Abstract:The reduction effect of thiourea-ascorbic acid was affected by the content of nitric acid in the determination of arsenic in grain samples by hydride generation-atomic fluorescence spectrometry. The content of nitric acid in the test solution is too high, and the redox reaction with thiourea-ascorbic acid solution will reduce its reduction efficiency. In this study, the best acid catching condition was obtained in the determination of As in grain by the method of Hydride Formation-Atomic Fluorescence Spectrometry with digestion by microwave through testing the acid catching time and the acid catching temperature. The result showed that the concentration of As in grain is linearly related to the fluorescence intensity, which is in accordance with the equation of y = 0.0028x - 0.1728 (R2= 0.9993). The detection limit is 1.72 ng/g. The relative standard deviation RSD of the 9 samples is in the range of 4.32% to7.59 %, and the relative error(RE) is less than ± 6.50 %. The method is stable in numerous tests and can be used for the rapid determination of arsenic in grain samples.