Mass Discrimination in High-Mass MALDI-MS

Abstract

In high-mass matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), the accessible m/z range is limited by the detector used. Therefore, special high-mass detectors based on ion conversion dynodes (ICDs) have been developed. Recently, we have found that mass bias may exist when such ICD detectors are used [Weidmann et al., Anal. Chem. 85(6), 3425-3432 (2013)]. In this contribution, the mass-dependent response of an ICD detector was systematically studied, the response factors for proteins with molecular weights from 35.9 to 129.9 kDa were determined, and the reasons for mass bias were identified. Compared with commonly employed microchannel plate detectors, we found that the mass discrimination is less pronounced, although ions with higher masses are weakly favored when using an ICD detector. The relative response was found to depend on the laser power used for MALDI; low-mass ions are discriminated against with higher laser power. The effect of mutual ion suppression in dependence of the proteins used and their molar ratio is shown. Mixtures consisting of protein oligomers that only differ in mass show less mass discrimination than mixtures consisting of different proteins with similar masses. Furthermore, mass discrimination increases for molar ratios far from 1. Finally, we present clear guidelines that help to choose the experimental parameters such that the response measured matches the actual molar fraction as closely as possible.

Do habitat features affect the composition of silk proteins by Namibian arid-adaptedAriadnaspiders (Araneae: Segestriidae)?

“…MALDI-TOF MS proved to be a fast and sensitive technique for the analysis of mixtures consisting of proteins, polypeptides (Domon and Aebersold 2006;Bich & Zenobi 2009;Chen et al 2013;Weidmann et al 2013) or synthetic polymers (Montaudo et al 2002(Montaudo et al , 2006. It is able to calculate the mass of individual molecules in a mixture of homologues, thus permitting the structural identification of single macromolecules.…”

Citric Acid Capped Iron Oxide Nanoparticles as an Effective MALDI Matrix for Polymers

“…Improvements in sample preparation and detector design have enabled analysis of polystyrene or polyphenylene in the megaDa range [56,57], but the successes of high mass MALDI experiments have been limited to a few polymer classes [54][55][56][57].…”

“…As Na + has been reported to assist PDMS ionization in MALDI [62], Na + present in the NPCA matrix is to serve as the cation source to form [C 3 H 9 Si(OSiC 2 H 6 ) n CH 3 + Na] + . The broad peak width typical for high mass MALDI [54,55] precludes repeating unit analysis of polymers. However, the MALDI spectra of a low mass PDMS (silicone oil) acquired with NPCA-NaOH clearly demonstrated the expected [C 3 H 9 Si(OSiC 2 H 6 ) n CH 3 + Na]…”

Detection of Large Ions in Time-of-Flight Mass Spectrometry: Effects of Ion Mass and Acceleration Voltage on Microchannel Plate Detector Response

“…In the latter case, which has the advantage of greatly decreased spectral complexity and correspondingly increased ion intensity, the ions must be analyzed by time-of-flight mass spectrometry (TOF-MS), as this is the only mass analyzer able to accommodate the high m/z range of such singly charged proteins. Although this is an attractive approach to the analysis of proteoform mixtures, in fact relatively little work has been reported of this type, largely due to limitations of existing MS instrumentation [10, 11]. One of the significant instrumentation challenges to consider is the efficiency of detection of the large, slow-moving protein ions produced in TOF-MS.…”