probe temperatures (and without an intervening gas chromatographic system) which we believe define the mass spectrum of N-methyltolbutamide more accurately than before. Similar data are presented for the analogous N-methylacetohexamide and show a rearrangement process for both substances not reported previously for this class of compounds.