The methyl substitution along and among the polymer chains of methyl cellulose (MC) is commonly analyzed by ESI-MS after perdeuteromethylation of the free-OH groups and partial hydrolysis to cello-oligosaccharides (COS). This method requires a correct quantification of the molar ratios of the constituents belonging to a particular degree of polymerization (DP). However, isotopic effects are most pronounced for H/D since their mass difference is 100%. Therefore, we investigated whether more precise and accurate results could be obtained for the methyl distribution of MC by MS of ¹³CH₃ instead of CD₃-etherified O-Me-COS. Internal isotope labeling with ¹³CH₃ makes the COS of each DP chemically and physically much more similar, reducing mass fractionation effects, but at the same time requires more complex isotopic correction for evaluation. Results from syringe pump infusion ESI-TOF-MS with ¹³CH₃ and CD₃ as isotope label were equal. However, in the case of LC-MS with a gradient system, ¹³CH₃ was superior to CD₃. In the case of CD₃, the occurrence of a partial separation of the isotopologs of a particular DP resulted in slight distortion of the methyl distribution since the signal response is significantly dependent on the solvent composition. Isocratic LC levels this problem, but one particular eluent-composition is not sufficient for a series of oligosaccharides with increasing DP due to peak broadening. In summary, ¹³CH₃ is more robust to determine the methyl distribution of MCs. Both syringe pump and gradient-LC-MS measurements are possible, and the more complex isotope correction is not a disadvantage.

Graphical abstract

中文翻译：

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使用质谱法比较 13C 甲基和氘代甲基同位素标记对甲基纤维素模式的定量

在游离羟基全氘甲基化和部分水解为纤维低聚糖 (COS) 后，通常通过 ESI-MS 分析甲基纤维素 (MC) 聚合物链沿线和聚合物链之间的甲基取代。该方法需要正确量化属于特定聚合度 (DP) 的成分的摩尔比。然而，同位素效应对于 H/D 最为明显，因为它们的质量差为 100%。因此，我们研究了通过¹³ CH _{3的 MS 代替 CD 3} -醚化的O -Me-COS是否可以获得更精确和准确的 MC 甲基分布结果。¹³ CH ₃内部同位素标记使每个 DP 的 COS 在化学和物理上更加相似，减少质量分馏效应，但同时需要更复杂的同位素校正来进行评估。以¹³ CH ₃和 CD ₃作为同位素标记的注射泵输注 ESI-TOF-MS 结果相同。然而，在具有梯度系统的LC-MS的情况下，¹³ CH ₃优于CD ₃。_{在 CD 3}的情况下，特定 DP 的同位素部分分离的发生导致甲基分布的轻微失真，因为信号响应显着取决于溶剂组成。等度 LC 解决了这个问题，但是一种特定的洗脱液组成不足以用于一系列由于峰展宽而具有增加的 DP 的寡糖。总之，¹³ CH ₃更稳健地确定MC的甲基分布。注射泵和梯度-LC-MS 测量都是可能的，更复杂的同位素校正不是缺点。

图形概要