ORIGINAL PAPER

Differential pulse anodic stripping voltammetricdetermination of traces of tin using a glassy carbon electrodemodified with bismuth and a film of poly(bromophenol blue)

Gongjun Yang & Yujuan Wang & Fen Qi

Received: 11 November 2011 /Accepted: 21 February 2012 /Published online: 3 March 2012# Springer-Verlag 2012

Abstract We report on an anodic stripping voltammetricmethod for the determination of tin using a glassy carbonelectrode modified with bismuth and poly(bromophenolblue). After an accumulation time of 60 s at −1.20 V (vs.SCE), the response of the electrode to tin in 1.0 M HCl islinear in the concentration ranges from 20 nM to 1.0 μM, andfrom 1.0 μM to 20 μM, with a detection limit of 7.0 nM (at anSNR of 3) and with relative standard deviations in the order of3.0–3.8%. The methodwas validated by comparing the resultswith those obtained by AAS and successfully applied to thedetermination of tin in canned food.

Keywords Poly(bromophenol blue) . Differential pulsevoltammetry . Tin . Canned food

Introduction

Anodic stripping voltammetry (ASV) is a powerful voltam-metric technique for the determination of trace metals invarious samples. It has been widely used in environmentalsciences and in analytical chemistry. Due to the advanta-geous analytical properties in the negative potential range,mercury film electrode (denoted as MFE) and the hangingmercury drop electrode (denoted as HMDE) were tradition-ally used to determine the trace amount of metal ions by thetechnique of ASV in the past decades [1]. However, the useof mercury in some countries is severely restricted because

of its extreme toxicity and the increased risks [2]. So thealternative electrode materials, which can potentially replacemercury, are continually sought by many scientists. Theother materials, such as gold, platinum, iridium, and so on,were suggested to replace mercury in stripping analysis, butnone of them approached the favorable electrochemicalbehavior of mercury [3, 4]. Recently, a new bismuth-filmelectrode (denoted as BiFE) has been proposed as compar-ing favorably with mercury analogues. The most significantadvantage of BiFE is environmentally friendly due toneglecting the toxicity of bismuth and its salts. It has beenwidely used in determination of some trace heavy metals byASV [5–8]. In order to protect the bismuth surface againstabrasion and adsorption of surface-active compounds andformation of intermetallic compounds, the new types ofbismuth/polymer film electrode, such as Nafion-coveredbismuth film electrode [9, 10], bismuth/poly(aniline) filmelectrode [11] and bismuth/poly(p-aminobenzene sulfonicacid) film electrode [12], were attractive for practical anodicstripping voltammetric applications.

Analytical chemistry plays an important role in the foodindustry, both in the control of its quality as in its safety.And now M. E. Diaz-Garcia et al. [13] have reviewed therecent progress made in analytical nanotechnology as ap-plied to the food industry and to food analysis. As we allknow, tin has been extensively used in industry for the lastfive decades. One of the biggest utilizers of tin is widelyused in food industry as packings of canned foods. It is alsoan essential trace element in plants, animals and humans.However, tin is a heavy metal element which can do certainharm to human health. So it is essential and important forthe determination of trace Sn2+ in the canned food samplesby using simply and reliable method. Several methods havebeen already developed for the determination of Sn2+ withits own advantages and limitations. Measurement techni-ques mainly include spectrophotometry [14], fluorescence[15], atomic absorption spectrometry [16, 17], ICP-MS [18],

G. Yang (*)School of Pharmacy, China Pharmaceutical University,Nanjing 210009, People’s Republic of Chinae-mail: yanggongjun888@163.com

Y. Wang : F. QiCollege of Chemistry and Chemical Engineering,Yangzhou University,Yangzhou 225002, People’s Republic of China

Microchim Acta (2012) 177:365–372DOI 10.1007/s00604-012-0790-9

atomic emission spectrometry [19], chemiluminescence[20], GC-MS [21], potentiometry [22], polarography [23],cathodic stripping voltammetry [24, 25], and ASV usingBiFE [26–29]. The recent results of determining the tin byASV using BiFE were summarized as follow. S. B. Hocevalet al. [26] reported the determination of at BiFE usingcatechol as a complexing agent for Sn (IV) to assist theanalyte deposition before the anodic stripping of the depos-ited metal. And the similar results were obtained when theanalysis was carried out in the presence of caffeic acid as acomplexing agent for Sn (II) [27]. C. Prior reported that themethod of ASV using a BiFE was applied to determining Sn(II) in the presence of cetyltrimethylammonium bromide[28] and trace concentration of Sn (IV) was analyzed witha BiFE by square-wave anodic stripping voltammetry in asupporting electrolyte of 2.5 M sodium bromide [29].,respectively.

