采用气相色谱-串联质谱法测定汽油中甲缩醛的含量，并对不确定度进行了评价。汽油样品直接进样，在气相色谱分离中用HP-5MS色谱柱（15 m×0.25 mm，0.25 μm）为固定相，在质谱分析中采用多反应监测模式。甲缩醛的线性范围为20~500 μL·L^-1，方法的检出限（3S/N）为0.01 μL·L^-1。方法用于汽油样品的分析，加标回收率为90.4%~113%，测定值的相对标准偏差（n=6）为0.90%~2.7%。不确定度主要来源于标准曲线不确定度。

GC-MS/MS was applied to the determination of methylal in gasoline,and the uncertainty was also evaluated. The gasoline sample was injected directly. The HP-5MS chromatographic column (15 m×0.25 mm, 0.25 μm) was used for GC separation and the multiple reaction monitoring mode was adopted in MS determination. Linearity range of methylal was found between 20 μL·L^-1 and 500 μL·L^-1 with detection limit (3S/N) of 0.01 μL·L^-1. The proposed method was applied to analysis of the gasoline sample, giving values of recovery and RSD's (n=6) in the ranges of 90.4%-113% and 0.90%-2.7% respectively. The uncertainty was mainly from standard curve.