Development of Polyacrylic Acid Based Electrochemical Sensor for Detection of Selected Heavy Metals in Water

Abstract

A simple differential pulse anodic stripping voltammetric sensor based on Polyacrylic acid/Glassy carbon electrode has been developed for simultaneous analysis of lead(II), cadmium(II) and cobalt(II) ions. Electrochemical characterization of the Polyacrylic acid/Glassy carbon electrode (PAA/GCE) using potassium ferricyanide standard revealed that the diffusion coefficients (Do) for the PAA/GC and GC plain electrodes were 0.0318x10-7 cm2/s and 0.00122x10-7 cm2/s respectively. The apparent electrochemical electron transfer rate constants (ko) were 9.074x10-3 cm/s and 0.0883x10-3 cm/s for PAA/GC and GC plain electrodes respectively. The Do and ko of the modified and unmodified electrodes indicates that modification of the GC electrode with PAA led to easier and faster charge transfer at the electrode surface. With differential pulse anodic stripping voltammetry, the following optimal conditions were determined: Deposition potential: -0.8 V, Accumulation time: 300 sec, amplitude: 0.06 V, pulse period: 0.02 sec, pulse width: 0.01 sec and sampling width: 0.0033 sec and pH 6.0. Accuracy, precision, linearity, range, limits of detection and quantification validation parameters were determined for this sensor in accordance with the ISO/IEC 17025 guidelines. The recovery degree for accuracy was in the range of 101 to 110% for Pb(II), 100 to 105% for Cd(II) and 93 to 104% for Co(II). These lies between the imposed limits of 90 to 110%. The precision was found to be less than 10% for ten determinations in line with the required 10% at the limit of quantitation. Linear concentration range was also investigated and found to lie in the range of 125 – 7.8 μM Pb(II), 16 – 2 μM Cd(II) and 2 – 0.125 mM Co(II). Also, limits of detection also found to be 0.9 nM Pb(II), 1.9 mM Cd(II) and 11.0 μM Co(II) and while limits of quantitation were 3.0 nM Pb(II), 6.3 nM Cd(II) and 36.7 μM Co(II). The effects of foreign substances like Cu2+, SO42-, K+, Na+, Cl-, NH4+ and O2 were found to have no significant effect on the electrochemical

responses of the three heavy metals. These results confirms that this sensor provides accurate, reliable and consistent results for the determination of Pb(II), Cd(II) and Co(II) heavy metals in waters.