Electrochemical detectors volume

The amperometric detector is currently the most widely used electrochemical detector, having the advantages of high sensitivity and very small internal cell volume. Three electrodes are used ... 

LCEC is a special case of steady-state hydrodynamic chronoamperometry. In LCEC, the concentration changes as the chromatographic zones flow past the detector. The electrode is operated in the limiting current region for the eluted compounds, even though the concentration varies as the zones enter and leave the detector compartment. It is important to note that the volume of solution in the active region of the typical electrochemical detector ( 1 pL or even less) is very small compared to the volume occupied by the typical chromatographic zone ( — 0.1-1 mL). 

Electrochemical detectors for liquid chromatography have reached a level of maturity in that thousands of these devices are used routinely for a variety of mundane purposes. Nevertheless, the technology is advancing rapidly in several respects. Multiple electrode and voltammetric detectors have been developed for more specialized applications. Small-volume transducers based on carbon fiber electrodes are being explored for capillary and micropacked columns. Recently, electrochemical detection has also been coupled to capillary electrophoresis [47]. Finally, new electrode materials with unique properties are likely to afford improved sensitivity and selectivity for important applications. 

Detectors are not limited to solo use they can be hooked in series to get more information from the same sample. In a serial operation, be sure that the refractive index detector or electrochemical detector is the last in the line. Their flow cells are more fragile than UV and fluorescence cells and won t take the increased back-pressure. Keep the tubing diameter fine and as short as possible to avoid band spreading. You must correct for connecting tubing volume (time) delay in comparing chromatograms from the two detectors. 

While electrochemical detectors are extremely popular and useful for some analyses, some analysts find them very difficult to use. However, since they are used in aqueous solutions typical of the popular reverse phase mode, their use continues to expand. They are selective and sensitive, and their very small cell volumes make them ideal for microbore columns. 

The electrochemical detector in the form described above is extremely sensitive but suffers from a number of drawbacks. Firstly, the mobile phase must be extremely pure and in particular free of oxygen and metal ions. A more serious problem arises, however, from the adsorption of the oxidation or reduction products on the surface of the working electrode. The consequent electrode contamination requires that the electrode system must be frequently calibrated to ensure accurate quantitative analysis. Ultimately, the detector must be dissembled and cleaned, usually by a mechanical abrasion procedure. Much effort has been put into reducing this contamination problem but, although diminished, the problem has not been completely eliminated particularly in the amperometric form of operation. Due to potentially low sensing volume the detector is very suitable for use with small bore columns. 

Chloride ion concentration was measured by ion chromatography with a Dionex Bio LC chromatograph equipped with a Dionex pulsed electrochemical detector and a Dionex PAX-100 metal-free anion column (25 cm long, 4.6 mm i.d.). The eluent was a mixture of 80% H20, 10% acetonitrile, and 10% 191-mM NaOH the flow rate was 1 mL/min, and the injection loop volume was 50 p,L. 

Because of the small elution peak volume obtained from narrow-bore packed columns, conventional concentration dependent detectors such as UV-vlslble absorbance, fluorometrlc, and electrochemical detectors must be purged with makeup solvent or miniaturized to allow minimum extra-column contribution to peak spreading. A cell volume 0.1 i Is desirable for narrow-bore packed columns of I.D. Ishll et. al. reported the reduction of an UV detector cell volume to OAiiZ by using a quartz tube of... 

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