Quantitative matrix-assisted laser desorption/ionization mass spectrometry

Abstract

This review summarizes the essential characteristics of matrix-assisted laser desorption/ionization (MALDI) timeof-flight mass spectrometry (TOF MS), especially as they relate to its applications in quantitative analysis. Approaches to quantification by MALDI-TOF MS are presented and published applications are critically reviewed.Keywords: quantification; quantitative analysis; MALDI; mass spectrometry; biomarkers OVERVIEWSince its inception in 1987 [1], matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (TOF MS) has been applied for the analysis of a wide range of biomolecules. Initial applications were almost exclusively for the qualitative analysis of biopolymers because MALDI-TOF MS provided a fast and accurate approach to molecular mass and purity information: Is my material the right mass and is it free from contaminants? Because of the speed of analysis, ease of use, relative low equipment cost, ease of data interpretation and limited potential for cross-contamination between samples/users, MALDI-TOF MS systems were considered walk-up instruments where investigators run their own samples and determine, within minutes, whether they were on the right track with their work.There were, however, two specific areas of application where MALDI-TOF MS was initially viewed as impractical: i.e. the analysis of low mass analytes and quantitative applications. Low mass analysis is complicated by the vast molar excess of the matrix that can swamp any analyte-specific signal in the low m/z region of the spectrum. Quantitative analysis was viewed as implausible because crystallization does not yield a uniform distribution of the analyte and matrix across the target surface and this gives rise to regions where the analyte signal is especially intense relative to other locations on the target surface. MALDI MS was therefore viewed as inherently irreproducible because, for a given amount of analyte loaded onto the target, the measured ion intensity varies.Subsequently, it has been shown that both these perceived limitations can be overcome and quantification can be routine, both for low and high mass analytes. Now, an extensive list of published applications includes quantification of amino acids, lipids, natural products, drugs, polymers, herbicides, metabolites, toxins, oligonucleotides, carbohydrates, peptides and proteins. (Selected applications from these areas are discussed at the end of this review.) Here, we focus on the quantitative applications of MALDI and illustrate applications relating to both low and high-molecular mass analytes. We also discuss the strategies for applying MALDI to relative and absolute quantification. While MALDI is most commonly combined with TOF analysers, other analyser options are possible and applications employing these are also presented. Our aim is not to provide an exhaustive catalogue of published applications, but to discuss the general principles and to illustrate the

Specificity of O -glycosylation in enhancing the stability and cellulose binding affinity of Family 1 carbohydrate-binding modules

“…Quantitative MALDI-TOF MS. For absolute CBM quantitation, internal reference standard solutions of each CBM glycoform were prepared per experiment by serial dilution (10 μL per concentration) (58). To all sample aliquots, 150 pmol CBM internal standard peptide (Δm/z ≥ 162 Da) in H 2 O:MeCN: AcOH (1:1:3.3% 3 μL) was added; 0.5 μL each sample was spotted directly on a 100-well MALDI target plate with 1.126 μL α-cyano-4-hydroxycinnamic acid matrix (6.2 mg/mL) in MeOH:MeCN:H 2 O (36:56:8) and allowed to air dry (∼5 min).…”

Quantitative Analysis of Polymer Additives with MALDI-TOF MS Using an Internal Standard Approach

“…MALDI-TOF MS has a long tradition in the analysis of polymeric materials but the studies concerning polymer additives are quite scarce [11][12][13][14]. Quantitative applications of MALDI are also very limited and it is well known that in conventional solvent-based dried droplet sample preparation, the sample and matrix are not uniformly distributed over a spot [15].…”

Investigations of Some Liquid Matrixes for Analyte Quantification by MALDI

“…In spite of its popularity, MALDI is not regarded as a useful quantitative tool, mainly because the ion signals produced by MALDI display shot-to-shot variation at spots, spot-tospot variation on samples, and sample-to-sample variation [1,6]. In the MALDI of a solid sample composed of an analyte-matrix mixture, sample inhomogeneity is one of the factors responsible for such variations [7][8][9].…”