Electroactivity of Functional Groups and Compounds

Electrochemically active compounds are typically aromatic and contain hydroxyl (phenols), methoxyl or amine moieties. Some aliphatic compounds, notably thiols 

1 Electrochemical Behavior of Some Specific Molecular Types 

Thiol-containing amino acids, such as cysteine and penicillamine, are readily oxidised at mercury electrodes. The use of this reaction to measure them is discussed in detail in Chapter 5. 

An unusual EC reaction applicable to the detection of most amino acids involves complexation with copper ions in solution. It was later shown that this also occurs at copper electrodes. Although sensitivity limits of 0.5 to 18 ng injected depending on the amino acid have been reported for this system, it is not widely used, probably because the difficulties of resolving 20-I-amino acids on reversed-phase columns. Most workers therefore use derivatisation of the amino acids prior to chromatography for their analysis. Even though many such derivatives, e.g. phenylisothiocyanate (PITC), are electroactive, most analysts favour fluorescence detection since it is more compatible with the necessary solvent gradients as well as being more selective. 

Sugars are difficult to assay with any significant sensitivity by most physicochemical methods, such as UV-visible detection, yet they are readily measured electrochemically. However, the optimum conditions for their reproducible 

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