ANALYTICAL SCIENCES MAY 2008, VOL. 24 2008 © The Japan Society for Analytical Chemistry
589
Determination of trace heavy Metals by Sequential Injection– anodic Stripping Voltammetry using Bismuth Film Screenprinted Carbon Electrode Suchada Chuanuwatanakul,* wijitar Dungchai,* orawon Chailapakul,* and Shoji Motomizu**† *Department of Chemistry, Faculty of Science, Chulalongkorn University, Phayathai Road, Pathumwan, Bangkok 10330, Thailand **Department of Chemistry, Faculty of Science, Okayama University, 3-1-1 Tsushimanaka, Okayama 700–8530, Japan
A sequential injection–square-wave anodic stripping voltammetry (SIA-SWASV) is proposed for the simultaneous determination of Pb(II), Cd(II) and Zn(II), employing an in situ plated bismuth film screen-printed carbon electrode (Bi-SPCE) as a working electrode and hydrochloric acid as a supporting electrolyte. Bi(III) and analyte metal ions were on-line deposited onto a SPCE at –1.4 V vs. Ag/AgCl for 180 s. At a stopped flow, a square-wave voltammogram was recorded from –1.3 to 0 V vs. Ag/AgCl. The experimental conditions were optimized. Under the optimum conditions, the linear ranges were 0 – 70 mg L–1 for Pb(II) and Cd(II), and 75 – 200 mg L–1 for Zn(II). The limits of detection (S/N = 3) were obtained at concentrations as low as 0.89 mg L–1 for Pb(II) and 0.69 mg L–1 for Cd(II) for a 180-s deposition time. The proposed method was applied to the determination of Pb(II), Cd(II) and Zn(II) in water samples with satisfactory results. (Received September 25, 2007; accepted December 7, 2007; published May 10, 2008)
Introduction One of the most serious problems facing the world today is contamination of the environment by heavy metals. Finally, these toxic metals are incorporated into drinking water and various food chains. To a small extent they can enter human bodies via food, drinking water and air. They tend to bioaccumulate. When they reach high levels in the body, they can be immediately poisonous, or can result in long-term health problems. Monitoring heavy metal ion levels in natural water, drinking water and food is essential and a requisite for human health and safety. The current methods for metal-ion analysis in natural water are atomic absorption spectroscopy (AAS), inductively coupled plasma–atomic emission spectroscopy (ICP-AES), inductively coupled plasma–mass spectrometry (ICP-MS) and anodic stripping voltammetry (ASV). Recently, ASV is recognized as one of the most powerful tools in the trace and ultratrace analysis of metal ions, because it provides a wide linear dynamic range, a low detection limit, and a multielement analysis capability. An additional advantage of ASV over AAS, ICPAES or ICP-MS is simplicity of the instrumentation, which is relatively inexpensive, requires low electrical power and low maintenance, and is portable as well as suitable for automation.1–4 Combining stripping voltammetry with flow systems has significant advantages over batch analysis, such as a high level To whom correspondence should be addressed. E-mail:
[email protected] †
of automation, speed of analysis, improvement of accuracy and precision, less risk of contamination and cost-effective operation.5–8 Sequential injection analysis (SIA) is one of the flow-analysis technique suited to stripping techniques that employ a preconcentration stage of the analyte on the working electrode before an actual measurement.9 SIA allows ASV to be performed with high precision because of the excellent reproducibility of the time and mixing conditions, leading to very reproducible mass transport between the electrode surface and the flowing stream solution.10 Various stripping voltammetric methods that were automated by SIA have been reported.5,6,8–12 Mercury-based electrodes have been traditionally used to obtain high sensitivity and reproducibility, as well as a wide cathodic potential limit in the ASV of trace metals. Because of the toxicity of mercury and environmental regulations, however, mercury-free electrodes were developed.2,13–15 One of environmentally friendly electrodes, which is comparable to mercury electrodes, is