Separation Mechanisms in Hydrophilic Interaction Chromatography

Hydrophilic interaction chromatography (HILIC) is a technique that has become increasingly popular for the separation of polar, hydrophilic, and ionizable compounds, which are diffi cult to separate by reversed phase chromatography (RP) due to their poor retention when RP is used. HILIC typically uses a polar stationary phase such as bare silica or a polar bonded phase, together with an eluent that contains at least 2.5% water and > 60% of an organic solvent such as acetonitrile (ACN). However, these values should not be regarded as defi nitive of the rather nebulous group of mobile and stationary phase conditions that are considered to constitute HILIC. Figure 1.1 shows the number of publications on HILIC between the years 1990 (when the term was fi rst employed) and 2010 according to the Web of Knowledge [1] using the search terms “ HILIC ” or “ hydrophilic interaction (liquid) chromatography. ” For the fi rst 12 years or so, the number of publications remained between 1 and 15, but after this period, interest increased rapidly from 19 publications 1.