Scholarly article on topic 'High sensitivity adsorptive stripping voltammetric method for antimony(III) determination in the presence of quercetin-5′-sulfonic acid. Substituent effect on sensitivity'

High sensitivity adsorptive stripping voltammetric method for antimony(III) determination in the presence of quercetin-5′-sulfonic acid. Substituent effect on sensitivity Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — Carlos Rojas, Verónica Arancibia, Marisol Gómez, Edgar Nagles

Abstract A high sensitivity method for voltammetric determination of Sb(III) using quercetin-5′-sulfonic acid (QSA) as complexing and adsorbing agent is presented. The Sb–QSA is accumulated on the electrode surface and then reduced at about −0.67V. Optimal analytical conditions were pH: 5.5, C QSA: 3.0μmolL−1, E ads: −0.10V and t ads: 60s. The detection limit (3σ) depends on accumulation time, reaching 3.6ngL−1 and 1.6ngL−1 with t ads of 60s and 180s, respectively. Peak current is proportional to Sb(III) concentration up to 10.0μgL−1 and 1.5μgL−1 with t ads of 60s and 180s, respectively. The relative standard deviation were 1.7% and 2.5% for a solution containing 1.0μgL−1 and 5.0μgL−1 of Sb(III), respectively (n =10). Interference by other metal ions was studied. The proposed method was applied to the determination of antimony in natural and spiked water samples, with satisfactory results. The method was designed in order to compare the sensitivity of the methods that use quercetin and the sulfonic derivative.

Academic research paper on topic "High sensitivity adsorptive stripping voltammetric method for antimony(III) determination in the presence of quercetin-5′-sulfonic acid. Substituent effect on sensitivity"

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Title: High sensitivity adsorptive stripping voltammetric method for antimony(III) determination in the presence of quercetin-5'-sulfonic acid. Substituent effect on sensitivity

Author: <ce:author id="aut0005" biographyid="vt0005"> Carlos Rojas<ce:author id="aut0010" biographyid="vt0010"> Veronica Arancibia<ce:author id="aut0015" biographyid="vt0015"> Marisol Gomez<ce:author id="aut0020" biographyid="vt0020"> Edgar Nagles

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S0925-4005(13)00631-X http://dx.doi.Org/doi:10.1016/j.snb.2013.05.058 SNB 15546

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Sensors and Actuators B

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27-3-2013 13-5-2013 16-5-2013

Please cite this article as: C. Rojas, V. Arancibia, M. Gomez, E. Nagles, High sensitivity adsorptive stripping voltammetric method for antimony(III) determination in the presence of quercetin-5'-sulfonic acid. Substituent effect on sensitivity, Sensors and Actuators B: Chemical (2013), http://dx.doi.org/10.1016Zj.snb.2013.05.058

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High sensitivity adsorptive stripping voltammetric method for antimony(III) determination in the presence of quercetin-5'-sulfonic acid. Substituent effect on sensitivity

Carlos Rojas, Verónica Arancibia*, Marisol Gómez, Edgar Nagles.

Facultad de Química, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago—7820436, Chile.

ABSTRACT

A high sensitivity method for voltammetric determination of Sb(III) using quercetin-5'-sulfonic acid (QSA) as complexing and adsorbing agent is presented. The Sb-QSA is accumulated on the electrode surface and then reduced at about -0.67 V. Optimal analytical conditions were pH: 5.5, Cqsa: 3.0 prnol L-1, Eads: -0.10 V and tads: 60 s. The detection limit (3 a) depends on accumulation time, reaching 3.6 and 1.6 ng L-1 with tads of 60 and 180 s, respectively. Peak current is proportional to Sb(III) concentration up to 10.0 (ig L-1 and 1.5 (ig L-1 with tads of 60 and 180 s, respectively. The relative standard deviation were 1.7 and 2.5% for a solution containing 1.0 and 5.0 (ig L-1 of Sb(III) respectively (n = 10). Interference by other metal ions was studied. The proposed method was applied to the determination of antimony in natural and spiked water samples, with satisfactory results. The method was designed in order to compare the sensitivity of the methods that use quercetin and the sulfonic derivative.

Keywords: Antimony, Quercetin-5'-sulfonic acid, Adsorptive Stripping Voltammetry

E-mail: darancim@uc.cl

1. Introduction

Antimony is a nonessential element considered a pollutant by the Agency for Toxicological Substances and Diseases Registry (ATSDR), the United States Environmental Protection Agency (USEPA) and the Council of the European Communities (EC), which have considered a maximum contaminant level of antimony in drinking water of about 5-6 (ig L-1. Its toxicity depends on the chemical species and oxidation state. Elemental antimony is more toxic than its salts, and Sb(III) compounds are more toxic than Sb(V) compounds by a factor of 10. Water or fruit juices bottled commercially in plastics often suffers from antimony contamination from the containers because antimony trioxide is extensively used by the polymer industry as a polycondensation catalyst in the production of polyethylene terephthalate [1-3]. Two complete reviews on the properties and the environmental chemistry of antimony were published by Filella et al. [4,5].

