Normal Phase IPC and Other Stationary Phases

While a hydrophobic ion-pair is retained on hydrophobic stationary phases better than an ionized analyte, the retention of the duplex on normal phases is easily predicted to be lower than that of the ionized analyte because polar interactions are reduced. Actually the trend of k versus IPR concentration under normal phase IPC is the opposite of reversed phase IPC [34]. An aminopropyl, a cyanoethyl, and a silica stationary phase were compared for the analysis of alcohol denaturants. The cyanoethyl phase was selected and anionic IPRs were used to reduce retention of cationic analyte, suppressing their interactions with negatively charged silanols 

IPC was also performed on a classical ion exchange colnmn to separate 17 anionic, neutral, and cationic arsenic species in a single chromatographic run, thanks to a multiplicity of retention modes on this packing material [39], Ion pairing proved also valuable in size exclusion chromatography of sulfonated lignins [40], 

In Chapter 6, recent developments in column technology will be discussed along with current strategies to obtain fast separation and increased efficiency (breakthroughs of sub-2-pm particles and monoliths). 

Analysis of nitrate ion in nettle (Urtica dioica L.) by ion-pair chromatographic method on a C30 stationary phase. J. Agr. Food Chem. 2006, 54, 4082-4086. Yokoyama, Y. et al. Optimum combination of reversed phase column type and mobile phase composition for gradient elution ion-pair chromatography of amino acids. Anal. Sci. 1997, 13, 963-967. 

and Sontag, G. Determination of some heterocyclic aromatic amines in soup cubes by ion-pair chromatography with coulometric electrode array detection. Anal. Chim. Acta 2000, 417, 77-83. 

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