rapidly renewable silver amalgam annular band electrode for voltammetry and polarography

Electrochemistry Communications 12 (2010) 816–819

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Electrochemistry Communications

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Rapidly renewable silver amalgam annular band electrode for voltammetryand polarography

Bogusław Baś a,⁎, Sebastian Baś b

a Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Mickiewicza 30, 30-059 Kraków, Polandb Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland

⁎ Corresponding author. Tel./fax: +48 12 634 1201.E-mail address: bas@agh.edu.pl (B. Baś).

1388-2481/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.elecom.2010.03.041

a b s t r a c t

Article history:Received 23 March 2010Received in revised form 29 March 2010Accepted 29 March 2010Available online 7 April 2010

Keywords:Mercury film electrodesSilver amalgamsVoltammetryPolarographyTensammetry

Thiswork describes a novel type ofworking electrode for use in voltammetry and polarography— the renewablesilver liquid amalgam film–modified silver solid amalgam annular band electrode (AgLAF–AgSAE). The electrodeis produced by mechanically refreshing the silver liquid amalgam film (AgLAF) before each measurement. Themain constituents of the electrode are: a specially constructed silver solid amalgam annular band electrode(AgSAE), two silicon O-rings, silver liquid amalgam and a polypropylene electrode body. Contaminants from theanalyzed solution are removed and theAgSAE surface is coveredwith a thick layer of fresh amalgamwhile pullingthe AgSAE into the sensor body. During movement in the reverse direction AgLAF is formed and homogenized.The time needed to refresh the film is less than 1 s. The electrode is characterized by excellent surfacerepeatability (∼1%) and long-term stability (over ten thousand measurement cycles).

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© 2010 Elsevier B.V. All rights reserved.

1. Introduction

Mercury is among the most widely used electrode materials inelectrochemistry. Three types of mercury electrodes: the droppingmercury electrode (DME), the hanging mercury drop electrode(HMDE), and the mercury film electrode (MFE) are most frequentlyused. While DMEs and HMDEs are easy to use and renew and offer verygood reproducibility and linearity, they also suffer from broader peaksand poorer mechanical stability compared to MFEs. The MFEs, due totheir large surface-to-volume ratio, give sharper stripping peaks andtherefore enhanced sensitivity [1–3]. One of the alternatives tomercuryis liquid and solid amalgams [4,5]. Related metal solid amalgamelectrodes (MeSAEs), polished solid amalgam disk (p-MeSAEs), orelectrodeswith their surfacemodified using, e.g.mercurymeniscus (m-MeSAEs) or mercury film (MF-MeSAEs) have been introduced morerecently to address the concerns related to the toxicity ofmercury [6–8].

For many years, the authors of numerous articles have describedsuch electrode constructions and procedures of plating mercury filmonto metal, carbon and solid amalgam substrates mechanically or viaelectrochemical deposition [6,8–10]. Many of the reported inconve-niences in MFEs preparation and use can be solved with the help of arenewable, cylindrical silver amalgam film electrode (Hg(Ag)FE)designed by Baś and Kowalski [11,12]. In recent years the Hg(Ag)FEwas used in trace element measurements using various techniques ofstripping voltammetry [13–24]. The main disadvantages of Hg(Ag)FE

use are: the fragility of a silver amalgam wire and the sucking in of theanalyzed solution into the interior of the electrode body. The Hg(Ag)FEcannot be used in polarographic measurements, as suchmeasurementsrequire repeated electrode renovation during the registration of a singlevoltammogram.

In the present work it was demonstrated that the renewable silverliquid amalgam film–modified silver solid amalgam annular bandelectrode (AgLAF–AgSAE), a very user-friendly electrode, offers severalinteresting properties. As shown on selected examples, the electrodeexhibits very desirable features (i.e. an easily and quickly renewablesurface, high sensitivity, good repeatability and reproducibility andlong-term stability) in stripping voltammetry, polarography andtensammetry applied for the determination of metal traces (Mn andCr) and riboflavin, as well as the estimation of non-ionic surfactants(NS) in model solutions [13,19,25,26].

2. Experimental

2.1. Instrumentation

Voltammetric and polarographic measurements were performedusing a 8KCA Potentiostat (AGH, Poland), and tensammetricmeasurements using a M23 Double Layer Capacitance Meter (MTM-ANKO, Poland) with a conventional three-electrode configuration forboth systems. A AgLAF–AgSAE electrode (surface area, 12 mm2) wasemployed as a working electrode with Ag/AgCl/3 M KCl and platinumwire as the reference and counter electrodes, respectively. Allsolutions used for analyses were purged with argon. Experiments

817B.ł Baś, S. Baś / Electrochemistry Communications 12 (2010) 816–819

were carried out at room temperature and the following techniquesand parameters were applied during measurements:

• Mn(II) — differential pulse anodic stripping voltammetry (DP ASV):conditioning potential , − 0.10 V for 5 s; accumulationpotential, −1.75 V for 30 s; initial potential, −1.68 V for 2 s; endpotential, −1.30 V; potential step, 2 mV; pulse amplitude, −25 mV;time step potential, 20 ms [19].

