Ni(II)-selective ion sensors of salen type Schiff base chelates Original Research Article

The two nickel chelates of Schiff bases, N-(2-hydroxybenzyl)-N′-(2-hydroxybenzylidene)ethylenediamine Ni(II) (I) and N-(2-hydroxybenzylidene)-N′-(2-picolyl)ethylenediamine Ni(II) (II), have been synthesized and explored as a neutral ionophores for preparing polyvinyl chloride based membrane sensors selective to Nickel(II). The addition of sodium tetraphenylborate and various plasticizers, viz., DOS, TEHP, DEP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor having membrane of chelate (II) with composition (w/w) chelate (1%):PVC (33%):CN (65.5%):NaTPB (0.5%). This sensor exhibits Nernstian response in the concentration range 3.2 × 10−6 to 5.0 × 10−2 M Ni(II), performs satisfactorily over wide pH range of (2.2–5.9) with a fast response time (∼10 s). The sensor was also 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 4 months. The response of the sensor was highly selective to Ni2+ over a large number of cations and it could therefore be used for Ni2+ estimation in the presence of a number of interfering ions. The sensor could be used successfully for the estimation of nickel at trace level in biological and environmental samples.