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Abstract Dumas combustion ammonia determination method（Dumas method）and Kjeldahl nitrogen determination method（Kjeldahl method）were used to detect crude protein content in 15 common vegetables．And method comparison and data analysis were carried out．The results showed that compared with Kjeldahl method, Dumas method had the advantages of safety，environmental protection，low energy consumption, etc．The coefficient of variation CV of Dumas method was 0.3%-2.1%，and recovery rate was 98.1%-101.9%．The CV range of Kjeldahl method was 0.3%-1.4%，and recovery rate was 98.7%-99.8%．The precision and recovery rate of these 2 methods all meet the confirmation requirements．The results of method testing showed that a significant linear correlation（R2 = 0.999 7）with 0.4%-8.1% precision range was in line with the national standard GB 5009.5—2016（RSD ＜ 10%）．For most vegetables，the difference between crude protein contents gained by these 2 methods were not significant．The significant differences only existed between Chinese cabbage，pakchoi and spinach with high nitrate content．Further studies found that high nitrate content in vegetables was not the only reason leading to the significant differences in test results by the 2 testing methods．The effect of vegetable substrate might be the another important reason，awaiting for further studies and confirmation．
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Received: 25 May 2020
Published: 08 July 2020
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