Table 4. Calibration Curve Data. The data show the area ratio of stable isotope-labeled peptide to tryptic peptide (H/L) from reverse calibration curves. In three experiments, duplicate curves were prepared by spiking dilution mixtures into a QC CSF sample. Six calibration points (1-3 and 5-7) and a blank (0), only containing bovine serum albumin protein, were analyzed.