[A multi-step distillation method for sample preparation in gas chromatographic analysis]

A sample pretreatment device based on multi-step distillation principle was constructed and evaluated. Trace components in the sample were extracted, separated and enriched at the cold receptor of the molecular diffusion distillation device. The cold receptor was designed as an exchangeable part to avoid the cross interferences from one sample to another one. A model sample containing four kinds of organophosphorus pesticides in ethyl actate was tested in the device, and the distillated and enriched solution was analyzed by a gas chromatograph. It was proven that the interferential components to gas chromatography such as protein, lipid and pigment could be removed effectively, and the enrichment factor for trace target components was more than 150 times. The recoveries of the method were from 90% to 117%, and the relative standard deviations (RSDs) from 1.3% to 10%. The limit of detection (LOD) of this method was 1 ng/mL without further concentration. The reused ratio of the organic reagents was more than 95%. Practical application was performed by using a spiked tea sample. The device can treat more than 100 g of samples with a boiling point range of 120 - 600 degrees C.