Evaluation of trypsin digestion efficiency in blood (red lines) as compared to plasma (black lines) for peptides from apoA-I (a), apoB (b-c), apoC-I (d), apoC-III (e), apoE (f-h), and HSA (i-j). The data points indicate the average response ratio, i.e., the endogenous peptide signal relative to the stable-isotope labeled peptide (added before digestion) signal, of three analytical replicates. Error bars indicate ± one standard deviation.