Nitrate-selective electrodes based on meso-tetrakis[(2-arylphenylurea)-phenyl]porphyrins as neutral lipophilic ionophores

Polymeric-membrane electrodes for NO3− anion based on (α,α,α,α)-5,10,15,20-tetrakis [2-(4-methylphenylurea)phenyl]porphyrin I and similar urea-functionalized porphyrins II–IV as neutral ionophores were prepared. The effects of polymeric-membrane composition and test solution pH were tested. The electrodes revealed good selectivity coefficients for NO3− over a wide variety of other anions, and the values of eight anions were measured. Of the various electrodes prepared, the electrode based on urea-functionalized porphyrin I exhibits a linear stable response over a wide concentration range (1.0×10−5 to 1.0×10−1) with a slope of −57.4 mV per decade, a detection limit of log[NO3−]=−5.72, and a selectivity coefficient for nitrate against perchlorate anion (log KNO3−,jpot=−1.81).