Response characteristics of lead-selective membrane sensors based on a newly synthesized quinoxaline derivatives as neutral carrier ionophores

Novel lead-selective polymeric membrane sensors were prepared based on the use of 2,2'-(quinoxaline-2,3-diyl bis (azanediyl)) dibenzoic acid (sensor I) and N'-(3-chloroquinoxalin-2-yl) nicotinohydrazide (sensor II) as novel synthetic neutral carrier ionophores embedded in a plasticized poly(vinyl chloride) (PVC) matrix. The sensors displayed near-Nernstian cationic slope of 35.3 and 37.18 mV/decade over the concentration range 7.0 x 10(-6)-1.0 x 10(-3) and 4.0 x 10(-6)-1.0 x 10(-3) M at pH 5 with lower detection limits of 4.7 x 10(-6) and 1.8 x 10(-6) M for sensors (I) and (II), respectively. The influence of anionic additive on the potentiometric responses of the prepared membrane sensors was studied. The selectivity studies showed high selectivity towards Pb(II) ions over large number of other cations for all the proposed sensors. Formal complex formation constants of the ionophores with Pb(II) and a series of interfering cations have been determined in the organic membrane phase. The formal complex formation constants found are in excellent agreement with those determined by potentiometric selectivity measurements. The sensors were subjected to lead assessment in biological fluid samples either in static and flow-through mode of operations. The results obtained agree fairly well with data obtained by atomic absorption spectrometry (AAS).