UPLC-MS/MS Determination of Residual Amounts of 51 Forbidden Pesticides in Roots of Angelica Dahurica

The TCM of root of Angelica dahurica was crushed to pass through sieve with bore of (250±9.9)μm. 2.00 g of the powdery sample was taken and after mixing with 10 mL of water it was extracted with 10.0 mL of acetonitrile containing 1% (volume fraction) acetic acid by swirling for 1 min, and then 4 g of anhydr. MgSO₄ and 1 g of sodium acetate were added, and the mixture was vibrated vigorously for 3 min. After centrifuging for 5 min, 5.0 mL of the supernatant was taken and added to the purification tube in which 900 mg of anhydr. MgSO₄, 450 mg of PSA and 300 mg of colloidal silica were placed in advance, and the mixture was vibrated vigorously for 5 min to fulfill purification, and after centrifuging for 5 min, 3.0 mL of the supernatant was taken and evaporated to near-dryness at 40℃ in a water bath under reduced pressure. 300 μL of 50 μg·L^-1 triphenyl phosphate internal standard solution were added into the residue, which was further dissolved and diluted to 1.0 mL with acetonitrile. The solution was filtered through 0.20 μm filtering membrane, and the filtrate was used for UPLC-MS/MS analysis under the working condition of the instrument. Eclipse Plus C₁₈ chromatographic column was selected as the stantionary phase and mixtures of (A) 0.1% (volume fraction) formic acid solution (containing 10 mmol·L^-1 of ammonium formate) and (B) acetonitrile in various ratios were used as mobile phases in programmed gradient elution in the LC separation of the 51 forbidden pesticides, and determined by MS/MS under the condition of ESI⁺ and dMRM. Standard curves were prepared by the mode of matrix matching. Linear relationships between values of peak areas found and the respective mass concentrations of the 51 pesticides were kept in definite ranges. Values of detection limits (3S/N) were found in the range of 0.3-5.0 μg·kg^-1. Recovery was tested by standard addition method, giving values of recovery of most of the 51 pesticides over 71%, and values of RSDs (n=6) found were less than 20%. Substantial samples from 70 batches of the TCM were analyzed by the present method and 16 pectidices were found in these samples. Phorate sulfoxide attained to a high detection rate of 95%, giving highest determined value of 15.2 μg·kg^-1. Two other pesticides (phorate sulfone and chlorpyrifos) gave same detection rate of 10%, and their highest determined values were 3.5, 45.0 μg·kg^-1. The remainder 13 pesticides all gave detection rates lower than 5% and their determined values were quite low.