Highly sensitive spectrophotometric determination of nitrite ion using 5,10,15,20-tetrakis(4-aminophenyl)porphine for application to natural waters

A water-soluble porphyrin having the aminophenyl group, 5,10,15,20-tetrakis(4-aminophenyl)porphine, reacts with nitrite ion, and produces a large spectral change (Delta epsilon = 3.0 x 10(5) l mol(-1) cm(-1), 434 nm). There are few interfering substances and it is easy to establish the reaction conditions because the spectral change mechanism is based only on diazotization. A highly sensitive spectrophotometric determination of nitrite was developed on this basis. The calibration graph was linear in the range 0 to 4.0 x 10(-7) mol l(-1) (0-18 ng ml(-1)). The detection limit {S/N = 3} was 4.0 x 10(-9) mol l(-1) (0.18 ng ml(-1)), and the relative standard deviation was 1.0% (at 2.0 x 10(-7) mol l(-1) nitrite, 10 determinations). This method has been applied to the determination of nitrite in rain, tap and spring water without any pretreatment.