In this experiment, headspace-Autosampler HS-20 instrument will be used. To suit for this headspace instrument, 20mm crimp headspace vial should be chosen. In aijiren product catalog, there are 6ml, 10ml, 20ml vials, whose size of mouth is 20mm crimp vial. A mixture of NDMA and NDEA was used to prepare calibration curves ranging from 2.5-10 ug/L.