noise - random fluctuation of the chromatographic signal; short-term noise (less than 1 sec) is often electrical in nature; long-term noise can be due to flow rate changes, temperature changes.

See noise and drift.

nonspecific interactions - type of intermolecular or surface interactions which is not related to any specific polar or ionasible group of the analyte molecule.

normalization - quantitative method commonly employed when the entire sample is eluted from the column; the area percent is taken as weight percent composition; of limited usefulness since most detectors give different responses to different samples.

normal-phase chromatography - a mode of chromatography carried out with a polar adsorbent surface and a nonpolar mobile phase. Adsorption on silica gel using hexane as a mobile phase would be a typical normal-phase system. Also refers to the use of polar bonded phases, such as CN or NH2 .

See also types of HPLC.