Antimony determination in environmental samples can be problematic due to the very low concentrations often present in unpolluted water (usually not higher than 1 (ig L-1 [4]). Anodic stripping voltammetry (ASV) has long been recognized as a powerful technique for trace metals owing to its sensitivity and relatively inexpensive instrumentation, and is suitable for the direct determination of Sb(III) and Sb(V) without previous separation. However, satisfactory results depend on the appropriate selection of operational parameters in the preconcentration and stripping steps, and the choice of a suitable working electrode. Mercury, as a drop (HMDE) or a film (HgFE) coated on an inert electrode, forms nearly ideal electrodes that have been used for anodic stripping voltammetry for many decades, due to their high cathodic hydrogen overpotential and for mercury's ability to dissolve many metals, aiding in the preconcentration process. Table 1 summarizes some of the

published work on the application of HMDE [6-16], SMDE [17], and other modified electrodes [18-26] for the determination of Sb(III) and/or Sb(V) by ASV. An alternative to anodic stripping voltammetry is adsorptive stripping voltammetry (AdSV), in which the metal ions must be converted into stable complexes with adequate surface-active ligands to be adsorbed on the working electrode by means of a non electrolytic process prior to the voltammetric scan, and the detection limit of AdSV is also usually better than that of ASV. The reaction of a suitable ligand with a metal ion to be determined may lead to the formation of a complex which is adsorbed on the surface of the electrode, or the reaction of a metal ion with the ligand adsorbed on the electrode's surface represent two other ways of adsorptive accumulation which is used for the determination of metals [27, 28]. However, there are fewer reports on the application of adsorptive stripping voltammetry for the determination of antimony, using quercetin [29], catechol [30,31], alizarin red S [32], 4-(2-thiazolylazo)-resorcinol [33], pyrogallol [34,35], pyrogallol red [36,37], bromopyrogallol red [38], gallocyanine [39], chloranilic acid [40-42], morin [43], or p-dimethyl-aminophenyl-fluorone [44] with different electrodes (Table 1).

Sometimes, no new signals appear after addition of trace metals to a ligand solution, even if their stability constants show that they are complexed. The complexes may not be adsorbed on the working electrode because their net charge is not adequate, because free ligand is preferentially adsorbed, or because the signal of the complex is occluded by the higher signal of excess free ligand. One possible way of enhancing the adsorptive process and the sensitivity of the method is the use of adequate substituents which can change the stability of the complex, the net charge, and the solubility of the ligand and the complex.

In this study we investigated the sensitive determination of Sb(III) using quercetin-5'-sulfonic acid (QSA, 3,5,7,3',4'-pentahydroxy-5'-sulfoflavone) as adsorbing and complexing ligand. Recently we published a method for the determination of antimony(III) using quercetin (3,5,7,3',4'-pentahydroxyflavone) as chelating agent [29]. We used the sulfonic derivative because this group, which does not participate directly in the metal-ligand bond, contributes with a negative charge to neutralize the positive charge of the antimony ion, and can increase the accumulation of the complex on the electrode's surface. Quercetin is a flavonoid used in analytical chemistry for the spectrophotometric and fluorimetric determination of metal ions. However, their application is restricted due to their insolubility in water. On the other hand, the sulfonate derivative is soluble in water and is more useful for analytical purposes [45].

2. Experimental

2.1. Chemicals and samples

Water used for sample preparation, dilution of reagents, and rinsing purposes was obtained from Merck. All the chemicals (nitric acid, hydrochloric acid, boric acid, acetic acid, EDTA, etc.) were analytical grade from Merck. The standard stock solution of 1.0 mg L-1 and 0.1 mg L-1 of Sb(III) was prepared from standard Sb(III) 1000 mg L-1 solution (Merck). Quercetin-5'-sulfonic acid was synthesized as reported by Kopacz [45] and the solutions were prepared in methanol. Britton Robinson (BR) buffer solutions were used to investigate pH in the 3.4-6.7 range. These buffers (0.4 mol L-1) were prepared by mixing equal amounts of orthophosphoric acid, acetic acid, and boric acid, adjusting to the required pH with 2.0 mol L-1 NaOH solution. To carry out the interference study a standard solution

(called standard solution A) containing 10.0 mg L 1 of Cu(II), Zn(II), Al(III), As(V), Cd(II), Pb(II), Co(II), Ni(II), Bi(III), Tl(I), Be(II), Na(I), K(I), Ca(II), Mg(II), Ag(I), Mo(VI), Cr(III) and Cr(VI) was prepared from different standard solutions of 1000 mg L-1 (Merck). Mineral water samples (Puyehue) were purchased in a supermarket and domestic tap water samples were collected in our laboratory.

