Normal & Reversed HPLC Column
Stationary Phase & Mobile Phase
The stationary phase is used to separate the substances, which is packed into HPLC Column directly; Mobile phase is the carrier, which carries the substances into the stationary phase and goes through the stationary phase.
It is gas in the vapor phase, and it is liquid in the liquid phase. Both are called a mobile phase.
Normal & Reversed Phase
While the polarity of stationary phase is greater than that of the mobile phase, it can be called normal phase chromatography; Oppositely, while the polarity of stationary phase is less than that of the mobile phase, it can be called reverse phase chromatography.
The stationary phases used in normal phase chromatography are usually silica gel (Silica), and the other bonded phase adsorbent with polar functional groups, such as (NH2, APS) and cyano group (CN, CPS). The HPLC Column made of this kind of absorbent is called normal phase HPLC Column; the absorbent used in reverse chromatography is usually based on silica gel, and the surface bonding phase has relatively weak functional groups. The commonly used reverse absorbent are C18 (ODS), C8 (MOS), C4 (Butyl), C6H5 (Phenyl) and so on. The HPLC Column made of this kind of absorbent is called reversed phase HPLC column.
Low polar mobile phases such as n-hexane can be used in normal phase chromatography and strong polar mobile phases such as methanol or water can be used in reverse phase chromatography.
Difference in Application
In the normal chromatography, the stationary phase is polar and the mobile phase is non-polar, which is suitable for separating strong polar substances, and the elution sequence is from weak to strong; the stationary phase of In the reversed phase, the stationary phase is non-polar and the mobile phase is polar, which is suitable for separating weak polar substances, and the elution sequence is from strong to weak.
Generally, the reversed chromatography is often used, and the normal chromatography is only used under special conditions, for example, the sample is sensitive for the water.