End-Column Electrochemical Detection for Capillary Electrophoresis

Combining amperometry and mass spectrometry as a dual detection approach for capillary electrophoresis

Dual detection concepts (DDCs) are becoming more and more popular in analytical chemistry. In this work, we describe a novel DDC for capillary electrophoresis (CE) consisting of an amperometric detector (AD) and a mass spectrometer (MS). This detector combination has a good complementarity as the AD exhibits high sensitivity, whereas the MS provides excellent selectivity. Both detectors are based on a destructive detection principle, making a serial detector arrangement impossible. Thus, for the realization of the DDC, the CE flow was divided into two parts with a flow splitter. The DDC was characterized in a proof-of-concept study with ferrocene derivates and a nonaqueous background electrolyte. We could show that splitting the CE flow was a suitable method for the instrumental realization of the DDC consisting of two destructive detectors. By lowering the height of the AD compared to the MS, it was possible to synchronize the detector responses. Additionally, for the chosen model system, we confirmed that the AD was much more reproducible and had lower limits of detection (LODs) than the MS. The LODs were identical for the DDC and the single-detection arrangements, indicating no sensitivity decrease due to the CE flow splitting. The DDC was successfully applied to determine the drug and doping agent trimetazidine.

Open source capillary electrophoresis

Open source paradigm is becoming widely accepted in scientific communities and open source hardware is finding its steady place in chemistry research. In this review article, we provide the reader with the most up-to-date information on open source hardware and software resources enabling the construction and utilization of an "open source capillary electrophoresis instrument". While CE is still underused as a separation technique, it offers unique flexibility, low-cost, and high efficiency and is particularly suitable for open source instrumental development. We overview the major parts of CE instruments, such as high voltage power supplies, detectors, data acquisition systems, and CE software resources with emphasis on availability of the open source information on the web and in the scientific literature. This review is the first of its kind, revealing accessible blueprints of most parts from which a fully functional open source CE system can be built. By collecting the extensive information on open source capillary electrophoresis in this review article, the authors aim at facilitating the dissemination of knowledge on CE within and outside the scientific community, fosters innovation and inspire other researchers to improve the shared CE blueprints.

A novel method for ranitidine hydrochloride determination in aqueous solution based on fluorescence quenching of functionalised CdS QDs through photoinduced charge transfer process: spectroscopic approach

A novel method for the quantitative determination of ranitidine hydrochloride (RNH) based on the fluorescence quenching of functionalised CdS quantum dots (QDs) by RNH in aqueous solution was proposed. The method is simple, rapid, specific and highly sensitive with good precision. The thioglycolic acid (TGA)-capped CdS QDs were synthesized from cadmium nitrate and sodium sulfide in alkaline solution. Under the optimal conditions, the Stern-Volmer calibration plot of F(0)/F against concentration of RNH was linear in the range of 0.50-15.0 μg mL(-1) with a correlation coefficient of 0.996. The limit of detection (LOD) was 0.38 μg mL(-1). The method was satisfactorily applied to the direct determination of RNH in pharmaceutical formulations with no significant interference from excipients. The results were found to be in good agreement with those obtained by the reference method and the claimed value. The accuracy and reliability of the method were further ascertained by recovery studies via the standard-addition method, with percentage recoveries in the range of 98.47 to 102.30%. The possible fluorescence quenching mechanism for the reaction was also discussed.

Fundamentals of electrochemical detection techniques for CE and MCE

The electroanalytical techniques of amperometry, conductometry and potentiometry match well with the instrumental simplicity of CE. Indeed, all three detection approaches have been reported for electrophoretic separations. However, the characteristics of the three methods are quite distinct and these are not related to the optical methods more commonly employed. A detailed discussion of the underlying principles of each is given. The issue of possible effects of the separation voltage on the electrochemical detection techniques is considered in depth, and approaches to the elimination of such interferences are also discussed for each case.

Indirect determination of pyruvic acid by capillary electrophoresis with amperometric detection

A method of indirectly measuring pyruvic acid (PA) by capillary electrophoresis with amperometric detection is proposed for the first time. It is based on the oximation reaction between PA and hydroxylamine (NH(2)OH), and the quantification of PA was performed by direct and sensitive amperometric detection of excessive NH(2)OH after the oximation reaction. This method displayed a good sensitivity, and the detection limits of NH(2)OH and PA are 1.76 x 10(-7) and 3.88 x 10(-7)mol/L, respectively at S/N=3. The linear relationship between the peak current and PA concentration is exhibited over the range from 4 x 10(-6) to 1 x 10(-4)mol/L. This method has been applied to determine PA in rat plasma with satisfactory results.

Capillary electrophoresis with microwave-enhanced electrochemical detection

A new experimental development concerning microwave-assisted electrochemical detection in conjunction with capillary electrophoresis is presented. Focused microwaves are readily incorporated into end-column detection systems for capillary electrophoresis, they induce strong localised thermal activation at microelectrodes, and they affect and modulate, in particular, signals for chemically irreversible redox processes.

