Electrical double-layer model for ion-pair chromatographic retention on octadecylsilyl bonded phases

Abstract

separations dramatically (22)(23)(24).While we have restricted attention to linear inlet gradients, similar effects could obviously arise for concave and convex gradients. Shocks could occur even sooner with convex gradients and later for concave gradients (which would tend to become more linear). The resulting effect on adsorbate separation would be along the lines of the foregoing discussion. CONCLUSIONSThe effect of accounting for the adsorption of the mobilephase modulator in gradient elution is examined quantitatively through numerical simulations for reversed-phase chromatography with water-acetonitrile as the mobile phase. The adsorption of the modulator gives rise to gradient deformation and, under extreme conditions, to the formation of a modulator shock layer. The possible consequences of such a shock layer on gradient separations include extreme concentration of adsorbates that lie just behind, or straddle, the shock layer and shoulders ("false peaks") on either the leading or the trailing edge of the band. Experimental verification is being attempted in our laboratory. ACKNOWLEDGMENTWe thank Richard Hendrickson, Paul Westgate, and Yiqi Yang for their helpful comments on the manuscript.

Sorption of magnesium–picolinate complexes on a macroporous styrene–divinylbenzene copolymer containing immobilized 8-hydroxyquinoline and on the copolymer itself

“…A greater slope for the isotherm at higher pH means that the cationic species MgP' is sorbed more strongly on XAD-OXINE as a result of an increase in the degree of ionization of the covalently bound oxine to form its anion oxinate. Increased sorption of a cationic sample species as the result of an increase in negative surface-charge density is qualitatively consistent with the theoretical predictions of the "double-layer ionic adsorption and exchange model" (13,28,29). Quantitative evaluation of the sorption of MgP+ on XAD-OXINE in terms of this theoretical model is not possible at this time because it was not possible accurately to measure the surface-charge density on XAD-OXINE (22).…”

Surface Impregnated Sulfonate Ion Exchangers: Preparation, Properties and Application

“…On the other hand, the same results indicate that SISIE can be successfully applied as convenient model systems to interpret the ion-exchange equilibrium in terms of the interaction between a charged surface of the ion exchanger and the counterions. Such an approach is widely applied in different electrostatic retention models for ion-exchange selectivity [90][91][92][93][94][95][96][97] based on the Gouy-Chapman-Stem theory of electric double layer. Similar and some other problems are considered in the next section of the paper dedicated to application of SISIE.…”

Rapid Screening of Volatile Ion-Pair Reagents Using UHPLC and Robust Analytical Method Development Using DoE for an Acetyl Cholinesterase Inhibitor: Galantamine HBr

“…In ion-pair chromatography, a molecule that contains both a fixed charge site and a hydrophobic tail is added to the mobile phase [19][20][21][22][23][24][25][26]. The hydrophobic portion of the molecule adsorbs onto the stationary phase and the fixed charged portion provides a site with which an analyte ion may interact.…”