the bismuth-film electrode (BiFE), as pioneered by Wang and coworker.16 Its attractive properties include high sensitivity, well-defined and highly reproducible stripping signal, good resolution of neighboring peaks, low background characteristics, a large cathodic working potential range, and being insensitive to dissolved oxygen, which eliminates the time-consuming de-oxygenation step.13–17 Bismuth can be plated on several substrates,18 such as glassy carbon,13–16,19,20 carbon paste,14,21,22 wax-impregnated graphite,14 pencil-lead,23 screen-printed carbon ink,24,25 carbon-fibers,16,26,27 gold,27 copper,28,29 and platinum.28 The majority of studies have used a glassy carbon or carbon fiber substrate for electrolytic bismuth film plating. The working surface of these electrodes
590 usually needs to be manually polished quite frequently; it leads to difficulty to use such electrodes with high precisions for online analysis with the use of automated systems and for on-site field-portable instruments.30 To overcome this problem, inexpensive, disposable, flexible in design and easy to produce, screen-printed carbon electrodes (SPCEs) were used as substrates for bismuth film electrodes. The applications of bismuth film screen-printed electrodes (Bi-SPCEs) have been reported for anodic stripping voltammetric measurements of trace Pb(II)24 as well as stripping chronopotentiometric measurements of Pb(II) and Cd(II)25 by batch analysis. They have not been used in the flow systems. In this work, a sensitive method for the on-line simultaneous determinations of Pb(II), Cd(II) and Zn(II) on in situ plated Bi-SPCE using a sequential injection system coupled with square-wave anodic stripping voltammetry (SIA-SWASV) was developed. The effects of various experimental conditions on the sensitivity and the reproducibility were studied. The limits of detection (S/N = 3) for Pb(II) and Cd(II) at sub ppb level with a deposition time of 180 s were obtained. In addition, the proposed method was applied to the determination of Pb(II), Cd(II) and Zn(II) in water samples with satisfactory results.
Experimental Reagents and chemicals All standard and reagent solutions were prepared with ultrapure water (resistivity ≥18.3 MW cm–1) from an Elix 3/ Milli-Q Element System (Nihon Millipore, Japan). Working standard solutions of Pb(II), Cd(II) and Zn(II) were daily prepared by appropriate dilution of the stock standard solutions (1000 mg L–1 atomic absorption analysis standard solution; Kanto Chemical, Japan) with a 1 M hydrochloric acid solution. A Bi(III) plating solution was prepared by appropriate dilution of the stock solution of Bi (1000 mg L–1 atomic absorption analysis standard solution; Kanto Chemical) with 1 M hydrochloric acid solution. A 1 M hydrochloric acid solution, which served as a supporting electrolyte, was prepared by appropriate dilution of hydrochloric acid (electronic grade, 36%, 1.18 g mL–1; Mitsubishi Chemicals, Japan). Working electrodes The electrodes were screen-printed in house using carbon ink (Electrodag PF-407C, Acheson, USA), silver ink (Electrodag 7019, Acheson) and ceramic substrates. Bi-SPCEs were prepared by on-line in situ plating. Apparatus A sequential injection system for the determination of Pb(II), Cd(II) and Zn(II) by SWASV, as shown in Fig. 1, consisted of a 3-way syringe pump (Hamilton, USA) and an 8-port selection valve (Hamilton, USA). PTFE tubing was used for flow lines (0.5 mm i.d.) and a holding coil (1.5 mm i.d.). The system was computer controlled by using a program written by LabVIEW® software, Ver. 7.1 (National Instrument). Electrochemical measurements were carried out in a thin-layer flow cell (Bioanalytical Systems, USA) using a PalmSens portable instrument (Palm Instruments BV, The Netherlands). The thin-layer flow cell consisted of a gasket as a spacer, a BiSPCE as a working electrode, a Ag/AgCl electrode (3 M KCl) as a reference electrode, and a stainless-steel tube as a counter electrode as well as a solution outlet of the flow cell. The experiments were carried out in a Faraday cage to reduce electrical noise.
