Electrode amino acid analysis with selective

Another example deals with amino acid analysis using immobilized specific microorganisms in combination with selective electrodes (35). Thus, glutamine could be analyzed by an electrode consisting of a potentiometric ammonia gas sensor and a layer of the bacterium Sarcina flava (American type culture collection 147) trapped in the volume between a NHo-permeable membrane on the surface of the electrode and a dialysis membrane in contact with the surrounding solution (Fig. 10). Using this electrode, steady state potentials were reached within 5 minutes. 

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. 

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