The performance of a new membrane sensor based on polyvinyl chloride (PVC) for Tl(I) assay was investigated using the statistical design as an optimization strategy. The PlackettBurman and BoxBehnken designs, respectively, were utilized to find out the influencing variables and optimization of conditions. In order to evaluate the relationship between the responses of electrode (slope) and significant variables along with their interactions, a mathematical model was presented. The interactions between significant variables were intuitively illustrated according to the response surface plots. Apart from that, the optimum conditions as a result of response surface methodology for both membrane ingredients and measuring conditions such as pH, PVC, internal solution concentration, calix[6]arene, 2nitrophenyloctylether, potassium tetrakis (pchlorophenyl)borate and time conditioning, respectively, were found to be: 6, 0.028 g, 0.001 M, 0.0035 g, 0.065 g, 0.0015 g and 20 h. The optimized sensor exhibits a Nernstian response for thallium(I) over a wide linear range from 2.0 × 10–6 to 2.0 × 10–2 M and the slope of 57.9 ± 0.1 mV/decade of the activity and limit of detection (LOD) 1.9 × 10–6 M. The relative standard deviations (RSD) for six replicates of the measurement at 1 × 10–5 and 1 × 10–4 M of Tl(I) were 2.7 and 3.0%, respectively. The favorable results were given through the direct determination of Tl(I) in spiked wastewater and artificial spiked urine sample with Tl(I). The elec trode was also successfully applied to the titration of a Tl(I) solution with KI.
