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Normal-Phase Liquid Chromatography

Liquid Chromatography

  1. William T. Cooper

Published Online: 15 SEP 2006

DOI: 10.1002/9780470027318.a5913

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Cooper, W. T. 2006. Normal-Phase Liquid Chromatography. Encyclopedia of Analytical Chemistry. .

Author Information

  1. Florida State University, Tallahassee, USA

Publication History

  1. Published Online: 15 SEP 2006

Abstract

Normal-phase liquid chromatography (NPLC) is a technique that uses columns packed with polar stationaryphases combined with nonpolar or moderately-polar mobile phases to separate the components of mixtures. The rate at which individual solutes migrate through NPLC columns is primarily a function of their polarity. Less polar solutes move the fastest and therefore exit the column and are detected first, followed by solutes of increasing polarity which move more slowly. However, polarity can sometimes play a secondary role relative to a solute's ability to experience a specific interaction with active sites on the stationary phase surface. The importance of these specific solute–stationary phase interactions in NPLC gives it some unique advantages over the more widely practised reversed-phase liquid chromatography (RPLC) technique. RPLC utilizes nonpolar stationary phases and aqueous-based polar mobile phases, and the elution order of solutes in a mixture is related to their hydrophobicity, not polarity; more polar solutes move the fastest and appear first, followed by solutes of decreasing polarity. RPLC is useful for separating mixtures in which components differ in molecular weight and/or water solubility. However, NPLC is preferred for many separation problems, including those in which the water solubility of sample compounds is limited. In addition, NPLC is a better technique for separating compounds that differ in the number or character of functional groups and is particularly useful for separating many types of isomers.