ARTICLE pubs.acs.org/ac
Matrix Interference-Free Method for the Analysis of Small Molecules by Using Negative Ion Laser Desorption/Ionization on Graphene Flakes Minghua Lu,† Yongquan Lai,† Guonan Chen,‡ and Zongwei Cai*,† † ‡
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong SAR, China Ministry of Education Key Laboratory of Analysis and Detection for Food Safety, Fuzhou University, Fuzhou 350002, Fujian, China
bS Supporting Information ABSTRACT: This work presents a new approach for the analysis of small molecules with direct negative ion laser desorption/ionization (LDI) on graphene flakes. A series of matrix interference-free mass spectra were obtained for the analysis of a wide range of small molecules including peptides, amino acids, fatty acids, as well as nucleosides and nucleotides. The mixture of analytes and graphene flakes suspension were directly pipetted onto a sample plate for LDI-time-of-flight mass spectrometry (TOFMS) analysis. Deprotonated monomeric species [MH] ions were homogeneously obtained on uniform graphene flakes film when negative ion mode was applied. In positive ion mode, the analytes were detected in form of multiple adduct ions such as sodium adduct [MþNa]þ, potassium adduct [MþK]þ, double sodium adduct [Mþ2NaH]þ, double potassium adduct [Mþ2KH]þ, as well as sodium and potassium mixed adduct [MþNaþKH]þ. Better sensitivity and reproducibility were achieved in negative ion mode compared to positive ion mode. It is believed that the new method of matrix interference-free negative ion LDI on graphene flakes may be expanded for LDI-MS analysis of various small molecules.
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atrix-assisted laser desorption/ionization (MALDI), a soft ionization technique proposed by Tanaka1 and Karas2 in late 1980s, has developed into an indispensable tool in the analysis of large molecules such as peptides/proteins,36 oligonucleotides,79 oligosaccharides,1012 and synthetic polymers.1315 Due to the interferences of matrix background ions in low molecule weight region (
