Fast Detection of the Emetic Toxin Cereulide in Cooked Rice and Dairy Products by Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry

A matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) method was developed for the rapid detection of the emetic toxin cereulide in cooked rice and dairy products. The splitting pattern of cereulide standard was analyzed, meanwhile, effects of matrix type, spotting methods, the type and dosage of matrix solvent, and laser intensity on the MS signal intensity of cereulide were investigated. Methodological validation and application to actual samples were conducted. As a result, α-cyano-4-hydroxycinnamic acid (HCCA) was chosen as the matrix and dispersed in a 1:1 acetonitrile-water mixture containing 0.1% trifluoroacetic acid, and the matrix and the samples were sequentially spotted. In MALDI-TOF MS screening of foods using positive ion reflectron and linear modes at 70% laser intensity, the target ion peaks of ([M + Na]⁺ and [M + K]⁺) in cereulide were detected with stable signals, high intensity and good response repeatability. The results of methodological validation showed that good linear relationship was observed between the overlapping areas of [M + Na]⁺ and [M + K]⁺ peaks and cereulide concentration in the range from 5 to 100 ng/mL, with a correlation coefficients (r) greater than 0.99. The limits of detection (LOD) of [M + Na]⁺ and [M + K]⁺ were 3.0 and 5.0 ng/g, respectively; the recoveries of spiked rice and milk samples were ranged from 73.3% to 118.2%, with relative standard deviations (RSDs) of 0.3% to 10.9% (n = 6). This method was characterized by rapidity, high accuracy, good sensitivity, and strong anti-interference ability, and was suitable for the detection of cereulide in cooked rice and dairy products without using any internal standard.