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Voltammetric Technique, A Panacea for Analytical Examination Of Environmental Samples.

Byline: ERUM ZAHIR, IFTIKHAR IMAM NAQVI AND SHAIKH MOHIUDDIN

Summary: Voltammetric methods for trace metal analysis in environmental samples of marine origin like mangrove, sediments and shrimps are generally recommended. Three different electro- analytical techniques i.e. polarography, anodic stripping voltammetry (ASV) and adsorptive stripping voltammetry (ADSV) have been used. Cd2+, Pb2+, Cu2+ and Mn2+ were determined through ASV, Cr6+ was analyzed by ADSV and Fe2+, Zn2+, Ni2+ and Co2+ were determined through polarography. Out of which pairs of Fe2+/Zn2+ and Ni2+/Co2+ were determined in two separate runs while Cd2+, Pb2+, Cu2+ were analyzed in single run of ASV. Sensitivity and speciation capabilities of voltammetric methods have been employed. Analysis conditions were optimized that includes selection of supporting electrolyte, pH, working electrodes, sweep rate etc. Stripping voltammetry was adopted for analysis at ultra trace levels.

Statistical parameters for analytical method development like selectivity factor, interference, repeatability (0.0065-0.130 (mu)g/g), reproducibility (0.08125-1.625 (mu)g/g), detection limits (0.032-5.06 (mu)g/g), limits of quantification (0.081-12.652(mu)g/g), sensitivities (5.636-2.15 nA mL (mu)g-1) etc. were also determined. The percentage recoveries were found in between 95-105% using certified reference materials. Real samples of complex marine environment from Karachi coastline were also analyzed. The standard addition method was employed where any matrix effect was evidenced.

Introduction

One of the most serious problems facing the humanity today is the contamination of its environment especially by chemical species. An area of particular interest has emerged towards the detection of heavy metals and metalloids, very pertinent contributors to pollution levels in environmental matrices and elucidation of their pathways through various environmental compartments [1-4].

Several analytical methods have been reported for the quantitative determination of metals in environmental matrices, like atomic absorption spectrometry,(AAS) [5-8] inductively coupled plasma optical emission spectroscopy(ICP-OES), liquid chromatography, gas chromatography (GC) [9]. These techniques however usually need pre- concentration steps to achieve the appropriate selectivity and/or sensitivity but often only meet one of these two. Electro-analytical techniques have potential for trace metal determination in complex matrix because these are sensitive, selective, rapid and suitable even when used as portable equipment [10]. Furthermore, cost, speed, adoptability etc. are also in favor of employing through these analytical techniques.

The voltammetric methods are valid and effectual option in the multi-component analysis of metals, since the high sensitivity of the voltammetric method [11-13], coupled with the considerable selectivity especially if the second harmonic alternating current techniques are employed [14-16]. Advantages include sensitivity, precision, accuracy, dynamic range, ease of automation, cost, specific response, low detection limits, suitability for studies on the spot, applicability to a wide range of substances and the capability for simultaneous determination of more than one species and ability to differentiate between different chemical forms of the metal.

Selection of voltammetric methods requires very basic knowledge of voltammetry and its techniques. Mostly it can be done for analytes that can either reduce or oxidize. For the higher concentrations (ppm or high ppb), direct measurement by differential pulse voltammetry (DPV) is possible, whereas, for lower concentrations, these voltammetric techniques are combined with a pre-concentration step (which may be electrochemical or non electrochemical). These later techniques are referred to as stripping techniques [17, 18]. Stripping voltammetry had considerable advantages compared with direct voltammetry. The major advantage is that the analyzable substances are pre-concentrated so that the voltammetric (stripping) current is less interfered by the charging current and accuracy of the method gets evaluated. Stripping analysis is applicable for analyzing compounds in very dilute solutions, as it is sensitive at very low metal concentrations pertaining to 10-9 to 10-12 M levels [19, 20].

