Injection port derivatization following sonication-assisted ion-pair liquid–liquid extraction of nonsteroidal anti-inflammatory drugs

In this paper, a sonication-assisted ion-pair liquid–liquid extraction approach, combined with injection port derivatization and gas chromatographic (GC) analysis, was developed to extract and detect nonsteroidal anti-inflammatory drugs (NSAIDs). In this procedure, the target analytes in the sample solution were converted into their ion-pair complexes (carboxylate ion-pairs) with tetrabutylammonium hydrogen sulfate. The ion-pairs were then extracted by an organic solvent (ethyl acetate) with the assistance of sonication. The factors influential to extraction, including type of organic solvent, concentration of ion-pair reagent, pH values of sample solution, sonication time duration and salt addition, were investigated in detail. After extraction, the organic phase containing ion-pair complexes was injected to GC sample port. Upon injection, the carboxylate ion-pairs were derivatized promptly under high temperature to yield butyl esters, which were more suitable for GC analysis. The conditions for injection port derivatization, such as injection port temperature and purge off time, were also examined. This newly established approach afforded the limits of detection between 0.44 and 2.75 ng L−1 for the tested NSAIDs, with relative standard deviations less than 5.4%.