Retention Prediction Based on the Solvatochromic Comparison Method in Reversed-Phase Capillary Electrochromatography

Theory and practical understanding of the migration behavior of proteins and peptides in CE and related techniques

CEC is defined as an analytical method, where the analytes are separated on a chromatographic column in the presence of an applied voltage. The separation of charged analytes in CEC is complex, since chromatographic interaction, electroosmosis and electrophoresis contribute to the experimentally observed behavior. The putative contribution of effects such as surface electrodiffusion has been suggested. A sound theoretical treatment incorporating all effects is currently not available. The question of whether the different effects contribute in an independent or an interdependent manner is still under discussion. In this contribution, the state-of-the-art in the theoretical description of the individual contributions as well as models for the retention behavior and in particular possible dimensionless 'retention factors' is discussed, together with the experimental database for the separation of charged analytes, in particular proteins and peptides, by CEC and related techniques.

Quantitative structure-retention relationships in comparative studies of behavior of stationary phases under high-performance liquid chromatography and capillary electrochromatography conditions

Quantitative structure-retention relationships (QSRR) have been employed in studying the molecular mechanism of chromatographic separations under pressure- (HPLC) and electro-driven (CEC) conditions. Logarithms of retention factors corresponding to zero percent of organic modifier in aqueous eluent, log k(w), were determined on eight reversed-phase stationary phases under both HPLC and CEC conditions at similar eluent flow velocities. QSRR equations describing log k(w) in terms of linear solvation energy relationship (LSER) parameters of analytes, in terms of simple structural descriptors acquired by calculation chemistry, and in terms of logarithms of n-octanol-water partition coefficients, were derived. Parameters of corresponding QSRR equations for individual stationary phases were compared for both HPLC andCEC modes and the resulting similarities and differences in retention mechanisms were discussed. It has been concluded that at least in the case of regular neutral analytes the specific inputs to separation mechanism due to the electric field in CEC are of secondary importance.

Effect of various modes of pressurization on the separation in capillary electrochromatography

In capillary electrophoresis and capillary electrochromatography, the driving factor of the separation is electroosmotic flow (EOF). Pressurized capillary electrochromatography, in which the separation is controlled by EOF as well as the pressure, becomes more and more attractive. We studied the influence of various pressures on capillary electrochromatographic separation. The results reveal that in pressurized capillary electrochromatography, which was performed by EOF combined with the forward and reverse pressure, the main driving factor is still the EOF. It was also found that, when reverse pressure was applied in capillary electrochromatography, the repeatability of the capillary electrochromatographic separation was increased dramatically.

Recent progress in capillary electrochromatography

Capillary electrochromatography (CEC) continues to captivate many separation scientists. A remarkable activity is apparent from the numerous publications in the literature using CEC. A review of the most recent progress in CEC is presented herein, covering an extensive fraction of the literature on CEC published from the year 1997 until the beginning of 2000. Most of the recent developments have concentrated on column technology.

Advances in column technology and instrumentation in capillary electrochromatography

Capillary electrochromatography (CEC) is an emerging technique gaining increased interest. Improvement of instrumentation and column technology will be of prime importance for the further development of this technique and its use in validated methods. In this paper, developments in column technology and instrumentation for CEC are reviewed with emphasis on developments within the last 3 years. Attention is directed to the employment of stationary phases specifically designed for CEC, the use of soft and rigid gels in place of packings, fritless packed capillaries, column dimensions, the optimization of injection and detection parameters, and gradient elution CEC.

Chromatographic properties of reversed-phase stationary phases under pressure- and electro-driven conditions

Seven different reversed-phase (RP) stationary phases were examined under high-performance liquid chromatographic (pressure-driven, HPLC), and capillary electrochromatographic (electro-driven, CEC) conditions. Characterization of the stationary phases was performed following well-established test procedures providing a number of distinct column descriptors: hydrophobicity, hydrophobic selectivity and silanol activity. These parameters were used to describe the behavior of the RP-columns under both HPLC and CEC conditions. It is shown that chromatographic characteristics of porous RP-phases greatly depend on the mode of operation. By contrast, column descriptors of a non-porous viz. solid RP-phase material hardly differed for HPLC and CEC conditions.