ASV is used for many metal/metalloid ions (e.g. Pb2+, Cu2+, Cd2+, Zn2+) at mercury electrode but there are some metal/metalloid ions that are not suitable for detection by ASV e.g. Co2+ and Ni2+ [21]. Another technique Polarography can be used for the analysis for these metal ions. The sensitivity of conventional Polarography is such that the measurements of concentrations of different ions down to about 10-5 M has been successfully undertaken. Cathodic stripping voltammetry (CSV) has even proved useful to determine Cr6+ in some of natural waters with a detection limit below nano- molar [22-29].

Although voltammetry is cost effective and fast method of analysis but it is not as popular as atomic absorption spectrometry, gas chromatography, high performance liquid chromatography (HPLC) etc. in environmental research. Perhaps less awareness of these techniques to environmental researchers is one of probable reasons. It may be due to lesser efforts on the part of instrument manufacturers to design automated voltammetric analyzers. Also it is seen cumbersome to choose several items like supporting electrolytes, electrodes, solvents, applied potential range etc. However this variety of selection of various objects in these techniques gives liberty to perform the experiments towards newer applications. There is no need to replace the basic unit of the equipment. We find that inexpensive and small objects like electrodes are to be changed to switch over between two types of analysis. This provides the versatility to adopt several analytical aspects using single equipment.

The present study established the feasibility of voltammetric methods in environmental related trace metal investigations and proposes the different experimental approaches for a particular environmental study. The procedures are such that they do not require knowledge of the usual parameters of voltammetry. First step is literature survey to pick any variety of electrochemical or even voltammetric method. One can choose the method according to the nature of analysis and availability of supporting equipment (electrode etc). Then designing or developing of method for usual analytical parameters is the next step, followed by investigation of possible interference(s) and their removal or making interfering agent ineffective.

Three different types of voltammetric techniques are reported in this study in order to analyze different metals simultaneously in several matrices, but such a simultaneous presence could cause interference in voltammetric signals by affecting electrochemical behaviors of the different elements [30-32]. For this reason the present study suggests an example of a fast, precise and accurate analytical procedure for the simultaneous heavy metal determinations by ASV, CSV and Polarography in complex environmental matrices. The samples of mangrove, shrimp and sediments were collected from ecological cycle of marine system along Karachi coastline of Arabian Sea in order to deal with different classes of environmental segments.

Result and discussion

Voltammetric techniques i.e. polarography, adsorptive stripping voltammetry (ADSV) and anodic stripping voltammetry (ASV) were chosen for potential determination of metals at trace levels due to their sensitivity and also to their speciation capabilities. The results thus obtained are shown in (Table-2) and bear sufficient accuracy and precision. Different analytes are categorized for different techniques and the selections are based upon several parameters like selectivity, sensitivity, limit of detection etc as these parameters were optimized for various possible alternative collections of metals, present in any sample matrix.

Different supporting electrolytes have been used for different analysis. Mostly these have been chosen from earlier reported research. In some cases the pH was also a crucial factor in analyses. For example manganese can be oxidized on an electrode surface forming insoluble manganese (IV) dioxide according to the equation, and hence the analytical procedure is pH dependent [38].

Mn2+ + 2H2O - MnO2 + 4 H+ + 2 e -

In order to achieve accurate, precise and interference free analytical outcomes, usually simple or normal voltammetric technique with fixed electrode are not popular due to the contamination of such electrode surface during run. Even environmental samples are mostly carrying heavy and unknown matrix that frequently contaminates the electrode surface. Although polishing can refresh electrode but this is quite tedious to do for a large number of environmental samples. Through polarography the problem of electrode contamination is overcome by employing dropping mercury electrode (DME). Also in stripping voltammetry the speed of contamination is far low because of altering electrical potential with higher gradient.

