Analysis of pendimethalin and oxyfluorfen residues in Zingiber officinale Roscoe and their dissipation dynamics in soil

An analytical method was developed for the determination of pendimethalin and oxyfluorfen in Zingiber officinale Roscoe (ginger), Z. officinale stem and soil using gas chromatography-tandem mass spectrometry (GC-MS). The final residues of the above two herbicides in Z. officinale and their dissipation dynamics in soil were studied using this new method. A simple and efficient pretreatment method called QuEChERS was used and samples were extracted with acetonitrile. Primary-secondary amine (PSA) and graphitized carbon black (GCB) were used to purify the Z. officinale and stem samples and Florisil was used to purify the soil samples.Ion scanning module (SIM) was selected for the mass spectrometry determination and the external standard and peak area method is employed for quantitative analysis. At the spiked levels of 0.01-0.5 mg/kg, the average recoveries of pendimethalin in Z. officinale, stem and soil were 91%-100%, 90%-98% and 86%-100%, respectively, and the relative standard deviations were 3.2%-3.7%, 2.7-4.2% and 3.2%-5.1%, respectively; the average recoveries of oxyfluorfen in Z. officinale, stem and soil were 90%-95%, 86%-91% and 85%-95%, respectively, and the relative standard deviations were 2.4%-4.4%, 3.9%-5.5% and 2.3%-4.9%, respectively, the limit of quantity (LOQ) of pendimethalin and oxyfluorfen samples were both 0.01 mg/kg. The dissipation half-lives of pendimethalin in soil were 12.5-20.5 days and the dissipation half-lives of oxyfluorfen in soil were 18.8-25.6 days in the ginger field study. When 33% pendimethalin emul-sifiable concentrate (EC) and 24% oxyfluorfen EC were sprayed at the recommended dose (active ingredients:693 g/hm² and 72 g/hm²) and high dose (active ingredients:1 039 g/hm² and 108 g/hm²) once after Z. officinale was planted, the pendimethalin and oxyfluorfen residues were not detected in Z. officinale in the harvest period. The results can provide a reference for the rational use and the maximum residue limits (MRL) standard development of pendimethalin and oxyfluorfen in Z. officinale.