A bacteria-modified carbon paste electrode has been prepared and used for the very sensitive and selective determination of trace amounts of gold(III). The modified electrode was able to detect a solution of 1.0 ppb Au(III) by applying cathodic stripping voltammetry. Advantages of the bacteria-modified electrode include high sensitivity, good stability, low cost and simple preparation. It could be a new class of modified electrode with practical value

Fu, JK

Hu, RZ

Liu, YY

Zhang, WD

胡荣宗

Analytical Communications

Xiamen University Institutional Repository

  C o m m u n i c a t i o nDetermination of trace amounts of gold(iii) by cathodicstripping voltammetry using a bacteria-modified carbon pasteelectrodeRongzong Hu,a Weide Zhang,*ab Yueying Liuc and Jinkun Fuaa Department of Chemistry, Xiamen University, Xiamen, Fujian 361005, Chinab State Key Laboratory for Physical Chemistry of Solid Surface, Xiamen University, Xiamen,Fujian 361005, P.R. China. E-mail: wdzhang@jingxian.xmu.edu.cnc Department of Biology, Xiamen University, Xiamen, Fujian 361005, ChinaReceived 21st January 1999, Accepted 8th March 1999A bacteria-modified carbon paste electrode has been pre-pared and used for the very sensitive and selective determi-nation of trace amounts of gold(iii). The modified electrodewas able to detect a solution of 1.0 ppb Au(iii) by applyingcathodic stripping voltammetry. Advantages of the bacteria-modified electrode include high sensitivity, good stability,low cost and simple preparation. It could be a new class ofmodified electrode with practical value.The determination of trace amounts of metal ions by electro-chemical analysis can be improved by using chemically-modified electrodes in stripping analysis.1–5 The use ofbacteria-modified electrodes has been reported for the determi-nation of enzyme6 and BOD (biochemical oxygen demand).7Other biomasses such as lichen have been used to preparemodified electrodes for the determination of metal ions,8 butthere is no report on the use of bacteria-modified electrodes inthe determination of metal ions. Here we introduce a novelmethod for the preparation of a bacteria-modified carbon pasteelectrode for the determination of gold(iii). Previously, bacteriahave been employed to adsorb the compounds of gold and othermetals in order to recover the noble metals or treat wastewater9,10 since some bacteria are able to concentrate the metalions. Now we adopt the bacteria to prepare an electrode withhigh sensitivity and selectivity for the determination of traceamounts of gold(iii). Under the tested conditions, a good lineardependence between the peak current and the gold(iii) concen-tration in the range of 10–85 ppm has been obtained. Thepreparation method is simple and the obtained electrode isstable.ExperimentalThe bacteria were isolated from the soil of mining areas. Thebacterial biomass D01 was screened out from different bacterialbiomasses because it has a strong ability for adsorbing Au(iii)and grows well in a medium containing 600 mg l21 Au(iii). Thebacterial biomass D01 is gram-positive and was identified asBacillus megatherium D01. It is easy to obtain and culture. Thebiomass D01 was cultured in a water solution containing beefgels, peptone and salt etc. It was separated by centrifugation andwashed with deionized water and alcohol before use.All of the detection experiments were conducted in a solutionof KCl (0.1 M). The pH value of the solution was adjusted by0.1 M HCl solution. Solutions of AuCl3 at varying concentra-tions were used as standard samples. All chemicals were ofanalytical grade. Deionized water was further double distilled.Voltammetric experiments were performed using a 8511Apotentiostat (Yanbian Yongheng, China). To prepare theworking electrode, 100 mg D01 was mixed with 1.4 g graphiteand 0.2 g paraffin wax. The mixture was ground thoroughly ina mortar. This modified paste was pressed into a Teflon filmtube, with a copper stick providing electrical contact. Theelectrode was carefully polished and cleaned before use.Surface renewal was achieved by replacement of the superficialmaterial with a small amount of freshly prepared modifiedpaste. A saturated calomel electrode (SCE) was used as areference electrode and a platinum electrode was used as acounter electrode for all experiments, thus potentials are quotedvs. SCE. The three electrodes were placed into a solution ofAuCl3 and pre-concentrated at +0.75 V for 10 min. The solutionwas purged with N2 in order to remove the oxygen for 10 min,and then a voltage scan was conducted at a speed of 100 mV s21from +0.75 V to 20.25 V.Results and discussionFig. 