IMPROVEMENT OF SIGNAL REPRODUCIBILITY AND MATRIX/COMATRIX EFFECTS IN MALDI ANALYSIS

The main problems associated with matrix-assisted laser desorption/ionization (MALDI) quantitative analysis are poor scot-to-shot reproducibility, crystal inhomogeneity, signal degradation, and data acquisition system nonlinearity, These problems are addressed in this paper, The instrumental setup was modified to obtain required linearity and measurement accuracy over a dynamic range of 10(3). To homogenize the crystal structure,ferulic acid (FA) and fucose were used to form a binary matrix, The optimum molar ratio was analyte/FA/fucose = 1:5000:5000, 2,5-Dihydroxybenzoic acid (DHB), fucose, and 5-methoxysalicylic acid (MSA) were used to form a multicomponent matrix; the optimum analyte/DHB/fucose/MSA molar ratio was 1:10(4):(3 x 10(3)-1 x 10(4)):500, Another preparation method that worked particularly well with DHB involved accelerated drying in high-now nitrogen at room temperature, Application of these methods gave significant enhancement in spectral reproducibility, signal intensity, and mass resolution. A relative standard deviation of 6-12% was obtained with a mass resolution of 350-400 (fwhm) at approximate to 6000 Da. The FA and DHB comatrices were compared with various matrices and a standard preparation of DHB and FA. The comatrices showed a ca, 50% increase in signal intensity, a 300% decrease in relative standard deviation, and a 30-40% higher resolution. In addition, the use of comatrices resulted in less signal degradation as a function of the number of laser shots in the same location. The visual and spectral differences in crystal structure between FA and DHB both with and without comatrices are illustrated. The laser power was optimized to avoid high abundance of cluster ions and to increase molecular signal, Based on the data presented, an analytical protocol for MALDI quantitative analysis was developed.