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High performance liquid chromatography-tandem mass spectrometry was applied to the determination of quaternary ammonium compounds, namely, dodecyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium chloride, hexadecyldimethylbenzylammonium chloride and didecyldimethylammonium chloride in pork, beer liver, apple, spinach, rice and white sugar. The analytes were extracted using a methanol-water mixture as the extraction solvent and were further purified with the Oasis WCX cartridge. The separation of quaternary ammonium compounds was performed on a CAPCELL PAK CR 1 : 4 column using acetonitrile-50 mmol L-1 ammonium formate aqueous solution containing 0.1% formic acid as the mobile phase in the gradient elution mode. The mass spectrometric detection was conducted using an electrospray ion source in the multiple reaction monitoring mode. The results showed that the linear range for 5 quaternary ammonium compounds was 5.00-500.00 mu g L-1 and the correlation coefficients were higher than 0.995. The limit of quantification for the analytes was 10.00 mu g L-1. Six types of real samples were analyzed and the recoveries of the analytes at three spiked levels ranged between 76.8% and 102.5% with the relative standard deviations of 1.09-8.33%. The present method is simple, reliable and accurate and can be applied to the determination of quaternary ammonium compounds in foodstuffs.