Efficiency enhancement in micellar liquid chromatography

Abstract

The use of mlcellar mobile phases can provlde unlque selectivities In llquld chromatography. A major drawback In all published reports, however, Is a loss of efflclency when compared to tradltlonal hydroorganlc moblle phases. This inefflclency is shown to arise from slow mass transfer, which comes principally from poor wettlng of the stationary phase. Low concentrations of organic modlflers are useful for modlfylng the surface of the stationary phase and provlding the wetting needed for good mass transfer. Elevated temperatures are also shown to be useful In overcomlng the hlgher vlscoslty of mlcellar mobile phases and thereby serving to Improve peak shape. Mobile phases contalnlng about 3% propanol and temperatures of about 40 OC provide efflclencies approachlng those of hydroorganic moblle phases.The popularity of modern liquid chromatography continues to increase. One of the reasons for this is the unique selectivities that can be generated in the mobile phase by the addition of chemical modifiers. Retention in reversed-phase LC is dominated by solvent-solute interactions, with stationary phase-solute interactions making secondary contributions. The key to separation is then to be able to change the solvent-solute interactions in such a way as to shift the retention of any overlapping compounds. In some cases the selectivity of the chromatographic system can be modified by simply changing the eluent strength or ratio of the hydroorganic mobile phase. Most often, however, changes in selectivity reached in this fashion are accompanied by concomitant changes in the retention of all sample components, and an appreciable change in relative retention is achieved only with capacity factors that fall outside the practical range of 0.3 < k' < 5. It is desirable to find ways to change the selectivity of the chromatographic system for closely eluting sample components without drastic changes in the eluent strength as a whole.One way that this has been done, particularly for ionogenic solutes, is by the addition of low concentrations of ionic surface active agents having an opposite charge to the solute. The surfactant will then coulombically interact with the solute and drastically alter its retention characteristics. Because of the nature of the surfactant, this technique was dubbed "soap chromatography" ( I ) and is now more commonly known as ion-pair chromatography.Until recently, only low concentrations of surfactant were used, and investigators intentionally stayed below critical micelle concentrations. Armstrong and Henry first effectively demonstrated the usefulness of reversed-phase mobile phases containing surfactants above the critical micelle concentration (2). They showed that the micelle can provide a hydrophobic site for interaction with the solute in the mobile phase and can be used in place of an organic modifier. Since then other reports have appeared (3-8) and certain advantages have been shown, including the selectivity of the micellar interaction and economy of operating expense when compared to expen...

Micellar Liquid Chromatographic Determination of Lamivudine, Indinavir and Ketoconazole in Dosage Forms and Biological Fluids

“…Also, the capability of simultaneous separation of hydrophobic and hydrophilic analytes in the same run without a gradient elution [4]. Unfortunately, some drawbacks were reported concerning the chromtographic efficiency and weak elution strength of pure micellar solution [5,6]. Many articles has been reported for determination of drugs in pharmaceutical preparations and biological fluids [7][8][9].…”

Evaluation of Some Empirical Retention Models for High Submicellar Liquid Chromatographic Separation of Aromatic Diamines

“…Also, the stable and reproducible behavior of micellar mobile phases enables the accurate prediction of solutes retention with a model that can be further used to optimize the separation of mixtures of solutes [1,2]. Most studies in MLC use a short-chain alcohol such as methanol, propanol, butanol, or pentanol [1,2] as an additive to micellar mobile phases to improve the peak shape and efficiency and increase the elution strength [3,4]. These organic modifiers decrease the mobile phase polarity and affect the amount of surfactant adsorbed on the stationary phase; also, micelle parameters, such as the CMC and surfactant aggregation number (i.e., number of surfactant monomers associated in a micelle), are altered through addition of modifier [5][6][7].…”

Chromatographic Separation of Heavy Metal Cations on a Silica Gel‐G with Amino Acid

“…Using a surfactant as the mobile phase gained popularity and became more widely applied due to its operational simplicity, cost effectiveness, relative non-toxicity and enhanced separation efficiency [5][6][7][8]. The use of silica gel and an alumina layer with surfactant mediated mobile phase systems [9][10][11][12][13][14][15] has been used to separate various inorganic species. Number of metal ions was systematically chromatographed on thin layer of urea formaldehyde polymer [16].…”