Journal
JOURNAL OF MASS SPECTROMETRY
Volume 51, Issue 10, Pages 938-946Publisher
WILEY-BLACKWELL
DOI: 10.1002/jms.3805
Keywords
nifedipine; matrix reagent; MALDI; polyphenols; photobase generator
Funding
- Tojuro Iijima Foundation for Food Science and Technology
- Research Grant for Young Investigators of Faculty of Agriculture, Kyushu University
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Matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) is widely used for the detection and analysis of ionizable compounds. However, the method has less potential for the analysis of neutral compounds, such as polyphenols, owing to their lack of favorable proton-attachment or -removal groups. In this study, we reported for the first time that nifedipine (2,6-dimethyl-3,5-dicarbomethoxy-4-(2-nitrophenyl)-1,4-dihydropyridine), which is a strong photobase generator commonly used in polymerization, can abstract protons from neutral compounds in negative mode-MALDI experiments. When nifedipine (5mg/ml) was used as a matrix reagent, the limit of detection (LOD) for epigallocatechin-3-O-gallate (EGCG) was determined to be 100fmol/spot, which constitutes >50-fold improvement compared to the LOD obtained when trans-3-indoleacrylic acid, a matrix reagent previously reported for polyphenol detection, was used. Of the dihydropyridines investigated, only nifedipine facilitated the detection of EGCG, suggesting that the nitrosophenyl pyridine derivative of nifedipine formed by photoreduction under laser irradiation at 355nm plays a crucial role in detecting polyphenols in negative mode. Reduced MS detection of 5-O-methylnaringenin indicated that nifedipine may preferably remove a proton from the 5-position OH group in the A ring of the flavonoid skeleton. The significant MS detection by nifedipine was extensively observed for polyphenols including flavones, flavonones, chalcones, stilbenoids and phenolic acids. In conclusion, nifedipine can act as a novel matrix for improving polyphenol detection by MALDI-MS in negative mode. Copyright (c) 2016 John Wiley & Sons, Ltd.
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