A handy detection cell for end-column electrochemical detection in capillary electrophoresis

A new sequential injection analysis-capillary electrophoresis system with amperometric detection

A novel and fully automated sequential injection analysis manifold coupled to a capillary electrophoresis apparatus with amperometric detection, is described. The sequential injection manifold was isolated from the high voltage by inserting an air plug into the circuit. Small buffer reservoirs were used to avoid the need to pump fresh buffer to the interface during the electrophoretic separation. No decoupling device was used to mitigate the interference from the high voltage electric field, instead the potential shift induced by the separation voltage, was accounted for. The new hydrodynamic injection method presented is based on the overpressure created in the circuit when a pinch valve is closed for a predetermined time. The injection method yields RSD values of peak height and area below 2.55 and 1.82%, respectively, at different durations of valve closure (n = 5). The capillary and working electrode alignment was achieved by adapting a commercial available capillary union. When the electrode was replaced, the alignment method proved to be very reliable, yielding RSD values of peak height and area lower than 2.64 and 2.08%, respectively (n = 8). Using this system with a gold microelectrode, dopamine, and epinephrine could be quantified within the concentration range of 1-500 μM and detected at a concentration of 0.3 μM. The methods here presented could be applied for the development of new capillary electrophoresis systems with amperometric detection and/or to the design of fully automated systems for online process monitoring purposes.

Analysis of inorganic and small organic ions by CE with amperometric detection

Capillary electrophoresis has become a widely useful analytical technology. Amperometric detection is extensively employed in capillary electrophoresis for its many inherent virtues, such as rapid response, remarkable sensitivity, and low cost of both detectors and instrumentations. Analysis of inorganic and small organic ions by capillary electrophoresis is an important research field. This review focuses on the recent developments of capillary electrophoresis coupled with amperometric detection for analysis of inorganic and small organic ions. Advancements in electrophoresis separation modes, amperometric detection modes, working electrodes, and applications of inorganic ions, amino acids, phenols, and amines are discussed.

Analytical applications of a carbon nanotubes composite modified with copper microparticles as detector in flow systems

In this work we report on the successful use of a composite prepared by dispersion of multi-wall carbon nanotubes (1-5 microm length, 20-50 nm diameter) and copper microparticles within mineral oil as detector for amino acids quantification in flow injection analysis and capillary electrophoresis. The resulting electrode displays a highly sensitive amperometric detection of amino acids, based on the copper dissolution facilitated by the strong activity of amino acids as ligands of Cu(II). The sensor makes possible the detection of amino acids, electroactive or not, at very low potentials (0.000 V) and physiological pH. A correlation between the sensitivity for the amino acids and the amount of copper within the composite is observed, demonstrating the importance of the metal in the sensor response. The best analytical performance is obtained for the electrode containing 12.0% (w/w) copper. The excellent results obtained with the carbon nanotube paste electrodes containing copper (CNTPE-Cu) as detector in flow systems makes them an interesting alternative for further analytical applications involving different bioanalytes.

Separation procedures capable of revealing DNA adducts

Detection and quantification of DNA adducts are very important in relation to diseases such as cancer. Both high sensitivity and high selectivity are required for the detection of DNA adducts because the content of adducts in DNA is very small compared with those of normal bases and only small amounts of DNA samples are available for analysis in general cases. In this paper are described separation procedures such as liquid chromatography, gas chromatography and capillary electrophoresis combined with a detection and identification method such as 32P-postlabeling, mass spectrometry, electrochemical detection, fluorescence detection and immunoassay. The merits and demerits of the procedures are also discussed.

Analysis of DNA adducts of acetaldehyde by liquid chromatography-mass spectrometry

A highly sensitive method using liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) was developed for the analysis of DNA adducts of acetaldehyde (AA). AA, which is the primary oxidative metabolite of ethanol, is considered to possess carcinogenic activity. AA reacts with the exocyclic amino group of guanine in DNA to form N2-ethylguanine (Et-Gua) and 1,N2-propanoguanine (Pr-Gua) adducts. With the present method, such adducts were detected as the base forms from DNA chains using depurination in the pretreatment process. In our measurement with LC-ESI-MS, the limits of detection (LODs) of the Et-Gua and Pr-Gua adducts of the base forms were 3.0 x 10(-10) and 1.0 x 10(-9) M, respectively, and the LODs are about two orders of magnitude lower than those of the nucleoside forms. Calf thymus DNA samples treated with AA and NaBH3CN were analyzed by this method. Et-Gua was clearly detected and, in the absence of NaBH3CN, Pr-Gua was detected predominantly. Furthermore, the method was also applied to study whether or not these two adducts are formed in DNA of cultured HL-60 cells during exposure to AA for 24 h. Pr-Gua was clearly detected and traces of Et-Gua were also detected in the DNA of the cells. Although the sensitivity of this method is lower by at least oneorder of magnitude than the 32P-postlabeling assay, currently the most sensitive method, our method does not involve complex enzymatic reactions for the postlabeling and the use of troublesome radioactive materials. Furthermore, it enables structural identification of guanine adducts. The present method would be a useful tool for studies of Et-Gua and Pr-Gua adducts in connection with carcinogenesis.

Amperometric and voltammetric detection for capillary electrophoresis

The focus of this article is amperometric and voltammetric detection coupled with capillary electrophoresis. Fundamental concepts and progress in the field of capillary electrophoresis with electrochemical detection (CEEC) that have occurred within the past three years, including new methodologies and unique applications, are highlighted. This review contains 95 references.

Capillary-electrode alignment by an optical-fiber connector for amperometric detection in capillary electrophoresis

We describe here an electrochemical cell ideal for routine analysis of CE-EC experiments (capillary electrophoresis coupled with electrochemical detection). The cell was modified from a fiber-optic connector, named MT, which allowed frequent change and fast alignment between a pair of 4-strand fiber ribbons. The relative standard deviations of the current response and migration time for 100 microM dopamine were, respectively, 3.7 and 0.5% in five repetitive routines of disconnecting, polishing, and assembling the CE cell. The time required for alignment of the separation capillary and the working electrode was < 10 s, once all components were assembled in an MT fiber-optic plug. These features enabled CE-EC users to polish the working electrode and reassemble the EC cell as in HPLC-EC. However, to accommodate the channel dimensions of the commercially available MT, a special order capillary with outer diameter of 125 microm is necessary at this stage.