Institute for Clinical and Experimental Pathology, ARUP Laboratories, 500 Chipeta Way, Salt Lake City, Utah 84108, United States.
Anal Chem. 2013 Apr 16;85(8):3879-85. doi: 10.1021/ac303096w. Epub 2013 Mar 29.
Stable isotope-labeled internal standards are of great utility in providing accurate quantitation in mass spectrometry (MS). An implicit assumption has been that there is no "cross talk" between signals of the internal standard and the target analyte. In some cases, however, naturally occurring isotopes of the analyte do contribute to the signal of the internal standard. This phenomenon becomes more pronounced for isotopically rich compounds, such as those containing sulfur, chlorine, or bromine, higher molecular weight compounds, and those at high analyte/internal standard concentration ratio. This can create nonlinear calibration behavior that may bias quantitative results. Here, we propose the use of a nonlinear but more accurate fitting of data for these situations that incorporates one or two constants determined experimentally for each analyte/internal standard combination and an adjustable calibration parameter. This fitting provides more accurate quantitation in MS-based assays where contributions from analyte to stable labeled internal standard signal exist. It can also correct for the reverse situation where an analyte is present in the internal standard as an impurity. The practical utility of this approach is described, and by using experimental data, the approach is compared to alternative fits.
稳定同位素标记的内标在质谱（MS）中提供准确定量具有重要作用。一个隐含的假设是，内标和目标分析物的信号之间没有“串扰”。然而，在某些情况下，分析物的天然同位素确实会对内标信号做出贡献。对于富含同位素的化合物（如含有硫、氯或溴的化合物、较高分子量的化合物以及在高分析物/内标浓度比下的化合物），这种现象更为明显。这可能会导致非线性校准行为，从而对定量结果产生偏差。在这里，我们提出在这些情况下使用非线性但更准确的数据拟合，为每个分析物/内标组合确定一个或两个实验确定的常数和一个可调校准参数。这种拟合可在存在分析物对稳定标记内标信号贡献的基于 MS 的测定中提供更准确的定量。它还可以纠正内标中存在分析物杂质的相反情况。描述了这种方法的实际用途，并通过使用实验数据，将该方法与替代拟合方法进行了比较。
