title: Impulse-driven heated-droplet deposition interface for capillary and microbore LC-MALDI MS and MS/MS.
abstract: An automated off-line liquid chromatography-matrix-assisted laser desorption ionization (LC-MALDI) interface capable of coupling both capillary and microbore LC separations with MALDI mass spectrometry (MS) and tandem mass spectrometry (MS/MS) has been developed. The interface is a combination of two concepts: analyte concentration from heated hanging droplets and impulse-driven droplet deposition of LC fractions onto a MALDI sample plate. At room temperature the interface allows the coupling of capillary LC separations (i.e., flow rate of <5 microL/min) with MALDI MS. With heating, it can be used to combine microbore LC operated at a relatively high flow rate of up to 50 microL/min with MALDI MS. The collected fractions can be analyzed by MALDI MS and MS/MS instruments, such as time-of-flight (TOF) and quadrupole-TOF MS. Performance of the interface was examined using several peptide and protein standards. It was shown that, using MALDI-TOF MS, [GLU1]-fibrinopeptide B could be detected with a total injection amount of 5 fmol to microbore LC. Chromatographic performance was also monitored. A peak width of 12 s at half-height for [GLU1]-fibrinopeptide B showed no evidence of band broadening due to the interface. The ability of the interface to mitigate ion suppression was studied using a mixture of 100 fmol of [GLU1]-fibrinopeptide B and 10 pmol of cytochrome c tryptic digest. Although fully suppressed under direct MALDI conditions, LC-MALDI analysis was able to detect the 100 fmol peptide with 10 s fraction collection. Finally, the ability to inject relatively large sample amounts to improve detectability of low-abundance peptides was illustrated in the analysis of phosphopeptides from alpha-casein tryptic digests. A digest loaded on column to 2.4 microg and analyzed by LC-MALDI MS/MS resulted in 82% sequence coverage and detection of all nine phosphoserine residues. It is concluded that, being able to handle both high- and low-flow LC separations, the impulse-driven heated-droplet interface provides the flexibility to carry out MALDI analysis of peptides and proteins depending on the information sought after, analysis speed, and sample size.
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
authors.forename: J Bryce
authors.initials: JB
authors.lastname: Young
authors.forename: Liang
authors.initials: L
authors.lastname: Li
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000378:metabolism; D002853:Chromatography, Liquid / Q000295:instrumentation / Q000379:methods*; D045304:Cytochromes c / Q000032:analysis* / Q000378:metabolism; D005345:Fibrinopeptide B / Q000032:analysis* / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D008969:Molecular Sequence Data; D010748:Phosphopeptides / Q000032:analysis* / Q000378:metabolism; D010768:Phosphoserine / Q000032:analysis* / Q000378:metabolism; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000295:instrumentation / Q000379:methods*; D014357:Trypsin / Q000378:metabolism
chemical_list: D002364:Caseins; D010748:Phosphopeptides; D010768:Phosphoserine; D005345:Fibrinopeptide B; D045304:Cytochromes c; D014357:Trypsin