Single‐drop microextraction combined in‐line with capillary electrophoresis for the determination of nonsteroidal anti‐inflammatory drugs in urine samples

This study describes a method to determine nonsteroidal anti‐inflammatory drugs (NSAIDs) in urine samples based on the use of single‐drop microextraction (SDME) in a three‐phase design as a preconcentration technique coupled in‐line to capillary electrophoresis. Different parameters affecting the extraction efficiency of the SDME process were evaluated (e.g. type of extractant, volume of the microdroplet, and extraction time). The developed method was successfully applied to the analysis of human urine samples with LODs ranging between 1.0 and 2.5 μg/mL for all of the NSAIDs under study. This method shows RSD values ranging from 8.5 to 15.3% in interday analysis. The enrichment factors were calculated, resulting 27‐fold for ketoprofen, 14‐fold for diclofenac, 12‐fold for ibuprofen, and 44‐fold naproxen. Samples were analyzed applying the SDME–CE method and the obtained results presented satisfactory recovery values (82–115%). The overall method can be considered a promising approach for the analysis of NSAIDs in urine samples after minimal sample pretreatment.