Extraction of cholecystokinin peptides from biological fluids using octadecylsilane-packed cartridges

Cholecystokinin is an important peptide hormone, which occurs naturally in molecular forms ranging in length from 4 to 58 amino acid residues and varying in charge from acidic to basic. In order to quantify the individual molecular forms of this hormone present in plasma or tissues, it is first necessary to efficiently extract all of the diverse forms. In this paper, we establish and validate a simple method to do this using octadecylsilane-packed cartridges. Peptide adsorption to the cartridge and subsequent elution from it is not significantly affected by the pH (3-7) or salt concentration (0-2 g per 100 ml) needed for extraction, or the protein concentration (0-10 g per 100 ml) in the applied sample. Peptides are extracted in a form which can be separated using reversed-phase high-performance liquid chromatography and subsequently quantified by a commonly available radioimmunoassay which recognizes both cholecystokinin and gastrin.