Characterization of etched electrochemical detection for electrophoresis in micron inner diameter capillaries

An enhanced etched electrochemical (EC) detection technique has been developed for CE in micron inner diameter capillaries. The design improvements allow for better alignment between the capillary bore and the electrode. This new method involves utilizing a carbon fiber microelectrode and etching both the carbon fiber and the detection end of a micrometer-sized inner diameter capillary to limit dead volume and analyte diffusion at the amperometric EC detector. To understand the factors affecting enhanced detector efficiency, a detailed examination of the relationship between detector design and performance has been completed by exploring the effects of varying electrode diameter, tip shape, and size, in addition to the etch length of the capillary outlet. The enhanced detection provides peak efficiencies as high as 75000 theoretical plates and estimated detection limits as low as 40 nM for dopamine. This etched detection method should further facilitate volume-limited sample analysis by CE.

Determination of hydroxyl radical by capillary zone electrophoresis with amperometric detection

Hydroxyl radical (OH*) can cause severe damage to cells and tissues. However, its analysis is very difficult for its high reactivity and very short half-life. In this paper, a simple and highly sensitive method, capillary zone electrophoresis with amperometric detection (CZE-AD) was introduced indirectly to determine OH* by determining its reaction products with salicylic acid (SAL), 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA). The optimum conditions of CZE-AD for the determination of 2,3-DHBA and 2,5-DHBA were explored. Under the optimum conditions, SAL, 2,3-DHBA and 2,5-DHBA could be perfectly separated within 15 min, and the linearity ranges of 2,3-DHBA and 2,5-DHBA were between 1.0 x 10(-7) and 1.0 x 10(-4) mol l(-1). Their detection limits were as low as 2 x 10(-8) mol l(-1), which were much lower than that in CE-UV method. The method was also applied to study the free OH* scavenging activity of angelica polysaccharide. The experimental results showed that this CZE-AD method was very sensitive and practical in both the determination of free OH* and the evaluation of free OH* scavenging activities of antioxidants.

Overview of the status and applications of capillary electrophoresis to the analysis of small molecules

The status of capillary electrophoresis (CE) in the analysis of small molecules is reviewed and summarised with the illustrative use of recent literature references. Examples are cited in this review which demonstrate that CE is now a recognised and established technique in many industries, law courts and government regulatory agencies. Each of the principal areas of CE application in small molecule analysis are covered in sections which highlight the recent developments and possibilities within that area. Application areas include the analysis of pharmaceuticals, agrochemicals, chiral separations, and forensics is covered. This is an update to a previous review article [J. Chromatogr. A 856 (1999) 443] and covers papers published between 1999 and 2002. Technical developments and improvements, such as the advent of capillary array instrumentation for increased sample throughput, and improved detection options are described. Overall it is concluded that CE has become a recognised and established technique in many areas and is still within a period of development of both instrumentation and application which will continue to expand usage.

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.

Microchip capillary electrophoresis coupled to sinusoidal voltammetry for the detection of native carbohydrates

The development of a microchip electrophoresis system involving integrated frequency based electrochemical detection is described. The use of poly(dimethylsiloxane) (PDMS) as the channel substrate greatly simplifies the fabrication process while decreasing cost and time consumption. Characterization of this system is accomplished through the detection of native carbohydrates at planar copper electrodes. Various photolithographic techniques are explored in the optimization of electrode area. Separation efficiency of 1 x 10(5) theoretical plates per meter is demonstrated. Sinusoidal voltammetry utilizes information in the frequency domain to achieve sensitive detection through either of two approaches, maximization of signal or minimization of noise. Mass detection limits (S/N = 3) of less than 200 amol have been accomplished for glucose and sucrose. Sinusoidal voltammetry also facilitated the selective isolation of an analyte signal from a pair of chromatographically unresolved species through the use of phase discrimination.

Determination of cannabinoids in hair using high-pH* non-aqueous electrolytes and electrochemical detection. Some aspects of sensitivity and selectivity

Non-aqueous capillary electrophoresis with electrochemical detection (NACE-ED) was applied to the determination of cannabinoids in hair. The effect of different electrolyte compositions on the selectivity of the separation of tetrahydrocannabinol (THC), cannabinol (CBN), cannabidiol (CBD) and tetrahydrocannabinol carboxylic acid (THCA) was studied. Complete electrophoretic resolution was obtained using a strongly basic background electrolyte consisting of 5 mM sodium hydroxide dissolved in acetonitrile-methanol (1:1). Electrochemical detection yielded well defined signals in the oxidation mode. In order to obtain low limits of detection experimental parameters, which determine the sensitivity and the noise level, were optimized. A crucial parameter for sensitive measurements using a wall-tube flow cell as end-column detector is the distance between the capillary outlet and the working electrode. The highest signal-to-noise ratio using a 50 microm I.D. capillary was obtained at a distance of 25 microm. When the capillary outlet was moved away from the working electrode, thus reducing the strength of the separation field present at the working electrode, a large low frequency noise developed. This rise was attributed to disturbances of the hydrodynamic pattern in the flow cell. Analytical aspects such as sensitivity, reproducibility and selectivity were addressed in this work. The precision of NACE-ED regarding migration time and peak height for a sample containing 1 microg/ml THC was 0.4% and 1.1% (RSD), respectively (n=5). The calibration curve was linear for concentrations ranging between 0.1 and 10 microg/ml (r=0.998). The limit of detection for THC was 37 ng/ml, which is almost two orders of magnitude lower when compared with on-column UV detection. The method was evaluated using hair samples containing cannabinoids as sample material.