• Cr(VI)— differential pulse catalytic adsorptive stripping voltammetry(DP CAdSV): conditioning potential, −0.10 V for 5 s; accumulationpotential, −1.00 V for 20 s; initial potential, −1.00 V; end potential,−1.35 V; potential step, 2 mV; pulse amplitude, 40 mV; time steppotential, 40 ms [13].

• B2— differential pulse polarography (DPP): initial potential,−0.30 V;endpotential,−0.75 V;potential step, 5 mV;pulse amplitude, 30 mV;potential step time, 2 s; current sampling time, 20 ms [25].

• TritonX-100—differential double layer capacitance in relation to time(Cd–t curves): AC impedance technique, signal amplitude 10 mVpeak-to-peak; frequency 50 Hz; polarization potential, −1.10 V [26].

2.2. Reagents and materials

All reagents used were of analytical grade. HNO3 65%, acetic acid96%, ammonia solution 25%, KNO3, KCl, K2CO3 and KOH (Merck,Suprapur®). Cr(VI) standard stock solution (1 g.L−1, Merck). 0.01 Mstandard stock solutions of manganese(II) were prepared bydissolving MnSO4·10H2O (Aldrich). β-riboflavin standard stocksolutions (1 g.L−1) were prepared just before measurements.Mercury GR for polarography and Triton X-100 (Merck). 1 M aceticbuffer, pH 6.0 and an alkaline 0.01 M borate buffer (pH 8.6). 0.1 Mdiethylenetriammine-N,N,N′,N′,N″-pentaacetic acid (DTPA), pH 6.2.Polycrystalline silver rod (ALFA AESAR, Germany, 99.9985%). Theresin was TRANSLUX D180 (AKSON, France). All solutions were

Fig. 1. (A) The AgLAF–AgSAE — ready-for-measurement configuration: (1) silver solid amalwt.%) silver liquid amalgam (AgLA); (5) PTFE centering element; (6) electrode body; (7) solesteel wire, (c,d) resin. (C) The AgLAF–AgSAE — standby configuration.

prepared with quadruply distilled water (last two stages fromquartz).

2.3. Preparation of the AgLAF–AgSAE

The structure of the applied electrode, which allows the silverliquid amalgam film to be refreshed before each measurement andis essential for its performance, is presented in Fig. 1. A shows thestructure of the automatically controlled AgLAF–AgSAE: silver solidamalgam annular band electrode (1); O-rings (ϕi.d=1.8 mm) madeof 3.5 mm and 1 mm thick silicon rubbers, respectively (2 and 3); 1%silver liquid amalgam drop, circa 50 μl, (4); PTFE fastening element(5a,b), fastened together in the polypropylene electrode body (6);linear actuator with solenoid drive (solenoid) (7); electric contactpin (8).

Fig. 1B shows the preparation of the AgSAE. The polycrystallinesilver tube (a) (ϕo.d=2mm, ϕi.d=1.2 mm, l=2 mm) was slid overand mechanically tightened on the stainless steel wire (ϕ=1.2 mm)(b). The steel wire below and above the silver tube was covered byresin (c). The excess resin was then mechanically removed (d). Aftermounting, the electrode surface (resins and silver) was ground byemery papers of decreasing roughness and was finally polished with0.3 μm Al2O3 powder. After thorough rinsing with a distilled waterstream, the electrode was placed for about 2–3 s in 5% HNO3 solutionand afterwards for 1 h in 1% liquid silver amalgam.

The procedure of refreshing of liquid amalgam film consists ofpulling up the AgSAE inside, across the liquid amalgam chamber(Fig. 1C) and then pushing it back outside the electrode body(Fig. 1A). During these movements, the AgSAE makes in contactwith the liquid amalgam twice. During the insertion of the AgSAEthrough the O-rings, the solid and gas contaminants are removedfrom its surface.

gam annular band electrode (AgSAE); (2) O-ring, 3.5 mm; (3) O-ring, 1 mm; (4) 1% (innoid; (8) electric contact pin. (B) Construction of the AgSAE: (a) silver tube, (b) stainless