Polarography is an efficient tool for metal analysis at trace levels but inappropriate for some analytes at ultra trace levels. In current study, concentration levels of Ni2+, Co2+, Fe2+, Zn2+ have been analyzed at trace levels in the samples selected from mangroves, sediment and shrimps. Although Mn+2 has been also found at trace levels comparable to the other metals but its determination is infeasible by normal polarography as discussed in preceding text. On the other hand, for analytes at ultra trace levels stripping voltammetric techniques are more suitable as it pre-concentrates the analyte during run. ASV was found appropriate for reducible analytes that may deposit at electrodes. Therefore for determination of Cd2+, Cu2+, Pb2+ and Mn2+ ASV were preferred. In contrast species that are likely to be oxidized can be analyzed through ADSV. Adsorptive stripping is also a useful tool for metal complexes.

As an example Cr6+ has been determined by forming complex with ethylene-diamine (en) through ADSV that is well-reported method [39, 40]. The interference of Cr3+ has been reported for different complexing agents. However in case of ethylene-diamine no overlapping of Cr+3 signals is obvious in (Fig. 1). Further to that organo-complexes of Cr3+ are also electrochemically inactive [40], in contrast to aqueous Cr3+ ions. Cr3+ is not considered for analysis due to less abundance of Cr3+ in environmental and biological systems and it is less important regarding toxicity studies pertaining to chromium [39].

Standard solutions of (Ni2+, Fe2+, Zn2+, Co2+) were run individually and formal potentials were found at (Ni2+, -0.99 V), (Co2+, -1.06 V), (Zn 2+, -1.20 V) and (Fe 2+, -1.44 V). Then binary mixtures of (Ni2+ -Co2+), (Co2+- Zn 2+) and (Zn 2+- Fe 2+) were run through Polarography for satisfactory selectivity.

Redox potentials for metal ions were noticed in presence of buffered supporting electrolyte of H3PO4 and sulfosalicylic acid at pH 9.5. The four metal ions (Ni2+, Fe 2+, Zn 2+, Co2+) were exhibiting formal potentials in the range of -0.9 to -1.5 V. So these four metal ions can be analyzed simultaneously in a single run subject to no possibility of interference owing to each other. It has been well documented that production of intermetallic compounds by Cu2+ and Zn2+ with mercury gives irregularities in voltammetric determinations. Therefore simultaneous determination of Cu2+ and Zn2+ is avoided and on the other hand simultaneous determination of Cu2+ and Pb2+ is recommended in their reported research [41]. Therefore in this study only Cu2+ and Pb2+ were simultaneously analyzed. It has also been reported that Pb2+ determination with different supporting electrolytes (KCl = 3 mM) produces signal at - 0.38V [42].

This potential was not valid for buffered supporting electrolyte used in Ni2+, Fe 2+, Zn 2+, Co2+ and it falls too away, thus Pb2+ determination is not recommended in a single run with these four analytes. Furthermore Pb2+ levels are expected to be present at lower quantification values; hence it is more suitable to use stripping analysis in the case of Pb2+ analyses. This criterion is also applicable for Cd2+ and Cu2+. Mn2+ forms insoluble Mn- hydroxide in basic pH [38], so it cannot be run by described polarographic method. So ASV was preferred for the analysis of Mn2+ as in (Fig. 2).

The above equilibrium is strongly dependent on pH. However, high pH values are not suitable for adsorptive stripping voltammetry because of the formation of Mn(OH)2, which is insoluble. At low pH, the equilibrium shifts to the left due to the excess of hydrogen ions in solution. Thus, the optimal pH corresponding to the highest signal is in the reported range of pH 7-7.6 [38] and pH 4-9 [10]. Against that for Cd2+, Cu2+ and Pb2+ determinations when employing ASV, the optimum pH 9.3 value for the entire element has been reported and the peak currents and that for all these elements were found higher at this pH value [43].

