Jakob E, Sievert C, Sommer S, Puhan Z
Eidgenössische Technische Hochschule Zürich, Labor für Milchwissenschaft, Schweiz.
Z Lebensm Unters Forsch. 1995 Apr;200(4):239-43. doi: 10.1007/BF01187511.
A nitrogen analyser based on the Dumas method (LECO FP-428) and equipped with a liquid injector has been tested. The intensive steam production during injection may result in poor nitrogen recoveries for volatile nitrogen compounds such as ethylene diamine. However, recoveries could be improved by slow injection and by filling the combustion tube with Cer(IV)-oxide. For the analysis of milk the instrument was calibrated with NaN3 solutions because their response was found to be less sensitive to burning conditions. Dumas-N and Kjeldahl-N of milk showed good correlation (r = 0.998). However, with the Dumas method about 6.7% (+ 0.035% N) higher nitrogen values were obtained. With a standard deviation of repeatability S(r) = 0.002% N (CVr = 0.33) and a between day reproducibility SD = 0.006% N (CVD = 1.1%) the precision of the Dumas method was similar to that reported for the Kjeldahl method. In order to avoid systematic errors the use of standard milk samples for calibration is recommended. It is concluded that modern instruments using the Dumas method allow precise measurements of nitrogen in milk with a high sample throughout.
对一台基于杜马斯法（LECO FP - 428）且配备液体进样器的氮分析仪进行了测试。进样过程中产生的大量蒸汽可能导致挥发性含氮化合物（如乙二胺）的氮回收率较低。然而，通过缓慢进样以及在燃烧管中填充二氧化铈（IV），回收率可以得到提高。对于牛奶分析，该仪器用叠氮化钠溶液进行校准，因为发现它们的响应对燃烧条件不太敏感。牛奶的杜马斯氮和凯氏氮显示出良好的相关性（r = 0.998）。然而，使用杜马斯法获得的氮值约高6.7%（+ 0.035% N）。杜马斯法的重复性标准偏差S(r) = 0.002% N（CVr = 0.33），日间再现性标准偏差SD = 0.006% N（CVD = 1.1%），其精密度与报道的凯氏法相似。为避免系统误差，建议使用标准牛奶样品进行校准。得出的结论是，使用杜马斯法的现代仪器能够在高通量样品的情况下精确测量牛奶中的氮。
