Stationary phase effects in reversed-phase liquid chromatography of acids and ion pairs

Retention behavior of carboxylic acids and their quaternary ammonium ion pairs in reversed phase chromatography with acetonitrile as organic modifier in the mobile phase

“…From Table I it follows that the coating of acetonitrile is about 0.24 mL/g of solid phase, when the mobile phase contains 30% v/v of acetonitrile. Wahlund et al (4) have found that an aqueous mobile phase saturated with 1-pentanol (2.5 % v/v) gave a pentanol coating on the same solid phase of about 0.64 mL/g, while Westerlund et al (5) found that a mobile phase of methanol and buffer (40 + 60) gives a coating of methanol of 0.18 mL/g. Our studies have not shown if the adsorbed acetonitrile forms a separate layer or is imbedded in the surface.…”

“…Systems for reversed phase ion pair chromatography of hydrophilic carboxylic acids of widely different structures as well as sulfonamides and barbiturates have been developed by Wahlund et al (1)(2)(3)(4) using mobile aqueous phases and a liquid stationary phase of 1-pentanol or butyronitrile dynamically coated on an alkyl-bonded support. Naphthalene acetic acid derivatives have been separated as ion pairs and as acids in reversed phase chromatographic systems using aqueous mobile phases containing methanol or acetonitrile (5).…”

Adsorption of 1-pentanol on alkyl-modified silica and its effect on the retention mechanism in reversed-phase liquid chromatography

“…where Vpe,a is the volume of adsorbed 1-pentanol and Vm is the volume of mobile phase in the column whereas k' is the measured capacity ratio. The factor 1.07 corrects for the presumed water content of the adsorbed 1-pentanol (1). The test should be done in that region of the adsorption isotherm (Figure 1) where a bulk layer exists, i.e,, above ca.…”

“…At the saturation point almost the whole pore volume is filled with 1-pentanol (1). Then the solutes can obviously partition into the total volume of this bulk layer.…”

“…In a previous paper (1) we studied the coating of alkylmodified silicas with 1-pentanol in order to produce reversed-phase columns for liquid-liquid chromatography. The coating was done by equilibrating the column packing with buffer solutions containing various concentrations of 1-pentanol up to saturated solutions which contain 2.30 vol % 1-pentanol.…”