SIMULTANEOUS EXTRACTION AND METHYLATION OF ACIDIC ANALYTES ADSORBED ONTO ION-EXCHANGE RESINS USING SUPERCRITICAL CARBON-DIOXIDE CONTAINING METHYL-IODIDE

Methylation of a wide range of organic acids with methyl iodide was si mply and efficiently performed on anion exchange resins with either su percritical carbon dioxide or acetonitrile as solvents. Analytes inclu ding chlorophenoxyacetic acids, pentachlorophenol, and quinoxaline-2-c arboxylic acid were displaced from the resin in a single step as their methyl esters or ethers in high yield using the supercritical fluid e xtraction (SFE) system, The conversion of 2,4-D and 2,4,5-T (solutions of 100 and 35 ppb, respectively) to their methyl esters was complete in 30 min and gave yields of 92% and 99% with coefficients of variatio n of 10%. Analytes in up to 200 mt of aqueous solution could be trappe d on 0.1 g of AG MP-1 anion exchange resin and derivatized and eluted using methyl iodide in supercritical carbon dioxide at 200 bar and 80 degrees C, Less acidic compounds including albendazole, fenbendazole, triclabendazole, and sulfadimidine could also be derivatized on the re sin under SFE conditions or in a quick and inexpensive procedure using acetonitrile; however, these compounds gave lower yields and multiple methylated products.