NITRITE-SENSITIVE LIQUID MEMBRANE ELECTRODES BASED ON METALLOPORPHYRIN DERIVATIVES

Liquid membrane electrodes based on some metalloporphyrin derivatives exhibit an anti-Hofmeister selectivity pattern: NO2- > SCN- > I- > F- > Br- > Cl- > ClO4- > NO3- : These derivatives include chloro(5,10,15, 20-tetraphenylporphyrinato)indium, 10,15,20-tetra(p-methoxyphenyl)porp hyrinato]indium and 2-nitro-5,10,15,20-tetraphehylporphyrinato)indium. The selectivity pattern is interpreted on the basis of the coordinati on chemistry of metalloporphyrins. The membrane electrode with optimum composition shows a linear potentiometric response towards nitrite io n in the range 6.3 x 10(-5)-0.1 mol l(-1) with a slope of 51 mV/pNO(2) (-) and a detection limit of 5.0 x 10(-6) mol l(-1). The electrode was applied to the determination of nitrite in Chinese cabbage.