The aim of this work was to further expand the applicationof poly(bromophenol blue) (poly(BCB)) in the electrochemi-cal field and to establish an anodic stripping volammentricmethod for the determination of trace Sn2+ using bismuth/poly(bromophenol blue) modified glassy carbon electrode(Bi/poly(BPB)/GCE). The experimental results showthat a codeposition technique of Bi and Sn on poly(BPB)/GCE can improve the repeatability of modifiedelectrode for the successively measuring Sn2+. The contents ofSn in the canned food samples obtained by this work were ingood agreement with those obtained by furnace atomicabsorption spectroscopy.

Experimental

Chemicals and reagent

Bromophenol blue was obtained from Shanghai ShiyiChemicals Reagent Co., Ltd. (http://www.shiyicr.com). Allchemicals used were of analytical-reagent grade and did notundergo further purification unless otherwise specified. Allsolutions were prepared with double-distilled deionizedwater.

The stock solution of 1.0×10-2 M Sn2+ was prepared bydissolving appropriate amount of SnCl2 in 1.0 M HCl.Working solutions were prepared by appropriate dilutionof the stock solution.

The concentration of HCl solution is determined throughthe acid/base titration by NaOH standard solution.

Apparatus

Voltammetric measurements were performed with a CHI660A electrochemical system (CH Instruments Inc., USA).Electrochemical impedance spectroscopic (denoted as EIS)

experiments were performed with an Autolab Electrochem-ical Analyzer (Ecochemie, Netherlands) coupled to a one-compartment three-electrode cell. The three-electrode sys-tem consisted of a Bi/poly(BPB)/GCE, poly(BPB)/GCE orbare GCE as working electrode, a saturated calomel elec-trode (SCE) as reference electrode and a platinum wireelectrode as counter electrode. The impedance spectra wererecorded in a frequency range of 10-1~106 Hz. All testswere conducted on an open circuit, and a single modulatedAC potential of 10 mV was applied for impedance measure-ment. S-480II FESEM scanning electronmicroscope (Hitachi,Japan) was used for surface image measurements.

The accuracy of this work was compared to that of graphitefurnace atomic absorption spectrometry using a PE 2100(PerkinElmer, USA) atomic absorption spectrometer.

All experiments were conducted at 25.0±0.5°C.

Preparation of the modified electrode by poly(BPB) film

Poly(BPB) film modified glassy carbon electrode was pre-pared according to the previous report [30]. Briefly, the glassycarbon electrodes (GCE, Φ 3 mm) were polished progressive-ly with finer emery-paper, then thoroughly with 0.05 μmAl2O3 slurry on polishing cloth and rinsed with doubly-distilled deionized water, followed by ultrasonication indoubly-distilled deionized water, ethanol (1:1, v/v), andHNO3 (1:1, v/v). After pretreatment, the glassy carbon elec-trode was cycled for 20 segments in 0.5 M H2SO4 with thepotential range from −0.5 to +1.4 Vat scan rate of 100 mV s-1

until the reproducible background was obtained. Then, thepoly(BPB) film was electrochemically deposited in 0.1 Mphosphate buffer solution (pH 5.6) containing 0.1 mM bro-mophenol blue with the cycling potential from −1.0 to +1.8 Vat scan rate of 100 mV s-1 for 10 segments.

Voltammetric procedures

A certain volume of 1.0 M HCl aqueous solution, as well asappropriate amounts of Sn2+ and 2.0 μM Bi3+, was added toan electrochemical cell. Then in situ bismuth film depositionon poly(BPB) film-modified electrode was carried out underthe deposition potential of −1.20 V for 60 s while the solutionwas stirred. After each anodic sweep, the used electrode wascleaned by holding the potential at +0.20 V for 30 s, thentransferred to the pure blank electrolyte and swept five suc-cessive cycles between −1.20 to 0.20 Vat 100 mV s-1 to cleanprevious deposits. The quantification of Sn2+ was achieved bymeasuring its anodic stripping peak current by differentialpulse voltammetry. The differential pulse voltammogramwere recorded during the potential sweep from −1.20 to0.20 V, and its parameters were selected: the increase potentialof 8 mV, pulse amplitude of 50 mV, pulse width of 0.06 s, andsampling width of 0.02 s.

