Because of the high stability and potential toxic effects of non-steroidal anti-inflammatory drugs (NSAIDs), it is important to closely monitor their concentrations in the environment using a sensitive analytical method. In this study, a simple, rapid, efficient, and sensitive analytical method based on gas chromatography-mass spectrometry (GC-MS) was developed to determine the levels of seven common NSAIDs in various types of surface water. To simplify sample preparation, in situ derivatization using methyl chloroformate was combined with ultrasound-assisted emulsification microextraction. For selection and optimization of significant variables, experiments were statistically designed using Plackett-Burman design and central composite design. The resulting optimal conditions for derivatization and extraction were 100 μL of chloroform (extraction solvent), 10.0 mL of sample, and 240 μL of pyridine (catalyst as a base in derivatization). The optimized sample preparation coupled with optimized GC-MS analysis in selected ion monitoring mode provided good linearity from 0.010 to 5.0 ng mL(-1), and a limit of detection between 0.0050 and 0.010 ng mL(-1), good intra-day and inter-day precision (0.30-6.3% and 5.1-9.5%, respectively), and good accuracy (relative recovery; 91-117% at 0.20 ng mL(-1) and 77-105% at 2.5 ng mL(-1)). Compared with previously reported methods, the current method requires a small volume of sample and simple sample preparation steps for sensitive determination of NSAID levels using a conventional GC-MS system. The method was successfully applied to determine the levels of seven common NSAIDs in various types of surface water.
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