Matrix-assisted effect

The matrix-assisted effect refers to enhanced ionization efficiency of molecules that is observed when they are desorbed with another molecule in the mixture that acts as a primary chromophore as compared to their direct laser desorption ionization efficiency as a pure compound. Thus, in a matrix-assisted laser desorption/ionization (MALDI) experiment, one must always add the matrix to enhance the ionization efficiency of the analytes. Good matrices generally have high absorption coefficients for the laser wavelength of interest and are usually acidic to be able to donate a proton (positive ion mode) in the plume. It is also often desirable for a matrix to form large, flat crystals upon evaporation of solvent. This latter requirement is particularly true for time-of-flight mass analyzers because the resolving power is dependent on the flatness of the sample surface. 

Most ion sources produce singly charged ions, i.e., z = I and the ranges shown here apply to such ions. Matrix assisted methods may produce ions with r > 1. When = 1, m/z. = m, viz., mass can be measured directly. An ES ion source produces ions with z > 1 and this effectively extends the mass ranges that can be examined. For example, with z = 1 and m = 10,000, the m/z value is 10,000 and this would be beyond tbe capabilities of a quadrupole instrument. 

Due to the high mass, low volatility, and thermal instability of chlorophylls and derivatives, molecular weight determination by electron impact (El) MS is not recommended. Desorption-ionization MS techniques such as chemical ionization, secondary ion MS, fast-atom bombardment (FAB), field, plasma- and matrix-assisted laser desorption have been very effective for molecular ion detection in the characterization of tetrapyrroles. These techniques do not require sample vaporization prior to ionization and they are effective tools for allomerization studies. 

Domin, M. A. Welham, K. J. Ashton, D. S. The effect of solvent and matrix combinations on the analysis of bacteria by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Rapid Comm. Mass Spectrom. 1999,13,222-226. 

Puretzky, A.A. Geohegan, D.B. Hurst, G.B. Buchanan, M.V. Luk yanchuk, B.S. Imaging of Vapor Plumes Produced by Matrix Assisted Laser Desorption A Plume Sharpening Effect. Phys. Rev. Lett. 1999,83,444-447. 

A toluene solution of polymer 15 was added to an aqueous mixture of peptides. After effective equUibration, the heterogeneous mixture was allowed to separate and the organic layer was analyzed by matrix assisted laser desorption ionization mass spectrometry analysis. Because the pH of the aqueous solution was 7.1, the peptides with pis above 7.1 were extracted and the peptides with pis below 7.1... 

ToF mass spectrometers as dynamic instruments gained popularity with the introduction of matrix assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) as effective pulsed ion sources for the soft ionization of large biomolecules (up to 10s dalton) due to their high ion transmission.38 ToF mass spectrometers, quadrupole analyzers and/or magnetic sector fields can be combined in tandem mass spectrometers (MS/MS) for the analysis of organic compounds. 

Luxembourg S, McDonnell L, Duursma M, Guo X, Heeren R (2003) Effect of local matrix crystal variations in matrix-assisted ionization techniques for mass spectrometry. Anal Chem 75 2333-2341. doi 10.1021/ac026434p... 

Knochenmuss, R., Dubois, F., Dale, M.J. and Zenobi, R. (1996) The matrix suppression effect and ionization mechanisms in matrix-assisted laser desorption/ionization. Rapid Conunun. Mass Spectram. 10, 871-877. 

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