Determination of Polyoxin B in Cucumber and Soil Using Liquid Chromatography Tandem Mass Spectrometry Coupled with a Modified QuEChERS Method

A sensitive and effective method based on a modified QuECHERS (quick, easy, cheap, effective, rugged, and safe) method for the determination of polyoxin B in cucumber and soil using liquid chromatography tandem-mass spectrometry (LC-MS/MS) was developed and validated. Samples were extracted using 1% formic acid in ultrapure water and purified via reversed-dispersive solid phase extraction (r-dSPE) using C-18. Recovery of polyoxin B ranged from 83.0% to 112.1% with relative standard deviation (RSD) (n = 5) of 3.0-5.2%. The limit of quantification (LOQ) and the limit of detection (LOD) were 0.01 and 0.003 mg/kg for cucumber and soil, respectively. The method was subsequently applied for real sample analysis. The dissipation experiments showed that half-lives of polyoxin B in cucumber and soil were 2.5-5.0 days. The terminal residues of polyoxin B at preharvest intervals (PHIs) of 3 days and 5 days in cucumber were less than 0.05 mg/kg. We therefore suggest that the developed method can be extrapolated to other agricultural crops or food for routine analysis. It also can be used to determine the PHIs. Moreover, these results will aid in establishing the maximum residue limit (MRL) for cucumber in China.