An improved analytical method for the determination of urea nitrogen isotopomers in biological samples utilizing continuous flow isotope ratio mass spectrometry.
An improved analytical method for the determination of urea nitrogen isotopomers in biological samples utilizing continuous flow isotope ratio mass spectrometry.
复制标题
DOI：
10.1002/rcm.2788
复制
发表时间：
2006-12
期刊：
影响因子：
--
通讯作者：
J. Marini;M. Attene-Ramos
中科院分区：
文献类型：
--
作者：
J. Marini;M. Attene-Ramos
在过去的几年中，许多双入口同位素比质谱（IRMS）的应用已经适应于连续流动系统，允许自动进样和更高的吞吐量。通过IRMS进行的尿素氮同位素分析需要在分析之前将尿素离线转化为氮气。用LiOBr氧化尿素导致尿素的单分子降解，这保留了母体尿素分子的特性，并且必须在真空下进行以防止被大气氮污染。我们已经开发了一种利用一次性Exetainers的尿素降解离线系统，其中大气中的氮气被氦气取代。尿素氮的回收率在所测试的标准品范围内（0至420微克氮）呈线性，并且15 N 15 N-尿素标准品的标准曲线显示出高的决定系数（R2 > 0.9998）。一小部分尿素以非单分子方式降解，并且已显示取决于样品中尿素的浓度。制备的样品的长期储存显示15 N15 N富集下降，表明空气污染。然而，样品可稳定储存24 h，这允许分析大样品批次。尿素代谢的兴趣，特别是在反刍动物物种，最近增加了由于尿素和氮排泄的农场动物的环境影响。这种新的分析方法将允许准确的测量和快速的吞吐量，以支持这些领域的研究。
Over the past few years numerous dual inlet isotope ratio mass spectrometry (IRMS) applications have been adapted to continuous flow systems which allow the automation of sample admission and a higher throughput. The isotopomer analysis of urea nitrogen by IRMS requires the offline conversion of urea into nitrogen gas before analysis. The oxidation of urea with LiOBr results in the monomolecular degradation of urea, which preserves the identity of the parent urea molecule, and has to be conducted under vacuum to prevent contamination with atmospheric nitrogen. We have developed an offline system of urea degradation utilizing disposable Exetainers, in which atmospheric nitrogen is displaced by helium. Recovery of urea nitrogen was linear within the range of the standards tested (0 to 420 microg nitrogen) and standard curves for 15N15N-urea standards showed high coefficients of determination (R2 > 0.9998). A small portion of urea degrades in a non-monomolecular fashion and has been shown to depend on the concentration of urea in the sample. Long-term storage of prepared samples showed a decline in 15N15N enrichment, suggesting air contamination. However, samples were stable for 24 h, which allows for the analysis of large sample batches. Interest in urea metabolism, particularly in ruminant species, has increased recently due to the environmental implications of urea and nitrogen excretion by farm animals. This novel analytical method will allow for accurate measurements and the rapid throughput needed in order to support these field studies.