ANALYTICAL SCIENCES MAY 2008, VOL. 24
HC
5000 mL
SV 7
Potentiostat 1 2
8 6
5
3 4
Waste Water
SP
Ce Bi S Waste
Thin-layer flow cell WE : Bi-SPCE RE : Ag/AgCl CE : Stainless steel
Fig. 1 Schematic diagram of the SIA-SWASV system for the determination of Pb(II), Cd(II) and Zn(II). SP, Syringe pump; SV, selection valve; HC, holding coil; Ce, electrode cleaning solution (0.5 M HCl); Bi, Bi(III) plating solution; S, sample solution; WE, working electrode; RE, reference electrode; CE, counter electrode.
Procedure The step sequences for the determinations of Pb(II), Cd(II) and Zn(II) by SIA-SWASV are given in Table 1. The sample and the Bi(III) plating solution were sequentially aspirated into the holding coil and dispensed in reverse direction into a thinlayer flow cell in which Bi and the analyte metals were deposited on SPCE at –1.4 V vs. Ag/AgCl for 180 s (steps 1 – 3). After a 10-s equilibration time at stopped-flow (step 4), the voltammogram was recorded from –1.3 to 0 V vs. Ag/AgCl by applying a potential with a square-wave waveform with a frequency of 50 Hz, a step potential of 4 mV, and a pulse amplitude of 40 mV (step 5). Finally, the electrode was cleaned to remove any remaining analyte metals and bismuth film at +0.3 V vs. Ag/AgCl in flowing of 0.5 M hydrochloric acid for 40 s (steps 6 – 7). All experiments were performed at room temperature (25˚C) in a nondeaerated solution.
Results and Discussion Optimization of experimental conditions Effect of a supporting electrolyte. The effect of the type of supporting electrolyte on the square-wave anodic stripping voltammetric signals of Pb(II), Cd(II) and Zn(II) was studied. Among the various supporting electrolytes examined, including hydrochloric acid, nitric acid and perchloric acid solution, the highest peak currents were obtained in a hydrochloric acid solution. This was probably due to the oxidizing properties of nitric acid and perchloric acid. In the deposition step, these acids could be reduced to the gaseous electroinactive products, NO2 and ClO2, which led to kinetic polarization; the reduction potentials of metal ions in these acids were shifted to more negative potentials. This caused a decrease in the peak currents. However, hydrochloric acid could not be reduced in the deposition step. Therefore, hydrochloric acid was used as the supporting electrolyte. The effect of the concentration of hydrochloric acid, as the supporting electrolyte, was also studied at 0.1, 0.5 and 1 M; maximum stripping peak currents of Pb(II), Cd(II) and Zn(II) were obtained in a 1 M hydrochloric acid solution. As the result of a high concentration of acid, the stripping of metal ions from the electrode became easy. Thus, a hydrochloric acid concentration of 1 M was selected for further experiments. Effect of the concentration of Bi(III) plating solution. In this work, bismuth film was generated on the SPCE by on-line in situ plating. The Bi(III) plating solution and the sample solution
ANALYTICAL SCIENCES MAY 2008, VOL. 24 Table 1
591
Step sequence for the determination of metal ions by SIA-SWASV
Step
Description
SV
Volume/mL
Flow rate/mL s–1
Duration/s
Electrode potential/V
1 2 3
Aspirate sample solution into HC Aspirate Bi(III) solution into HC Dispense Bi(III) solution and sample solution into flow cell for in situ plating of Bi and deposition of metal Equilibration Stripping and recording of voltammogram Aspirate 0.5 M HCl into HC Dispense 0.5 M HCl into flow cell for electrode cleaning
1 2 3
1440 720 2160
200 200 12
7.2 3.6 180
–1.0a –1.0a –1.4
3 3 4 3
— — 1200 1200
0 0 200 30
10 10 6 40
–1.4 Scan (–1.3 to 0) +0.3 +0.3
4 5 6 7
a. Conditioning potential.
