Studies on porphyrins as ultra-highly sensitive analytical reagents

Water-soluble porphyrins have been extensively studied in analytical chemistry. In order to evaluate the analytical function of these reagents, the following items are reviewed and discussed: acid-base reactions, complex formation and spectral properties (Soret absorption band, fluorescence and phosphorescence of porphyrins). Based on these fundamental facts, various spectrophotometric methods for ppb-level trace metal ions are summarized in this article. Recently, determinations below the ppb levels of metal ions have been performed by the following methods: chemical amplification, a new pre-concentration method using fluoro-surfactant and laser analysis. Moreover, new determination methods for anion species and polyelectrolytes are described. Finally, the possibility of water-soluble porphyrins is discussed based on novel molecular designs.