Electronic Supplementary Material
Trace determination of zirconium by adsorptive anodic stripping voltammetry of its complex with alizarin violet using a glassy carbon electrode modified with acetylene black-dihexadecyl hydrogen phosphate composite film
Peihong Deng a,[(], Yonglan Feng a, Junjie Fei b
a Department of Chemistry and Material Science, Hengyang Normal University, Hengyang 421008, P. R. China
b College of Chemistry, Xiangtan University, Xiangtan 411105, P. R. China
Optimization of analytical parameters
Effect of Medium
A series of supporting electrolytes such as HAc–NaAc, HAc–NH4Ac, Britton-Robinson(B–R), (CH2)6N4–HCl, NaH2PO4–Na2HPO4, KH2PO4, KHP buffers(each 0.1 mol/L) were tested. Both the peak height and the peak shape were taken into consideration when choosing the supporting electrolyte. Of these, HAc–NaAc buffer gave the best response. Furthermore, different concentrations of HAc–NaAc buffer ranged from 0.05 to 1.0 mol L-1 were tested. The optimum concentration is in the range of 0.4 mol L-1~0.6 mol L-1 and 0.5 mol L-1 was selected for subsequent uses.
Effect of pH
The effect of pH on the stripping peak current of the Zr(IV)-AV complex was investigated in the pH range situated between 4.5 to 5.5 (Figure S1). At first, the peak current increased with increasing pH, when pH reached 4.8 the peak current tended to level off, but dropped clearly when pH was higher than 5.1. This is readily explained because at lower pH values, complexation is less effective, whereas at higher pH, the hydrolysis of Zr(IV) interferes with the complexation. Therefore, pH 5.0 was chosen for analytical purposes.
Figure S1 Effect of pH on the peak current.
2.0´10-7 mol L-1 Zr(IV); accumulation potential: -200 mV; accumulation time: 180 s; scan rate: 100 mV s-1.
Effect of Ligand Concentration
Different concentrations of AV ranged from 5.0×10-7 mol L-1 to 7.0×10-6 mol L-1 in the presence of 1.0×10-6 mol L-1 Zr(IV) were studied (Figure S2). It was noticed that the peak current increased with increasing AV concentration up to 2.0×10-6 mol L-1, and decreased when the concentration of AV was higher than 4.0×10-6 mol L-1, probably due to the competition of AV with Zr(IV)-AV complex for adsorptive sites. Eexperimental results also showed that the effect of AV is related to the Zr(IV) concentration. In all further studies, 2.0×10-6 mol L-1 (c Zr(IV) ≥ 1.0×10-8 mol L-1) and 2.0×10-7 mol L-1 (c Zr(IV) < 1.0×10-8 mol L-1) were selected as optimum ligand concentration for the determination of different concentrations of Zr(IV).
Figure S2 Effect of AV concentration on the peak current.
1.0´10-6 mol L-1 Zr(IV); accumulation potential: -200 mV; accumulation time: 180 s; scan rate: 100 mV s-1.
Effect of accumulation potential
The effect of accumulation potential on the peak current was examined over the potential range 0 mV to -400 mV. As shown in Figure S3, the peak current increased with changing potential from 0 mV to -200 mV, then decreased rapidly with changing potential from -200 mV to -400 mV. Thus an optimal accumulation potential of -200 mV was chosen for further experiments.
Figure S3 Effect of accumulation potential on the peak current.
2.0´10-7 mol L-1 Zr(IV); accumulation time: 180 s; scan rate: 100 mV s-1.
Effect of accumulation time
Figure S4 exhibits the dependence of the peak current of the complex on the accumulation time for 2.0×10-7 mol L-1 (curve a) and 2.0×10-8 mol L-1 Zr(IV) (curve b), respectively. At first, the peak current increased with accumulation time, indicating that before adsorption equilibrium between the complex on the surface of the AB-DHP/GCE and that in the solution was established, the longer the accumulation time, the more the complex was adsorbed and the peak current became larger. However, after a specific accumulation period, the peak current tended to level off, indicating the adsorption equilibrium was achieved. When the Zr(IV) concentration is lower, the accumulation time needed for the anodic peak to attain a maximum is longer. However, use of a long accumulation time is inconvenient. Thus an accumulation time of 180 s was used for further experiments as a compromise between sensitivity and analysis speed.
Figure S4 Effect of accumulation time on the peak current.
a) 2.0´10-7 mol L-1 Zr(IV); b) 2.0´10-8 mol L-1 Zr(IV).
accumulation potential: -200 mV; scan rate: 100 mV s-1.
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