Distribution mechanism of ionizable substances in dynamic anion-exchange systems using cationic surfactants in high-performance liquid chromatography

Characterization and evaluation of the use of nonionic polyoxyethylene(23)dodecanol micellar mobile phases in reversed-phase high-performance liquid chromatography

“…Although there are some discrepancies, it has also been reported that ionic surfactant additivies in the mobile phase strongly adsorb to and coat C-18 (and C-8) bonded stationary phases (8, 17, 46-49). Ionic surfactants generally follow Langmuir adsorption isotherms and there is apparently no additional adsorption once the surfactant concentration in the mobile phase is above the CMC value (8,17,20,(44)(45)(46). In fact, if the multipartition theory of MLC is to be strictly valid for a particular micellar mobile phase, this is one of the conditions that must be met (4, 21).…”

“…Surprisingly, all work with MLC to date appears to have involved only charged, ionic micellar mobile phase systems composed of either anionic sodium dodecyl sulfate (NaLS) (1-7, 9-11, [13][14][15][17][18][19][20] or the cationic surfactants hexadecyltrimethylammonium bromide or chloride (CTAB or CTAC) and dodecyltrimethylammonium bromide (DTAB) (6,8,(11)(12)(13)15,16). The use of uncharged, nonionic surfactants seems to have been largely neglected.…”

Investigations of stationary phase modification by the mobile phase surfactant in micellar liquid chromatography

“…l-Fluoro-2,4-dinitrobenzene (FDNB) has been proposed as a label in the determination of the amino acid sequence of proteins (1), for active site labeling of enzymes, and for studying protein tertiary structures (2). Besides its use in structural analysis, FDNB has been employed for the spectrophotometric determination of amino acids and primary and secondary amines (3)(4)(5)(6)(7)(8)(9), amino acid nitrogen in plasma and urine (10,11), isoniazid (12), various aminoglycoside antibiotics (13), phenols (14), and the enzyme amidase (15). It has also been used in the gravimetric determination of morphine (a phenolic alkaloid) (16) and other phenols (17), as a derivative reagent in gas-liquid chromatography (GLC) for phenols (18) and amines (19), in high-performance liquid chromatography (HPLC) for amines and aminoglycosides (20)(21)(22), and in thin-layer chromatography (TLC) and mass spectrometry for amines (23).…”

“…It is clear that in many of the systems studied, surfactant adsorbs into the chromatographic stationary phase, although the contribution to the retention mechanism thus produced continues to be a topic of discussion and experiment (2). Dynamic modifications of silica oxide, titanium boride, zirconium oxide, activated carbon, and bonded C18 stationary phases have been observed with charged surfactants and combinations of nonionic and charged surfactants (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). The extent of dynamic modification in some cases approaches a mass loading equivalent to the original bonded stationary phase, with surface concentrations as great as 8 µ /m2 reported.…”

High-Performance Liquid Chromatography of Catecholamines and their Metabolites in Biological Material

“…In summary, these can be described as 1. the dynamic ion-exchange model (Knox and Hartwick, 1981): the anionic surfactant is adsorbed to the alkyl-silica and converts the column dynamically into a cation-exchanger, 2. the ion-pair distribution model (Terweij-Groen et al, 1978): ion-pair formation occurs in the mobile phase and the ion-pairs are equilibrated between the mobile and stationary phases, 3. the dynamic complex exchange model (Melander and Horvath, 1980): equilibria are established where the ion-pair formed in the mobile phase will displace the anionic surfactant bound to the alkyl silica. In summary, these can be described as 1. the dynamic ion-exchange model (Knox and Hartwick, 1981): the anionic surfactant is adsorbed to the alkyl-silica and converts the column dynamically into a cation-exchanger, 2. the ion-pair distribution model (Terweij-Groen et al, 1978): ion-pair formation occurs in the mobile phase and the ion-pairs are equilibrated between the mobile and stationary phases, 3. the dynamic complex exchange model (Melander and Horvath, 1980): equilibria are established where the ion-pair formed in the mobile phase will displace the anionic surfactant bound to the alkyl silica.…”