Fig. 2. (A) DP ASV of Mn(II) in 0.01 M borate buffer (pH 8.6). DPmode: potential step, 2 mV; pulse amplitude,−25 mV; pulsewidth, 20 ms; electrodeposition for 30 s at−1.75 V. (B)DP CAdSV of Cr(VI) in supporting electrolyte: 0.1 M acetic buffer (pH 6), 0.25 M KNO3, 0.01 M DTPA. DP mode: potential step, 2 mV; pulse amplitude, 40 mV; pulse width, 40 ms;electrodeposition for 20 s at −1.00 V. (C) DPP of β-riboflavin in supporting electrolyte: 0.05 M KCl, 0.05 M K2CO3, 50 mg L−1 Triton X-100. DPP mode: potential step, 5 mV; pulseamplitude, 30 mV; potential step time, 2 s; current sampling time, 20 ms. (D) Cd–t curves corresponding to different concentrations of Triton X-100 in 0.25 M KNO3. AC impedancetechnique, signal amplitude 10 mV peak-to-peak, frequency 50 Hz; polarization potential, −1.10 V.

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Depending on the technical solution the electrode may operatein manual or automatic mode. The second solution is necessary inthe case of polarographic and tensametric measurements.

3. Results and discussion

3.1. Characteristic features of the AgLAF–AgSAE

The AgLAF–AgSAE maintains its perfect repeatability and reproduc-ibility for several thousand cycles (up to ten thousand) under thecondition that: a) for AgSAE preparation, silver with proper texture isused, preferablywithfibrous texture; b) for AgSAE regeneration, a silverliquid amalgam and not puremercury should be used, as proven earlier[11]. During theperformed experiments, theuse of polycrystalline silverALFA AESAR ensured AgSAE's stability for 6 months of AgLAF–AgSAEtests. The silver liquid amalgam does not disturb the AgSAE surface;even though it is exposed to constant contact for several weeks, filmsrefreshed using the amalgam do not change their properties for manyminutes, and the hydrogen overpotential is comparable to that of themercury electrode [11]. The applied 1% (in wt.%) silver amalgam wasprepared by sinking several silverwires (0.5 mm in diameter) in 0.5 mLof mercury for 1–2 weeks. The content of silver in the liquid amalgamwas determined using atomic absorption spectrometry (AAS) method.A pure mercury film is characterized by a low background current,which is comparable with the current of a drop mercury electrode, butthe AgLAF–AgSAE is usable less than 6–8 weeks. The use of puremercury is inevitable in the determination of non-ionic surfactants. Inthis case, the AgLAF did not ensure satisfactory linearity of thecalibration curve (rb0.950). Perfect repeatability of Cd–t curves wasachieved by partially filling the electrode body with a fumed silicasuspension in distilled water. This method effectively removes thetraces of surfactants from the electrode base [13]. After refreshmentusing the silver liquid amalgam, traces ofmercury oxidesmay remain onthe surface of the AgAF–AgSARE which may interfere withmeasurements. In such a case, electrode conditioning prior tomeasurement is necessary [11].

3.2. Performance of the AgLAF–AgSAE

The electrode was tested for 6 months. Fig. 2 shows examples ofvoltammograms and Cd–t curves registered in conditions suitable forthe presentation of the AgLAF–AgSAE properties and advantages.

Fig. 2A shows the anodic stripping curves of manganese(II). In thecase of ASV peak current, the peak potential and its half-width dependon the electrode surface and the thickness of the mercury film [2,27–29]. The obtained results (RSD≅1.3%; rN0.999; peak potential,−1512±3 mV; half-width, 41±2 mV) proved, that the AgLAF wasdeposited in a repeatable and reproducible way and film thickness didnot change during depolarizer preconcentration. The backgroundcurrent for the AgLAF–AgSAE in the range of high negative potentialswas as low as for mercury electrodes. Fig. 2B shows the DP CAdSVcurves of chromium(VI). High sensitivity and the repeatability of theregistered voltammograms (RSD≅1.4%) for nanomolar concentra-tions of Cr(VI) confirm the excellent reproducibility of the AgLAF–AgSAE surface and the homogeneity of the deposited film in eachcycle of electrode regeneration. This is the basic condition for usingAdSV. Fig. 2C shows the DP polarograms of riboflavin. In the course ofeach polarogram registration, the electrode surface was renovatedevery second, 90 times. The high sensitivity of riboflavin determina-tion, the polarograms' shape and the precision of measurements(RSD≅3%) prove that the AgLAF–AgSAE has features characteristiconly of the DME. Fig. 2D shows Cd–t curves for Triton X-100. Thesecurves are almost identical in shape to those registered for thecontrolled growth mercury electrode (CGME) [26]. The linear

calibration dependencies 1ffiffiffi

ϑp = f cNSð Þ and Cd= f(cNS) (ϑ — time of

maximum coverage of the electrode surface and cNS — concentrationof the non-ionic surfactant [26]) (r≅0.996), as well as the goodaccuracy of Triton X-100 determination prove that the AgLAF–AgSAEmay be used for the assessment of NS concentration.

