Distribution coefficients electrophoresis

Kitagawa, S., Watanabe, H., and Tsuda, T., Voltage-induced variation of distribution coefficient in electrochromatography, Electrophoresis, 20, 9, 1999. 

The use of capillary electrophoresis (CE) during the synthetic drug development is described from the preclinical development phase to the final marketed stage. The chapter comprises the determination of physicochemical properties, such as acid—base dissociation constants (pKJ, octanol—water distribution coefficients (logP), and analysis of pharmaceutical counterions and functional excipients. 

Chromatographic and related electrophoretic methods for the separation of transition metal complexes or their ligands were reviewed . Micellar electrokinetic chromatography (MEKC) presents a new development in the field of capillary zone electrophoresis (CZE). The use of micellar solutions expands the application of CZE to electronically neutral solutes, as well as charged ones. Thus, electrically neutral / -diketonates Cr(dik)3, Co(dik)3, Rd(dik)3, Pt(dik)2 and Pd(dik)2 were separated by CZE in micellar solutions of sds. A linear log-log relationship was found between the distribution coefficient and the partition coefficient of the complex between dodecane and water, which was used for prediction of both the distribution coefficients and the migration times of different metal complexes . 

Analysis of histones is frequently carried out in the presence of detergents which may bind to them. Binding of the nonionic detergent Triton X-100 to histones from calf thymus can be analysed by gel chromatography. The binding of Triton to histones was abolished if 8 M urea was present in 0.01 M HCl or 0.9 M acetic acid [110]. Subsequently [111], the effects of the cationic detergent cetyltrimethyl ammonium bromide (CTAB), and the anionic detergent sodium dodecyl sulphate (SDS), in GPC and electrophoresis were compared. The results showed that, in the presence of CTAB, the values of the retardation and distribution coefficients were linear in respect to the molecular mass of histones, while in the presence of SDS, deviations from this type were observed. 

The first and most often encountered separation mechanism in CE is based on mobility differences of the analytes in an electric field these differences are dependent on the size and charge-to-mass ratio of the analyte ion. Analyte ions are separated into distinct zones when the mobility of one analyte differs sufficiently from the mobility of the next. This mechanism is exemplified by capillary zone electrophoresis (CZE) which is the simplest CE mode. A number of other recognized CE modes are variations of CZE. These are micellar electrokinetic capillary chromatography (MECC), capillary gel electrophoresis (CGE), capillary electrochromatography (CEC), and chiral CE. In MECC the separation is similar to CZE, but an additional mechanism is in effect that is based on differences in the partition coefficients of the solutes between the buffer and micelles present in the buffer. In CGE the additional mechanism is based on solute size, as the capillary is filled with a gel or a polymer network that inhibits the passage of larger molecules. In chiral CE the additional separation mechanism is based on chiral selectivity. Finally, in CEC the capillary is packed with a stationary phase that can retain solutes on basis of the same distribution equilibria found in chromatography. 

In Chapter 3 we found that all relative transport processes, whether induced by external fields or diffusion, proceed at a rate inversely proportional to the friction coefficient /. Since virtually all separation methods require a certain level of completion of transport, or a certain number of transport steps, the time scale of the separation is linked to the time scale of the required transport both ultimately hinge on the magnitude of /. This conclusion is valid whether one is using methods such as chromatography where the transport processes must maintain the distribution of components between phases at a point near equilibrium, or electrophoresis where transport proceeds only fractionally to equilibrium. 

Several other techniques have been applied to the study of physical properties of HS. Field-flow fractionation (described in Section 7.6.3) has been applied to the study of size distribution of HS (Beckett, Jue, and Giddings 1987 Lead et al. 2000). Electrophoresis has been largely applied in the separation of charged components of HS, but was employed only a few times for the determination of molecular weight and size of HS (Senesi and Loffredo 1998). The retardation of macromolecules in a gel media under an applied electric field is related to the size of the pores and the migrating molecules. The retardation coefficient can be related to the molecular weight by... 

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