Comparative Study of Poly(Vinyl Chloride) Based Polymeric Membrane Sensors for the Determination of Erbium (III)

The three chelates 1,5-bis(o-aminobenzoate)-3-thiapentane (L1), 1,5-bis(omethoxybenzoate)- 3-thiapentane (L2), 1,5-bis(o-chlorobenzoate)-3-thiapentane (L3) have been synthesized and explored as a neutral ionophores for preparing poly(vinyl chloride) based membrane sensors selective to Er3+. The addition of sodiumtetraphenylborate and various plasticizers, viz., o-NPOE, TBP, DBBP, TEP and DOS has been found to substantially improve the performance of the sensor. The best performance was obtained with the sensor no.6 having membrane of ionophore (L2) with composition PVC: o-NPOE: ionophore (L2): NaTPB (%w/w) of 35:56:2:7. This sensor exhibits Nernstian response with slope 22.1±0.3 mV decade-1 of activity in concentration range 3.0×10-9 to 1.0×10-2 M Er3+, performs satisfactorily over wide pH range (1.5-6.7), with a fast response time (8 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 20% content of methanol, ethanol or acetone and could be used for a period of 5 months without any change in response characteristics. The Er3+ selective sensor was used as an indicator electrode for the titration of 25 ml 1×10-3 M EDTA solution and for the determination of Er3+ ion in different synthetic samples. The proposed electrode no. 6 was also used for the determination of fluoride ion in two mouth wash sample.