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 (L-1), 1,5-bis(o-methoxybenzoate)- 3-thiapentane (L-2), 1,5-bis(o-chlorobenzoate)-3-thiapentane (L-3) 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 (L-2) with composition PVC: o-NPOE: ionophore (L-2): 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 3.0x10(-9) to 1.0x10(-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 x 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.