40
50 Cd(II)
Pb(II)
40
Cd(II)
20 10 Zn(II)
Current / mA
Current / mA
30
Pb(II) 30 20
Zn(II)
10
0
0
500
1000
1500
2000
Bi(III) concentration / mg L–1
Fig. 2 Effect of the concentration of the Bi(III) plating solution on the stripping peak currents of a solution containing 50 mg L–1 Pb(II), 50 mg L–1 Cd(II) and 100 mg L–1 Zn(II) in 1 M HCl. Conditions: flow rate, 5 mL s–1; conditioning potential, –1.0 V for 10 s; deposition potential, –1.4 V for 180 s; equilibration time, 10 s; pulse amplitude, 0.040 V; step potential, 0.004 V; frequency, 50 Hz.
were aspirated and delivered to the thin-layer flow cell, where a potential of –1.4 V vs. Ag/AgCl was applied to the SPCE to form a bismuth film simultaneously with analyte metals deposition. After the voltammogram was recorded, the BiSPCE was cleaned with a 0.5 M hydrochloric acid solution, while the potential of the electrode was held at +0.3 V for 40 s. Therefore, the bismuth film and analyte metals were stripped out completely, which minimized the accumulative fouling of the electrode. The stripping peak current was affected by the thickness of the Bi film, which was controlled by the concentration of the Bi(III) plating solution.14 The effect of the concentration of the Bi(III) plating solution on the stripping peak currents of Pb(II), Cd(II) and Zn(II) was investigated in the concentration range of 100 to 2000 mg L–1. The results are shown in Fig. 2. As the Bi(III) concentration was increased, the stripping peak currents of Pb(II) and Cd(II) were increased up to 1000 mg L–1, and then remained constant for Pb(II) and slightly decreased for Cd(II). However, the stripping peak current of Zn(II) decreased with increasing the concentration of Bi(III), and the Zn(II) signal disappeared at a Bi(III) concentration of 2000 mg L–1, because the background current at the negative potential increased. Therefore, the Bi(III) concentration of 500 mg L–1 was chosen for the simultaneous determinations of Pb(II), Cd(II) and Zn(II). Effect of deposition potential and time. The influence of the deposition potential on the stripping peak currents of Pb(II), Cd(II) and Zn(II) was examined at –1.3, –1.4 and –1.5 V vs. Ag/AgCl. A deposition potential of –1.4 V vs. Ag/AgCl was
0 0
50
100
150
200
250
300
Time / s
Fig. 3 Effect of the deposition time on the stripping peak currents of a solution containing 50 mg L–1 Pb(II), 50 mg L–1 Cd(II) and 100 mg L–1 Zn(II) in 1 M HCl. Conditions: concentration of Bi(III) plating solution, 500 mg L–1; flow rate, 5 mL s–1; conditioning potential, –1.0 V for 10 s; deposition potential, –1.4 V; equilibration time, 10 s; pulse amplitude, 0.040 V; step potential, 0.004 V; frequency, 50 Hz.
