This review summarizes the essential characteristics of matrix-assisted laser desorption/ionization (MALDI) time-of-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.
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"To date, MALDI-TOF MS mostly has been utilized qualitatively to identify MC variants in cyanobacterial colonies and surface water blooms (Erhard et al., 1997; Ferranti et al., 2011; Welker et al., 2002), and its use for MC quantification is rather recent (Howard and Boyer, 2007; Puddick et al., 2011). Quantitative detection by MALDI-TOF based on peak response has poor reproducibility, mainly due to spotto-spot variability in crystal formation (Duncan et al., 2008; Szajli et al., 2008). However, this can be overcome using an Fig. 1. "
[Show abstract][Hide abstract] ABSTRACT: The freshwater cyanotoxins, microcystins (MCs), pose a global public health threat as potent hepatotoxins in cyanobacterial blooms; their persistence in drinking and recreational water has been associated with potential chronic effects in addition to acute intoxications. Rapid and accurate detection of the over 80 structural congeners is challenged by the rigorous and time consuming clean up required to overcome interference found in raw water samples. MALDI-MS has shown promise for rapid quantification of individual congeners in raw water samples, with very low operative cost, but so far limited sensitivity and lack of available and versatile internal standards (ISs) has limited its use. Two easily synthesized S-hydroxyethyl–Cys(7)-MC-LR and –RR ISs were used to generate linear standard curves in a reflectron MALDI instrument, reproducible across several orders of magnitude for MC –LR, -RR and –YR. Minimum quantification limits in direct water samples with no clean up or concentration step involved were consistently below 7 μg/L, with recoveries from spiked samples between 80 and 119%. This method improves sensitivity by 30 fold over previous reports of quantitative MALDI-TOF applications to MCs and provides a salient option for rapid throughput analysis for multiple MC congeners in untreated raw surface water blooms as a means to identify source public health threats and target intervention strategies within a watershed. As demonstrated by analysis of a set of samples from Uruguay, utilizing the reaction of different MC congeners with alternate sulfhydryl compounds, the m/z of the IS can be customized to avoid overlap with interfering compounds in local surface water samples.
"Application of MALDI to analyte quantification while possible requires careful attention to matrix/analyte sample preparation, a detailed understanding of the crystallization process with regard to the analyte, and careful many spot analyses (to find the sample signal average which often varies by orders of magnitude as a function of laser position). (Duncan, Roder et al. 2011) This desire to find a discriminative, sensitive and more easily quantifiable alternative to MALDI has lead us to re-examine another molecular desorption method that doesn't require the use of a matrix. The first observation of this method of molecular desorption (later called Laser Induced Acoustic Desorption, LIAD) belongs (to the best of our knowledge) to B. "
"Secondly, MALDI‐TOF is known to exhibit a substantial variability in ionisation due to heterogeneous co‐crystallisation of analyte and matrix.  To reduce this effect a large number of shots on different places of the spot are accumulated in one measurement. Thirdly, if the wrong isotope is selected by the automatic or manual peak‐picking procedure, attribution of this component by database search may fail. "
[Show abstract][Hide abstract] ABSTRACT: Proteomics techniques are increasingly applied for the identification of protein binders in historical paints. The complex nature of paint samples, with different kinds of pigments mixed into, and degradation by long term exposure to light, humidity and temperature variations, requires solid analysis and interpretation methods. In this study matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectra of tryptic-digested paint replicas are subjected to principal component analysis (PCA) and soft independent modelling of class analogy (SIMCA) in order to distinguish proteinaceous binders based on animal glues, egg white, egg yolk and milk casein from each other. The most meaningful peptide peaks for a given protein class will be determined, and if possible, annotated with their corresponding amino acid sequence. The methodology was subsequently applied on egg temperas, as well as on animal glues from different species. In the latter small differences in the MALDI-TOF mass spectra can allow the determination of a mammal or sturgeon origin of the glue. Finally, paint samples from the 16(th) century altarpiece of St Margaret of Antioch (Mlynica, Slovakia) were analysed. Several expected peaks are either present in lower abundance or completely missing in these natural aged paints, due to degradation of the paints. In spite of this mammalian glue was identified in the St Margaret samples.
Rapid Communications in Mass Spectrometry 06/2011; 25(11):1631-40. DOI:10.1002/rcm.5027 · 2.25 Impact Factor