土壤样品(5.000 g)用乙腈-水(80+20)混合溶液超声波提取2次,每次用20 mL,提取时间为20 min。提取液滤入已盛有氯化钠3 g的100 mL具塞量筒中,剧烈振摇1 min,并静置10 min,待乙腈与水分相后,移取上层乙腈溶液10.0 mL,于40 ℃吹氮蒸至0.5 mL,加水4 mL。将溶液通过已活化的C18固相萃取小柱分离杂质,用甲醇4 mL洗脱,吹氮蒸至1.5 mL,以C18色谱柱为固定相,不同比例混合的乙腈和水的混合溶液为流动相进行梯度淋洗。按洗脱程序,在不同时段和不同的波长条件下测定19种农药的含量。方法的检出限(3S/N)为0.001~0.15 mg·kg-1,回收率在70.1%~117.9%之间。

Sample of soil (5.000 g) was extracted ultrasonically twice with mixed solvent of acetonitrile and water (80+20) (20 mL for each extraction) for 20 min. The extracts were filtered into a 100 mL cyclinder with stopper, in which 3 g of NaCl were added previously. The mixture was shaked vigorously for 1 min and stayed for 10 min to have the phases of acetonitrile and water separated. Ten mL of the supernatant acetonitrile solution were taken and evaporated to 0.5 mL by blowing with nitrogen at 40 ℃. Four mL of pure water were added, and purified by passing through activated C18 SPE microcolumn. Methanol (4 mL) was used as eluant and the eluate was evaporated by N2-blowing to 1.5 mL which were used for HPLC analysis. C18 chromatographic column was used as stationary phase and mixtures of acetonitrile and water of various proportions were used as mobile phase in the gradient elution. The 19 pecticides were determined in various time intervals and at various wavelengths in UV-region as described in the gradient elution program. Detection limits found were in the range of 0.001 to 0.15 mg·kg-1. Values of recovery found were ranged from 70.1% to 117.9%.