Department of Chemistry, Box 351700, University of Washington, Seattle, WA 98195, USA.
Talanta. 2010 Apr 15;81(1-2):120-8. doi: 10.1016/j.talanta.2009.11.046. Epub 2009 Dec 4.
A critical comparison of methods for correcting severely retention time shifted gas chromatography-mass spectrometry (GC-MS) data is presented. The method reported herein is an adaptation to the piecewise alignment algorithm to quickly align severely shifted one-dimensional (1D) total ion current (TIC) data, then applying these shifts to broadly align all mass channels throughout the separation, referred to as a TIC shift function (SF). The maximum shift varied from (-) 5s in the beginning of the chromatographic separation to (+) 20s toward the end of the separation, equivalent to a maximum shift of over 5 peak widths. Implementing the TIC shift function (TIC SF) prior to Fisher Ratio (F-Ratio) feature selection and then principal component analysis (PCA) was found to be a viable approach to classify complex chromatograms, that in this study were obtained from GC-MS separations of three gasoline samples serving as complex test mixtures, referred to as types C, M and S. The reported alignment algorithm via the TIC SF approach corrects for large dynamic shifting in the data as well as subtle peak-to-peak shifts. The benefits of the overall TIC SF alignment and feature selection approach were quantified using the degree-of-class separation (DCS) metric of the PCA scores plots using the type C and M samples, since they were the most similar, and thus the most challenging samples to properly classify. The DCS values showed an increase from an initial value of essentially zero for the unaligned GC-TIC data to a value of 7.9 following alignment; however, the DCS was unchanged by feature selection using F-Ratios for the GC-TIC data. The full mass spectral data provided an increase to a final DCS of 13.7 after alignment and two-dimensional (2D) F-Ratio feature selection.
本文提出了一种对严重保留时间偏移气相色谱-质谱（GC-MS）数据的校正方法的比较。本文所报道的方法是对分段对齐算法的一种改进，用于快速对齐严重偏移的一维（1D）总离子流（TIC）数据，然后将这些偏移应用于广泛对齐整个分离过程中的所有质量通道，称为 TIC 偏移函数（SF）。最大偏移量从色谱分离开始时的（-）5s 变化到分离结束时的（+）20s，相当于超过 5 个峰宽的最大偏移量。在进行 Fisher 比（F-Ratio）特征选择和主成分分析（PCA）之前，实施 TIC 偏移函数（TIC SF）被发现是一种可行的方法，可用于对复杂的色谱图进行分类，在本研究中，这些色谱图是通过 GC-MS 分离三种汽油样品获得的，作为复杂的测试混合物，分别称为 C、M 和 S 型。通过 TIC SF 方法报告的对齐算法可校正数据中的大动态偏移以及细微的峰对峰偏移。通过使用 PCA 得分图的 DCS 度量对 C 型和 M 型样品进行量化，评估了整体 TIC SF 对齐和特征选择方法的优势，因为它们是最相似的，因此是最难正确分类的样品。DCS 值从未经对齐的 GC-TIC 数据的初始值基本上为零增加到对齐后的 7.9；然而，通过使用 F-Ratios 对 GC-TIC 数据进行特征选择，DCS 没有变化。在对齐和二维（2D）F-Ratio 特征选择后，完整的质谱数据提供了最终 DCS 值增加到 13.7。