366 G. Yang et al.

Sample preparation

A 10.0 mL sample (juice of canned pineapple, orange,grape, and mango) was transferred to a 100 mL conicalflask, then 2.5 mL concentrated nitric acid and 1.0 mLconcentrated sulfuric acid were added. The sample was thencarefully heated and evaporated to near dryness. After cool-ing, the digested sample was neutralized by sodium hydrox-ide solution. Then the solution was transferred and diluted to100.0 mL with 1.0 M HCl.

Results and discussion

Characterization of the poly(BPB) film modified GCE

Electrochemical impedance spectroscopy (EIS) can besuccessfully used as a sensitive method to prove theinterface properties of surface-modified electrode. In atypical impedance spectrum which is presented in theform of Nyquist plot, it includes a semicircle part and a

linear part. The semicircle part at higher frequenciescorresponds to the electron-transfer limited process andits diameter is equal to the electron transfer resistance(Rct) which controls the electron transfer kinetics of theredox probe at the electrode interface. Figure 1a showsthe Nyquist plot of the EIS measurement of poly(BPB)/GCE and bare GCE in the presence of 1.0 mM [Fe(CN)6]

3-/4- and 0.1 M KNO3. It can be seen that only

0 1000 2000 3000 4000 5000

0

1000

2000

3000

4000 A

100 150 200 250 300 350 400

0

50

100

150

200

250

Zim

()

Zre ( )

2

1

Zim

()

Zre ( )

B

Fig. 1 a Nyquist plot (Zim vs. Zre) for Faradaic impedance measure-ments in 1.0 mM K3[Fe(CN)6]/K4[Fe(CN)6] and 0.1 M KNO3 at bareGCE (a) and poly(BPB)/GCE (b). Inset: Curve a is zoomed in. b SEMimage of poly(BPB) film modified electrode

-0.8 -0.6 -0.4 -0.2 0.0-8

-7

-6

-5

-4

-3

-2

-1

0

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d'

c'd'

a'

c'

b'

i (A

)

E (V) vs. SCEd

c

b

a

E (V) vs. SCE

i (A

)

Fig. 2 Differential pulse stripping voltammetric response of 1.5×10-6 MSn2+ and differential pulse voltammograms without Sn2+ (Inset) at theGCE (curve a, a’), poly(BPB)/GCE (curve b, b’), the bismuth film-modified glassy carbon electrode (curve c, c’), and the Bi/poly(BPB)/GCE (curve d, d’) in 1.0 M HCl) without 2.0 μMBi3+ (curve a, a’, b andb’) and with 2.0 μM Bi3+(curve c, c’, d and d’), respectively. Accumu-lation potential: -1.20 V; Accumulation time: 60 s

-0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2

-200

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-150

-125

-100

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-50

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0

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i (A

)

E (V) vs. SCE

i (A

)

E (V) vs.SCE

Fig. 3 Differential pulse stripping voltammetric responses of Sn2+ atBi/Poly(BPB)/GCE in 1.0 M HCl . Sn2+ concentration (μM): 0.020,0.10, 0.30, 0.50, 0.70, 1.0, 3.0, 5.0, 7.0, 10.0 and 20.0. Inset: Differ-ential pulse stripping voltammograms of circle portion at low Sn2+

concentration are zoomed in

Differential pulse anodic stripping voltammetric determination 367

very small semicircle with an almost straight tail linefor a bare GCE could be observed (Fig. 1a inset). Thisis the indicative characteristic of a diffusion-controlledelectrode process. A semicircular Nyquist impedancespectrum is observed for poly(BPB)/GCE (curve 2), thisphenomenon indicates that the electron transfer resis-tance at the electrode/electrolyte interface increases afterpoly(BPB) was electrochemically deposited on the elec-trode surface. At the same time, Fig. 1b showed theSEM images of poly(BPB) coated electrode surface. Itfurther confirmed the formation of a continuous poly(BPB)film on the GC electrode.

Based on previous reports, the surface coverage (θ) ofpoly(BPB) film on a bare GCE can be evaluated from theEIS according to the equation [31, 32]:

θ ¼ 1� Rbarect

RpolyðBPBÞct

ð1Þ

where Rctbare denotes the charge transfer resistance of the bare

GCE, Rctpoly(BPB) is the charge transfer resistance of the mod-

ifiedGCE by poly(BPB) filmwith 10 cyclic times. The surfacecoverage (θ) of electrode was estimated to be about 98.5%.

