High performance normal phase chromatography

A relationship between solvent strength and retention time can be derived as follows  

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Most HPLC is based on the use of so-called normal-phase columns (useful for class separations), reverse-phase columns (useful for homolog separations), and polar columns (used in either the normal- or reverse-phase mode). Since reverse-phase HPLC columns are generally easier to work with, almost all authors use high-performance reverse-phase liquid chromatography with octade-cyl chemically bonded silica as the stationary phase and nonaqueous solvents as mobile phases (so-called NARP, or nonaqueous reverse-phase chromatography). 

High performance preparative liquid chromatography can often be employed to rapidly fractionate the sample. Maximum separation efficiency can be obtained 1f different chromatographic systems are used 1n the preparative and analytical separations. For example, normal phase chromatography could be used for the Initial fract1on1zat1on and reverse phase chromatography used for the anlaytlcal separation. 

Using aminopropyl-modified silica gel plates in a normal phase system, the retention behavior of 12 acidic drugs and biologically active aromatic acids was investigated by high-performance thin layer chromatography. 

The techniques of normal and reversed-phase thin-layer chromatography, 14 115 and high performance thin-layer chromatography (HPTLC)116 have also been described. 

As we will see in Chapter 10, many studies have demonstrated that the use of a fully hydroxylated high-purity silica as the basis for reversed-phase bonded phases results in superior chromatographic performance of these phases. In normal-phase chromatography, the situation is not as clearcut. Good results can be obtained on several different silicas, and the dominant factor for the differences is probably the acidity/basicity as described in the previous paragraphs. 

SEPARATION OF BILE ACIDS BY NORMAL PHASE HIGH-PERFORMANCE THIN-LAYER CHROMATOGRAPHY (NP-HPTLC) ON CYANO-AND DIOL-MODIFIED SILICA GEL AT ROOM... 

Normal-phase chromatography and the bonded-phase sorbents that are used for this mode of chromatography have been discussed. It can be used with fewer reproducibility problems than the adsorption mode simply because the bonded sorbents used for NP chromatography have fewer silanols. Fewer silanols mean less sensitivity to water than is often found in variable amounts in the solvents used for high-performance liquid chromatography (HPLC). 

Olah, N.-K. Muresan, L. CTmpan, G. Gocan, S. Normal-phase high-performance thin-layer chromatography and automated multiple development of hydroalcoholic extracts of Artemisia abrotanum Artemisia absinthium, Artemisia vulgaris and Artemisia cinia. J. Planar Chromatogr. 1998,... 

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