Pizzala Hélène, Claeys-Bruno Magalie, Monnier Valérie, Sergent Michelle, Charles Laurence
Aix Marseille Université, CNRS, UMR 7273, Institut de Chimie Radicalaire, Marseille, France.
Aix Marseille Université, UMR CNRS IRD 7263, Institut Méditerranéen de Biodiversité Marine et Continentale, Marseille, France.
Front Chem. 2021 Sep 9;9:740495. doi: 10.3389/fchem.2021.740495. eCollection 2021.
Matrix-assisted laser/desorption ionization (MALDI) has become a very popular ionization technique for mass spectrometry of synthetic polymers because it allows high throughput analysis of low amounts of sample while avoiding the complexity introduced by extensive multiple charging of electrospray ionization. Yet, fundamental mechanisms underlying this ionization process are not fully understood, so development of sample preparation methods remains empirical. Reliable prediction for the optimal matrix/analyte/salt system is indeed still not possible for homopolymers and it becomes even more challenging in the case of amphiphilic block copolymers where conditions dictated by one block are not compatible with MALDI requirements of the second block. In order to perform MALDI of copolymers composed of poly (ethylene oxide) (PEO) and polystyrene (PS) blocks, it was postulated here that experimental conditions suitable for both species would also be successful for PEO--PS. Accordingly, designs of experiments based on Quantitative Structure Activity Relationship (QSAR) analysis were first implemented, studying the influence of 19 matrices and 26 salts on the laser fluence requested for successful MALDI. This analysis first permitted to highlight correlations between the investigated 10 descriptors of matrices and salts and the analytical response, and then to construct models that permits reliable predictions of matrix/salt couples to be used for one or the other homopolymer. Selected couples were then used for MALDI of a PEO--PS copolymer but no general trend was observed: experimental conditions expected to work often failed whereas ionic adducts of the copolymer were clearly detected with some matrix/salt systems that were shown to badly perform for constituting homopolymers. Overall, this rules out the working assumption stating that the MALDI behavior of chains composed of PEO and PS segments should combine the behavior of the two polymeric species. Yet, although requiring a dedicated design of experiments, MALDI of the amphiphilic PEO--PS copolymer was achieved for the first time.
基质辅助激光解吸电离（MALDI）已成为合成聚合物质谱分析中一种非常流行的电离技术，因为它允许对少量样品进行高通量分析，同时避免了电喷雾电离中大量多重电荷引入的复杂性。然而，这种电离过程的基本机制尚未完全理解，因此样品制备方法的开发仍然是经验性的。对于均聚物，确实仍然无法可靠预测最佳的基质/分析物/盐体系，而对于两亲性嵌段共聚物，情况变得更加具有挑战性，因为一个嵌段所要求的条件与第二个嵌段的MALDI要求不兼容。为了进行由聚环氧乙烷（PEO）和聚苯乙烯（PS）嵌段组成的共聚物的MALDI分析，本文假设适用于两种物质的实验条件对PEO-PS也会成功。因此，首先实施了基于定量构效关系（QSAR）分析的实验设计，研究了19种基质和26种盐对成功进行MALDI所需激光能量密度的影响。该分析首先允许突出所研究的基质和盐的10个描述符与分析响应之间的相关性，然后构建模型，该模型允许可靠预测用于一种或另一种均聚物的基质/盐组合。然后将选定的组合用于PEO-PS共聚物的MALDI分析，但未观察到一般趋势：预期有效的实验条件经常失败，而共聚物的离子加合物在一些对构成均聚物表现不佳的基质/盐体系中却能被清楚地检测到。总体而言，这排除了这样一种工作假设，即由PEO和PS链段组成的链的MALDI行为应结合两种聚合物的行为。然而，尽管需要专门的实验设计，但首次实现了两亲性PEO-PS共聚物的MALDI分析。
