Stabilization and gas chromatographic analysis of the four stereoisomers of 1,2,2-trimethylpropyl methylphosphonofluoridate (soman) in rat blood☆

Abstract A method for the stabilization and gas chromatographic analysis of the four stereoisomers of C(±)P(±)-1,2,2-trimethylpropyl methylphosphonofluoridate (C(±)P(±)-soman) in rat blood samples is described. Satisfactory stabilization of all four stereoisomers is obtained by (i) acidification of the blood sample to pH 4.2 at 0°C, to stabilize the C(±)P(+) isomers, (ii) addition of aluminum ions (2.5 m m ) for complexation of fluoride ions, which prevents regeneration of C(±)P(−)-soman by free fluoride ions from soman-inhibited aliesterase, and (iii) addition of 2,2-dimethylpropyl methylphosphonofluoridate in order to occupy covalent binding sites for C(±)P(−)-soman. The stereoisomers of soman and internal standard are extracted from the blood-stabilizing buffer mixture with a Sep-Pak C 18 cartridge and are subsequently eluted with ethyl acetate with overall extration recoveries of 52 ± 8%. The four soman stereoisomers are resolved and analyzed on a wide-bore capillary Chirasil Val column, synthesized, and coated in house, which also resolves the internal standard C(±)P(+)-1,2,2-[U- 2 H]trimethylpropyl methylphosphonofluoridate from C(±)P(±)-soman. Alternatively, the gas chromatographic analysis can be performed on a wide-bore capillary Chirasil Val column, identical with the commercially available Chirasil Val column, when combined in series with a Carbowax 20M column. This system resolves the four stereoisomers of soman and the internal standard C(−)P(+)-1,2,2-trimethylpropyl [U- 2 H]methylphosphonofluoridate. Using an alkali flame ionization detector, the detection limit of our procedure is ca. 250 pg soman isomer/blood sample.