1 shows the cathodic stripping voltammetric curvesobtained in a solution of 84.7 ppm AuCl3 with a carbon pasteelectrode with and without bacteria-modification. One can seethat there is a peak at 350 mV, corresponding to the reduction ofAu(iii). The peak current detected by the bacteria-modifiedcarbon paste electrode is about 280 mA, which is much strongerthan that detected by the unmodified one, which is about 110mA. This result indicated that the bacteria-modified electrode ismuch more sensitive than the unmodified electrode. Thecathodic stripping voltammetric curve obtained with theelectrode for a solution of 1.0 ppb Au(iii) is shown in Fig. 2.Although a background current (of about 3.0 mA) does exist, apeak with ca. 0.8 mA peak current appears obviously in thecurve. In other words, the electrode can determine 1.0 ppbAu(iii) in the solution. The sensitivity is much higher than thatreported by other authors up till now.1,3 Another experimentusing the bacteria-modified electrode to determine a solutionFig. 1 Cathodic stripping voltammetric curve in a solution of 84.7 ppmAuCl3 (pH 1.18) with (a) bacteria-modified and (b) unmodified carbonpaste electrode.Anal. Commun., 1999, 36, 147–148 147Downloaded on 18 July 2012Published on 01 January 1999 on http://pubs.rsc.org | doi:10.1039/A900600AView Online / Journal Homepage / Table of Contents for this issuecontaining Ag(i) or Cu(ii) showed that there is no reductionpeak corresponding to Ag(i) or Cu(ii) in the detection range.These results indicated that the bacteria-modified electrode isboth sensitive and selective for the determination of Au(iii). Inorder to examine the reproducibility, the electrode was renewedwith freshly prepared bacteria-modified paste before every test.A solution of 84.7 ppm Au(iii) was detected 6 times. Therelative standard deviation was 3.4%, showing that the electrodeis precise. The electrode has also been used to determinesolutions of Au(iii) at varying concentrations. The results showthat the position of the reduction peak is not changed with theconcentration of Au(iii), while the strength of the peak currentis in good linear dependence with the concentration of Au(iii).The relationship of the peak current (Ipk, mA) and theconcentration of Au(iii) ([Au], ppm) can be described by thefollowing equation:Ipk = 3.165[Au] + 9.646The relation coefficient is 0.99945.The above results clearly show that we have obtained by asimple method a highly sensitive and selective bacteria-modified electrode. The role of the bacteria has been proved tobe helpful for the adsorption and reduction of Au(iii) on theelectrode surface, thus increasing the sensitivity of the elec-trode. We have also demonstrated that the stripping currentincreased with both the pre-concentration time and the amountof bacteria (with bacteria < 7%). Furthermore, in a backgroundsolution of HCl at pH 4.0, a peak positioned at 0.25 V appearedin the voltammetric curve with the bacteria-modified carbonpaste electrode. In contrast, there is no peak in the curve with theunmodified electrode (Fig. 3). This indicates that the biomassD01 itself is reduced electrochemically. The reduction potential(0.25 V) of D01 confirmed that the D01 is able to reduce Au(iii).This is beneficial for the electrochemical reduction of Au(iii) onthe surface of the electrode. The concentration and reduction ofAu(iii) by the bacteria increased the sensitivity of the electrodein cathodic stripping.Support of this work by the Research Laboratory of SEDC ofAnalytical Science for Materials and Life Chemistry, XiamenUniversity is gratefully acknowledged.References1 G. Wang, T. Peng, P. Wang, P. Zhu and L. Qu, Anal. Lab., 1994,13(1), 54.2 R. M. Izatt, K. Pawlak and J. S. Bradshaw, Chem. Rev., 1991, 91,1721.3 S. Dong and Y. Wang, Anal. Chim. Acta, 1988, 212, 341.4 I. Turyan and D. Mandler, Anal. Chem., 1993, 65, 2089.5 M. Korolczuk, Fresenius’ J. Anal. Chem., 1996, 356, 480.6 J. Deng, H. He and J. Kong, Chem. Sens., 1993, 13(1), 59.7 G. Xin, H. Zhou, C. Yin, R. Zhang and Y. Sun, Chem. Sens., 1995,15(4), 306.8 E. Dempsey and M. R. Smyth, Analyst, 1992, 117, 1467.9 D. W. Darnall, B. Greene, M. T. Henzl, R. A. McPherson, J. Sneddonand M. D. Alexander, Environ. Sci. Technol., 1986, 20, 206.10 J. A. Brierley and D. B. Vance, in Biohydrometallurgy Proc. Int.Symp., 1987, Warwick, UK, ed. P. R. Norris and D. P. Kelly, ScienceTechnology Letter, Kew, UK, 1988, p. 477.Paper 9/00600AFig. 2 Cathodic stripping voltammetric curve in a solution of 1 ppb AuCl3with bacteria-modified electrode.Fig. 3 Voltammetric curves in a background solution of HCl at pH 4.0with (a) bacteria-modified and (b) unmodified carbon paste electrode.148 Anal. Commun., 1999, 36, 147–148Downloaded on 18 July 2012Published on 01 January 1999 on http://pubs.rsc.org | doi:10.1039/A900600AView Online

Determination of trace amounts of gold(III) by cathodic stripping voltammetry using a bacteria-modified carbon paste electrode

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Determination of trace amounts of gold(III) by cathodic stripping voltammetry using a bacteria-modified carbon paste electrode

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