Matrices flight mass spectra

Josten, M., Reif, M., Szekat, C., Al-Sabti, N., Roemer, T., Sparbier, K., Kostrzewa, M., Rohde, H Sahl, H.G., and Bierbaum, G. (2013) Analysis of the matrix-assisted laser desorption ionization-time of flight mass spectrum of Staphylococcus aureus identifies mutations that allow differentiation of the main clonal lineages. J. Clin. Microbiol, 51,1809-1817. 

Figure 8 Positive ion matrix-assisted laser desorption (MALDI) time-of-flight mass spectrum of P-cryptoxanthin paknitate isolated from tangerine juice. Post source decay was used to enhance detection of structurally significant fragment ions such as loss of toluene (m/z 698), loss of palmitic acid (m/z 534), and loss of both toluene and palmitic acid (m/z 442). (From Ref. 320.)... 

Finally, Figure 11.21 shows the IR-MALDl time-of-flight mass spectrum of oligomadylic acids generated by limited hydrolysis of poly-U, using an Er YAG laser and succininc acid as the matrix. ... 

Enhanced molecular ion implies reduced matrix interference. An SMB-El mass spectrum usually provides information comparable to field ionisation, but fragmentation can be promoted through increase of the electron energy. For many compounds the sensitivity of HSI can be up to 100 times that of El. Aromatics are ionised with a much greater efficiency than saturated compounds. Supersonic molecular beams are used in mass spectrometry in conjunction with GC-MS [44], LC-MS [45] and laser-induced multiphoton ionisation followed by time-of-flight analysis [46]. 

We have used accurate mass measurements obtained by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) to differentiate and profile saponins from M. truncatula roots. An example is provided (Fig.3.11) showing the MALDI-TOFMS spectra of a solid-phase extract of M truncatula root tissue. In this spectrum, we can identify multiple saponins. 

For the quick characterisation of polydisperse surfactants with relative high molecular weight distributions matrix-assisted laser desorption/ionisation (MALDI)-time of flight (TOF)-MS represented an interesting alternative since low mass compounds did not interfere with the mass spectrometric detection of the compounds of interest. For example, the mass spectrum of C12-APG (Fig. 2.7.8) exhibited equally spaced signals with Am/z 162 corresponding to sodiated adduct ions of the mono- (m/z 371) to heptaglucosides (m/z 1343) [7]. 

There are at least three possibile ways in which the inhibitor can bind to the active site (1) formation of a sulfide bond to a cysteine residue, with elimination of hydrogen bromide [Eq. (10)], (2) formation of a thiol ester bond with a cysteine residue at the active site [Eq. (11)], and (3) formation of a salt between the carboxyl group of the inhibitor and some basic side chain of the enzyme [Eq. (12)]. To distinguish between these three possibilities, the mass numbers of the enzyme and enzyme-inhibitor complex were measured with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI). The mass number of the native AMDase was observed as 24766, which is in good agreement with the calculated value, 24734. An aqueous solution of a-bromo-phenylacetic acid was added to the enzyme solution, and the mass spectrum of the complex was measured after 10 minutes. The peak is observed at mass number 24967. If the inhibitor and the enzyme bind to form a sulfide with elimination of HBr, the mass number should be 24868, which is smaller by about one... 

Figure 3-11 Matrix-assisted laser desorption / ionization time-of-flight (MALDI-TOF) mass spectrum of bovine erythrocyte Cu-Zn superoxide dismutase averaged over ten shots with background smoothing. One-half pi of solution containing 10 pmol of the enzyme in 5 mM ammonium bicarbonate was mixed with 0.5 pi of 50 mM a-cyanohydroxycinnamic acid dissolved in 30% (v / v) of acetoni-trile-0.1% (v / v) of trifluoroacetic acid. The mixture was dried at 37° C before analysis. The spectrum shows a dimer of molecular mass of 31,388 Da, singly charged and doubly charged molecular ions at 15,716, and 7870 Da, respectively. The unidentified ion at mass 8095.6 may represent an adduct of the matrix with the doubly charged molecular ion. Courtesy of Louisa Tabatabai.

Fig. 1. Matrix-assisted laser desorption/ionization (MALDI)-time-of-flight (TOF) spectrum of a trypsin-digested one-dimensional gel band. Peaks are labeled with their monoisotopic masses. Note that these are not the masses of the peptides, but of the peptide (pseudo)molecular ions. In MALDI spectra, peptide molecular ions arise predominantly through the addition of a proton to the peptide, giving a mass increase of 1.007 Da. The molecular ions are usually denoted as MH+ or [M+H]+.

Since the signals are very short, simultaneous detection analysers or time-of-flight analysers are required. The probability of obtaining a useful mass spectrum depends critically on the specific physical proprieties of the analyte (e.g. photoabsorption, volatility, etc.). Furthermore, the produced ions are almost always fragmentation products of the original molecule if its mass is above approximately 500 Da. This situation changed dramatically with the development of matrix-assisted laser desorption ionization (MALDI) [17,18]. 

ESMS was perfonned with a Fisons VG Quattro outfitted with a Hsons Electrospray Source. Samples were dissolved in 1.0 mL of 50% methanol-1% acetic acid, then diluted 1 10 with 50% acetonitrile-1.0 mM anmumium acetate to give 25 pmol/pL. A 10 pL aliquot of each sample was injected into a 10 pL/min stream of 50% acetonitrile-1.0 mM ammonium acetate. Data was processed using Fisons MassLynx Software. MALDI-MS was performed with a Vestec Benchtop lit linear dme-of-flight mass spectrometer, opmted in the linear mode with an N2 laser (337 nm). Samples were dissolved in 1.0 mL of 25% acetonitrile-0.1% TFA, then diluted 3 100 to give 5-10 pmol/pL. A 0.5 pL aliquot of each sample solution was added to 0.5 pL of matrix [a-cyano-4-hydroxycinnamic aci saturated solution in 50% acetonitrile-2% TFA]. Samples were dried at ambient temperature and pressure. Each spectrum was the sum of ion intensity from 10-50 larer pulses. Tlie mass axis was calibrated externally. 

Since its discovery in 1987, matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) has become a common technique in the mass spectral analysis of biopolymers (1, 2). Its ease of operation, theoretically unlimited mass range, and ability to acquire an entire mass spectrum without scanning make the technique an excellent method to analyze high mass biopolymers. Combining such advantages with the capability of analyzing sub-picomole quantities of biopolymers makes MALDI-TOF MS extremely useful for routine mass analysis. 

Figure 6.31. Positive-ion MALDI-TOF reflectron mode mass spectrum of grape seed extract (matrix 2,5-dihydroxybenzoic acid). (Reprinted from Journal of Agricultural and Food Chemistry, 48, Yang and Chien, Characterization of grape procyanidins using high-performance liquid chromatography/mass spectrometry and matrix-assisted laser desorption time-of-flight mass spectrometry, p. 3993, Copyright 2000, with permission from American Chemical Society.)...

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