QUANTITATIVE-ANALYSIS OF LOW-MOLECULAR-WEIGHT COMPOUNDS OF BIOLOGICAL INTEREST BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION

Internal standards were used to demonstrate that matrix-assisted laser desorption/ionization (MALDI) mass spectrometry can be applied to the quantitative analysis of low molecular weight polar compounds. Three examples were tested: a standard curve for 3,4-dihydroxyphenylalanine (DOPA) was prepared using a stable isotope analogue (i.e., [C-13(6)]DOPA) as an internal standard; [H-2(16)]-acetylcholine was employed as an internal standard for the quantification of acetylcholine; and in the final example, the peptide Ac-Ser-Ile-Arg-His-Tyr-NH2 was used as an internal standard for the quantification of the peptide H-Ser-Ala-Leu-Arg-His-Tyr-NH2. In each instance, straight line fits (r2 > 0.95) demonstrate that MALDI is a viable approach for the quantitative analysis of low molecular weight analytes.