Simultaneous Extraction and Methylation of Acidic Analytes Adsorbed onto Ion Exchange Resins Using Supercritical Carbon Dioxide Containing Methyl Iodide

Abstract

Methylation of a wide range of organic acids with methyl iodide was simply and efficiently performed on anion exchange resins with either supercritical carbon dioxide or acetonitrile as solvents. Analytes including chlorophenoxyacetic acids, pentachlorophenol, and quinoxaline-2-carboxylic acid were displaced from the resin in a single step as they methyl esters or ethers in high yield using the supercritical fluid extraction (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 variation of 10%. Analytes in up to 200 mL of aqueous solution could be trapped 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 o C. Less acidic compounds including albendazole, fenbendazole, triclabendazole, and sulfadimidine could also be derivated on the resin under SFE conditions or in a quick and inexpensive procedure using acetonitrile; however, these compounds gave lower yields and multiple methylated product