A comparative study of Pb2+ selective sensors based on derivatized tetrapyrazole and calix[4]arene receptors

Two neutral ionophores, 2,12-dimethyl-7,17-diphenyltetrapyrazole (I) and 5,11-dibromo-25,27-dipropoxycalix[4]arene (II) have been explored for preparing PVC based membrane sensors selective to Pb2+. The addition of sodium tetraphenylborate and various plasticizers viz. DOS, TEHP, DBP, DOP and TBP has been found to substantially improve the performance (working concentration range, slope and response time) of the sensors. The best performance was obtained with the sensor having a membrane of composition (w/w) of (I) (1%):PVC (33%):TBP (65%):NaTPB (1%). The sensor exhibits Nernstian response in the concentration range 2.5 × 10−6 to 5.0 × 10−2 M Pb2+, performs satisfactorily over wide pH range (1.6–6.0) with a fast response time (∼10 s). The sensor was found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetone, methanol or ethanol and could be used over a period of 5 months. Potentiometric selectivity coefficients as determined by match potential method (MPM) indicate excellent selectivity for Pb2+ ions. The sensors could be used successfully in the estimation of lead in Eveready battery waste and also as an indicator electrode in potentiometric titration.