Electrospray sample preparation for improved quantitation in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Abstract

The goal of this work is the development of a rapid and objective matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) method for the quantitation of peptides and proteins in human plasma suitable for use in the Good Laboratory Practices (GLP) environment, where the analytical method, validation and pharmacokinetic parameters derived from concentration data will be scrutinized by global regulatory agencies. Electrospray deposition has traditionally been used to prepare thin, uniform samples for a number of techniques, including Cf-252 plasma desorption and secondary ion mass spectrometry. Here the electrospray process of sample application is used to reduce the segregation of analyte from matrix during the sample drying step. The small droplets formed during the electrospray process are found to significantly improve the homogeneity of the sample surface prepared. Experiments comparing the traditional air dried and electrosprayed methods of sample preparation show that the increase in sample homogeneity from electrosprayed samples decreases both the within-sample spot and between-sample spot variability, resulting in a decrease in percent coefficient of variation (%CV) for the recorded MALDI mass spectra. The increase in sample homogeneity permits a more objective use of MALDI-TOFMS as a quantitative analytical method and has led to the development of an assay for the determination of desamino-[8-D-arginine] vasopressin (DDAVP) using arginine vasopressin (AVP) as internal standard in human plasma. The range of quantitation observed (2.0-10 micrograms/mL) is of limited value for bioanalytical application; however, the analysis of neat standards shows lower quantitation limits are easily achieved.

Analysis of Amphiphilic Lipids and Hydrophobic Proteins Using Nonresonant Femtosecond Laser Vaporization with Electrospray Post-Ionization

“…The variance is due to vaporization of an inconsistent amount of sample as a function of position on the stainless steel slide. A similar situation was observed for quantitative MALDI analysis prior to electrospray deposition of sample [26]. Nonetheless, despite the differences in size and polarity of the lipids applied to the surface, both can be detected and discriminated as a function of concentration.…”

Gold-Enhanced Biomolecular Surface Imaging of Cells and Tissue by SIMS and MALDI Mass Spectrometry

“…ME-SIMS matrix was applied using electrospray deposition as described previously. 44,45 Briefly, a 15 mg/mL solution of DHB in 50% MeOH/0.1% TFA was pumped for 10 min at a flow rate of 12 µL/h from a stainless steel capillary (o.d. 220 µm, i.d.…”

Evaluation of a novel approach for peptide sequencing: Laser-induced acoustic desorption combined with P(OCH3)2+ chemical ionization and collision-activated dissociation in a fourier transform ion cyclotron resonance mass spectrometer

“…Slightly different LIAD probes were used in the Extrel [13a, 13b] and Nicolet instruments [13c, 13d]. About 100 nmol of a peptide sample was deposited on the surface of a about 12.7 m thick titanium foil by using electrospray [17,18]. A high-intensity laser pulse from a Nd:YAG laser (3 ns pulsewidth, 532 nm wavelength, fluence of 1 ϫ 10 9 W cm Ϫ2 at the metal surface) was used to initiate acoustic waves at the back side of the metal foil.…”