After distillation of the sample, the alkylmercury in the distillate is derivatized with derivatization reagents (such as ethylation reagents or propylation reagents) to generate volatile alkylmercury products. After blowing, they are captured by Tenax tubes, and the thermally desorbed components are separated by gas chromatography and then high-temperature cracked into mercury vapor, which is detected by a cold atomic fluorescence detector.