| Summary: | Modified carbon paste electrode (CPE) and screen printed electrode (SPE) based on ethyl benzoyl acetate (EBA) were prepared and investigated as lanthanum ion selective electrodes. Effect of various plasticizers (o-NPOE, TCP, DBP, DOS, and DOP) and ionophore content was studied. The reaction mechanism between La(III) and β-diketone ionophore at the electrode surface was studied through scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and IR spectra measurement. The best performance was obtained using modified SPE and CPE electrodes with o-NPOE and TCP plasticizers. These electrodes showed potentiometric response with a Nernstian slope of 21.0, 19.5 and 20.5 mV decade−1 over a concentration range from 1.0 × 10−6 to 1.0 × 10−2 mol L−1 with a fast response time of 9, 10 and 13 s over the linear concentration range for modified SPE (electrode I; TCP plasticizer) and two modified CPE plasticized with o-NPOE (electrode II) and TCP (electrode III), respectively. The electrodes exhibited constant potentiometric response in pH range 4–8, 5–8 and 4–7 for electrodes I, II and III, respectively. They showed satisfactory good sensitivity toward lanthanum ions with regard to most common transition metal ions. The sensors were applied for determination of La(III) ion in different water samples (tap water and wastewater) with satisfactory and good reproducibility results. Keywords: SPE, CPE, Lanthanum(III), β-diketone, SEM, EDX
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