Abstract: In order to better control the effective content of ¹³C in ¹³C-urea reagent, the technique and the conditions for converting ¹³C-
urea sample into the sample gas used in gas isotopic mass spectrometry detection by means of nitrite oxidation method and high temperature burning method were investigated. The results showed that the ¹³CO₂ gas obtained from nitrite oxidation method with 2 mg¹³C-urea samples and that from high temperature burning method with 1 mg ¹³C-urea samples can satisfy the demand of the mass spectrometer detection. The sodium nitrite reagent dosage, the reaction temperature and the reaction time of the sample gas preparation, as well as the treatment effect of copper oxide reagent etc. were sought experimentally. The high abundance ¹³C-urea testing was completed, the calculation and expression of the detection data were also determined, and the standard deviation were less than ±0.07%.