Journal of Chromatography , 461(1989) 129- l 38 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands CHROM. 21238 GAS CHROMATOGRAPHIC DETERMINATION OF METHYLPHOSPHO- NIC ACIDS BY METHYLATION WITH TRIMETHYLPHENYLAMMONIUM HYDROXIDE J. Aa. TORNES* and B. A. JOHNSEN Norwegian Defence Research Establishment, Division for Environmental Toxicology, P.O. Box 25, N-2007 Kjeller (Norway) (First received October 3rd, 1988; revised manuscript received December 29th, 1988) SUMMARY A method is described for the isolation of decomposition products of nerve agents from aqueous solutions and their determination by gas chromatography. The methylphosphonic acids were retained on an aminopropyl ion exchanger and eluted with trimethylphenylammonium hydroxide, which also acted as a methylating re- agent. The procedure was applied to environmental samples in a field exercise in which samples contaminated with the nerve agents sarin and soman were exposed to the prevailing weather for periods of up to 4 weeks. The methylphosphonic acids were detected in all the samples examined. INTRODUCTION In connection with the verification of the use of chemical warfare agents, addi- tional information can be obtained from the determination of the degradation prod- ucts of unstable compounds such as nerve agents. Hence it is important to have methods available for the determination of such compounds. The nerve agents iso- propyl methylphosphonofluoridate (satin, GB), 1,2,2-trimethylpropyl methylphos- phonofluoridate (soman, GD) and ethyl S-2-diisopropylaminoethyl methylphospho- nothiolate (VX) are hydrolysed to methylphosphonic acids according to the scheme outlined in Fig 1. The methylphosphonic acids are polar, non-volatile compounds, and should therefore be well suited for determination by high-performance liquid chromatogra- phy (HPLC)rp3. The problem, however, is that no sensitive detectors for compounds such as methylphosphonic acids are available. These compounds have therefore often been determined by gas chromatography (GC) with prior derivatization. The most common derivatization methods have been the formation of trimethylsilyl (TMS) ethers or tert.-butyldimethylsilyl (t-BDMS) ethers from the acids4*5 or methylation with diazomethane6*‘. Experiments carried out in our laboratory have shown that the formation of t-BDMS ethers gave poor yields, especially from methylphosphonic acids with small alkyl groups. In addition, the silyl ethers were unstable and sensitive to moisture. 0021-9673/89/$03.50 0 1989 Elsevier Science Publishers B.V.