selected for the highest stripping peak currents and the minimum side reactions due to the results that the stripping peak currents of Pb(II) and Cd(II) at –1.5 V vs. Ag/AgCl were significantly lower than at –1.3 and –1.4 V vs. Ag/AgCl. This was the result of the hydrogen evolution background that occurred at more negative potentials. Moreover, the stripping peak current for Zn(II) was too low at –1.3 V vs. Ag/AgCl, because this applied potential was not sufficient for Zn(II) to be electrolyzed.31 The effect of the deposition time on the stripping peak currents of Pb(II), Cd(II) and Zn(II) was studied in the range of 60 to 270 s. The results are shown in Fig. 3. The stripping peak currents of Pb(II), Cd(II) and Zn(II) were found to increase with increasing the deposition time over the range of 60 to 270 s. However, the peak currents slowly increased, and a large error bar was obtained after 180 s. Thus, a deposition time of 180 s was chosen as a compromise between the sensitivity, the reproducibility and the analysis time. Effect of the flow rate. In a deposition step of Bi and the analyte metals on the SPCE, the flow rate plays an important role on the sensitivity of the analysis. Therefore, the influence of the flow rate on the stripping peak currents was investigated in the range of 1 to 18 mL s–1 at a 180-s deposition time by using various volumes of the metal ion solution and a Bi(III) plating solution at a ratio of 2:1. It was observed that the stripping peak currents increased with an increasing flow rate due to an enhancement of the mass-transfer rates of the metal ions to the electrode surface
592
ANALYTICAL SCIENCES MAY 2008, VOL. 24 100
Table 2 Optimization of the experimental conditions of the SIA-SWASV system for the determination of Pb(II), Cd(II) and Zn(II) Optimized parameter
Type of supporting HCl HNO3, HCl, HClO4 electrolyte Concentration of 0.1, 0.5, 1 M 1M supporting electrolyte Concentration of Bi(III) 100 to 2000 mg L–1 500 mg L–1 plating solution Deposition potential –1.3, –1.4, –1.5 V –1.4 V vs. Ag/AgCl Deposition time 60 to 270 s 180 s Flow rate 1 to 18 mL s–1 12 mL s–1
80
Current / mA
Parameter examined
Parameter
90
70
60 50 40 30 –1.4
–1.2
Current / mA
80
Cd
Pb
Zn
40 30 20
y(Cd) = 0.6310x - 0.5833 R2 = 0.9953
10 0 0
40
(a)
20
(b) –1.1
–0.9
–0.7
–0.5
–0.3
–0.1
0.1
Potential / V vs. Ag/AgCl
Fig. 4 Comparison of square-wave anodic stripping voltammograms on (a) in situ plated Bi-SPCE and (b) bare SPCE of a solution containing 50 mg L–1 Pb(II), 50 mg L–1 Cd(II) and 100 mg L–1 Zn(II) in 1 M HCl. Conditions: concentration of Bi(III) plating solution, 500 mg L–1; flow rate, 12 mL s–1; conditioning potential, –1.0 V for 10 s; deposition potential, –1.4 V for 180 s; equilibration time, 10 s; pulse amplitude, 0.040 V; step potential, 0.004 V; frequency, 50 Hz.
during the deposition step. Moreover, when the flow rate increased, the stripping peak currents increased rapidly in the range of 1 to 12 mL s–1, and slowly after 12 mL s–1. Therefore, a flow rate of 12 mL s–1 was selected for high sensitivity, good reproducibility (small error bar) and low consumption of the sample and the reagents. The optimum conditions obtained are summarized in Table 2. In order to evaluate the effectiveness of Bi-SPCE for Pb(II), Cd(II) and Zn(II) determinations, SIA-SWASV of a solution containing 50 mg L–1 Pb(II), 50 mg L–1 Cd(II) and 100 mg L–1 Zn(II) in 1 M hydrochloric acid was performed on a bare SPCE and in situ plated Bi-SPCE under the optimum experimental conditions. As can be seen in Fig. 4, the sensitivity for all metal ions was better on the Bi-SPCE than on the bare SPCE, especially for Zn(II) determination. Analytical characteristics The analytical characteristics of the proposed SIA-SWASV method for the on-line simultaneous determination of Pb(II), Cd(II) and Zn(II) on Bi-SPCE was evaluated under the optimum conditions. Figure 5(a) shows a series of square-wave voltammograms for the simultaneous determination of Pb(II), Cd(II) and Zn(II) on Bi-SPCE using standard solutions containing Pb(II), Cd(II) and Zn(II) of increasing concentration. The calibration graph for the deposition time of 180 s was linear
–0.6
–0.4
–0.2
0.0
40 y(Pb) = 0.7262x - 0.1667 R2 = 0.9934
50
(b)
20
40
60
Concentration / mg L–1
80
Current / mA
Current / mA
Bi
100
0 –1.3
–0.8
60
120
60
–1.0
Potential / V vs. Ag/AgCl
(a)
y(Zn) = 0.2697x - 19.419 R2 = 0.9954
30 20 10 0 50
100
150
200
250
Concentration / mg L–1
Fig. 5 (a) Square-wave anodic stripping voltammograms on BiSPCE of solutions containing Pb(II), Cd(II) and Zn(II) of increasing concentrations, from 0 to 70 mg L–1 in steps of 10 mg L–1 for Pb(II) and Cd(II) and from 75 to 200 mg L–1 in steps of 25 mg L–1 for Zn(II). (b) The calibration graphs of Pb(II), Cd(II) and Zn(II). Other experimental conditions are the same as in Fig. 4.
