Abstract
Screen-printed membrane sensors based on the use of paper and ceramic substrates are fabricated, characterized, and used for rapid batch and continuous monitoring of Cr-III in the form of CrO42- in some industrial products and wastewater samples. Strips of paper and ceramic platforms (15 x 5 mm) were covered with conductive carbon paint and then modified with polyaniline (PANI) film, to act as an ion-to-electron transducer, followed by a drop casting of plasticized poly (vinyl chloride) (PVC) Rhodamine-B chromate membrane as a recognition sensing material. In a 5.0 mmol L-1 Trizma buffer solution of pH similar to 8, the fabricated paper and ceramic based membrane sensors exhibited a near Nernstian response for Cr-VI ion with slopes of -29.7 +/- 0.5 and -28.6 +/- 0.3 mV decade(-1), limit of detection 2.5 x 10(-5) and 2.4 x 10(-6) mol L-1 (1.3-0.12 mu g mL(-1)), and linear concentration range 7.5 x 10(-3)-5.0 x 10(-5) and 7.5 x 10(-3)-1.0 x 10(-5) mol L-1 (390-0.5 mu g mL(-1)), respectively. Both sensors exhibited fast and stable potentiometric response, excellent reproducibility, and good selectivity with respect to a number of common foreign inorganic species. Impedance spectroscopy and chronopotentiometry data revealed a small resistance and a larger double layer capacitance due to the presence of the intermediate polyaniline (PAN) conductive layer. Furthermore, the formation of a water layer between the ion selective membrane (ISM) and the underlying conductor polymer and between the conducting polymer and the carbon conducting surface was greatly reduced. The developed disposable solid-contact potentiometric sensors offer the advantages of simple design, long term potential stability, flexibility, miniaturization ability, short conditioning time, and cost effectiveness that enable mass production. The sensors were successfully used for static and hydrodynamic measurements of total chromium in some leather tanning wastewater and nickel-chrome alloy samples. The results compare favorably with data obtained by atomic absorption spectrometry.