Quantitative analysis of peptides using internal standards was carried out with the use of matrix-assisted laser desorption/ionization (MALDI) on a time-of-flight mass spectrometer in a ferulic acid matrix. Spectra were collected and averaged over several areas of the sample surface at constant laser energy, and a defocused beam was used to improve reproducibility. A calibration curve was plotted, showing a correlation coefficient of 0.992 and a relative standard deviation of 1.83%. The accuracy and precision of this technique were sensitive to the crystal structure of the matrix and saturation effects of the instrument's detector.