in the concentration range of 0 – 70 mg L–1 for Pb(II) (R2 = 0.9953), 0 – 70 mg L–1 for Cd(II) (R2 = 0.9934), and 75 – 200 mg L–1 for Zn(II) (R2 = 0.9954), as shown in Fig. 5(b). Moreover, signals of 1 mg L–1 of Pb(II) and Cd(II) could be detected, which suggests the high sensitivity of the proposed method. Nevertheless, the signals of Zn(II) at a concentration lower than 75 mg L–1 were hindered by the high background current as a result of the reduction of hydrogen ions. The limits of detection (LOD, the concentration corresponding to three times the standard deviation of blank) were obtained at concentrations as low as 0.89 mg L–1 for Pb(II), 0.69 mg L–1 for Cd(II) and 54 mg L–1 for Zn(II) for 180 s deposition. The reproducibility of a single SPCE was studied with 10 repetitive measurements of a solution containing 50 mg L–1 Pb(II), 50 mg L–1 Cd(II) and 100 mg L–1 Zn(II) in 1 M hydrochloric acid. The relative standard deviations (RSD) of the stripping peak currents of Pb(II), Cd(II) and Zn(II) were 6.3, 5.4 and 8.8%, respectively. The reproducibility among different SPCEs was also examined. Calibration graphs with five different SPCEs were obtained for Pb(II), Cd(II) and Zn(II). The RSDs of the calibration slope (sensitivity) were 5.8% for Pb(II), 5.8% for Cd(II) and 9.8% for Zn(II). Interference study The analytical results obtained with ASV can be affected by the potential interaction between metals that have been co-deposited onto the electrode surface.15,32 The interfering effect of Cu(II) at different concentrations (0 – 10 mg L–1) on the stripping peak currents of Pb(II) and Cd(II) (10 and 40 mg L–1) and Zn(II) (170 and 200 mg L–1) is illustrated in Fig. 6. The Zn(II) peak was more sensitive to the presence of Cu(II) than
ANALYTICAL SCIENCES MAY 2008, VOL. 24 35
593 Table 3 Results of Pb(II), Cd(II) and Zn(II) determinations in a spiked river-water certified reference material (JSAC 0302)
30
Concentration (mg L–1 ± SD)
Current / mA
25 Cd(II) 40 ppb Cd(II) 10 ppb Pb(II) 40 ppb Pb(II) 10 ppb Zn(II) 200 ppb Zn(II) 170 ppb
20 15 10 5 0 0
2
4
6
8
10
12
14
Metal ion
Certified value
Proposed method
10.1 ± 0.2 1.01 ± 0.01 10.2 ± 0.3
10.2 ± 0.7 1.00 ± 0.08 ND
Pb(II) Cd(II) Zn(II)
SD: standard deviation (n = 3). ND: not detectable.
Concentration of Cu(II) / mg L–1
Fig. 6 Influence of Cu(II) at various concentrations on the stripping peak currents of Pb(II), Cd(II) and Zn(II).
