Korn Maria das Graças A, Dos Santos Wagna P C, Korn Mauro, Ferreira Sérgio L C
Núcleo de Excelência em Química Analítica (NQA-PRONEX), Grupo de Pesquisa em Química Analítica, Instituto de Química, Universidade Federal da Bahia, Campus Universitário de Ondina, Salvador, Bahia 40170-290, Brazil.
Talanta. 2005 Feb 15;65(3):710-5. doi: 10.1016/j.talanta.2004.07.047. Epub 2004 Sep 25.
In the present paper a focused-microwave Kjeldahl digestion procedure without metal catalyst for nitrogen determination in bean samples was developed. Temperature at which the decomposition plateau occurs, mass of potassium sulphate and either volume of sulphuric acid or hydrogen peroxide were optimised. Results of the two-level full factorial design (2(4)) based on an analysis of variance demonstrated that only the decomposition plateau temperature and the sulphuric acid volume were statistically significant. Optimal conditions for the digestion of bean samples were obtained by using Doehlert design. The modified digestion procedure of 0.25g of bean samples has been performed in 27min at optimised conditions. The accuracy of the developed procedure by the analysis of the two certified reference materials, peach leaves (NIST 1547) and apple leaves (NIST 1515). The t-test applied to the results revealed that they are in agreement (p > 0.05) with the certified values. The precision, expressed as relative standard deviation (R.S.D.) was of 0.96% for four successive Kjeldahl nitrogen determinations. In addition, interlaboratory exercises were performed with several bean samples in reference Brazilian food control laboratory.
本文开发了一种用于测定豆类样品中氮含量的无金属催化剂聚焦微波凯氏定氮法。对分解平稳期出现时的温度、硫酸钾质量以及硫酸或过氧化氢的体积进行了优化。基于方差分析的两水平全因子设计（2(4)）结果表明，只有分解平稳期温度和硫酸体积具有统计学意义。通过Doehlert设计获得了豆类样品消化的最佳条件。在优化条件下，0.25g豆类样品的改进消化程序在27分钟内完成。通过分析两种有证标准物质桃叶（NIST 1547）和苹果叶（NIST 1515）来验证所开发方法的准确性。对结果进行的t检验表明，结果与认证值一致（p > 0.05）。连续四次凯氏定氮测定的精密度以相对标准偏差（R.S.D.）表示为0.96%。此外，在巴西参考食品控制实验室对多个豆类样品进行了实验室间比对实验。
