injector valve - six-port valve designed to introduce a liquid sample into the HPLC system without noticeable flow interruption, and without depressurizing the system.

See also injectors.

internal standards (IS) - substance used as reference in quantitative analysis; the internal standard is first mixed with standard solutions; later it is added to the unknown, and the ratio of peak heights (or areas) of internal standard and analyte is used for quantitative analysis.

interstitial volume - (Vo) - the total volume of mobile phase within the length of the column It is made up of the intraparticle volume (inside the packing itself) and interparticle volume (between the packing particles). Same as void volume or dead volume . Also abbreviated Vi or Vm.

ion chromatography (IC) - An ion-exchange technique in which low concentrations of anions or cations are determined using low-capacity ion exchangers with weak buffers. Conductivity detectors are often used. Ion chromatography is practiced in two forms. In suppressed IC, a second column is used to remove the buffer ions so that sample ions can be more easily detected; membrane separator is sometimes used. In nonsuppressed IC, weakly conducting buffers at low concentration are carefully selected, and the entire effluent is passed through the detector; ions are detected above the background signal.