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. Author manuscript; available in PMC: 2012 Feb 1.
Published in final edited form as: J Immunol Methods. 2010 Nov 13;364(1-2):50–64. doi: 10.1016/j.jim.2010.11.001

Figure 8.

Figure 8

Quantitation of a protein C inhibitor (PCI) specific peptide in trypsin-digested human plasma. Stable isotope labeled (heavy) peptide with the same sequence as the endogenous PCI peptide was spiked into the reaction mixture at different levels. One μg of purified RabMAb 58-4 was used to capture both heavy and endogenous peptides from 10 mL of digested plasma. The captured peptides were eluted using 25 μL of 5% acetic acid and were analyzed by MALDI-TOF MS. The ratio of accumulated peak intensity of heavy:endogenous peptide was used to determine the amount of endogenous peptide. The coefficient of variation from 16 samples was determined to be 5.3%.