Determination of total maleic acid, fumaric acid, p-hydroxybenzoic acid and benzoic acid in food by ultra performance liquid chromatography-tandem mass spectrometry

Hydrolysis reaction coupling to ultra performance liquid chromatography-triple quadrupole tandem mass spectrometry (UPLC-MS/MS) was applied for the determination of total maleic acid, fumaric acid, p-hydroxybenzoic acid and benzoic acid in milk-based infant formula, soy-based infant formula, beef jerky, starch and cake. Samples were hydrolyzed by sodium hydroxide and then acidified. The hydrolysis solution was then precipitated by acetonitrile. After being centrifuged, a part of the supernatant was blown dry by nitrogen gas and then dissolved in water for testing. The testing solution was separated by a reverse phase column and then detected by triple quadrupole tandem mass spectrometry operated in a multiple-reaction-monitoring mode. Matrix-matched calibrations were used for quantification. Methyl esters of the acids were used to optimize the influential parameters of the hydrolysis reaction. The matrix effects of the samples on the four acids ranged from 45.7% to 157%. Most of the recoveries at the 50 mg kg(-1) and 200 mg kg(-1) levels were from 74.6% to 129%, with relative standard deviations ranging from 3.5% to 21%. The limits of detection ranged from 1.0 mg kg(-1) to 10.0 mg kg(-1). Fifty samples from the local market were tested.