Simultaneous determination and residue levels of flonicamid, spirotetramat, and their seven metabolites in cottonseed under field conditions

To determine the residue levels of flonicamid and its metabolites 4-trifluoromethylnicotinamide (TFNA-AM), 4-trifluoromethylnicotinic acid (TFNA), N-(4-trifluoromethylnicotinoyl) glycine (TFNG), and spirotetramat and its metabolites spirotetramat-enol (B-enol), spirotetramat-monohydroxy (B-mono), spirotetramat-keto-hydroxy (B-keto), and spirotetramat-enol-glucoside (B-glu) in cottonseed from eight regions of China, a simultaneous detection method for these nine compounds in cottonseed was developed based on a modified QuEChERS and LC-MS/MS. The cottonseed samples were extracted using 10 mL acetonitrile, 30 mg citric acid, and citrate buffer, then purified with 10 mg chitin, 20 mg C18, and 5 mg GCB. The average recoveries of all target compounds ranged from 72% to 105% with relative standard deviations (RSDs) of 0.4%-10.4%. The limits of quantitation (LOQs) of all target compounds were 0.01 mg/kg. Supervised cotton field trials were conducted under Good Agricultural Practices (GAP) conditions, and flonicamid-spirotetramat 40% suspended concentrate (SC) was sprayed once at the highest recommended dosage of 108 g active ingredient/ha (g a.i./ha) during the early stages of cotton aphid infestation. The results indicated that the residue levels of nine target compounds in cottonseed samples were less than 0.01 mg/kg at a 14-day pre-harvest interval (PHI, 14 d). This study provides scientific guidance for the safe use of flonicamid and spirotetramat on cotton.