Table 4 Results of Pb(II), Cd(II) and Zn(II) determinations in a drinking-water sample by a standard addition method Metal ion
20 mA
Found
0 10 20 30 40 0 10 20 30 40 0 170 180 190 200
ND 10.6 19.1 29.3 40.8 ND 9.9 19.7 31.1 39.4 ND 169.0 181.0 190.9 199.0
Current / mA
Pb Cd (c)
Cd(II)
(b)
(a)
–1.4
Added
Pb(II)
Bi
Zn
Concentration/mg L–1
–1.2
–1.0
–0.8
–0.6
–0.4
–0.2
Zn(II)
–0.0
Potential / V vs. Ag/AgCl
Fig. 7 Square-wave anodic stripping voltammograms on Bi-SPCE of solutions containing 40 mg L–1 Pb(II), 40 mg L–1 Cd(II) and 200 mg L–1 Zn(II) in 1 M HCl (a) in the absence of Cu(II), (b) in the presence of 10 mg L–1 Cu(II), (c) in the presence of 10 mg L–1 Cu(II) and 600 mg L–1 Ga(III). Other experimental conditions are the same as in Fig. 4.
the Pb(II) or Cd(II) peak. As the concentration of Cu(II) increased, the stripping peak current of Zn(II) was suppressed. The suppression of the stripping peak by Cu(II) is probably due to competition between electrodeposited Bi and Cu for surface sites on the electrode as well as the formation of an intermetallic compound between Cu and Zn. The Cu-Zn intermetallic effect can be minimized by the addition of Ga(III), which preferentially formed an intermetallic compound with Cu.15,33 Figure 7 shows that the addition of 600 mg L–1 Ga(III) into a solution containing 40 mg L–1 Pb(II), 40 mg L–1 Cd(II), 200 mg L–1 Zn(II) and 10 mg L–1 Cu(II) can minimize the interfering effect of Cu(II) on the stripping peak currents of Cd(II) and Zn(II). Analytical applications In order to evaluate the proposed method, three replicate determinations of Pb(II), Cd(II) and Zn(II) in a spiked riverwater certified reference material (JSAC 0302, The Japan Society for Analytical Chemistry) were carried out under the optimum conditions by a standard addition method. The obtained results are given in Table 3. These results are comparable to the certified values. Although there was Cu(II) in this certified reference material at a concentration of 10.3 ± 0.2 mg L–1, the Cu intermetallic interference could be corrected by
Recovery, % — 106 95.5 97.6 102 — 99.0 98.3 104 98.4 — 99.4 101 101 99.5
the conventional standard addition method.31 The proposed method was also applied to the determination of Pb(II), Cd(II) and Zn(II) in a bottled drinking water under the optimum conditions by the standard addition method. The obtained results are given in Table 4. The recoveries of Pb(II), Cd(II) and Zn(II) were in the range of 95.5 – 106%. The obtained results obtained show that the proposed method could be successfully applied to the on-line simultaneous determination of Pb(II), Cd(II) and Zn(II) in water samples.
Conclusions In this work, an inexpensive and disposable screen-printed carbon electrode (SPCE) was used as a substrate for the in situ plating of a bismuth film, and the simultaneous determinations of Pb(II), Cd(II) and Zn(II) by SIA-SWASV with good sensitivity and acceptable reproducibility. The proposed method was successfully applied to the determination of Pb(II), Cd(II) and Zn(II) in water samples.
Acknowledgements S. C. gratefully acknowledges the Japan Society for Promotion of Science (JSPS) for awarding RONPAKU Fellowship FY20062007 (NCRT-10623), under which this work was carried out.
