title: Preparation of Homogeneous MALDI Samples for Quantitative Applications.
abstract: This protocol demonstrates a simple sample preparation to reduce spatial heterogeneity in ion signals during matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The heterogeneity of ion signals is a severe problem in MALDI, which results in poor data reproducibility and makes MALDI unsuitable for quantitative analysis. By regulating sample plate temperature during sample preparation, thermal-induced hydrodynamic flows inside droplets of sample solution are able to reduce the heterogeneity problem. A room-temperature sample preparation chamber equipped with a temperature-regulated copper base block that holds MALDI sample plates facilitates precise control of the sample drying condition. After drying of sample droplets, the temperature of sample plates is returned to room temperature and removed from the chamber for subsequent mass spectrometric analysis. The areas of samples are examined with MALDI-imaging mass spectrometry to obtain the spatial distribution of all components in the sample. In comparison with the conventional dried-droplet method that prepares samples under ambient conditions without temperature control, the samples prepared with the method demonstrated herein show significantly better spatial distribution and signal intensity. According to observations using carbohydrate and peptide samples, decreasing substrate temperature while maintaining the surroundings at ambient temperature during the drying process can effectively reduce the heterogeneity of ion signals. This method is generally applicable to various combinations of samples and matrices.
authors.affiliation: Genomic Research Center, Academia Sinica; Department of Chemistry, National Taiwan University.
authors.forename: Yu-Meng
authors.initials: YM
authors.lastname: Ou
authors.affiliation: Genomic Research Center, Academia Sinica; Department of Chemical Engineering and Biotechnology, National Taipei University of Technology.
authors.forename: Chien-Wei
authors.initials: CW
authors.lastname: Tsao
authors.affiliation: Genomic Research Center, Academia Sinica.
authors.forename: Yin-Hung
authors.initials: YH
authors.lastname: Lai
authors.affiliation: Genomic Research Center, Academia Sinica.
authors.forename: Hsun
authors.initials: H
authors.lastname: Lee
authors.affiliation: Department of Chemistry, National Taiwan University.
authors.forename: Huan-Tsung
authors.initials: HT
authors.lastname: Chang
authors.affiliation: Genomic Research Center, Academia Sinica; wer@gate.sinica.edu.tw.
authors.forename: Yi-Sheng
authors.initials: YS
authors.lastname: Wang
mesh_terms: D002241:Carbohydrates; D010455:Peptides; D015203:Reproducibility of Results; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D002241:Carbohydrates; D010455:Peptides