Negative Chemical Ionization Mass Spectrometry ( NCI-MS) is amenable to organic compounds with high electronegativity. However, nothing has previously been reported about the comparative study of a different reaction gas. In this paper, the methane, isobutane, ammonia, ammonia in methane, ammonia in isobutane as reaction gases for NCI are introduced. The effect factors of reaction gas pressure, source temperature, filament emission current and electron energy are evaluated for each high electronegativity pesticide considered in this study. Finally, the pure ammonia led to a remarkable reduction in background noise with a significant improvement for overall sensitivity of the method. Combining with ASE extraction, the limit of detection (LOD) for residue pesticides in soil is between 0.01 -0.32 (jug/kg, the recovery is 73.3% -108. 1% and the RSD is between 2.5% -8.8%.%在气相色谱-质谱分析中,负化学电离源质谱特别适合于高电负性目标物的分析,但不同反应气的对比研究工作至今未见报道.本研究采用甲烷、异丁烷、氨气、甲烷+氨气混合气、异丁烷+氨气混合气作为反应气,在负化学离子源内对电负性较高的有机磷农药进行电离实验,对反应气压力、离子源温度、灯丝发射电流等多项参数进行了考察.结果表明:采用纯氨气作为反应气,检测背景低,质谱真空负荷小,并可在负化学源质谱上获得最高的灵敏度.配合加速溶剂萃取方法,对土壤中的有机磷农药残留进行分析,方法全流程回收率为73.3％ ～ 108.1％,精密度为2.5％ ～8.8％,检出限为0.01 ～0.32 μg/kg,各项指标均可满足实际样品测试需求.
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