Lipidomics data require consideration of ions with near-identical masses, which comprises amongst others the Type-II isotopic overlap. This overlap occurs in series of lipid species differing only by number of double bonds (DB) mainly due to the natural abundance of ¹³C-atoms. High-resolution mass spectrometry, such as Fourier-Transform mass spectrometry (FTMS), is capable of resolving Type-II overlap depending on mass resolving power. In this work, we evaluated FTMS quantification accuracy of lipid species affected by Type-II overlap. Spike experiments with lipid species pairs of various lipid classes were analyzed by flow-injection-analysis (FIA)-FTMS. Accuracy of quantification was evaluated without and with Type-II correction (using relative isotope abundance) as well as utilizing the first isotopic peak (M+1). Isobaric peaks, which were sufficiently resolved, were most accurate without Type-II correction. In cases of partially resolved peaks, we observed peak interference causing distortions in mass and intensity, which is a well described phenomenon in FTMS. Concentrations of respective species were more accurate when calculated from M+1. Moreover, some minor species, affected by considerable Type-II overlap, could only be quantified by M+1. Unexpectedly, even completely unresolved peaks were substantially overcorrected by Type-II correction due to peak interference. The described method was validated including intra and inter-day precisions for human serum and fibroblast samples. Taken together, our results show that accurate quantification of lipid species by FTMS requires resolution-depended data analysis.

中文翻译：

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傅里叶变换质谱中受同量异位重叠影响的脂质种类的准确定量。

脂质组学数据需要考虑具有几乎相同质量的离子，其中包括 II 型同位素重叠。这种重叠发生在一系列仅双键 (DB) 数量不同的脂质种类中，这主要是由于^{13 个}C 原子的自然丰度所致。高分辨率质谱，例如傅里叶变换质谱 (FTMS)，能够根据质量分辨能力解决 II 型重叠。在这项工作中，我们评估了受 II 型重叠影响的脂质种类的 FTMS 定量准确性。通过流动注射分析 (FIA)-FTMS 分析了不同脂质类别的脂质物种对的加标实验。在不使用和使用 II 型校正（使用相对同位素丰度）以及利用第一个同位素峰 (M+1) 的情况下评估定量的准确性。充分解析的同量异位峰在没有 II 型校正的情况下是最准确的。在部分解析峰的情况下，我们观察到峰干扰导致质量和强度失真，这是 FTMS 中很好描述的现象。从 M+1 计算时，各个物种的浓度更加准确。此外，一些较小的物种，受到相当大的II型重叠的影响，只能通过M+1来量化。出乎意料的是，由于峰干扰，即使是完全未解析的峰也会被 II 型校正严重过度校正。所描述的方法经过验证，包括人血清和成纤维细胞样品的日内和日间精度。总而言之，我们的结果表明，通过 FTMS 准确定量脂质种类需要依赖于分辨率的数据分析。