The quantitative aspects of matrix-assisted laser desorption/ionization time-of-flight mass spectrometr

The use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOFMS) has largely been restricted to the area of qualitative analysis. We believe one of the major obstacles hindering the use of MALDI for quantitative applications lies in the method of sample preparation. In the research described herein, we present to the reader the aspects of conventional dried drop methods of sample preparation that lead to non-quantitative MALDI, or at best, highly subjective means of quantitation. We further suggest that electrospray sample preparation is a means by which samples may be prepared for more objective quantitative analysis using MALDI TOFMS. Experimental data is provided to support this notion. Additionally, reference calibration curves in neat solutions and from extracts of complex biological matrices are provided. Observations regarding the optimization of the electrospray preparation of samples for quantitative MALDI are also provided. The ability to perform quantitative analysis using electrospray sample preparation for MALDI TOFMS has also allowed us to initiate investigations into the relationships between peptide structure and MALDI ion signal intensities. These preliminary investigations have lead us to hypothesize that there is a positive relationship between the hydrophilicity of a peptide, the number of basic amino acid residues (including amino-terminal groups) contained within the peptide and the MALDI ion signal intensity of that peptide when the sample is prepared using electrospray sample preparation in 2,5-dihydroxybenzoic acid. Specific examples are presented along with the results of a multiple linear regression analysis summarizing the results from our initial investigations. An experimental outline of proposed future work is also presented.