Electrochemical detectors

Many different detectors are used in RPLC, including ultraviolet-visible spectrophotometers (UV-VIS), refractive index (RI) detectors, electrochemical (EC) detectors, evaporative light-scattering detectors, fluorimeters, and... 

Detectors. Fluorescence and UV detectors are used in the HPLC analysis. The high sensitivity and specificity of fluorescence detection in tocopherols and tocotrienols make the fluorescence detector the first choice. The fluorescence detector is ten times more sensitive and has less background noise than the UV detector. Electrochemical detectors are also used in the analysis of tocopherols and tocotrienols (Murphy and Kehrer, 1987 Sanchez-Perez et al., 2000). As a high-polarity mobile phase is needed for the electrolytes when using an elec-... 

Fig. 11.12. Schematic diagram of a column-switching HPLC system. V-l, V-2, and V-3 switching valves. The position of °—c means position 1, and ° ° is position 2. P-1 and P-2 pumping system at 0.2 mL min-1 flow rate. Detector electrochemical detector with diamond electrodes. Column-1 and Column-2 Inertsil ODS-3. Loop 500 pL. A Mobile phase of 60% methanol-water containing 0.5% phosphoric acid.

Rocuronium Vecuronium Column CN Venous plasma of spherisorb column dog (15 cm x 4.6 mm). Column temperature maintained at 35 °C Mobile phase water ACN MeOH = 55 35 10 (adjusted to pH 4.75) Detector electrochemical detector (Coulochem II, ESA) set at 750 mV... 

Fluorometric detector Electrochemical detectors 1 x 10-11 g 1 x 105 For fluorescent species with conjugated bonding and aromaticity Relatively insensitive to temperature and flow fluctuations nondestructive can be used with gradient elution often, chemical derivatization is done on analytes to form fluorescent species uses deuteriem lamp for 190-400 nm or tungsten lamp for 350-600 nm... 

Due to the selective nature of the most sensitive detectors, electrochemical and fluorescence, derivatisation is often required to take advantage of these. Derivatisation has also been used to improve sensitivity of methods using UV detection by adding a more strongly absorbing chromophore. Derivatisation can be combined with trace enrichment a detection level of 70ngr for aldicarb (2-methyl-2-(methylthio) propanol 0-[(methyl-amino)carbonyl] oxime), aldicarb sulphoxide and aldicarb sulphone has been quoted for 10-ml sample volumes using this technique. 

Very often baseline problems are related to detector problems. Many detectors are available for HPLC systems. The most common are fixed and variable wavelength ultraviolet spectrophotometers, refractive index, and conductivity detectors. Electrochemical and fluorescence detectors are less frequently used, as they are more selective. Detector problems fall into two categories electrical and mechanical/optical. The instrument manufacturer should correct electrical problems. Mechanical or optical problems can usually be traced to the flow cell however, improvements in detector cell technology have made them more durable and easier to use. Detector-related problems include leaks, air bubbles, and cell contamination. These usually produce spikes or baseline noise on the chromatograms or decreased sensitivity. Some cells, especially those used in refractive index detectors, are sensitive to flow and pressure variations. Flow rates or backpressures that exceed the manufacturer s recommendation will break the cell window. Old or defective source lamps, as well as incorrect detector rise time, gain, or attenuation settings will reduce sensitivity and peak height. Faulty or reversed cable connections can also be the source of problems. 

Detection systems mainly used in routine analysis are universal UVA/lS-detectors, selective fluorescence-detectors, electrochemical-detectors and, in recent years, the Diode-Array-detector. 

Cylinder, graduated, 10 mL 1 Detector, electrochemical, like Wescan Model 271... 

Another critical part of flow methods is the detector (electrochemical flow cell). An electrochemical detector uses the electrochemical properties of analytes for determination in the flowing stream. Electrochemical detection is usually performed by controlling the potential of the working electrode at a fixed value and monitoring the current as a function... 

Electrochemical Detectors— Electrochemical detectors specific to sulfur may be used. 

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