Simultaneous measurement of multiple labile heavy metals in soils by diffusive gradients in thin film technique

Purpose Development of new binding gels for rapid and simultaneous quantification of bioavailability concentrations of various heavy metals in soils by diffusive gradients in thin film technique. Methods Four binding gels including zinc-aluminum hydrogel (ZnAl-LDH), ethylenediaminetetraacetic acid intercalated zinc-aluminum hydrogel (ZnAl-EDTA-LDHs), polyglutamic acid (PGA), and polyglutamic acid–sodium alginate resin (SA-PGA) were prepared and used for the simultaneous measurement of Cr, Ni, Cu, Cd, and Pb. Results The adsorption process reached equilibrium in 2 h, which could be considered a pseudo-second-order reaction. Three mol L −1 nitric acid was the best eluent with elution efficiency over 91% for the five heavy metals. Then, SA-PGA gel was assembled into DGT device (SA-PGA-DGT). Its performance was virtually unaffected by pH (5–9), ionic strength (1–50 mM), and soil properties with adsorption capacities 5.02 μg cm −2 , 11.38 μg cm −2 , 8.16 μg cm −2 , 17.11 μg cm −2 , and 89.43 μg cm −2 for Cr, Ni, Cu, Cd, and Pb, respectively. A good linear correlation was observed between the concentrations of Cr, Ni, Cu, Cd, and Pb determined by SA-PGA-DGT in soil samples from Tanggu District in China and the exchangeable contents of the five metals determined by the Tessier method, with R values of 0.64, 0.63, 0.59, 0.72, and 0.64 ( p < 0.01). Conclusion SA-PGA gel exhibited the best adsorption properties among the four gels. SA-PGA-DGT can be used as a reliable tool for rapid and simultaneous quantification of bioavailability concentrations of multiple heavy metals.