Determination of stereoisomers of dimethomorph in tobacco by supercritical fluid chromatography coupled with tandem mass spectrometry

In order to achieve the stereoselective separation and determination of stereoisomers of dimethomorph in tobacco, a method coupled supercritical fluid chromatography with tandem mass spectrometry (SFC-MS/MS) was developed to quickly separate and determine the stereoisomers of dimethomorph. Tobacco samples were extracted and purified by QuEChERS method, then the dimethomorph stereoisomers were well separated on a Chiralcel OD-3 column with CO₂-methanol as the mobile phase at the flow rate of 2 mL/min. Matrix matching standard working curve was used to conduct quantitative analysis. The results showed that: 1)The stereoisomers of dimethomorph reached baseline separation, and the separation time was only 5 minutes. 2)At the mass fractions of 0.02, 0.20 and 2.00 mg/kg, the recoveries of two isomers were in the range of 87.3%-102.3% with the inter-day relative standard deviations (RSDs) of 3.3%-5.9%. Good coefficients of determination (R²≥0.994 3) were achieved for two isomers over the isomers concentration range of 2-100 ng/mL in tobacco. The limits of detection (LODs) and limits of quantification (LOQs) for two isomers were 0.006-0.008 and 0.021-0.026 mg/kg respectively. 3) Ten tobacco samples were tested by this method, and (E)-dimethomorph (1.18 mg/kg) and (Z)-dimethomorph (1.22 mg/kg) were detected only in one sample. This method is fast, environmentally friendly, stable, reliable, and suitable for the stereoselective determination of dimethomorph isomers in tobacco.