Electrochemical detection in HPLC

The HPLC pump, the damping system, injector, column, capillaries, tube fittings, etc., must be in perfect working order. The system is much more sensitive to column contamination and to pressure fluctuations due to pump operation or imperfect fittings than is, for example, that of UV detection. 

All of the usual precautions for trace analysis must be taken. Corrosion of steel parts in contact with the eluent must be avoided, since the presence of Fe can seriously interfere. The eluent substances, in addition, must not contain complex-forming substances. 

Where a single-stage pump is used, it is common to find that pressure fluctuations occur in the ceU, causing serious noise in the detector signal. An additional pulse damper working on the Bourdon tube principle can assist in minimising noise from this source. 

Many of the solvents normal to HPLC use can be used for the eluent make-up. The additional conductivity required for electrochemical detection is provided by the addition of an electrolyte in the range of 1 to 10 g/L, yielding conductivities of 1 to 10 mS/cm. The eluent is degassed in the usual manner, using hehum or a vacuum. 

The eluent, wherever possible, should be used as the sample solvent in order to avoid disturbances caused by a change in the solvent front. 

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WR. LaCourse, Pulsed Electrochemical Detection in HPLC, Wiley, New York, 1997. 

Pacakova V, Stulik K. Electrochemical detection in HPLC 2. Applications. Nahrung-Eood 29, 651-664, 1985. 

Fig. 12 Applied voltage waveforms for various modes of electrochemical detection in HPLC.

Flanagan, R. J., D. Perrett, and R. Whelpton. 2005. Electrochemical detection in HPLC Analysis of drugs and poisons. Cambridge, England Royal Sodety of Chemistry... 

M.F. Cardosi, Electrochemical detection in HPLC An overview, Chromatogr. 

Electrochemical Detection in HPLC Analysis of Drugs and Poisons... 

Polarographic also can be utilized for the determination of many organic compounds present in the air, e.g. in the vicinity of factories, in the industrial atmosphere, etc. In [23] are listed compounds like formaldehyde, acrolein, acetaldehyde, furfurol, hexachlorbutadiene, and nitro-cyclohexane. The tested air is passed through a trap containing the supporting electrolyte. Application of electrochemical detection in HPLC to the measurement of toxic substances in air is the subject of a paper[24]. Derivatives of phenols and amines were chosen as examples. 

Flanagan, R.J., Perrett, D., and Whelpton, R., 2005. Electrochemical Detection in HPLC Analysis of Drugs and Poisons. RSC Chromatography Monographs. RSC PubUshing, Cambridge, UK. 56 p. 

R. J. Flanagan, D. Perrett and R. Whelpton, Electrochemical Detection in HPLC - Analysis of Drugs and Poisons, Royal Society of Chemistiy, 2005. 

Whilst the application of electrochemical detection in HPLC is becoming established for certain classes of compounds, such as biogenic amines [2] and plant phenolic materials [3], its use for compounds that are less easily oxidized has not been widely examined. 

Electrochemical detection in HPLC has become established for some, more specialized, applications such as catecholamine analysis though it can be exploited for a far wider range of compounds. The work in this paper has attempted to investigate some of the basic properties of an electrochemical detection system and some more difficult applications. The detector has a linear dynamic range and precision that are comparable with those of other detectors for HPLC. It is, however, more dependent on temperature than, for example, the UV absorption detector and must be operated in a temperature controlled environment to obtain the lowest detection limits. For many electroactive compounds with moderate oxidation potentials, the electrochemical detector can yield sub-nanogram detection limits. 

Future developments of electrochemical detector cells and applications to a wider range of compounds can be foreseen and could lead to greater exploitation of these detectors. j There is still scope for improvement in cell design, particularly in the improvement in flow patterns to reduce noise./ Novel electrode materials could be profitably exploited, for example, if electrocatalysis towards a given substrate could be demonstrated or low background currents achieved. Chemical derivatization has been frequently exploited in polarography to expand its range of applicability and similar techniques, particularly if implemented post-column and in-line, could likewise expand the areas of application of electrochemical detection in HPLC. 

ELECTROCHEMICAL DETECTION IN HPLC IN A NATURAL PRODUCT PROBLEM... 

Electrochemical Detection in HPLC Natural Product Problem Roger M. Smith... 

Fedorowski J, LaCourse WR. A review of post-column photochemical reaction systems coupled to electrochemical detection in HPLC. Anal Chim Acta 2010 657 1-8. 

Another way to modify electrodes and which circumvents these problems is to incorporate the modifying compound into the carbon paste of a carbon paste electrode . Such a senor is easy to construct, eliminates the immobilization procedure, offers a surface easy to renew and allows the incorporation of numerous compounds. Several electrodes have been prepared following this procedure by incorporation of quinones , aromatic diamines , metalloporphyrins and metallic phthalocyanins . These latter compounds Ifave been selected as redox catalysts for electrochemical detection in HPLC 2 ... 

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