Typical Column Packings Used in HPLC:
Cyclodextrin-bonded stationary phases have been demonstrated to be particularly efficient in resolving structural isomers. Some examples are- prostaglandin A1, A2 and B1B2, α- and β-naphthols, o,o′ and p, p′-biphenyls and the ortho-, meta- and para- isomers of nitrophenol, nitroaniline, xylene, cresol and aminobenzoic acid.
Recently introduced graphitized carbon and new generation of rigid porous polymeric microbeads based on styrene/divinyl benzene as alternatives to silica can be used over a wide range of pH between 1 to 13. Some examples of column packings used in HPLC and their applications are listed in Table.
Table: Some Typical Column Packings Used in HPLC
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Packing
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Mode of HPLC
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Applications
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Microparticulate silicas; spherical or irregular particles; mean particle size
3, 5 and 10µ m chemically modified versions of the above
(bonded-phase packings)
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LSC (adsorption)
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Non-polar to moderately polar mixtures, e.g., polyaromatics, fats, oils, mixtures of isomers
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Octadecyl (ODS or C18)
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BP (bonded phase) and Ion Pair Chromatography
(IPC)
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Wide range of moderately polar mixtures, e.g., pharmaceuticals and drugs, amino acids
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Octyl (C8)
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BPC, IPC
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More polar mixtures, e.g., pesticides, herbicides, peptides, metabolites in body fluids
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Short chain (C3 or less)
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BPC, IPC
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IPC applications of above three packings include bases, dyestuffs and other multiply charged species; used instead of IEC
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Diol
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BPC
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Very polar and water-soluble compounds, e.g., food and drink additives
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Nitrile
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Normal phase and
BPC
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Alternative to silica, can give better results
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Aminoakyl
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BPC
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Carbohydrates including sugars
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Anion and cation exchangers
(tertiary amine or sulphonic acid)
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IEC (Ion-exchange chromatography)
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Ionic and ionizable compounds, e.g., vitamins, water-soluble drugs, amino acids, food and drink additives
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Controlled porosity silicas (chemically modified to reduce adsorption effects)
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Size exclusion
Chromatography
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Polymer mixtures, screening of unknown samples. Increasing use for separating mixtures of smaller molecules before other modes of HPLC
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Chiral amino acids bound to aminopropyl
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Chiral Chromatography (CC)
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Mixtures of enantiomers especially of drugs
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Chiral peptides
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CC
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Cyclodextrins
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CC
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It may be mentioned that besides various modes of HPLC discussed above, thin layer chromatography is another mode which is already discussed in Unit 6. Hence, it is not included in the discussion here.