Alkali Halides as Matrices for the Detection of Saccharides and PEG600 by Electrospray Droplet Impact/Secondary Ion...

Saccharides are often analyzed by matrix-assisted laser desorption/ionization mass spectrometry and electrospray ionization mass spectrometry. In this study, electrospray droplet impact/secondary ion mass spectrometry (EDI/SIMS) was applied to the analysis of saccharides and PEG600 with and without using matrices of alkali halides AX (A: alkali, X: halide).

1 μL aqueous solutions of 2 × 10^-3 mol·L^-1 analytes M (glucose, sucrose, raffinose or PEG 600) and 2 × 10^-3 mol·L^-1 alkali halide mixture of [Li, Na, K, Rb, Cs]X for X = F, Cl, Br, and I were deposited on the substrate. After drying in vacuum, EDI mass spectra of analytes were measured with and without the AX matrices. The charged water droplets were generated by electrospraying 10^-2 mol⋅L^-1 aqueous solution of CF₃COOH.

By the addition of four sets of AX matrices, relative intensities of [M + H]⁺ and [M + A]⁺ in the positive mode, and [M - H]^-, [M + CF₃COO]^-, and [M + X]^- in the negative mode showed characteristic behavior depending on the combination of A and X. The matrices which gave the strongest ion signals were LiI for [M + Li]⁺, and LiF for [saccharide + CF₃COO]^- and [saccharide - H]^-. CsF gave a relatively strong ion signal for [PEG600 + Cs]⁺.

The high detection sensitivities obtained by LiI for [M + Li]⁺ may be due to the largest bond energies of Li⁺⋅⋅⋅M and the weak lattice energy of LiI. LiF gave good results for the detection of [saccharide - H]^- and [saccharide + CF₃COO]^- due to the segregation of analytes on the LiF matrix.