title: Improving the Sensitivity of Matrix-Assisted Ionization (MAI) Mass Spectrometry Using Ammonium Salts.
abstract: In matrix-assisted ionization (MAI), analyte incorporated in a small molecule matrix is introduced into an aperture linking atmospheric pressure with the vacuum of a mass spectrometer. Gas-phase analyte ions are spontaneously produced without use of a laser or high voltage. Here we investigate analyte and background ion abundances upon addition of ammonium salts to various MAI matrix/analyte solutions. Regardless of the ammonium salt or matrix used, chemical background ions are suppressed and/or analyte ion abundance improved for basic small molecules, peptides, and proteins. Background ion abundances increase with increasing inlet temperature, but are suppressed with addition of any of a variety of ammonium salts without much effect on the total ion abundances of the analyte ions. However, at lower inlet temperature using the matrices 2-bromo-2-nitropropane-1,3-diol, 1,2-dicyanobenzene, and 3-nitrobenzonitrile (3-NBN), analyte ion abundance increases and any chemical background decreases upon addition of ammonium salt. The improvement in sensitivity using 3-NBN with ammonium salt allows full acquisition mass spectra consuming as little as 1 fmol of ubiquitin. More complete peptide coverage for 100 fmol of a BSA tryptic digest, and increased sensitivity of drugs spiked in urine and saliva were observed after ammonium salt addition to the 3-NBN matrix.
authors.affiliation: University of the Sciences, Philadelphia, PA, 19104, USA.
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Chubatyi
authors.affiliation: University of the Sciences, Philadelphia, PA, 19104, USA. c.mcewen@usciences.edu.
authors.forename: Charles N
authors.initials: CN
authors.lastname: McEwen
keywords: 1,2-Dicyanobenzene; 2,5-Dihydroxyacetophenone; 3-Nitrobenzonitrile; Ammonium salt; Background ions; Bronopol; Drugs; MAI; Matrix-assisted ionization; Peptides; Proteins; Sensitivity