Electrochemical response of Sn2+ at Bi/poly(BPB) modifiedelectrode

Figure 2 shows the differential pulse voltammetric responsewith 1.5×10-6 M and without Sn2+ (Inset) in 1.0 M HCl at a

bare GCE (curve a, a’), poly(BPB)/GCE (curve b, b’),bismuth film-modified GCE (curve c, c’) and a Bi/poly(BPB)/GCE (curve d, d’). It can be seen that that the anodic peak atthe potential of −0.18 V (vs. SCE) was corresponding to theoxidation of Bi to form Bi(III) and the other larger anodicstripping signal at the potential of −0.62 V (vs. SCE) wasobtained at the Bi/poly(BPB)/GCE than that at the other threetypes of electrode. The reasons can be interpreted as follow.On the one hand, tin ions adsorbed from bulk solution on thesurface of Bi/poly(BPB)/GCE by the electrostatic interactionsdue to the sulfonic group of poly(BPB) during the accumula-tion process. On the other hand, bismuth film coating GCEserves as both the sensing element and the transducer of thesignal (current) by codeposition technique of Bi and Sn onpoly(BPB)/GCE [33].

In order to explain the mechanism of the signal formation,some experiments were carried out. Firstly, 1.5×10–6 M Sn2+

was accumulated for 60 s at −1.20 V in 0.1 M HCl containing2.0 μM Bi3+ at Bi/poly(BPB)/GCE. Then the differentialpulse voltammogram of Sn2+ was recorded, and theanodic peak can be obtained obviously. Finally, the pre-vious swept modified electrode in blank solution wasalso swept in another blank solution, and the anodic peakof Sn2+ can not be observed. So the mechanism could besuggested as the following:

Sn2þ þ Bi3þ þ poly BPBð Þmem ����! Sn2þ Bi3þ � poly BPBð Þmem

�� �ads

ð1Þ

Sn2þ Bi3þ� � poly BPBð Þmem

� �ads ���������������!

Electrochemical reductionSn0 Bi0 � poly BPBð Þmem

�� �ads ð2Þ

Sn0 Bi0 � poly BPBð Þmem

�� �ads ���������������!

Electrochemical oxidationSn2þ þBi3þ þ poly BPBð Þmem ð3Þ

Table 1 Comparison of linear range and detection limit for Sn2+ at the different electrodes

Type of electrodes Linear range Detection limit

Nafion®-modified electrode [24] / 0.1 ng mL-1 (8.4×10–10 M)

Rotating mercury[34] / 2.0×10–8 M

dropping mercury working electrode (DME) [23] 2.0×10-8 ~ 1.0×10-6 g mL-1 (1.7×10-7 ~ 8.4×10-6 M) 1.0×10-8 g mL-1 (8.4×10-8 M)

Bismuth film electrode [26] 1.0 ~ 100 μg L-1 (8.4×10–9 ~ 8.4×10–5 M) 0.26 μg L-1 (2.2×10–9 M)

Bismuth film electrode [27] 1.7×10–7 ~ 7.83×10–6 M 1.4×10–7 M

Bismuth film electrode [28] 5.0 ~ 50 μg L-1 (4.2×10–8 ~ 4.2×10–7 M) 1.9 μg L-1 (1.6×10–8 M)

Bismuth film electrode [29] 20.0 ~ 200 μg L-1 (1.7×10–7 ~ 1.7×10–6 M)

glassy carbon mercury film electrode [35] 0 to 35 μg L-1 (0 ~ 2.95×10-7 M) 0.5 μg L-1 (4.21×10-9 M)

Bi/Poly(BPB)/GCE [This work] 2.0×10–8 ~ 2.0×10–5 M 7.0×10-9 M

368 G. Yang et al.

Optimization of experimental conditions for determiningSn2+

In order to obtain the highest anodic stripping peak currentand the best anodic stripping peak shape, the anodic strip-ping responses of Sn2+ in different supporting electrolytes,such as 1.0 M HCl, 1.0 M H2SO4 and 1.0 M HNO3, 1.0 MHAc-NaAC buffer solution (pH 4.5), were investigated atBi/poly(BPB)/GCE. The experimental results showed thatthe supporting electrolyte of 1.0 M HCl was optimal medi-um for determining Sn2+. At the same time, the influence ofHCl concentration in the range of 0.5 and 2.0 M on theanodic peak current of Sn2+ was also investigated. Theexperimental results manifested that the maximum responseof current appeared at the concentration of 1.0 M. So the1.0 M HCl was chosen as the supporting electrolyte forfurther studies.