2.2. Instrumentation

The voltammograms were obtained on a Metrohm model 797 VA Trace Analyzer processor with an Electrode Stand with automated hanging mercury drop electrode. The reference electrode was Ag/AgCl/KCl 3 mol L-1, and the auxiliary electrode was a platinum wire. Solutions were stirred with a rotating PTFE rod during the purging and deposition steps. The solutions were deaerated using high-purity nitrogen. The pH measurements were carried out with an 0rion-430 digital pH/mV meter equipped with combined pH glass electrode.

2.3. Procedure for getting adsorptive voltammograms with synthetic solutions

Voltammetric measurements were made using the following procedure: 8.97 mL of deionized water, 1.0 mL of BR buffer (0.4 mol L-1), 30 ^L of QSA (1x10~3 mol L-1), and aliquots of Sb(III) solution (1.0 mg L-1 or 0.1 mg L-1) were pipetted into the voltammetric cell. The solution was purged with nitrogen (saturated with water vapor) for 5 minutes. Then, after eliminating some drops, a new mercury drop was extruded to initiate the preconcentration for a given tads and Eads at a stirring rate of 1400 rpm. After an equilibration time of 10 s, the adsorptive voltammogram was recorded, while the potential was scanned from -0.05 to -1.40 V using square wave modulation with 25 mV step

amplitude, 10 mV pulse amplitude, and a frequency of 50 Hz. The calibration curves were obtained; linear regression and detection limits were calculated. The proposed method was applied to the determination of Sb(III) in tap water and mineral water; in order to eliminate matrix effects the standard addition method was used.

2.4. Procedure for getting adsorptive voltammograms with water samples

For the analysis of mineral water 9.00 mL of sample, 1.0 mL of BR buffer (0.4 mol L-1), 50 ^L of QSA (1x10 mol L ) and 10 p,L of EDTA (0.1 mol L ) were used, applying an Eads of -0.10 V for 60 s. On the other hand, 5.00 mL of sample, 3.75 mL of deionized water, 1.0 mL of BR buffer (0.4 mol L-1), 50 ^L of QSA (1x103 mol L-1) and 10 p,L of EDTA (0.1 mol L-1) were used for the analysis of tap water, and the previous procedure was performed. Each voltammogram was repeated three times.

3. Results and discussion

Quercetin presents five hydroxy groups in its structure whose dissociation constants are 7.10; 9.09 and 11.12 (for groups 7, 4' and 5, respectively) [46]. The presence of the sulfonate group does not considerably change the acidic properties of the OH groups, (7.18; 9.33 and 10.03), but it increases the acidity of the molecule, which can be considered as an advantageous property due to the fact that it precludes the possibility of metal ion hydrolysis. It has been reported that QSA forms complexes with Hg(II), Cd(II), Pb(II), Co(II), Ni(II), Cu(II), Fe(II), Fe(III), Sb(III), Cr(III), Bi(III), Al(III), Ga(III), In(III), La(III), Ce(III), Tm(III), Yb(III), Lu(III), Sm(III), Tb(III), Ho(III), etc., in solution and in the solid

state in a similar way as quercetin, and it is considered an antidote in case of poisoning with some of these metal ions. In the complexation, 4 CO and 3 OH groups are the donor centers [45,47-49]. It has been reported that the stoichiometries of the complexes with quercetin and QSA are pH-dependent. Quercetin forms a complex with Sb(III) with a M:L ratio of 1:1 [50], while QSA forms a complex whose structure is Sb0QSAx4H20 in the solid state (pH 1-3) [51]. Using spectrometric techniques, we determined the stoichiometry of the antimony complex with quercetin, finding an M:L ratio of 1:1, while using voltammetric techniques we determined the stoichiometry of the antimony complex with quercetin-5'-sulfonic acid and got an Sb:QSA ratio of 1:2 at pH 5.5.

