UV-MALDI

Figure 9.8 UV MALDI-MS spectrum of a mixture of polymer additives. After Jackson et al. [57]. Reprinted from A.T. Jackson et al., Rapid Communications in Mass Spectrometry, 10, 1449-1458 (1996). Copyright 1996 John Wiley Sons, Ltd. Reproduced with permission...

Kirpekar, F. Berkenkamp, S. Hillenkamp, F. Detection of double-stranded DNA by IR- and UV-MALDI mass spectrometry. Anal. Chem. 1999, 71,2334-2339. 

MALDI, the molecules must possess a suitable chromophore because energy absorption is based on the strong absorption, and thus the resulting electronic excitation of the matrices. Therefore, the structure of UV-MALDI matrices is based on some aromatic core suitably functionalized to achieve the desired properties. 

Bogan MJ, Agnes GR. 2004. WaU-less sample preparation of micron-sized sample spots for femtomole detection limits of proteins from liquid based UV-MALDI matrices. J Am Soc Mass Spectrom 15 486. 

The matrix in MALDI MS fulfils several essential functions. First, the matrix absorbs the laser light via electronic (UV-MALDI) or vibrational (IR-MALDl) excitation and transfers this energy smoothly onto the analyte. Due to the high molar excess of the matrix over the analyte, the intermolecular interactions of analyte molecules are reduced, thus facilitating transfer into the gas phase. Last but not least, matrix-analyte interactions play an active role both in the ionization of the analyte as well as in its desorption [34]. 

MALDI spectra obtained with UV or IR lasers are essentially identical for most analysed samples. There are only very small differences. Indeed, when an IR laser is used, only less fragmentation is observed, indicating that the IR-MALDI is somewhat cooler. On the other hand, IR-MALDI induces a larger depth of vaporization per shot that leads to shorter lifetime of the sample. Compared with UV-MALDI, a somewhat lower sensitivity is observed. 

Common UV-MALDI matrices are listed in Table 1.2 with the class of compounds with which they are used. The matrices used with IR lasers, such as urea, caboxylic acids, alcohols and even water, are often closer to the natural solutions than the highly aromatic UV-MALDI matrices. In addition, there are many more potential matrices for IR-MALDI owing to the strong absorption of molecular compounds at IR wavelengths, even if the correlation between ion formation and matrix absorption in IR-MALDI is not clear [36],... 

M. Ciancia, Y. Sato, H. Nonami, A. S. Cerezo, R. Erra-Balsells, and M. C. Matulewicz, Autohydrolysis of a partially cyclized mu/nu-carrageenan and structural elucidation of the oligosaccharides by chemical analysis, NMR spectroscopy and UV-MALDI mass spectrometry, ARKIVOC, Xii (2005) 319-331. 

R. Erra-Balsells and H. Nonami, UV-MALDI-TOF MS analysis of carbohydrates. Reviewing comparative studies performed using nor-harmane and classical UV-MALDI matrices, Environ. Control Biol., 46 (2008) 65-90. 

The synthesis and characterisation of photocleavable peptide-DNA conjugates have been studied. The peptide portions have been used as mass tags, released during ionisation by UV-MALDI to identify unique DNA sequences. The conjugates were evaluated as hybridisation probes, and the photocleavable peptide had no effect on the thermal stability of DNA duplexes. 

IR-MALDI spectra show a lower mass resolution compared to that obtained by UV-MALDI. However, the IR-MALDl technique may be used for the analysis of halogenated polymers, which often show extensive fragmentation in UV-MALDl. ... 

Mass spectra of desalted Photofrin, in the positive ionization modes, obtained by (A) FAB/MS, (B) UV-MALDI/MS, (C) IR-MALDI/MS, (D) ESI/MS (nozzle-skimmer voltage 100 V). (E) Mass spectrum of per-methyl ester of Photofrin, in the positive ionization mode, obtained by LD/... 

R. Knochenmuss, Photoionization pathways and free electrons in UV-MALDI, Anal. Chem. 76, 3179-3184 (2004). 

One important feature is the way in which the matrix and analyte interact in the MALDI sample. In a typical UV-MALDI dried dropleC sample preparation, small volumes of an about M solution of the analyte and a near-saturated (ca. 

Equation (1.2) is at the core of the MALDI process. If a matrix is chosen with a sufficiently high absorption coefficient a, a relatively low fluence Ho suffices for achieving the critical energy density necessary to initiahze ablation and ionization of a top layer of the sample. Values for Hq of 50-500 J m are representative for most UV-MALDI applications. 

Figure 1.4 UV-MALDI mass spectrum of myoglobin. Matrix DHBs (2,5-dihydroxybenzoic acid [2,5-DHB] plus 2-hydroxy-5-methoxysalicylic acid [MSA] 9 1 [w/w]). Wavelength, 337nm mass analyzer, reflectron TOF.

IR-MALDl enables comparably soft desorption processes and is, therefore, more appropriate for noncovalent complex analysis than UV-MALDl. This is reflected by the successful detection of intact double-stranded DNA as well as enzyme-oligosaccharide complexes in combination with glycerol as matrix which were not detectable or underwent significant fragmentation when UV-MALDI was employed [126, 127]. 

UV-MALDI MALDI with ultraviolet laser wavelengths... 

Ion yields in UV-MALDI mass spectrometry as a function of excitation laser wavelength and optical and physico-chemical properties of classical and novel halogen-substituted MALDI matrices. Anal. Chem., 84, 6567-5575. 

Towers, M.W., Mckendrick, J.E., and Cramer, R. (2010) Introduction of 4-chloro-a-cyanocinnamic acid liquid matrices for high sensitivity UV-MALDI MS./. Proteome Res., 9, 1931-1940. 

Figure 5.3 Sections of UV MALDI mass spectra of 70, 80, and 90mer DNA strands desorbed from 3-3-hydroxypicolinic acid as a matrix and analyzed in an orthogonal TOF. The MALDI ions first pass a quadmpole before they enter a reflectron TOF section. Independent of the ion source used and the mass of the molecules, the O-TOF analyzer provides a constant instmmental resolution throughout the whole mass range rather than a mass-dependent resolution as in axial MALDI-TOF. The indicated full width at...

If some of the physico-chemical properties of nucleic acids pose many challenges to their analysis by MALDI-TOF, then some others afford intrinsic advantages as compared to proteins /peptides and other biomolecules. For instance, their primary structure is much more homogeneous than that of proteins, consisting of only four relatively similar building blocks. Because of this structural simplicity and homogeneity, relative and even absolute (with an internal standard) quantification can be readily accomplished and this constitutes the basis for a number of assays (as discussed below). The remainder of this chapter is mostly devoted to descriptions of the different assays that have been developed for the analysis of NAs, under the somewhat restrictive boundary conditions of UV-MALDI-TOF-MS. 

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