Small organic matrixes are still the most commonly used ones in matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) because of their advantages of high sensitivity, convenience, and cost-effectiveness. However, due to the matrix interference in the low mass region, the direct analysis of low molecular weight amines in complex surroundings with conventional organic matrixes remains a challenge. Here, a new Brønsted-Lowry acid compound 2,3,4,5-tetrakis(3',4'-dihydroxylphenyl)thiophene (DHPT) was designed, synthesized, and applied as a matrix for analysis of low molecular weight amines by MALDI-TOF MS. DHPT displays good selectivity in the analysis of amines without matrix-related interference and the low picomole/femtomole limit-of-detection was obtained in positive ion mode. With DHPT, the metabolites including creatinine, glycine, alloxan, allantoin, and 3-hydroxyhippuric acid in human urine were directly analyzed by MALDI-TOF MS. The identity of these metabolites was confirmed by tandem mass spectrometry. Furthermore, the urine creatinine was quantitatively determined using isotope-labeled internal standard. This DHPT-assisted LDI MS method provides a general approach for both qualitative and quantitative analysis of low molecular weight amines.
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Chen et al. (2012) studied this question.
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