C4, C8, C18, etc. - refers to the alkyl chain length of a reversed-phase adsorbent.
See popular bonded phases.
calibration curve - dependence of peak areas on the concentration of injected samples
capillary tubing - tubing for connecting various parts of the chromatograph. Most capillary tubing used in HPLC is <0.020 in. i.d. The smallest useful i.d. is about 0.004 in.
cartridge column - a type of column that has no endfittings and is held in a cartridge holder. The column is a tube; the packing is contained by frits in each end of the tube. Cartridges are easy to change and are less expensive and more convenient than conventional columns with endfittings.
cation-exchange chromatography - the form of ion-exchange chromatography that uses resins or packing with functional groups that can separate cations. A sulfonic acid would be an example of a strong cation-exchange group; a carboxylic acid would be a weak cation-exchange group.