Preparation of homogeneous solid samples for reproducible and quantitative MALDI

Abstract

Preparing samples with good homogeneity is one of the requirements for generating reproducible matrixassisted laser desorption ionization (MALDI) spectra and for using them in analyte quantification. Thus far, we have not been successful in producing homogeneous solid samples from popular matrixes apart from α-cyano-4-hydroxycinnamic acid (CHCA). In this work, we demonstrate the production of an outwardly homogeneous solid sample by loading a methanol solution of a matrix into a shallow reservoir on a coated MALDI sample plate and then vacuum-drying it. Out of ten popular matrixes tested, seven yielded homogeneous samples. These were 9-aminoacridine, 6-aza-2-thiothymine, CHCA, 2,5-dihydroxybenzoic acid, ferulic acid, sinapinic acid, and 2,4,6-trihydroxyacetophenone. For MALDI with these matrixes, linear calibration curves covering wide dynamic ranges were acquired. Performances of these matrixes in various aspects of analyte quantification have been investigated.