On the potentiometric response of mercury(II) membrane sensors based on symmetrical thiourea derivatives-Experimental and theoretical approaches

Mercury(II) sensors based on two bis-thioureas: 4,4′-bis-(3-phenylthiourea)diphenyl methane (L1) and 2-2-[10-[(E)-2-(aminocarbothioyl)hydrazono]-1,4-dihydroxy-9(10H)-anthracenyliden]-1 hydrazinecarbothioamide (L2) were prepared and studied. The best response characteristics were obtained using the composition-L2:KTpClPB:PVC:DOP in the percentage ratio of 3.5:1.5:32:63 (w:w). The electrode exhibited a near Nernstian response of 30.3 mV decade−1 to mercury ions over the activity range 1.0 × 10−7 to 1.0 × 10−2 M with a limit of detection 7.9 × 10−8 M. The pH independent plateau ranges between 1.5 and 4.0. The proposed sensor revealed fairly good discriminating ability toward Hg2+ ion in comparison with many hard and soft metal ions. It could be applied to determination of mercury in waste water as a real sample. Besides, theoretical calculations performed using the Gaussian 09 programs indicate a S atom is the most favorite reactive site and mainly responsible for the observed electrochemical behaviors in Hg(II)-selective electrodes toward the different cations.