Method for the determination of dialkyl phosphates in urine by strong anion exchange disk extraction and in-vial derivatization

A method for the determination of four dialkylphosphate metabolites in urine by strong anion exchange disk (SAX) was investigated. Calcium hydroxide was added to a 1-mL urine sample to reduce interference. The aliquot was passed through the SAX disk to accumulate dialkylphosphate metabolites on the disk. The retained dialkylphosphate metabolites were derivatized with methyl iodide in acetonitrile online, and the resulting methyl esters of dialkylphosphate metabolites were directly analyzed by capillary column gas chromatography with flame photometric detection. The recoveries of these dialkylphosphate metabolites were found to be stable. When the intact sample was diluted with deionized water at a 1:1 ratio, the recoveries were both increased and stabilized. The urine samples collected from eight fruit farmers showed that levels of dialkylphosphate metabolites in urine were significantly different before and after pesticide application, indicating the method established in this study is applicable for real sample analysis. Compared with previous studies, this method not only can greatly simplify sample preparation, but it can also significantly reduce the consumption of toxic solvents in sample preparation.