Amperometric detection aldehydes

Pulsed amperometric detection (PAD), introduced by Johnson and LaCourse (64, 65) has greatly enhanced the scope of liquid chromatography/electrochemistry (66). This detection mode overcomes the problem of loss of activity of noble metal electrodes associated with the fixed-potential detection of compounds such as carbohydrates, alcohols, amino acids, or aldehydes. Pulsed amperometric detection couples tlie process of anodic detection with anodic cleaning and cathodic reactivation of a noble metal electrode, thus assuring a continuously cleaned and active... 

Pulsed amperometric detection is used for the analysis of carbohydrates and other nonchromophoric molecules such as alcohols, aldehydes, and amines. In the DC mode the products of the oxidation reaction of those compounds poison the surface of the working electrode, and further analyte oxidation is inhibited. This results in peaks that decrease rapidly in height. To maintain a stable and active electrode surface, alternatively positive and negative potentials are repeatedly pulsed. 

Rocklin, R., Slingsby, R.W., and Woodruff, A. (1995) Optimization of conditions for the determination of alcohols and aldehydes using separation on high capacity ion-exchange resins and pulsed amperometric detection. Presentation No. 264, Pittsburgh Conference, New Orleans, LA, USA. 

R. Rocklin, R.W. Slingsby and A. Woodruff, Optimization of Conditions for the Determination of Alcohols and Aldehydes Using Separation on High Capacity lon-Ex-change Resins and Pulsed Amperometric Detection. Presentation No. 254, Pittsburgh Conference, New Orleans, 1995. 

Electrochemical detectors measure the current resulting from the application of a potential (voltage) across electrodes in a flow cell. They respond to substances that are either oxidizable or reducible and may be used for the detection of compounds such as catecholamines, carboxylic acids, sulfonic acids, phosphonic acids, alcohols, glycols, aldehydes, carbohydrates, amines, and many other sulfur-containing species and inorganic anions and cations. Potentiometric, amperometric, and conductivity detectors are all classified as electrochemical detectors. 

From studies on numerous compounds in aqueous alkaline solutions, Johnson concluded that all aldehydes, alcohols, polyalcohols, and carbohydrates are electrochemi-cally detected by the pulsed amperometric scheme described above [61-63] these compounds include the oligosaccharides [64, 65]. Detection limits are typically less than 0.1 ppm for early eluting peaks when the sample volume is approximately 50 pL. 

There have been several in vitro assay methods reported recently that are based on spectrophotometric, fluorometric, or amperometric means of detection. These assays were investigated using various natural, commercially available substrates or from specially designed and synthesized probes. The prerequisite for the donor substrate is a ketol moiety, and for the acceptor substrate an aldehyde function. 

Dithiocarbamate fungicides inhibit aldehyde dehydrogenase. In order to produce an amperometric biosensor with this enzyme also a bi-enzymatic system was designed with the enzyme diaphorase. Reaction of propiraialdehyde and NAD" in the presence of ADH produced NADH which could be detected via its reaction with hexacyanoferrate(in) by diaphorase. The changes of hexacyanoferrate (11) concentrations were monitored amperometrically with a Pt electrode or bi-amperometrically with two platinum electrodes. A bi-amperometric biosensor was also developed in screen-printed configuration with Pt-sputtered carbon paste In aU these biosensors both enzymes were immobilized in a poly(vinyl alcohol)-styrylpyridinium (PVA-SbQ) layer. 

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