Effect of scan cycles was investigated during the electro-polymerization of bromophenol blue by cyclic voltammetry

on anodic peak current of Sn2+. The experimental resultsshowed that the anodic stripping peak current graduallyincreased with the increase of scan cycles of electropolyme-rization. When the cycles were beyond 10, the anodic peakcurrent decreased. So scan cycles of 10 was selected in theelectropolymerization, and the maximum anodic strippingpeak current response of Sn2+ was obtained.

The effect of Bi3+ concentration on the anodic strippingpeak current of Sn2+ was studied for a solution containing8.5×10-7 M Sn2+ in 1.0 M HCl at in situ plated Bi/poly(BPB)/GCE. In this case, the concentration of the Bi3+

solution controls the thickness of the Bi film. When Bi3+

concentration is less than 2.0 μM, the anodic strippingcurrent of Sn2+ increased with the increasing concentrationof Bi3+. However, for Bi3+ concentration higher than2.0 μM, the thicker bismuth film will hold back the targetmetal and resulted in the decrease of the anodic strippingcurrent of Sn2+. Thus, the optimal 2.0 μM Bi3+ was chosenin the following work.

a

2015101 5

0.1 A

b

20151051

0.5 A

c

2015101 5

5

d

6

54

321

0.5 AA

Fig. 4 Reproducibility of theanodic stripping peak currentsat three levels of Sn2+

concentration of 2.0×10-7 M(a), 8.5×10-7 M (b), 4.0×10-6 M (c) on the same Bi/poly(BPB)/GCE and at the identicalsurface of poly(BPB)/GCEcontaining 1.5×10-6 M Sn2+ (d)in 1.0 M HCl

Table 2 Repeatability of Sn2+ atthe identical electrode surfacesand reproducibility of Sn2+ at therenewed ones

Concentration (M) At the identical surfaces (n020) At the renewed surfaces (n08)

Average current (μA) RSD (%) Average current (μA) RSD (%)

2.0×10-7 0.580 3.8 0.54 4.6

8.0×10-7 2.71 3.2 2.83 4.3

4.0×10-6 31.3 3.0 31.8 3.9

Differential pulse anodic stripping voltammetric determination 369

The effects of accumulation potentials and accumulationtime on the anodic stripping peak current responses of Sn2+

were investigated. On the condition of the accumulationtime of 60 s, the maximum anodic peak current appearedat the potential of −1.20 V (vs. SCE). Thus, –1.20 V waselected as the optimal accumulation potential. At the sametime, the study of the accumulation time was also carried outat the potential of −1.20 V. The experimental results showedthat the anodic stripping peak current of Sn2+ increasedgradually with increasing accumulation time, which indicat-ed that the sensitivity of determination of Sn2+ would in-crease as extending accumulation time. In this work, forrapid and sensitive analysis of tin, the accumulation timeof 60 s was selected.

Calibration curve

Under the optimized experimental conditions, the calibra-tion plot for Sn2+ detection was carried out at the Bi/poly(BPB)/GCE while varying the concentrations of Sn2+.Figure 3a illustrated the differential pulse voltammetric re-sponse at the Bi/poly(BPB)/GCE while varying the concen-trations of Sn2+. The anodic striping peak current (ipa) isproportional to the concentration of Cd2+ from 2.0×10-8 to

1.0×10-6 M and from 1.0×10-6 to 2.0×10-5 M, with aregression equation of:

ipa=10�6A ¼ �0:1121 þ 3:378CSn2þ=10

�6MðR2

¼ 0:9922Þ regression equation Ið Þ

and

ipa=10�6A ¼ �7:921þ 9:897CSn2þ=10

�6MðR2

¼ 0:9990Þ regression equation IIð Þ; respectively:

For 60 s accumulation, the detection limit was 7.0×10-9 M(S/N03) based on the regression equation I. These values werein the trace analytical concentration range. From the results ofTable 1, it can be seen that this work has lower detection limitand wide linear range detection of Sn2+ than the earlier reports[23, 27–29, 34], or the detection limit reached the same orderof magnitude in the previous reports [26, 35].

