Colorimetric detection, with porphyrins

A. Colorimetric Detection of Azanone with Manganese Porphyrins 129... 

The quantitative assay for PBG and ALA (Bio Rad, Hercules, CA, USA) that is based on the classical method by Mauzerall and Granick may be used for determination of the porphyrin precursors. PBG is absorbed by the anion-exchange column and ALA by the cation-exchange column interferences are washed out. After elution from the column, ALA is derivatized by acetyl acetone to form a pyrrole. Both ALA and PBG are determined colorimetrically with the modified Ehrlichs reagent. Instead of this broadly used standard method ALA, but not PBG may be detected and quantified using amino acid chromatography. However, our experience has shown that this method is only valid for detecting massively increased concentrations of ALA. 

The reversible inhibition of an enzyme by an association-sensitive colorimetric agent is the novel aspect of this detection technique. In detail, the poiphyrin interacts with the enzyme in a manner that requires its dissociation to allow analyte binding. The porphyrin-enzyme complex absorbance spectrum is different from that of the porphyrin alone. Changes in the absorbance spectrum that occur upon dissociation of the porphyrin from the enzyme are used to indicate the presence of the analyte. In addition, the degree of change is analyte concentration dependent. 

Amao Y (2003) Probes and polymers for optical sensing of oxygen. Mikrochim Acta 143 1-12 Amao Y, Nakamura N (2004) Optical CO2 sensor with the combination of colorimetric change of a-naphtholphthalein and internal reference fluorescent porphyrin dye. Sens Actuators B 100 347-351 Ando M, Kobayashi T, Haruta M (1994) Enhancement in the optical CO sensitivity of NiO film by the deposition of ultrafine gold particles. J Chem Soc Faraday Trans 90 1011-1013 Ando M, Kobayashi T, Haruta M (1995) Optical CO detection by use of CuO/Au composite films. Sens Actuators B 24-25 851-853... 

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