Online eluent-switching technique coupled anion-exchange liquid chromatography-ion trap tandem mass spectrometry for analysis of non-steroidal anti-inflammatory drugs in pig serum

A novel method for online extraction, pH-gradient separation, and analysis of nine non-steroidal anti-inflammatory drugs (NSAIDs) was developed by coupling online eluent-switching technique to single anion-exchange chromatographic column/ion trap mass spectrometer (MS) and used for monitoring NSAIDs residues in pig serum. A neutral eluent and a pH-gradient eluent were used for extraction and separation of NSAIDs, respectively. Each of nine NSAIDs has an MS precursor ion of either [M−H]− or [M−Na]−. The extracted ion chromatogram for a specific product ion of each NSAID was used for its quantitative analysis. The dynamic linear ranges of calibration curves were all 0-200 ng mL−1 (R2 > 0.9950). The analysis accuracies estimated by spiking standard concentrations at 20, 100, and 200 ng mL−1 were 80.5-99.9%. The corresponding intra-day and inter-day precisions (RSD%) were 2.5-14.5% and 2.9-15.2%, respectively. The limit of detection/limit of quantitation of NSAIDs were 1.3/4.3, 0.5/1.6, 0.2/0.5, 2.5/8.2, 1.5/4.9, 0.6/2.1, 0.6/2.0, 0.5/1.7, and 0.6/2.1 ng mL−1 for carprofen, diclofenac, flunixin, ibuprofen, ketoprofen, meclofenamic acid sodium, mefenamic acid, niflumic acid, and tolfenamic acid, respectively. After 1 h injection of a dose containing 2 mg kg−1 weight pig of flunixin and tolfenamic acid to the pigs, a residue amount of 3480 ± 36 ng mL−1 and 431 ± 13 ng mL−1, respectively, was reached for the incurred pig serum specimens and both residues were reduced to about 20 ng mL−1 at the time of 24 h.