Temperature dependencies of negative ions formation by capture of low-energy electrons for some typical MALDI matrices

Abstract

Some typical matrix assisted laser desorption/ionization (MALDI) matrices (gentisic, nicotinic, succinic, sinapinic, caffeic acids, urea and 6-aza-2-thiothymine) have been investigated by electron capture negative ions mass spectrometry (ECNI-MS) with purpose to find such decay channels of target molecule that may be important for processes of desorption and “primary” ions formation in MALDI. The temperature dependencies of the process of dissociative electron attachment to molecules of MALDI matrices were obtained for six different temperatures in the range of 70–300 °C. Also the relative dissociative attachment peak cross-sections for molecules under investigation were measured and ionization and desorption abilities of the MALDI matrices were calculated. The general conclusions are (1) a capture of low energy electrons by molecules of MALDI matrices leads to an appearance of anions CN − and [M−H] − that may take part in formation of analyte anions, (2) gas molecules in MALDI (CO 2, H 2, CH 3CN and so on) are formed by a capture of low energy electrons that may leads to desorption of the analyte in according to CO 2-MALDI model, (3) the dissociative attachment cross-section for molecules of matrix determines the ability to form both anions and gas bubbles as well as indicates how well a matrix preserves positive analyte ions from neutralization by the free low energy electrons.