Cationic Cellulose Derivatives In The Application Of Capillary Electrophoresis

Capillary electrophoresis (CE) is a powerful and efficient separation technique. CE has played an important role in Human Genome Project, and has been applied in a variety of fields, such as biomedicine, pharmacy, environment and forensic medicine. The capillary coating is crucial for a variety of applications. The development of new coatings for CE still remains as an active area of research. Cellulose is one of the most abundant renewable resources in the nature with fascinating merits such as cheap and biodegradable. However, cellulose cannot be used for coating because it is insoluble in aqueous or most organic solvents. In order to search new environmentally friendly coatings for improved CE applications, in this dissertation some cationic cellulose derivatives were synthesized by modifying the cellulose directly and were used as a dynamic coating for CE. The separation performances of these cellulose derivative additives and their possible interactions with the analytes were investigated. Main points of this work are listed as following:1. Cationic cellulose derivative, quaternized cellulose (QC) was homogeneously synthesized at first by reacting cellulose (cotton linter pulp) with etherifying agent. Dodecyl modified quaternized cellulose (DMQC) was then obtained by the further modification of QC. When the DMQC was added in the background electrolyte as the additive, the capillaries generated stable and fast reverves EOF over broad pH range (pH3.0-12.0). The salicylic, p-nitrobenzoic, p-aminobenzosulfonic acid and acerylsalicylic acid could be separated within8min. Six sulfa drugs were separated in less than10min. In addition, neutral compounds, alkyl-phenyl ketone homologues, could be partly separated. Both the direction and the magnitude of the EOF were changed with the addition of DMQC. The use of DMQC incorporated a possible hydrophobic interaction that improved the separation of neutral analytes.2. A novel cellulose derivative, octadecyl modified quaternized cellulose (ODMQC), was synthesized. ODMQC could self-assemble to form stable nano-scaled micelle structure in aqueous solution because it carried both hydrophobic groups and hydrophilic groups. When added in the background electrolyte, the capillaries could generate applicable anodal EOF in range of pH3.0-12.0. Due to the lack of UV active groups, ODMQC could not interfere with the UV detection. It is shown that ODMQC-added capillaries allow the separation of basic proteins by reducing their adsorption onto the capillary wall. Also, the addition of ODMQC provides adequate separation of aromatic acids with low pKa values and improved separation of sulfa drugs. It is worthy to note that ODMQC not only a polycation for coating but also a micellar structure which functioned as pseudo stationary phase in micellar electrokinetic chromatography (MEKC).3. A new cellulose derivative, octyl-modified quaternized cellulose (OMQC), was synthesized and used as electrolyte additive for the analysis of5-methylcytosine by capillary electrophoresis with UV detection. While added in the background electrolyte, OMQC carrying octyl groups and quaternary ammonium groups exhibited dynamic coating ability. Capillary coated with OMQC was able to generate astable anodal electro-osmotic flow even at pH12.0. After several running conditions were optimized, cytosine and5-methylcytosine were separated with a resolution near4.0in less than10min, and the interference from other bases was avoided effectively. The detection limits (S/N=3) were1.1and1.5μg/mL for cytosine and5-methylcytosine, respectively. A new method for quantification of genomic methylation level was then developed on the basis of hydrolysis of DNA by formic acid and separation of nucleic acid bases by capillary electrophoresis. The method was fast, reproducible, sensitive, and selective. In addition, the method is unbiased and cost-effective since no enzyme is used in the procedure. It could be a practical alternative to the methods available for quantification of global DNA methylation levels, and may have other potential applications.4. QC/TiO2nanocomposite was synthesized via sol-gel by adding tetrabutyl titanate into the QC aqueous solution in ice-bath, and the structure of this nanocomposite was characterized by instrumental analytical methods. When the QC/TiO2nanocomposite was used as dynamic coating, the capillaries generated relatively strong reversed EOF. The eight acidic and basic proteins, namely ovalbumin (OVA), α-Lactoalbumin, conalbumin (ConA), myoglobin (Mb), monoclonal antibody, RNAse A, horseradish Peroxidase (HRP) and cytochrome C, were simultaneously separated. The separation of glycoisoforms of OVA further demonstrated the introduction of TiO2had led to enhanced separation selectivity. The QC/TiO2composite may have great potential in protein analysis.