National Measurement Institute (NMI), Pymble, NSW 2073, Australia.
Rapid Commun Mass Spectrom. 2011 Jun 15;25(11):1641-51. doi: 10.1002/rcm.4983.
An alternative calibration procedure for use when performing carbon isotope ratio measurements by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) has been developed. This calibration procedure does not rely on the corrections in-built in the instrument software, as the carbon isotope ratios of a sample are calculated from the measured raw peak areas. The method was developed for the certification of a urine reference material for sports drug testing, as the estimation of measurement uncertainty is greatly simplified. To ensure that the method is free from bias arising from the choice of calibration material and instrument, the carbon isotope ratios of steroids in urine extracts were measured using two different instruments in different laboratories, and three different reference materials (CU/USADA steroid standards from Brenna Laboratory, Cornell University; NIST RM8539 mineral oil; methane calibrated against NIST RM8560 natural gas). The measurements were performed at LGC and the Australian National Measurement Institute (NMI). It was found that there was no significant difference in measurement results when different instruments and reference materials were used to measure the carbon isotope ratio of the major testosterone metabolites androsterone and etiocholanolone, or the endogenous reference compounds pregnanediol, 11- ketoetiocholanolone and 11β-hydroxyandrosterone. Expanded measurement uncertainties at the 95% coverage probability ranged from 0.21‰ to 1.4‰, depending on analyte, instrument and reference material. The measurement results of this comparison were used to estimate a measurement uncertainty of δ(13)C for the certification of the urine reference material being performed on a single instrument using a single reference material at NMI.
已经开发出一种替代的校准程序，用于通过气相色谱/燃烧/同位素比质谱（GC/C/IRMS）进行碳同位素比测量。该校准程序不依赖于仪器软件中的内置校正，因为样品的碳同位素比是从测量的原始峰面积计算得出的。该方法是为运动药物检测用尿液参考物质的认证而开发的，因为测量不确定度的估计大大简化了。为了确保该方法不受校准材料和仪器选择引起的偏差的影响，使用两种不同的仪器在两个不同的实验室中测量尿液提取物中的类固醇的碳同位素比，并使用三种不同的参考物质（Brenna 实验室的 CU/USADA 类固醇标准品，康奈尔大学；NIST RM8539 矿物油；用 NIST RM8560 天然气校准的甲烷）。测量是在 LGC 和澳大利亚国家测量研究所（NMI）进行的。结果发现，当使用不同的仪器和参考材料测量主要睾酮代谢物雄酮和表雄酮，以及内源性参考化合物孕烷二醇、11-酮表雄烷酮和 11β-羟基雄酮的碳同位素比值时，测量结果没有显著差异。在 95%置信概率下扩展的测量不确定度范围为 0.21‰至 1.4‰，具体取决于分析物、仪器和参考材料。该比较的测量结果用于估计在 NMI 上使用单个仪器和单个参考材料对尿液参考物质进行认证时 δ(13)C 的测量不确定度。
