Microemulsion electrokinetic chromatography of drugs varying in charge and hydrophobicity Part II: Strategies for optimization of separation

Abstract

The separation of anionic, cationic, and neutral drugs in microemulsion electrokinetic chromatography (MEEKC) was studied. The concentration of sodium dodecyl sulfate (SDS; surfactant) and 2-propanol (organic solvent) was varied in a three-level full factorial design. 29 different model substances were chosen with different hydrophobicities and charges (neutral, positive, and negative). The models were calculated by means of multiple linear regression (MLR). The compounds were divided into five different subgroups, and different strategies for optimization of the separation within each group were investigated. The optimization was done by maximizing the selectivity using response surface plots in MODDE, by calculation of different chromatographic functions, and by using the software DryLab. For all the different groups, MODDE, almost all chromatographic functions and DryLab gave approximately the same settings of the factors for optimum separation. Attempts were made to fit descriptors of the compounds to the retention data from the three-level full factorial design by means of partial least squares projection to latent structures (PLS). Between 86 and 89% of all predictions of migration times were acceptable (80-120% of the observed value).

Sample stacking for the analysis of penicillins by microemulsion electrokinetic capillary chromatography

“…The surface tension is further lowered by adding a short-chain alcohol called a co-surfactant, which stabilizes the microemulsion system [22,23]. Therefore, a typical microemulsion used for MEEKC may consist of 0.8% n-octane, 3.3% sodium dodecyl sulfate (SDS), 6.6% 1-butanol and 89.3% 10 mM borate buffer at pH 9.2 [24][25][26][27]. It should be taken into account that solutes in MEEKC are more able to penetrate the surface of the droplet than the surface of a micelle, which is much more rigid.…”

“…One of the advantages of MEEKC is that it takes into account many parameters: the type and concentration of the oil, buffer, surfactant, co-surfactant, counter-ion and the pH all affect the separation performance [26]. As well as the mostly aqueous electrolyte solution and the surfactant responsible for stabilizing the oil droplets, various organic solvents with different properties play an important role in the composition of the microemulsions used in MEEKC [28].…”

Comparison of oil‐in‐water and water‐in‐oil microemulsion electrokinetic chromatography as methods for the analysis of eight phenolic acids and five diterpenoids

“…Many reports on O/W MEEKC concluded that variations in the nature and concentration of oils, organic modifier and surfactant had a noticeable effect on separation [38][39][40]. Similarly, the above three factors were also utilized to improve MEEKC separations.…”

Experimental design as a tool when evaluating stationary phases for the capillary electrochromatographic separation of basic peptides

“…In this paper the constants A i and B were set to 2 and 0, respectively, thereby excluding the time factor. Harang et al [35] have shown that the time factor is sometimes far too dominant in the response function, despite the weighting of the resolution factor. This results in models that poorly describe the experimental data with poor ability to predict optimum conditions.…”