A highly sensitive method for the analysis of nitrite ions by capillary zone electrophoresis using water-soluble aminophenylporphyrin derivative as chromogenic reagent.
The water soluble 5-p-aminophenyl)-10,15,20-tris(p-sulfonatophenyl) porphyrin, 4, acts as an extremely efficient chromogenic reagent for the detection of very low amounts of nitrites. The amino group of porphyrin 4 reacts smoothly with nitrite in acidic conditions 0.2 M HCl) producing the corresponding diazo-porphyrin derivative which is stable and does not show any appreciable hydrolysis to phenol within 6 h. The reaction is carried out in the presence of 25 mM heptakis-(2,6-di-O-methyl)-beta-cyclodextrin that prevents precipitation of the protonated form of porphyrins 4 or 5 due to the formation of strong inclusion complexes. The capillary zone electrophoresis of the diazoporphyrin and amino-porphyrin mixture shows severe peak tailing. However, symmetrical peaks can be obtained by adding 5 mM beta-cyclodextrin to the background electrolyte (20 mM phosphate buffer, pH 7.0). Calibration curve for nitrite analysis is linear up to 0.25 mM nitrite and the detection limit (at a signal-to-noise ratio of 3) has been estimated to be a 1 microM (50 ppb) of nitrite concentration in aqueous solutions.
Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, Università di Padova, Italy.
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P
Andrighetto
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Carofiglio
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R
Fornasier
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U
Tonellato
D002863:Chromogenic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D003505:Cyclodextrins / Q000737:chemistry; D019075:Electrophoresis, Capillary / Q000379:methods*; D007202:Indicators and Reagents / Q000138:chemical synthesis / Q000737:chemistry*; D007477:Ions; D015394:Molecular Structure; D009573:Nitrites / Q000032:analysis*; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012995:Solubility; D014867:Water; D047392:beta-Cyclodextrins
D002863:Chromogenic Compounds; D003505:Cyclodextrins; D007202:Indicators and Reagents; D007477:Ions; D009573:Nitrites; D011166:Porphyrins; D047392:beta-Cyclodextrins; D014867:Water; C000609658:heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin; C038119:heptakis(2,6-O-dimethyl)beta-cyclodextrin