Highly selective in situ metal ion determination by hybrid electrochemical "adsorption-desorption" and colorimetric methods.

A novel and facile hybrid analytical method coupling electrochemical "adsorption-desorption" and colorimetric analyses was developed to detect heavy metal ions in turbid water samples. The target metal ions were deposited onto an electrode inserted into the original sample, which was referred to as the "adsorption" process. After changing the medium, the concentrated target metal ions were dissolved in a new, clean buffer (blank buffer), which was referred to as the "desorption" process. The concentrations of the target metal ions were measured by colorimetric analyses after the addition of specific indicator amounts. We demonstrated the applicability of this method by detecting Cd(2+), Pb(2+) and Cu(2+) with co-depositing Bi(3+) on portable screen-printed electrodes (SPEs). A good correlation (correlation coefficient of R=0.997) was observed between concentrations ranging from 1 to 200 μM and absorbance values. After the multiple "desorption" process, the even better detection limits as low as 10, 10 and 100 nM were achieved for Cd(2+), Pb(2+) and Cu(2+), respectively. The practicality of this hybrid method was confirmed by the detection of Cd(2+), Pb(2+) and Cu(2+) in wastewater samples, and these results were in agreement with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Overall, this hybrid method provides a simple, selective and effective technique for environmental pollutant analyses.