3.1. Effect of operational parameters 3.1.1. Effect of pH

The pH of the solution is very important because the conditional stability constant of the Sb-QSA complex and the position of the reduction peaks of the ligand and complex depend on pH. This study was carried out in the pH range 3.4-6.7 using BR buffer (0.04 mol L-1). The results obtained using Csb(m): 1.0 p,g L-1 and Cqsa: 5.0 (xmol L-1 (tads: 60 s; Eads: -0.10 V; step amplitude: 25 mV; pulse amplitude: 10 mV; frequency: 50 Hz) are shown in Fig.1A. The peak potentials of the Sb-QSA peak shifted towards more negative values with increasing pH (-0.50 to -0.72 V), and maximum peak current was obtained at a pH range of 4.6-4.9. However, above pH 6.5 the peak current decreased with increasing pH, probably due to hydrolysis of Sb(III). For an M:L stoichiometry of 1:2 at pH about 7, the net charge of the complex is -1.

With the aim of studying the resolution of the Sb-QSA peak in the presence of interferences, aliquots of a solution containing 18 metal ions (standard solution A) were added to the electroanalytical cell with Csb(m): 1.0 p,g L-1 and Cqsa: 5.0 (xmol L-1 (tads: 60 s; Eads: -0.10 V) at pH 4.5; 4.8; 5.0; 5.5; 5.8 and 6.3. As shown in Fig. 1B, a time-stable Sb-QSA peak can be obtained without peaks overlapping at these pH values. Comparing these signals the best resolution was obtained at pH 5.5 and the signal of the Sb-QSA complex was seen at -0.67 V. Above pH 6.5 overlapping peaks interfering with the measurement of the Sb-QSA peak were observed (not shown) and the peak current decreased. An optimum pH of 5.5 was selected for further experiments.

3.1.2. Effect of adsorptive potential

Fig. 2 shows the effect of adsorptive potential on the stripping peak current of the Sb-QSA complex at pH 5.5 over the 0.00 to -0.70 V range. The experimental conditions were: Csb(m): 1.0 p,g L-1; Cqsa: 5.0 prnol L-1 and tads: 60 s. As shown in Fig. 2, the peak current of the Sb-QSA complex increases slightly with changing potential from 0.00 to -0.10 V. However, it decreased strongly when the potential was changed from -0.20 to -0.60 V. An adsorptive potential of -0.10 V was chosen for further optimization studies.

3.1.3. Effect of adsorptive time

Fig. 3 shows the effect of accumulation time on the stripping peak current of the Sb-QSA complex at pH 5.5 over the 0-600 s range. The experimental conditions were: Csb(ni): 1.0 p,g L-1; Cqsa: 5.0 prnol L-1; Eads: -0.10 V. Peak current increases with increasing accumulation prior to the potential scan, indicating that the Sb-QSA complex is readily adsorbed on the HMDE. Peak current increased linearly with time up to 600 s.

However, considering the speed of the measurements, tads of 60 s was used for further studies, but in the analysis of real samples, if Sb(III) concentration is low, longer times can be used to achieve good sensitivity.

3.1.4. Effect of ligand concentration

QSA concentration had a considerable effect on the method's linear range and sensitivity. The effect of Cqsa (range 0.0 to 10.0 prnol L-1) on the peak current of Sb-QSA was studied for Sb(III) at concentration levels of 0.1, 1.0 and 30.0 ^g L-1 (pH: 5.5; Eads -0.10 V; tads 60 s) and it is illustrated in Fig.4. The results show that peak current increases with increasing ligand concentration up to 2.0 prnol L-1 for an Sb(III) level of 1.0 p,g L-1 and 3.0 prnol L-1 for an Sb(III) level of 30.0 p,g L-1, and it remains almost constant, indicating that the ligand does not compete with the complex for the surface of the mercury electrode. An optimum QSA concentration of 3.0 prnol L-1 was selected for further experiments with synthetic solutions. However, when the spiked or real water samples contain many metal ions, a higher ligand concentration must be used to ensure complete complex formation.

3.2. Analytical properties

3.2.1. Linear range, limit of detection, and reproducibility of the method

The linear range for Sb(III) determination were evaluated at 60 s and 180 s of accumulation time under optimal conditions: pH 5.5; Cqsa 3.0 (xmol L-1 and Eads -0.10 V. The peak current increased linearly with antimony concentration up to 10.0 ^g L-1 (R = 0.998) and 1.5 ^g L-1 (R = 0.996) Sb(III) concentrations, with accumulation times of 60 and 180 s respectively (Ip = 14.2 + 44.0 [Sb(III)]. tads = 60 s. Fig.5). The limit of detection

