A novel detection method for quaternization of amino acid and peptide was reported. In this method Ag 2CO 3 was employed instead of KHCO 3 to catalyze the occurrence of quaternization reaction. The absence of metal ions in the reaction system enabled us to in situ detect the quaternizing products by using electrospray ionization mass spectrometry(ESI-MS). We analyzed quaternizing products of six amino acids and two peptides in situ, and obtained the ratio of major product to by-product, which suggests the new method possesses prominent advantages over the old one. This method could offer a potential chance to combine quaternization with mass spectrometry which is helpful for the future use of quaternization reaction in quantitative proteomics.
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 adducts. Matrix clusters and adducts interfere with peptide ionization and peptide mass spectrum interpretation, especially at low sample concentrations and within m/z 500-1 000 range. These matrix adducts, especially within m/z 500-1 000, are significantly reduced with addition of ammonium citrate, ammonium sulfate, ammonium benzoate, ammonium bicarbonate, ammonium citrate and potassium dihydrogen phosphate to the matrix and the samples were deposited onto the MALDI target. The reduction of matrix adducts improves peptide ionization and signal-to-noise ratio, which enhances the reliability of database searching.
An auxiliary electrode was used to improve the electric field distribution between the nESI emitter and the MS sampler. The results show an improvement in the ratio of signal to noise for nanoliter electrospray using a home-made nanoliter electrospray tip, evaluated by spraying a 25 pg/μL reserpine solution. In addition, the average ratios of signal to noise of reserpine acquired within 30 min at different concentrations were compared with those obtained with an auxiliary electrode. The experimental results suggest that an auxiliary electrode could dramatically improve the ratio of signal to noise and provide confident trends for future application of auxiliary electrode in nanoliter electrospray.
