Determination of Copper(II) Based on Its Inhibitory Effect on The

Electronic Supplementary Material

Determination of copper(II) based on its inhibitory effect on the cathodicelectrochemiluminescence of lucigenin

Wenyue Gao,a,bPan Hui,a,cLiming Qi,a,b Zhongyuan Liu,a Wei Zhang,a,*and Guobao Xua,*

aState Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China

bUniversity of Chinese Academy of Sciences, Beijing 100049, PR China

cSchool of Chemistry and Environmental Engineering, Changchun University ofScience and Technology, Changchun, Jilin 130022, China

*Corresponding author: Prof. G. B. Xu,E-mail: , Tel/Fax: (+86) 431-85262747; Ms. W. Zhang, E-mail:

Scheme S1. The equations showing the reaction mechanism.

Fig. S1 ECL intensity−potential proﬁles of lucigenin in the absence (the black line) and presence (the red line) of ascorbic acid. Phosphate buffer: 0.1 M, pH 10.1; c(lucigenin): 100.0 μM; c(ascorbic acid): 100.0 μM.

Fig. S2 shows the effectsof pH on the ECL inhibition efficiencies. I0and I represent the ECL intensity of lucigenin in the absence and presence of Cu2+, respectively. (I0I)/I0 represents ECL inhibition efficiency after the addition of copper ions. The ECL inhibition efficiency increase with increasing pH from 8.6 to 10.1, and then decrease aspH increase further. The increase in ECL inhibition efficiencies with increasing pH from 8.6 to 10.1 are attributed to the faster generation of effective peroxide intermediates from the reduction of oxygen at higher pH. When the pH becomes higher than 10.1, the hydrolysis of Cu2+and the formation of Cu3(PO4)2may result in the decrease in ECL inhibition efficiency. Therefore, the following experiments werecarried out in 0.1 M phosphate buffer at pH 10.1.

Fig.S2pH effect on the ECL inhibition efficiency. I0and I represent the ECL intensity of lucigenin in the absence and presence of Cu2+, respectively. (I0I)/I0 represents ECL inhibition efficiency after the addition of copper ions. c(lucigenin): 100.0μM; c(Cu2+): 100.0 nM; phosphate buffer: 0.1 M; scanning range from 0 to 1.0 V; photomultiplier tube voltage: 1000V.

The effects of lucigenin concentrations on ECL inhibition efficiencies were also investigated (Fig. S3). The ECLsignals gradually increase with the increasing concentration of lucigenin.However, the ECL inhibition efficiency reached the largest at a concentration of 100.0 M. Therefore, the optimal concentration of lucigenin is 100.0 M.

Fig. S3 (a) ECL intensities of the solutions containing different concentrations of lucigeninin the absence (black columns) and presence (red columns) of Cu2+.c(lucigenin): 20.0, 40.0, 80.0, 100.0, 150.0 and 200.0 M (from columns 1 to 6, respectively) (b) Effect of lucigenin concentrations on ECL inhibition efficiencies. c(Cu2+): 100.0 nM.

Fig. S4 shows the eﬀects of initial potential on the ECL inhibition efficiencies. As the initial potential increased from 0.1 to 0.6 V, the ECL intensities of lucigenin solutions in the absence and presence of copper ions both increased slightly and then decreased notably when the initial potential higher than 0 V. The ECL inhibition efficiencies changed little at different initial potentials. To obtain maximum signal-to-backgroundratio, 0 V was chosen as the optimum initial potential.

Fig. S4 (a) ECL intensities of lucigenin solutions in the absence (black line) and presence (red line) of copper ions at different initial potentials. (b) Eﬀect of initial potentials on the ECL inhibition efficiency. c(lucigenin): 100.0 μM; c(Cu2+): 100.0 nM; phosphate buffer: 0.1 M, pH 10.1.

We investigated the effects of scan rates on ECL inhibition efficiencies using linear sweep voltammetry (Fig. S5). The reduction peak currents in the absence and presence of copper ions both increase continuously with scan rates increasing from 20 to 250 mV·s-1. And the peak currents have good linear relationships with the square root of scan rates. It suggests that the electrochemical reactions both in the absence and presence of copper ions were diffusion-controlled processes. The ECL inhibition efficiencies of copper ions reached the maximum at the scan rate of 50 mV·s-1. Thus, 50 mV·s-1was used for analytical purposes in the following experiments.

Fig.S5 Linear sweep voltammograms of lucigenin solutions in the absence (a) and presence (b) of copper ions at different scan rates. (c) Dependence of the reduction peak current on scan rate in the absence and presence of copper ions. (d) Eﬀect of scan rate on ECL inhibition efficiency on a glassy carbon electrode with a scanning potential from 0 V to －1.0 V.c(lucigenin): 100.0μM; c(Cu2+): 100.0 nM; phosphate buffer: 0.1 M, pH 10.1.