594
References 1. B. S. Sherigara, Y. Shivaraj, R. J. Mascarenhas, and A. K. Satpati, Electrochim. Acta, 2007, 52, 3137. 2. E. A. McGaw and G. M. Swain, Anal. Chim. Acta, 2006, 575, 180. 3. P. Sonthalia, E. McGaw, Y. Show, and G. M. Swain, Anal. Chim. Acta, 2004, 522, 35. 4. W. Martinotti, G. Queirazza, A. Guarinoni, and G. Mori, Anal. Chim. Acta, 1995, 305, 183. 5. G. Kefala and A. Economou, Anal. Chim. Acta, 2006, 576, 283. 6. A. Economou and A. Voulgaropoulos, Talanta, 2007, 71, 758. 7. P. Masawat, S. Liawruangrath, and J. M. Slater, Sens. Actuators, B, 2003, 91, 52. 8. S. Suteerapataranon, J. Jakmunee, Y. Vaneesorn, and K. Grudpan, Talanta, 2002, 58, 1235. 9. A. Economou and A. Voulgaropoulos, J. Autom. Methods Manage. Chem., 2003, 25, 133. 10. A. C. Vieira dos Santos and J. C. Masini, Anal. Bioanal. Chem., 2006, 385, 1538. 11. A. Ivaska and W. W. Kubiak, Talanta, 1997, 44, 713. 12. C. L. da Silva and J. C. Masini, Fresenius J. Anal. Chem., 2000, 367, 284. 13. E. A. Hutton, B. Ogorevc, S. B. Hobevar, F. Weldon, M. R. Smyth, and J. Wang, Electrochem. Commun., 2001, 3, 707. 14. G. Kefala, A. Economou, A. Voulgaropoulos, and M. Sofoniou, Talanta, 2003, 61, 603. 15. J. Wang, J. Lu, Ü. A. Kirgöz, S. B. Hobevar, and B. Ogorevc, Anal. Chim. Acta, 2001, 434, 29. 16. J. Wang, J. Lu, S. B. Hobevar, and P. A. M. Farias, Anal. Chem., 2000, 72, 3218.
ANALYTICAL SCIENCES MAY 2008, VOL. 24 17. J. Wang, Electroanalysis, 2005, 17, 1341. 18. A. Economou, Trends Anal. Chem., 2005, 24, 334. 19. A. Charalambous and A. Economou, Anal. Chim. Acta, 2005, 547, 53. 20. Z. Guo, F. Feng, Y. Hou, and N. Jaffrezic-Renault, Talanta, 2005, 65, 1052. 21. A. Królicka, R. Pauliukaite, I. Švancara, R. Metelka, A. Bobrowski, E. Norkus, K. Kalcher, and K. Vyt@as, Electrochem. Commun., 2002, 4, 193. 22. L. Baldrianova, I. Svancara, M. Vlcek, A. Economou, and S. Sotiropoulos, Electrochim. Acta, 2006, 52, 481. 23. D. Demetriades, A. Economou, and A. Voulgaropoulos, Anal. Chim. Acta, 2004, 519, 167. 24. J. Wang, J. Lu, S. B. Hocevar, and B. Ogorevc, Electroanalysis, 2001, 13, 13. 25. R. O. Kadara and I. E. Tothill, Anal. Bioanal. Chem., 2004, 378, 770. 26. E. A. Hutton, S. B. Hobevar, and B. Ogorevc, Anal. Chim. Acta, 2005, 537, 285. 27. L. Baldrianova, I. Svancara, A. Economou, and S. Sotiropoulos, Anal. Chim. Acta, 2006, 580, 24. 28. S. Legeai, K. Soropogui, M. Cretinon, O. Vittori, A. H. de Oliveira, F. Barbier, and M.-F. Grenier-Loustalot, Anal. Bioanal. Chem., 2005, 383, 839. 29. S. Legeai, S. Bois, and O. Vittori, J. Electroanal. Chem., 2006, 591, 93. 30. N. A. Malakhova, N. Yu. Stojko, and K. Z. Brainina, Electrochem. Commun., 2007, 9, 221. 31. J. Wang, “Stripping Analysis: Principles, Instrumentation, and Applications”, 1985, VCH, Weinheim. 32. R. O. Kadara and I. E. Tothill, Talanta, 2005, 66, 1089. 33. C. M. A. Brett, M. B. Q. Garcia, and J. L. F. C. Lima, Anal. Chim. Acta, 1997, 339, 167.
