Capillary zone electrophoresis , drug analysis

After a short introduction into the relevance of Impurity profiling for regulatory authorities, public health, and the pharmaceutical industry, an overview is presented based on the various modes of capillary electrophoresis that have been used in drug impurity analysis. The applications of capillary zone electrophoresis, non-aqueous capillary electrophoresis, micellar electrokinetic capillary chromatography, microemulsion electrokinetic capillary chromatography, capillary gel electrophoresis, and capillary electrochromatography are presented consecutively. 

Tagliaro, F., Smith, F. P., Turrina, S., Equisetto, V., and Marigo, M. (1996). Complementary use of capillary zone electrophoresis and micellar electrokinetic capillary chromatography for mutual confirmation of results in forensic drug analysis. /. Chromatogr. A 735, 227—235. 

Dedicated applications of capillary zone electrophoresis (CZE) coupled to MS are discussed, particularly in the field of drug analysis. Development of other capillary-based electrodriven separation techniques such as non-aqueous capillary electrophoresis (NACE), micellar electrokinetic chromatography (MEKC), and capillary electrochromatography (CEC) hyphenated with MS are also treated. The successful coupling of these electromigration schemes with MS detection provides an efficient and sensitive analytical tool for the separation, quantitation, and identification of numerous pharmaceutical, biological, therapeutic, and environmental compounds. 

Capillary zone electrophoresis (CZE) is the most common electrophoretic separation technique due to its simplicity of operation and its flexibility. It is the standard mode for drug analysis, identification of impurities, and pharmacokinetic studies. Other separation modes, such as capillary isotachopho-resis (CITP), micellar electrokinetc chromatography (MEKC), capillary electrochromatography (CEC), capillary gel electrophoresis (CGE), capillary isoelectric focusing, and affinity capillary electrophoresis (ACE), have then-advantages in solving specific separation problems, since the separation mechanism of each mode is different. 

Plasma protein binding is also an important parameter in the pharmacokinetic field. Frontal analysis combined with capillary zone electrophoresis (CZE-FA) (67-69) is a powerful technique for high-throughput assay, because it is relatively rapid and easy to automate, in comparison with conventional methods such as dialysis, ultrafiltration, and ultracentrifugation. Recently, we introduced the EKC approach with ionic CDs to frontal analysis for anionic drugs that cannot be analyzed by conventional CZE-FA (70). In this approach, ionic CDs work as an EKC pseudostationary not for proteins but for small solutes. 

W. Steuer, I. Grant, and F. Erni, Comparison of high-performance liquid chromatography, Supercritical fluid chromatography and capillary zone electrophoresis in drug analysis, J. Chromatogr., 507 125 (1990). 

S. Fanali, M. Cristalli, and A. Nardi, Capillary zone electrophoresis for drug analysis rapid determination of minoxidil on pharmaceutical formulations, Farmaio, 47 1 (1992). 

Gottardo R, Polettini A, Sorio D, Pascali JP, Bortolotti F, Liotta E, Tagliaro F (2008) Capillary zone electrophoresis (CZE) coupled to time-of-flight mass spectrometry (TOF-MS) applied to the analysis of illicit and controlled drugs in blood. Electrophoresis 29(19) 4078 1087. doi 10.1002/elps.200800087... 

CE has many separation modes that are beneficial to protein impurity analysis. Within the many thousands of potential protein impurities in a recombinant product there will be several that have only minor physicochemical differences from the drug product. The application of different CE modes can potentially resolve these impurities. CE methods can be divided into four principle modes that are applicable to recombinant protein impurity analysis capillary zone electrophoresis, capillary isoelectric focusing, capillary gel electrophoresis, and micellar electrokinetic capillary chromatography. Each mode will be discussed briefly. Since the technology is so young and still very exploratory, CE methods are developed empirically for specific separations. It is difficult to provide standard protocols for CE impurity analysis. Instead, protocols that can be used as a starting point for impurity analysis will be provided as well as the citation of examples of impurity analyses from the literature to provide additional sources of protocols for interested readers. 

Boone CM, Jonkers EZ, Franke JP, de Zeeuw RA, Ensing K. Dynamically coated capillaries improve the identification power of capillary zone electrophoresis for basic drugs in toxicological analysis. J Chromatogr A 2001 927 203. 

Gottardo R, Bortolotti F, De Paoli G, Pascal JP, Miksik I, Tagliaro F (2007) Hair analysis for illicit drugs by using capillary zone electrophoresis-electrospray ionization-ion trap mass spectrometry. J Chromatogr A 1159(1-2) 185-189... 

Capillary zone electrophoresis, CZE, is the simplest CE mode in which the separation is based on differences in the charge-to-mass ratio of the analytes. This approach can be effective in a number of applications in particular, quaternary alkaloids owing to the permanent charge are ideal solutes in CZE, regardless of the pH of the running buffer. Below, the most important parameters affecting the CZE separation will be considered with emphasis on the relevant aspects involved in analysis of alkaloids in herbal drugs and medicinal plants. 

Li 2002) determined sildenafil and its metabolite in human serum by capillary zone electrophoresis-mass spectrometry analysis using covalently bonded PMIM Q to a silica capillary. Scheme representation of the IL coating procedure is presented on Fig.l3. The adsorption of the analytes onto the bare capillary wall was eliminated by the IL coating and the drugs were baseline-sep)arated within 14 min with detection limits of 14 and 17 ng/mL for sildenafil and metabolite respectively. 

A variety of on line sample pretreatment procedures have been described for the coupling to on-line capillary zone electrophoresis (CZE)-MS, including capillary isotachophoresis, electrodialysis, liquid-liquid electroextraction and SPE on Empore disks. The latter system was applied to the analysis of the neuroleptic drug haloperidol in patients urine by on-line Empore-disk SPE-CZE-MS. 

Although affinity capillary electrophoresis (ACE) in its classical mode (one of the reagent is dissolved in a BGE, another is injected) is the most widely used technique in the literature, other capillary electrophoretic methods exist which are even more favorable concerning the information about binding parameters obtainable the Hummel-Dreyer (HD) method, frontal analysis (FA), the vacancy peak (VP) method, and vacancy affinity capillary electrophoresis (VACE) (see, e.g., Refs. 49-57). All the methods need as a precondition that the equilibrium between the reactants (say, protein P, drug D, and complex formed PD) is established rapidly compared to the dislocation of the electropho-retically migrating zones. The experimental setup of the HD and the ACE methods is identical, and so is the setup for the VP and the VACE methods. FA differs from all the other techniques. 

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