Chitosan as Cationic Polyelectrolyte for the Modification of Electroosmotic Flow and Its Utilization for the Separation of Inorganic Anions by Capillary Zone Electrophoresis

Abstract

IntroductionIn the analysis of anionic species by capillary zone electrophoresis (CZE), control of the direction and speed of the electroosmotic flow (EOF) is essential, because the direction of the electrophoretic migration of anions is opposite to that of the EOF, when a usual fused silica capillary is used. When the analyte anions possessing large electrophoretic mobility, such as inorganic anions, are supposed to be detected, the electrophoretic mobility of the analytes is larger than the EOF or almost equivalent to it at alkaline solution, and it takes a longer separation time even using the reversal of the electric field. Therefore, the speed of the EOF is usually suppressed or reversed for the analysis of anionic species. Selection of an acidic migrating solution is one answer and the EOF will be reduced with the migrating solution. Since cationic surfactants are used to form bi-layers by the dynamic coating of the capillary [1][2][3] and the EOF is reversed as a result, a surface-refining reagent is indispensable in the CZE separation of anionic species.In addition to the cationic surfactants, cationic polyelectrolytes are promising alternatives to reverse the direction of the EOF; poly(1,1-dimethyl-3,5-dimethylenepiperidinium) chromate, hexadimethrine chromate, poly(1,1-dimethyl-3,5-dimethylenepyrrolidinium) chromate, diethylaminoethyl dextran chromate were used as such polyelectrolytes, and the analyte anions were indirectly detected with chromate ions. 4 The cationic polyelectrolytes play an additional role to work as interacting reagent with the analyte anions. Haddad and his coworkers investigated the ion-exchange mechanism in the CZE separation by simulation and practical resolution improvement, and they proposed ion chromatography-capillary electrophoresis. 5,6 Electrophoretic mobility of some organic anions was reduced by ion-exchange with poly(diallyldimethylammonium)phthalate background electrolyte, and the selectivity among the anions were also developed.Chitosan, an N-deacetylation product of chitin, is one of the useful cationic polyelectrolytes, and has several characteristics such as being made of relatively hydrophilic saccharine groups, safe and biodegradable materials present in nature. Chitosan is soluble in acidic solution with the protonation of the amino groups (pKa = 6.5). 7 Chitin and chitosan oligosaccharides were separated and detected by capillary zone electrophoresis after derivatization with 8-aminopyrene-1,3,6-trisulfonic acid. 8 High-molecular chitosan was also analyzed by CZE. 9 Chitosan has also been used as coating material on fused silica capillary for the separation of basic proteins, 10 and coupled chitosan has been used for both basic and acidic proteins. 11In this study, chitosan as a cationic polyelectrolyte was used to reverse the EOF by dynamic coating of the capillary innerwall, and the capillary was used for the separation of inorganic anions. The interactions with analyte anions were also investigated through the changes in electrophoretic mobility of some ino...

Use of contactless conductivity detection for non-invasive characterisation of monolithic stationary-phase coatings for application in capillary ion chromatography

“…Capillary-based separation techniques for ion analysis have received considerable attention over the past two decades, with new applications of capillary-based methods continuing to appear regularly. The majority of these recent reports are either based upon capillary zone electrophoresis (CZE), [1][2][3][4] capillary electrochromatography (CEC) [5][6][7] or capillary ion chromatography (CIC). [8][9][10] In the fields of CEC and CIC, owing to the relative lack of commercially available capillary format ion-exchange columns, a significant number of the above studies have employed dynamically-modified or permanently/semi-permanently-coated reversed-phase stationary phases, including open tubular, 6 particle-based 11,12 and newer monolithic-type columns.…”

A novel isotachophoresis of cobalt and copper complexes by metal ion substitution reaction in a continuous moving chelation boundary

“…[51][52][53] This kind of chelation reaction has been used for: (1) the probing for indirect photometric detection via the complexation prior to injection in the capillary zone electrophoresis (CZE), 54,55 and (2) the online separation of metal ions via on-capillary complexation in CZE. [56][57][58][59][60] In the chelation reaction system (I), the equilibrium reaction between Cu(II) and EDTA took dominant as compared with that between Co(II) and EDTA, because the stability constants of [Co-EDTA] 2À (lgK Co ¼ 16.31) was less than that of [Cu-EDTA] 2À (lgK Cu ¼ 18.80). 61…”

Surface functionalization of low-cost textile-based microfluidics for manipulation of electrophoretic selectivity of charged analytes

“…In these systems, the electromigration of anionic analytes is in a counter direction with respect to the EOF (i.e., cathode to anode). Therefore, it is often desirable to suppress or reverse the EOF to achieve a more rapid analysis of the anionic species of interest (Takayanagi and Motomizu 2006). Similarly, during the analysis of cationic species, the strong interaction between the negatively charged silica capillary walls and the positively charged analyte, as in the case of protein analysis, can result in reduced separation efficiency (Stutz 2009).…”