Generation of Highly Charged Peptide and Protein Ions by Atmospheric Pressure Matrix-Assisted Infrared Laser Desorption/Ionization Ion Trap Mass Spectrometry

Abstract

We show that highly charged ions can be generated if a pulsed infrared laser and a glycerol matrix are employed for atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry with a quadrupole ion trap. Already for small peptides like bradykinin, doubly protonated ions form the most abundant analyte signal in the mass spectra. The center of the charge-state distribution increases with the size of the analyte. For example, insulin is detected with a most abundant ion signal corresponding to a charge state of four, whereas for cytochrome c, the 10 times protonated ion species produces the most intense signal. Myoglobin is observed with up to 13 charges. The high m/z ratios allow us to use the Paul trap for the detection of MALDI-generated protein ions that are, owing to their high molecular weight, not amenable in their singly protonated charge state. Formation of multiple charges critically depends on the addition of diluted acid to the analyte-matrix solution. Tandem mass spectra generated by collision-induced dissociation of doubly charged peptides are also presented. The findings allow speculations about the involvement of electrospray ionization processes in these MALDI experiments.

Development and Characterization of an Ionization Technique for Analysis of Biological Macromolecules: Liquid Matrix-Assisted Laser Desorption Electrospray Ionization

“…13 Recently, liquid sample analysis was demonstrated by ultraviolet laser desorption from matrix containing liquid samples followed by post-ionization by ESI using ELDI 11 and using infrared laser desorption from liquid samples without ESI post-ionization using AP-IR-MALDI. 15 In a similar method described herein, a variation of our MALDESI source, liquid matrix-assisted laser desorption electrospray ionization (liq-MALDESI) utilizes an ultraviolet laser directed onto the surface of an analyte containing liquid droplet biased at a high potential. In this method, the charged droplet acts as a macroscopic ESI droplet, from which offspring droplets are laser desorbed which then undergo an ESI-like desorption and ionization process generating multiply-charged ions.…”

Covalent attachment and dissociative loss of sinapinic acid to/from cysteine-containing proteins from bacterial cell lysates analyzed by MALDI-TOF-TOF mass spectrometry

“…MALDI-MS is now used in the analysis of synthetic polymers [3], in bottom-up [4] and top-down [5] proteomics, in microorganism identification [6,7], in differential tissue imaging (healthy versus diseased) or in mapping drug distribution [8], in DNA oligonucleotide analysis [9], etc. Although MALDI has been coupled with a number of different mass analyzers (ion traps [10], FT-ICR [11], hybrid instruments [12][13][14], the most significant combination has been with time-of-flight (TOF) instruments [15], and more recently with tandem TOF instruments (TOF-TOF) [16,17].…”

Continuous Flow Atmospheric Pressure Laser Desorption/Ionization Using a 6–7-µm-Band Mid-Infrared Tunable Laser for Biomolecular Mass Spectrometry

“…In previous research using the AP-IR-MALDI of peptides and proteins [27], multiply-charged ions were produced instead of singly-charged ions, which are chiefly observed in UV-MALDI. In addition, it was recently reported that liquid AP-UV-MALDI enables stable ion yields of multiply-charged ions of peptides and proteins [28].…”