(LoD), calculated according LoD = 3o/m, where o is the S.D. of the blank and m the slope of the calibration curve [52], were evaluated at 60 s and 180 s of accumulation time and were 3.6 and 1.6 ng L-1, respectively. Repeated voltammograms after 60 s of accumulation time show that the relative standard deviation for 1.0 and 5.0 (ig L-1 antimony were 1.7 and 2.5% respectively (n = 10). This difference with is due to the signal obtained with 1.0 ^g L-1 is thinner than 5.0 ^g L-1 and exist less error in determining the peak area. On the other hand, when we used quercetin as complexing agent, optimal conditions were found to be pH: 3.7, Cq: 6.0 (xmol L-1 and Eads: -0.10 V, and the linear range for Sb(III) determination was up to 10.0 ^g L-1 (R = 0.997) with an accumulation time of 60 s also. The LoDs were evaluated at 60 s and 120 s of accumulation time and were 76 and 40 ng L-1, respectively. Repeatability was 2.0% for 8.0 ^g L-1 of Sb(III) (tads: 60 s, n = 10) [29]. These results show that the determination of Sb(III) using the sulfonic derivative was more effective and sensitive than quercetin as complexing and adsorbing ligand. On the other hand, the Sb-QSA complex is reduced at -0.61 V and the Sb-Q complex is reduced to -0.60 V under the same conditions (pH 4.9), indicating that the conditional stability constants of these two complex are similar, but the different charges change the accumulation process.

3.2.2. Interference studies

Several metal ions can interfere with the Sb(III) determination forming complexes with QSA and consuming it, decreasing the peak current of the Sb(III)-QS complex and/or overlapping their reduction signal partially or completely. At high acid concentrations Sb(V) interferes with Sb(III), but at 5.5 pH only predominates Sb(III). The influence of 18 foreign metal ions on the determination of 1.0 (ig L-1 antimony was investigated by AdSV

under the above optimized conditions. In this study aliquots of EDTA were added with the purpose of obtaining charged complexes with foreign metal ions which are not adsorbed on the surface of the working electrode. The optimal EDTA concentration was 100.0 (xmol L-1. For this purpose,: CSb(III): 10 ^g L-1; BR buffer (pH 5.5); EDTA: 100.0 ^mol L-1, and standard solution A at the level of 100 (ig L-1 were added to the solution (Section 2.2). Because this sample contained many metal ions, a higher ligand concentration was added (Cqsa: 10.0 (xmol L 1) for to ensure complete complex formation. Then, aliquots of each metal ion were added in individual form. The tolerance limit was taken as the maximum concentration of the foreign substances, which caused an approximately ±5% relative error in the determination of 1.0 (ig L-1 antimony. The results are presented in Table 2, and it is concluded that none of these metal ions interfere with the determination of Sb(III) when they are at the 100 ^g L-1 level. The levels of Na(I), Mg(II), Cr(VI), Cu(II), Ag(I), Pb(II), Zn(II), Co(II), Cd(II), Ni(II), Ca(II), Bi(III) can even be higher than 1.0 mg L-1 and K(I) can be higher than 50 mg L-1. However, Mo(VI) and Be(II) cannot exceed 100 and 200 (ig L-1, respectively.

3.2.3. Accuracy of the method

Aliquots of deionized water (Merck) were contaminated with different concentrations of Sb(III) in the presence of foreign metal ions (standard solution A) at different levels and the determination was carried out using the standard addition method under optimized experimental conditions (pH: 5.5, Cqsa: 3.0 (xmol L-1 and Eads: -0.10 V) using different adsorptive time. Results and recovery percentages are shown in Table 3 and they can be used to check the accuracy of the method. The results obtained for the validation of the method with Sb(III) concentrations of 0.025; 0.15 and 1.00 (ig L 1 in the presence of

foreign metal ions at the levels of 75.0; 150.0 and 100.0 (ig L-1, respectively, were satisfactory (recovery of 95, 97 and 98%, respectively) (tads: 60 s). Fig. 6 shows adsorptive voltammograms and the calibration curve obtained with the solution containing 0.025 (ig L-1 Sb(III). The best results were obtained for an Sb(III) concentration of 0.025 (ig L in the presence of foreign metal ions at concentrations of 75.0 (ig L-1 applying tads of 300 s (100% recovery). The worst results were obtained for an Sb(III) concentration of 1.0 (ig L-1 in the presence of 18 foreign metal ions at concentrations of 500.0 (ig L-1 applying tads of 60 s (60 to 74% recovery). However, the level of the foreign metal ions is very high and saturation of the working electrode can occur.

3.2.4. Real sample analysis

The proposed method was successfully applied to the determination of antimony in tap water and a commercial mineral water (Puyehue) without previous treatment of the samples. In order to eliminate matrix effects, the standard addition method was used. Moreover, in the case of mineral waters containing antimony below the limit of detection, the accuracy of the proposed method was evaluated again by performing a recovery test after spiking the samples (Table 3). Recovery was between 96.0% and 98.0%, suggesting that the determination of antimony was effective and sensitive. On the other hand, Sb(III) in tap water samples was 3.59 ± 0.09 p,g L-1 (three samples). Fig. 7 shows adsorptive voltammograms and the calibration curve obtained with a sample of tap water.

