Ultraviolet MALDI

Gluckmann, M. Karas, M. The Initial Ion Velocity and Its Dependence on Matrix, Analyte and Preparation Method in Ultraviolet MALDI. J. Mass Spectrom. 1999, 34,461 All. 

LUdemann, H.-C. Redmond, R. W. Hillenkamp, F. Singlet-singlet annihilation in ultraviolet MALDI studied by fluorescence spectroscopy. Rapid Comm. Mass Spectrom. 2002, 16, 1287-1294. 

Kristyan, S. Bencsura, A. Vertes, A. Modeling the cluster formation during infrared and ultraviolet MALDI of oligonucleotides in succinic acid matrix with molecular mechanics. Theor. Chem. Acc. 2002, 107, 319-325. 

If no references for the degradation products or impurities are available in the laboratory, the sample should be exposed to stress conditions such as heat (50-80 °C), ultraviolet light (2000 lux), acid and base (0.1-1 M HC1 and NaOH), and oxidant (3% H2O2). After incubation in the allotted time, the purity and identity of the analyte peak/spot should be proved by using DAD or MS detection (for LC), MS (for GC), or in situ UV-Vis measurement using a densitometry or TLC-MALDI MS (for TLC). 

FIGURE 15.2 Common protein ionization methods used for MS-based proteomics. Two common ionization technologies are currently available for protein analysis. Top ESI volatilizes and ionizes peptides and proteins in solution. Bottom MALDI uses analytes that are co-crystallized in a matrix composed of organic acid on a solid support. A pulse of ultraviolet laser evaporates the matrix and analyte into gas phase, resulting in generation of single charge ions. 

Both LDI and MALDI make use of the absorption of laser light by a solid sample layer. The energy uptake upon laser irradiation then causes evaporation and ionization of the sample. Wavelengths ranging from ultraviolet (UV) to infrared (IR) have been employed, e.g., nitrogen lasers (337 nm), excimer lasers (193, 248, 308 and 351 nm), Q-switched, frequency-tripled and quadrupled Nd Yag lasers (355 and 266 nm, respectively), [24] Er Yag lasers (2.94 pm) [24,25] and TEA-CO2 lasers (10.6 pm). [16,26]... 

Nordhoff, E. Ingendoh, A. Cramer, R. Overberg, A. Stahl, B. Karas, M. Hillenkamp, F. Crain, P.F. MALDI-MS of Nucleic Acids With Wavelengths in the Ultraviolet and Infrared. Rapid Commun. Mass Spectrom. 1992, 6, 771-776. 

Figure 6 MALDI-TOF distribution of PMAA chains as a function of molecular weight for the degradation products of a disk of poly(MSA) polymerized with 100 mW/cm ultraviolet light.

Mark-Honwink eqnation Relates limiting viscosity number (LVN) to molecular weight LVN = KM . matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) MS in which the sample is placed in a matrix that contains a strong ultraviolet (LTV) absorber chosen to match the UV absorption of the laser, which allows the molecules to become volatilized with minimal fragmentation. 

Major methods for introducing proteins and other macromolecules into mass spectrometers are electrospray and matrix-assisted laser desorption/ionization (MALDI).18-27 Most often, MALDI is used with a time-of-flight mass spectrometer, which can measure mlz up to 106. Typically, 1 p,L of a 10 jxM solution of analyte is mixed with 1 p,L of a 1-100 mM solution of an ultraviolet-absorbing compound such as 2,5-dihydroxybenzoic acid (the matrix) directly on a probe that fits into the source of the spectrometer. Evaporation of the liquid leaves an intimate mixture of fine crystals of matrix plus analyte. 

In the MALDI technique a pulsed laser beam strikes a solid sample and heats, vaporizes, and ionizes compounds with little decomposition.201-209 Proteins or other biopolymers are mixed with a "matrix" Fiat absorbs the heat of Fie laser beam. The protein sample together with Fie matrix is dried. Most proteins form crystals and Fie laser beam is directed toward individual protein crystals or aggregates. Various materials are used for the matrix. Compounds as simple as glycerol, succinic acid, or urea can be used with an infrared laser. For proteins an ultraviolet nitrogen laser tuned to 337 nm is usually employed with an ultraviolet light-absorbing matrix such as hydroxy-benzoic acid, 2,5-dihydroxybenzoic acid, a-hydroxy-... 

Today, MALDI ion mobility MS instruments have longer drift cells and use both ultraviolet (UV) and infrared (IR) laser ionization. In addition, the longer drift cells have nonlinear electric fields, which help to focus the ions into the center of the tube and increase the transmission efficiency of the ion, reducing both resolving power and cross-section accuracy. MALDI ion mobility MS has been used for the analysis of very complex biological samples. Figure 9.5 is a typical MALDI ion mobility MS... 

Information about the degradation pathways occurring in polyolefins exposed to vacuum-ultraviolet radiation (VUV) were obtained by MALDI-TOF analysis of oligomers formed by VUV photolysis of linear C36-alkane. ° Both molar masses and end-groups of degradation product were studied. 

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