In all presented determinations, short-term stability of the AgLAF–AgSAE was excellent. Over longer periods (two weeks), of the signalfluctuates by about 5%.

4. Conclusions

The idea of the renewable silver liquid amalgam film–modifiedsilver solid amalgam annular band electrode described above is basedon cyclic renovation of the electrode surface through the applicationof fresh liquid amalgam film before each measurement [30]. Thesimple, mechanical system of film refreshment provides excellentelectrode surface repeatability (∼1%) and reproducibility (2–5%) andlong-term stability (more than ten thousand measurement cycles)that is not available for other mercury film electrodes. The AgLAF–AgSAE demonstrates many properties which are specific only to thedropping and hanging mercury electrodes. In the automaticallycontrolled film-refresh mode the refresh time is less than 1 s. It wasfound that in most cases the AgLAF–AgSAE can be used to detect thesame analyte in the same matrix as with the mercury drop electrodein stripping voltammetry and polarography. It was also shown thatthe electrode can be used for tensametric estimation of non-ionicsurfactants.

Acknowledgements

The authors are grateful to Prof. Zygmunt Kowalski for his helpfuladvice.

The study was financed as an R&D project by the Polish Ministry ofScience and Education from research funds for the years 2007–2010.No. 15 020 02.

References

[1] L. Airey, Analyst 72 (1947) 304.[2] W.T. De Vries, E. van Dalen, J. Electroanal. Chem. 14 (1967) 315.[3] Cynthia G. Zoski, Handbook of Electrochemistry, Elsevier B.V, The Netherlands,

2007.[4] M. Lovric, Š. Komorsky-Lovric, A.M. Bond, J. Electroanal. Chem. 319 (1991) 1.[5] L.K. Bieniasz, J. Electroanal. Chem. 527 (2002) 21.[6] Z. Stojek, Z. Kublik, Chem. Anal. (Warsaw) 30 (1985) 363.[7] B. Yosypchuk, L. Novotný, Crit. Rev. Anal. Chem. 32 (2002) 141.[8] Ø. Mikkelsen, K.H. Schrøder, Electroanalysis 15 (2003) 679.[9] V.A. Jgolinski, O.N. Gurjanowa, Elektrokhimja 11 (1975) 57.

[10] J. Davis, F. Javier del Campo, F. Marken, R.G. Compton, E. Cordemans, J. AppliedElectrochem. 31 (2001) 475.

[11] B. Baś, Z. Kowalski, Electroanalysis 14 (2002) 1067.[12] Polish Patent No P-319 984 1997.[13] B. Baś, Anal. Chim. Acta 570 (2006) 195.[14] R. Piech, B. Baś, W.W. Kubiak, Electroanalysis 19 (2007) 2342.[15] P. Kapturski, A. Bobrowski, Electroanalysis 19 (2007) 1863.[16] R. Piech, Electroanalysis 20 (2008) 2475.[17] R. Piech, B. Baś, E. Niewiara, W.W. Kubiak, Electroanalysis 20 (2008) 809.[18] P. Kapturski, A. Bobrowski, J. Electroanal. Chem. 617 (2008) 1.[19] R. Piech, B. Baś, W.W. Kubiak, J. Electroanal. Chem. 621 (2008) 43.[20] R. Piech, B. Baś, W.W. Kubiak, Talanta 76 (2008) 295.[21] R. Piech, B. Baś, B. Paczosa-Bator, W.W. Kubiak, J. Electroanal. Chem. 633 (2009)

333.[22] M. Grabarczyk, B. Baś, M. Korolczuk, Microchim. Acta 164 (2009) 465.[23] A. Bobrowski, M. Gawlicki, P. Kapturski, V. Mirceski, F. Spasovski, J. Zarębski,

Electroanalysis 21 (2009) 36.[24] R. Piech, Electroanalysis 21 (2009) 1842.[25] J. Wang, D.B. Luo, P.A.M. Farias, J.S. Mahmoud, Anal. Chem. 57 (1985) 158.[26] B. Baś, M. Jakubowska, Anal. Chim. Acta 592 (2007) 218.[27] J.C. Ball, R.G. Compton, J. Phys. Chem. B 102 (1998) 3967.[28] B.F. Nazarov, A.G. Stromberg Russ, J. Electrochem. 41 (2005) 49.[29] D. Menshykau, R.G. Compton, J. Phys. Chem. C 113 (2009) 15602.[30] Polish patent claim No P-390 660 (09.03.2010).