4. Conclusions

The present study shows that the adsorptive stripping voltammetric determination of antimony in the presence of quercetin-5'-sulfonic acid as complexing and adsorbing agent

is excellent for the determination of ng L-1 concentrations of antimony in water samples, because of its high sensitivity and selectivity not present in previously reported electroanalytical methods. Moreover, due to the high sensitivity of this method it is possible to carry out the dilution of samples so that the effect of the matrix is minimized. We found that the sulfonic derivative was more adequate than the unsubstituted compound for Sb(III) determination. In AdSV, the method's sensitivity also depends on several parameters such as ligand and complex charge, acid-base properties, and interaction with the electrode surface, and to a smaller extent on stability constants.

Acknowledgements

Financial support by FONDECYT under Regular Project No 1130081 and CONICYT by doctoral fellowship (No 21120190. Carlos Rojas) are gratefully acknowledged.

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Biographies

Carlos Rojas is a young PhD student at the Catholic University of Chile. His research interests include the development of new configurations of modified electrodes for improving the determination of heavy metals with different ligands and substituent effect on sensitivity.

Veronica Arancibia is a full Professor of analytical chemistry and a group leader at Catholic University of Chile. She received her Ph.D. in 1987. Her research interest comprises the optimization of electroanalytical procedures employing different electrodes, their application to the determination of trace metals in environmental, biological and food samples and the effect of extern factors (ion pairs, surfactants, ionic liquids, sonoelectrochemistry, etc) in the sensitivity of the techniques.

Marisol Gomez is a student who will receive the PhD's degree next year. Her current field of interest is the preparation and development of solid amalgam electrodes for voltammetric determination of organic and inorganic analytes.

Edgar Nagles received his Ph.D. degree from the Catholic University of Chile in 2011 and has published over 18 papers to date. He is currently completing his postdoctoral training on the preparation and development of new structures on electrodes surfaces for improving

the determination of heavy metals in natural waters and sediments and the effect of ionic liquids.

Table captions

Table 1: Selected published data for the application of different electrodes in the anodic or

Table 2: Tolerance level of foreign metal ions in the presence of Sb(III) and QSA (pH 5.5)

Table 3: Sb(III) concentrations found in natural and spiked water samples.

Figure captions

Fig. 1. (A) Effect of pH on the potential and peak current of the Sb-QSA complex. (B) Adsorptive voltammograms and ip vs pH curve obtained at pH 4.5; 4.8; 5.0; 5.5; 5.8 and 6.3 in presence of 18 foreign metal ions (100 p,g L-1). Conditions: CSb(m) 1.0 p,g L-1; Cqsa: 5.0 prnol L-1; tads: 60 s; Eads: -0.10V; step amplitude: 25 mV; pulse amplitude: 10 mV; frequency: 50 Hz.

Fig. 2. Effect of Eads on the peak current of the Sb-QSA complex. Conditions: pH 5.5; CSb(iii): 1.0 p,g L-1; Cqsa: 5.0 p,mol L-1; tads: 60 s. Other conditions as in Fig. 1.

Fig. 3. Effect of tads on the peak current of the Sb-QSA complex. Conditions: pH 5.5; CSb(III): 1.0 p,g L-1; Cqsa: 5.0 p,mol L-1; Eads: -0.10 V. Other conditions as in Fig. 1.

Fig. 4. Effect of Cqsa on the peak current of the Sb-QSA complex. Conditions: pH 5.5; CSb(III): 0.1, 1.0 and 30.0 p,g L-1; Eads: -0.10 V; tads: 60 s. Other conditions as in Fig.1.

Fig. 5. Adsorptive voltammograms and calibration curve obtained with synthetic solutions of Sb(III). Conditions: pH 5.5; Cqsa: 3.0 prnol L-1; Eads: -0.10 V; tads: 60 s; step amplitude: 25 mV; pulse amplitude: 10 mV; frequency: 50 Hz.

Fig. 6. Adsorptive voltammograms and calibration curve obtained in the validation study with synthetic solutions spiked with 25.0 ng L-1 Sb(III) in the presence of 18 foreign metal ions (75 (ig L-1). Conditions: pH 5.5; Cqsa: 3.0 prnol L-1; CEDTA: 0.1 mmol L-1; tads: 60 s; Eads: -0.10 V; step amplitude: 25 mV; pulse amplitude: 10 mV; frequency: 50 Hz.

adsorptive stripping voltammetry of antimony and other metal ions.

