Discussion on Determination of Residues of 33 Forbidden Pesticides in Chinese Medicinal Materials by Chromatography-Tandem Mass Spectrometry

The samples were treated by solid phase extraction and QuEChERS method, and the residues of 33 forbidden pesticides in Chinese medicinal materials were determined by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS). The differences of the results of different pretreatment methods and different detection methods were discussed. The operation steps of solid phase extraction were as follows. The mixture of sample powder (5 g) and sodium chloride (1 g) was extracted twice with acetonitrile (50 mL). The supernatant combined was concentrated to 1-3 mL under reduced pressure, and then made its volume up to 10 mL with acetonitrile. The above extraction solution (4 mL) was put onto an amino composite solid phase extraction small column with graphitized carbon black, eluted with a mixture (25 mL) of acetonitrile and toluene at volume ratio of 3:1, and concentrated to nearly dry in a water bath at 40℃. The residue was added into internal standard solution (0.02 mL) and acetonitrile (2 mL), and the mixture was filtered with 0.22 μm organic filter membrane. The filtrate was obtained for test. The operation steps of QuEChERS method were as follows. The sample powder (3 g) was put into a 50 mL-polystyrene centrifuge tube with stopper, dissolved with 1% (φ) glacial acetic acid solution (15 mL), extracted with acetonitrile (15 mL), and a mixed powder (7.5 g) of anhydrous magnesium sulfate and anhydrous sodium acetate at mass ratio of 4:1 was added. The above solution was purified with a purification tube containing 400 mg of N-propylethylenediamine, 400 mg of C₁₈ adsorbent, 200 mg of graphitized carbon black and 1 200 mg of magnesium sulfate. The supernatant (5 mL) was absorbed, concentrated to nearly dry in a water bath at 40℃. The residue was added into internal standard solution (0.01 mL), and the mixture was diluted to 1 mL with acetonitrile for test. External standard method was used for quantitative analysis on HPLC-MS/MS, and internal standard method was used for quantitative analysis on GC-MS/MS. It was shown that linear ranges of standard curves of 33 pesticides and their isomers or oxygen analogues were 5-200 μg·L^-1 (HPLC-MS/MS) or 10-200 μg·L^-1 (GC-MS/MS), with detection limits in the ranges of 0.002 8-3.0 μg·kg^-1 (HPLC-MS/MS) or 1.4-3.2 μg·kg^-1 (GC-MS/MS). Recovery test was made on the negative Radix Scutellariae sample by standard addition method, giving results in the range of 54.8%-128%, and RSDs (n=6) of the determined values were ranged from 0.99% to 21%. This method was used for analysis of 8 kinds of samples, including Radix Scutellariae, Folium Perillae, Scutellaria lateriflora, Cortex Phellodendri, Fructus Foeniculi, Radix Angelicae sinensis, Rhizoma Pinelliae and Radix Liriopes. Organophosphorus and carbamate pesticides were mainly detected, and the detection amounts of isofenphos-methyl in Scutellaria lateriflora, phorate and carbofuran in Fructus Foeniculi and isocarbophos in Rhizoma Pinelliae were exceeded the limits of pharmacopoeia.