Improvement in the detection of low concentration protein digests on a MALDI TOF/TOF workstation by reducing alpha-cyano-4-hydroxycinnamic acid adduct ions.

Alpha-cyano-4-hydroxycinnamic acid (alpha-CHCA) as a matrix facilitates the ionization of proteins and peptides in a matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer. The matrix itself also ionizes and so do its sodium and potassium adducts. Matrix clusters and metal ion adducts interfere with peptide ionization and peptide mass spectrum interpretation. These matrix adducts are significantly reduced with addition of ammonium monobasic phosphate or ammonium dibasic citrate to the matrix and sample deposited onto the MALDI target. The reduction of matrix adducts results in the increase of peptide intensity and signal-to-noise ratio as well as in improvement of peptide ionization for samples deposited onto the target at levels of 10 fmol or below. These improvements were particularly significant in the detection of peptides at amol levels when reduced amounts of matrix were also used.