Interference studies

In order to evaluate the ability of anti-jamming of somesubstances, the interference study was performed by adding

Table 3 Determination of tin incanned fruit juice samples

aFurnace atomic absorptionspectroscopy methodbValues are expressed as meanstandard deviation (n05)

Sample Amount found by proposed method(×10-5 M)

RSD(%)

Amount found by reference methoda

(×10-5 M)

pineapple 1.14±0.05 b 4.3 1.17±0.05

orange 4.51±0.20 4.1 4.47±0.18

grape 2.82±0.11 3.5 2.86±0.10

mango 0.750±0.03 3.8 7.33±0.03

Table 4 Recoveries of samplesby the proposed method

aDetermined after the pretreatedsample solutions were dilutedfor 100 timesbDetermined after the pretreatedsample solutions were dilutedfor 10 times

Sample Added (×10-7 M) Determined (×10-7 M) Recovery (%) RSD (%)

pineapplea 3.00 4.19 101.67 3.1

10.0 11.03 98.90 4.3

30.0 32.41 104.23 2.9

80.00 78.84 97.12 3.0

orangea 3.00 7.43 97.33 3.8

10.0 14.82 103.10 3.9

30.00 33.53 96.73 3.2

80.00 85.87 101.70 2.9

grapea 3.00 5.93 103.66 3.4

10.0 12.69 98.70 3.6

30.0 31.85 96.77 3.1

80.00 84.01 101.49 3.2

Mangob 1.00 8.54 104.00 4.0

10.0 17.79 102.90 3.5

30.0 37.02 98.40 3.7

80.00 86.13 98.51 3.4

370 G. Yang et al.

various potentially interfering ions into a standard solutioncontaining 8.5×10-7 M Sn2+ and 2.0 μM Bi3+ under theconditions of accumulation potential of −1.20 V and accu-mulation time of 60 s. 1000-fold concentration of Na+, K+,Ca2+, Mg2+, Mn2+, Ni2+, SO4

2-, Cl-, 60-fold that of Co2+,Zn2+, 10-fold that of Pb2+, 5-fold that of Hg2+, and the sameconcentration of Cu2+, Cd2+, Fe3+did not influence the an-odic stripping current response of 8.5×10-7 M Sn2+ in 1.0 MHCl (signal change below ± 5.0%). The above experimentalresults indicated that this work electrochemical method per-formed the ability of anti-jamming.

Precision

The repeatability was also evaluated by successively mea-suring the three concentration of Sn2+ (2.0×10-7, 8.0×10-7

and 4.0×10-6 M) for twenty times at the identical surface ofBi/poly(BPB)/GCE (Fig. 4a, b, c). Additionally, the repro-ducibility between multiple electrode preparations (n08)was estimated by comparing the oxidation peak current ofthe above three levels of Sn2+. The results of average cur-rents and RSD were listed in Table 2. At the same time, thereproducibility of poly(BPB)/GCE was also investigated(Fig. 4d). It can be seen that the anodic stripping peakcurrents were gradually decreased with the increase of suc-cessive measurement at the identical poly(BPB)/GCE. Thus,based on the experimental results of Figs. 2 and 4, theaddition of Bi3+ can enhance the anodic peak current andimprove the repeatability of modified electrode.

Determination of Sn2+ in canned food samples

In order to estimate its application in real samples, Bi/poly(BPB)/GCE was directly applied to the determination of tinin canned fruit juice samples. The Sn2+ concentration in pre-treated sample solutions of pineapple, orange, grape and man-go were determined for 1.14×10-6, 4.51×10-6, 2.82×10-6,7.50×10-7 M using this work by the standard addition methodcontents, respectively. The results of tin contents in real sam-ples, which were obtained by this method, were in goodagreement with those obtained by the method of furnace atom-ic absorption spectroscopy (Table 3). At the same time, therecoveries in real sample were also determined, and the resultswere shown in Table 4. FromTable 4, recoveries in the range of96.73~104.23% were obtained by analysis of spiked real sam-ples. The above experimental results showed that this electro-chemical method can reliably apply to determination of tin ion.

Conclusions

In this work, we have demonstrated the applicability of theBi/poly(BPB)/GCE on the determination of Sn2+ in canned

food samples at low levels by anodic stripping differentialpulse voltammetry. More importantly, it has been demon-strated that the poly(BPB) film can improve the sensitivityof determining tin by electrostatic interaction and bismuthfilm deposited on surface of electrode confer significantimprovements of reproducibility. Bi/poly(BPB)/GCE wassuccessfully applied to the determination of Sn in cannedjuice, and the results were in satisfactory agreement withthose obtained by furnace atomic absorption spectroscopymethod. Compared to the method of AAS, this methodperforms good characteristics, such as inexpensive instru-mentations and simple operation. It will expand the potentialapplications for the monitoring of other heavy metals inenvironment, food and medicine.

Acknowledgements This project was financially supported by theNational Natural Science Foundation (No. 21075108) of China.

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