Fig. 7. Adsorptive voltammograms and calibration curve obtained in analysis of Sb(III) in a tap water sample. Conditions: pH 5.5; Cqsa: 3.0 prnol L-1; Cedta: 0.1 mmol L-1; tads: 60 s; Eads: -0.10 V; step amplitude: 25 mV; pulse amplitude: 10 mV; frequency: 50 Hz.

Electrode Analyte Ligand Mode LR (^g L-1) LoD (^g L-1) tacc (s) Ref.

HMDE Cr(VI),Tl(III),Cd(I I),Pb(II),Cu(II),Sb( III)** ASV 0.16-200 0.04 120 [4]

HMDE Zn(II),Cr(VI),Cu(I I),Sn(II),Pb(II) Sb(I II)** ASV 10-275 10 < 210 [5]

HMDE Cu(II),Cr(VI),Tl(I) ,Pb(II),Sn(II),Sb(II I),Zn(II)** ASV N/R 70 270 [6]

HMDE Sb(III),Cd(II),Pb(II ),Cu(II),Bi(III)* ASV N/R 16 [7]

HMDE Sb(III) ASV N/R 3 60 [8]

HMDE Sb(III),Sb(III,V) ASV N/R N/R [9]

HMDE Cu(II),Sb(III) * ASV N/R 121.8 90 [10]

HMDE Sb(III) ASV 200-1000 N/R [11]

HMDE Sb(III,V) ASV N/R N/R [12]

HMDE Sb(III) ASV N/R 0.044 240 [13]

HMDE Sb(III) - ASV N/R 1.22 [14]

Sb(V) N/R N/R

Sb(III,V) 20-20000

SMDE Sb(III) - ASV N/R 11 600 [15]

Sb(III,V) 33 600

AuMWE Sb(III),As(III) - ASV 0.12 600 [16]

MWCNTs Sb(III) - ^ ASV 0.32 360 [17]

BiFE Sb(III,V) - ASV 0.01-0.1; 0.1-1; 1-18 0.005 180 [18]

HgFSPE Sb(III) - ASV 1.2-8.10 1.55 718 [19]

CGMDE Cu(II),Sb(III) - ASV N/R 0.12 45 [20]

Au-nps-CSPE Sb(III) ASV N/R 0.115 200 [21]

Ag-nps-CSPE Sb(III) - ASV N/R 0.083 200 [22]

GTE Sb(III) - ASV 1-10 0.32 600 [23]

Sb(V) 1-15 0.19 600

AuFE Sb(III),As(III) - ASV 5-25 0.41 180 [24]

HMDE Sb(III),Mo(VI) quercetin AdSV 0.076-10 0.076 60 [27]

HMDE Sb(III,V) catechol AdSV 0.5 - 8 0.1 480 [28]

HMDE Sb(III),Pb(II)* catechol AdSV 0.24- 60.1 0.15 60 [29]

AdSV 0.24- 85.2 0.088 60

HMDE Sb(III) alizarin red S AdSV 4.8-30 1.45 5 [30]

HMDE Sb(III) 4-(2- thiazolylazo)-resorcinol AdSV 0.16- 11.6 0.049 150 [31]

HMDE Sb(III) pyrogallol k-LSV 3-120 1.2 [32]

Sb(V) 10-240 2.8

HMDE Sb(III) pyrogallol AdSV 0.013 - 194.8 0.012 400 [33]

Sb(V) 1.2 - 170 1.15 400

HMDE Sb(III) pyrogallol red AdSV 1.2-15.5 1.2 257 [34]

Sb(V) 5.9 -15.7 5.9 257

CPE Sb(III) pyrogallol red AdASV 0.24- 61 0.12 150 [35]

CPE Sb(III) bromopyrogal ol red AdASV 0.12-61 0.061 150 [36]

HMDE Sb(III) gallocyanine AdSV N/R 0.25 240 [37]

HMDE Mo(VI), U(VI), V(V), Sb(III)* chloranilic acid AdSV 0.27-100 0.27 60 [38]

HMDE Sb(III,V) - ASV N/R N/R [39]

Sb(III) chloranilic acid AdSV N/R N/R

HMDE Sb(III) chloranilic acid AdSV N/R 0.21 300 [40]

Sb(V) 0.56 600

SMDE Sb(IIII) morin AdSV 0.12-36.5 0.085 120 [41]

HMDE Sb(III) p-DMPF AdSV 0.49 -48.7 0.12 300 [42]

