Preparation of Homogeneous Solid Samples for Reproducible and Quantitative MALDI

Preparing samples with good homogeneity is one of the requirements for generating reproducible matrix-assisted 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 -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.