Improvement of signal reproducibility and matrix/comatrix effects in MALDI analysis

Gusev, Arkady I.; Wilkinson, William B.; Proctor, Andrew; Hercules, David M.

doi:10.1021/ac00102a003

Cited by 236 publications

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“…Lately MALDI-TOF MS has become a popular method for quantitative analysis of biomolecules (oligonucleotides, proteins, glycoproteins, etc.) originating from various sample types (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) or even for imaging tissue sections (13)(14)(15)(16)(17)(18)(23)(24)(25)(26). At the same time, several studies discuss the non-quantitative nature of MALDI-TOF MS (7, 8, 13, 19, 22, 26 -30).…”

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confidence: 99%

Investigating the Quantitative Nature of MALDI-TOF MS

Szaéjli

Feheér

Medzihradszky

2008

Molecular & Cellular Proteomics

138

116

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MALDI-TOF MS has been applied by several groups to relative quantitative measurements. At the same time, the non-quantitative character of this method has been widely reported. We conducted experiments to test the reliability of this technique for quantitation using the statistical method of inverse confidence limit calculation for the first time in this context. The relationship between relative intensities of known amounts of standard peptides and their concentration ratios was investigated. We found that the concentration ratios determined by relative intensity measurements were highly inaccurate and strongly influenced by the molecular milieu of the sample analyzed. Thus, we emphasize the necessity of using the sample itself for calibration. We also performed experiments using an isotope-labeled derivative of the analyte as an internal standard for calibration line generation. As expected, the use of such standard led to a dramatic increase in precision and a less pronounced improvement in accuracy. We recommend performing a similar statistical analysis as a demonstration of reliability for every system where MALDI-TOF MS is used for quantitative measurements. Molecular & Cellular Proteomics 7: 2410 -2418, 2008.MALDI-TOF MS is a widely used analytical technique because of its excellent sensitivity, relatively high speed, and simplicity. As a consequence of producing mostly singly charged ions (1, 2) MALDI is especially suitable for mixture analysis. It is commonly used in proteomic studies (3) frequently without any prefractionation (4) as well as in the analysis of other biomolecules. Lately MALDI-TOF MS has become a popular method for quantitative analysis of biomolecules (oligonucleotides, proteins, glycoproteins, etc.) originating from various sample types (5-22) or even for imaging tissue sections (13)(14)(15)(16)(17)(18)(23)(24)(25)(26). At the same time, several studies discuss the non-quantitative nature of MALDI-TOF MS (7, 8, 13, 19, 22, 26 -30). The main problem of MALDI is its poor reproducibility (sample to sample and shot to shot), which makes most quantitative measurements quite difficult at best (19,27,31). This is especially true for complex samples. The presence of so-called hot spots or sweet spots is the main cause of the poor reproducibility and is therefore a factor strongly increasing measurement times and complicating automated measurements. Furthermore this phenomenon is one of the major factors hampering the use of MALDI MS for spatially resolved imaging (27). The reasons for sweet spot formation are not completely understood. It could be caused by variation in the amount and the crystallization of the matrix, the latter being a function of local analyte concentration. Dependence of signal intensities on the orientation of the matrix-analyte crystals relative to the spectrometer axis is also possible (27). The extent of hot spot formation depends strongly on the matrix used. For example, preparations with ␣-cyano-4-hydroxycinnamic acid (CHCA) 1 deliver relatively homogenous samples (...

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confidence: 99%

Investigating the Quantitative Nature of MALDI-TOF MS

Szaéjli

Feheér

Medzihradszky

2008

Molecular & Cellular Proteomics

138

116

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“…PEG ions resulting from these distributions should be expected to have the same ionization efficiency and would logically be detected in similar abundance. However, in practice it is difficult to obtain such a result due to the influence of various factors such as matrix concentration, [19 -21] sample morphology, [22] crystallite size, [23] buffer type, [24,25] laser energy, [26] delayed extraction, [27] cation choice, [28,29], and laser fluence [30 -32]. Figure 1 contains MALDI-FTMS spectra obtained for an equimolar mixture of PEG 2K, 4K, 6K, and 8K as a function of relative amount of DHB matrix added.…”

Section: Resultsmentioning

confidence: 99%

Trapping of wide range mass-to-charge ions and dependence on matrix amount in internal source MALDI-FTMS

Jaber

Kaufman

Liyanage

et al. 2005

J. Am. Soc. Mass Spectrom.

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“…However, the biggest problem hindering the integrated intensity is sample inhomogeneity [21], which has long been the significant flaw of the MALDI method. A number of publications have represented the developed methods of decreasing the sample inhomogeneity, e.g., using liquid matrices [22], adding comatrices to form a binary matrix [23], fast evaporation methods with fast evaporating solvents [24], electrospray-based sample dotting method [25], and the solgel-based system [26]. All efforts contribute to the good co-crystallization of the sample.…”

Section: Quantitative Analysismentioning

confidence: 99%

Quantitation of synthetic polymers using an internal standard by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Chen

2005

J. Am. Soc. Mass Spectrom.

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MALDI-TOF MS is utilized to perform quantitative analysis on synthetic polymers. Despite the inherent limitations of MALDI, good quantitative results have been obtained in the three sets of experiments described here. An internal standard with similar molecular properties as the analytes is introduced. Plots of relative integrated intensity ratios as a function of theoretical ratios of stoichiometry are drawn based on the results. In the case of synthetic polymer quantitative analysis, much less effort has been made compared to that of biomolecules. In industry, many polymers are in fact copolymers which take advantage of the properties of two (or more) different classes of monomer. Therefore, the reliable method of measuring the fraction of each component precisely is crucial. However, some indigenous factors of MALDI hinder the quantitative analysis on synthetic polymers. The limitations arise mainly from factors such as the homogeneity of the sample/ matrix/cationization salt spot on the target, which is considered to contribute to the notable instability of signal intensities of analytes in the spectra, the different ionization efficiencies and differences in desorption and detection of the different components which are concerned as the most critical parameter in determining the intensities of peaks in the MALDI spectra, the distribution of molecular weights of oligomer chains and subunits which causes the signal to appear more complicated in the mass spectra of polymer than the single peak in the case of biomolecules, the mass discrimination in the process of ionization, and transmission and detection which makes the intensities of the mass spectra lower both in low mass range and high mass range. Combined, these factors are believed to compromise the precision, reproducibility, and practicality with which quantitative measurement on synthetic polymers can be made.Despite the limitations, some achievement has been accomplished in quantitation of synthetic polymers by MALDI-TOF. For instance, Gardella and his coworkers [15] reported quantitative MALDI-TOF measurements of polydimethylsiloxane of two different molecular weights. Murgasova and Hercules [16] carried out the quantitative characterization of a polystyrene/polymethylstyrene blend using coupled size-exclusion chromatography and MALDI mass spectrometry. Additionally, in our previous study [17], we demonstrated the possibility of quantitative analysis of different components of a polymer sample. Two polyethylene glycols with different end-groups were regarded as different components of a simulated "polymer" through artificial mixture. The relative ion intensity ratios of two components were found to have quantitative relations with their ratios of moles.Although the work above conducted the quantitative

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Improvement of signal reproducibility and matrix/comatrix effects in MALDI analysis

Cited by 236 publications

References 0 publications

Investigating the Quantitative Nature of MALDI-TOF MS

Investigating the Quantitative Nature of MALDI-TOF MS

Trapping of wide range mass-to-charge ions and dependence on matrix amount in internal source MALDI-FTMS

Quantitation of synthetic polymers using an internal standard by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

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