Ag-nps-CSPE: Silver Nanoparticles-modified Carbon Screen Printed Electrode. Au-nps-CSPE: Gold Nanoparticles-modified Carbon Screen Printed Electrode. CGMDE: Controlled Growth Mercury Drop Electrode. AuMWE: Gold Microwire Electrode. MWCNTs: Multiwall Carbon Nanotubes. AuFE: Gold Film Electrode. GTE: Gold Tubular Electrode. HgFSPE: Mercury Film Screen Printed Electrode. HT18C6-RH-CPE: Hexathia 18C6 (HT18C6) and Rice Husk (RH) Modified Carbon Paste Electrode. k-LSAdSV: Kinetic determination using Linear Sweep Adsorptive Stripping Voltammetry. p-DMPF: p-dimethyl-aminophenyl-fluorone . PhFCPE: Phenylfluorone Modified Carbon Paste Electrode. PolyPGF: PolyPyrogallol Film. PPs: PolyPhenols. PSA: Potenciometric Stripping Analysis. SWCNTs-a-SiMo12O404~: modified with single-walled carbon nanotubes (SWCNTs) and polyoxometalate. *: Simultaneous. **: Sequential. n.a: no apply. N/R: Not reported.

Table 2

Metal ion Concentration (mg L-1)

Mo, Be 0.1

Tl 0.2

Al 0.6

As 0.7

Na, Mg, Cr, Cu, Ag 1.0

Pb 1.5

Zn 2.0

Co 2.5

Cd, Ni 3.0

Ca, Bi 4.0

K 50.0

Table 3

Water Sample Sb(III) added fog L-1) Sol. A* fog L-1) EDTA (nM) tacc (s) Sb(III) found fog L-1) Sb(III) R (%) Sb(III) sample fog L-1)

Validation

Milli-Q 0.025 75.0 0.10 300 0.025 ± 0.001 100 -

Milli-Q 1.00 100.0 0.10 60 0.98 ± 0.02 98 -

Milli-Q 0.150 150.0 0.10 60 0.145 ± 0.002 97 -

Milli-Q 0.025 75.0 0.10 60 0.024 ± 0.001 95 -

Milli-Q 1.00 100.0 0.0 60 0.89 ± 0.03 89 -

Milli-Q 1.00 250.0 0.0 60 0.84 ± 0.03 84 -

Milli-Q 1.00 250.0 0.10 60 0.84 ± 0.06 84 -

Milli-Q 1.00 250.0 0.60 60 0.78 ± 0.02 78 -

Milli-Q 1.00 500.0 5.0 4 60 0.74 ± 0.03 74 -

Milli-Q 1.00 500.0 10.0 60 0.72 ± 0.04 72 -

Milli-Q 1.00 500.0 0.30 60 0.60 ± 0.06 60 -

Water samples

Mineral water - - 0.10 300 < DL < DL

Mineral water 0.025 0.10 90 0.024 ± 0.002 96 -

Mineral water 0.050 - 0.10 90 0.049 ± 0.002 98 -

Mineral water 0.100 - 0.10 60 0.097 ± 0.005 97 -

Tap water - - 0.10 60 1.79 ± 0.04 - 3.59 ± 0.09

Tap water 0.50 - 0.10 60 2.31 ± 0.03 100 3.62 ± 0.05

<DL : under detection limit. Not quantified. * Standard solution A contain 18 foreign metal ions.

Sb-QSA

0.0 1.0 2.0 3.0 4.0 5.0

Sb(lll) (Mg L"1)

-0.2 -0.4 -0.6 -0.8

-1.0 -1.2 E(V)

Sb(lll)(ng L"1)

Sb-QSA

-0.1 -0.2 -0.3 -0.4 -0.5 -0.6

-0.7 -0.8

-200--400--600--800-

-0.5 -0.6 -0.7 -0.8

7.0 14.0 21.0 28.0 35.0

Sb(lll) (и0 L-1)

~i-1-1-1-1-1-1

0.9 -1.0 -1.1 -1.2

1000 H

«H 0.0

^^ ^^ ^^ ^^ ^^ ^^

4 * А А А А

★ Sb(lll) 0.1 цд L'1

• Sb(lll) 1.0 (лд L"1 ▲ Sbflll) 30.0 цд L"1

• • • • • •

★ ★ ★

6.0 8.0 10.0

QSA (цто1 L"1)

300 п

£ 250-Q.

2001501009

50- • *

0 90 180

270 360 450 540

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0Л-.-1-.-1-.-Г-

0.0 -0.1 -0.2 -0.3

-0.4 -0.5 -0.6 -0.7

Eads 00

0OQ о

40 Ü0

Г -0.75

- -0.70

I- -0.65

h -0.60 <

- -0.55

- -0.50