Department of Chemistry & Biochemistry, The University of Alabama, Tuscaloosa, Alabama 35487, United States.
Department of Chemical Sciences, Indian Institute of Science Education and Research Mohali, Punjab 140306, India.
Anal Chem. 2024 Jan 30;96(4):1668-1677. doi: 10.1021/acs.analchem.3c04684. Epub 2024 Jan 16.
A new matrix framework is presented in this study for the improved ionization efficiency of complex mixtures by matrix-assisted laser desorption ionization (MALDI) mass spectrometry/imaging. Five nitro indole (NI) derivatives [3-methyl-4-nitro-1H-indole (3,4-MNI), 3-methyl-6-nitro-1H-indole (3,6-MNI), 2,3-dimethyl-4-nitro-1H-indole (2,3,4-DMNI), 2,3-dimethyl-6-nitro-1H-indole (2,3,6-DMNI), and 4-nitro-1H-indole (4-NI)] were synthesized and shown to produce both positive and negative ions with a broad class of analytes as MALDI matrices. NI matrices were compared to several common matrices, such as 2,5-dihydroxybenzoic acid (DHB), alpha-cyano-4-hydroxylcinnamic acid (CHCA), sinapinic acid (SA), 1,5-diaminonaphthelene (1,5-DAN), and 9-aminoacridine (9-AA), for the analysis of lipid, peptide, protein, glycan, and perfluorooctanesulfonic acid (PFOS) compounds. 3,4-MNI demonstrated the best performance among the NI matrices. This matrix resulted in reduced ion suppression and better detection sensitivity for complex mixtures, for example, egg lipids/milk proteins/PFOS in tap water, while 2,3,6-DMNI was the best matrix for blueberry tissue imaging. Several important aspects of this work are reported: (1) dual-polarity ion production with NI matrices and complex mixtures; (2) quantitative analysis of PFOS with a LOQ of 0.5 ppb in tap water and 0.05 ppb in MQ water (without solid phase extraction enrichment), with accuracy and precision within 5%; (3) MALDI imaging with 2,3,6-DMNI as a matrix for plant metabolite/lipid identification with ionization enhancement in the negative ion mode / 600-900 region; and (4) development of a thin film deposition under/above tissue method for MALDI imaging with a vacuum sublimation matrix on a high-vacuum MALDI instrument.
本研究提出了一种新的基质框架，用于通过基质辅助激光解吸电离（MALDI）质谱/成像提高复杂混合物的离化效率。合成了五种硝基吲哚（NI）衍生物[3-甲基-4-硝基-1H-吲哚（3,4-MNI）、3-甲基-6-硝基-1H-吲哚（3,6-MNI）、2,3-二甲基-4-硝基-1H-吲哚（2,3,4-DMNI）、2,3-二甲基-6-硝基-1H-吲哚（2,3,6-DMNI）和 4-硝基-1H-吲哚（4-NI）]，并证明它们可以作为 MALDI 基质与广泛类别的分析物一起产生正离子和负离子。NI 基质与几种常见的基质（如 2,5-二羟基苯甲酸（DHB）、α-氰基-4-羟基肉桂酸（CHCA）、香豆素酸（SA）、1,5-二氨基萘（1,5-DAN）和 9-氨基吖啶（9-AA））进行了比较，用于分析脂质、肽、蛋白质、聚糖和全氟辛烷磺酸（PFOS）化合物。3,4-MNI 在 NI 基质中表现出最佳性能。这种基质可减少复杂混合物的离子抑制作用并提高检测灵敏度，例如，自来水中的鸡蛋脂质/牛奶蛋白/PFOS，而 2,3,6-DMNI 是蓝莓组织成像的最佳基质。本工作报道了几个重要方面：（1）NI 基质与复杂混合物的双极性离子产生；（2）在自来水中以 0.5 ppb 的 LOQ 和 MQ 水中（无需固相萃取富集）以 0.05 ppb 的 LOQ 对 PFOS 进行定量分析，准确度和精密度在 5%以内；（3）用 2,3,6-DMNI 作为基质进行 MALDI 成像，在负离子模式/600-900 区域增强离子化，用于植物代谢物/脂质鉴定；（4）在高真空 MALDI 仪器上用真空升华基质开发一种用于 MALDI 成像的组织上下薄膜沉积方法。
