Biosensor Determination of Heavy Metals (Cd2+, Cu2+, and Pb2+) in Model Solution
Figure 4 (I) shows amperometric responses of Pt/PANI/HRP to successive additions of 0.05 mM H2O2 (denoted by r) followed by addition of Cd2+ (denoted by i). The other two heavy metal ions (Pb2+ and Cu2+) showed the same behavior. Calibration plots for the determination of the metals in the range 0.05 to 60.8 ppb were obtained (Figures not shown). The linear ranges were established as 4.76-55.3 ppb for Cd2+ and Pb2+ while that for Cu2+ was 2.38-52.8 ppb. The limits of detection (LOD) and limits of quantification (LOQ) of the method were calculated (Table 1) according to the 3 x SD/m and 10 x SD/m criteria, respectively, where SD is the standard deviation of blank signal and m is the slope of the calibration curve. The low LOD and LOQ values (Table 1) confirmed good sensitivity of the proposed biosensor method for the determination of heavy metals. The biosensor showed stability for repeated metal determinations beyond 10 runs. This suggests that heavy metals are the reversible inhibitors (Songa et al. 2009).