In current study ASV was applied for analysis of Cd2+, Cu2+ and Pb2+ using HMDE. These three metals were run separately using their standard solutions in order to optimize individual peak potential. Then binary mixtures of Cd2+- Pb2+ and Pb2+- Cu2+ were run to investigate selectivity coefficient. In order to ensure selectivity of analyte, selectivity coefficients (SC) were estimated with the help of following equation

SC= ai / aA ---------------Equation (1).

Where ai and aA are the ratios of diffusion current at concentrations of interfering agent and analyte respectively.

Zn2+- Fe2+ were run in order to determine selectivity coefficients for the judgment of any possible interference. It was noticed that selectivity coefficient for Cd2+-Pb 2+, Pb2+- Cu2+and Zn2+-Fe2+ pair is zero, as there is no overlapping in respective peaks in voltammogram (Fig 3, 4). In case of Ni2+ selectivity coefficients for possible interference due to Co2+ is 0.04 and for Co2+ due to Ni2+ it is 0.08. A little overlapping in Ni2+ and Co2+ signals in Fig. 5 also supports these SC values. However, greater overlapping has also been reported [44, 41]. Lower values of selectivity coefficients reveal negligible interference in these analytes. This fact is also evident from voltammogram outputs (Fig. 5). Even ASV has good sensitivity but it is not recommended to analyze Ni2+ and Co2+ simultaneously through ASV [21].

Sweep rate has been chosen by running standards to optimize the voltammogram. Different sweep rates have been selected for different types of determinations (Table-1). Stripping voltammetry was optimized for stirring speed in the range of 1800-2100 rpm in order to have less deposition time and maximum current output as increasing stirring speed reduces the duration for deposition. In case of higher stirring time one should take care to have suitable equilibration time for making the cell content stagnant prior to stripping.

Usually an external standard method is simple to employ for calibration system. External standard method means a procedure where an external standard and the sample are analyzed in separate runs. Two problems are associated with such method. Firstly the peak positions for standard and sample analytes are noticeably different. This is expected as the change in matrix of voltammetric cell can affect the formal potential of redox system, due to the presence of a variety of compounds in sample matrix, whereas these are absent in standards solutions. Secondly, the current responses for analytes are different in standard and sample solutions as described in experimental section. For example in analysis of Pb2+ using ASV running 0.7 ppm standard solution results 629.7 nA diffusion current at -417 mV and another run an aliquot of digested sample results into 47.4nA and further to that the same account of 0.7 ppm Pb2+ was added to same sample results 569.4nA for both at -417 mV (Table-1).

The effects of matrix interference can be overcome by adopting standard addition method. It has been ensured that the increment of standard solution to the same sample aliquot is proportional to the diffusion current. In order to overcome that same volume of 0.7 ppm standard concentration has been added to the last spiked run that doubles the concentration of Pb2+ standards in cell. The outcome of this run was 1.098 (mu)A. It means that diffusion current of 1.050 (mu)A was due to the standard analyte that was about double that of the value 569.4 (mu)A for single addition of standard. Thus the above experiment provides an option for employing standard addition method in the analysis (Fig .6-14).

In case of unstable experimental conditions, internal standard method can also be employed.It should be noticed that internal standard must not be present in the sample at all or at least the concentration of internal standard already present in the sample is known. Moreover, peak potentials for analyte and the internal standard have to be close to each other.

The basic analytical parameters like linearity, sensitivity, precision (repeatability), limit of detection (LD) and limit of quantification was assessed in preliminary investigative procedures, in order to validate these voltammetric measurements for environmental samples. The parameters thus established are listed in (Table-3). Linearity has been measured by running different working standard solution for all analytes. Statistical correlation coefficients for each analyte have been evaluated and were found in between 0.96 - 0.99. This was showing a good linear proportionality between the current and the concentrations. Sensitivity values were determined by the least square analysis of the current -concentration order paired data for different working standard, the slopes obtained in consequences of least square analysis are sensitivities of respective analyte.

To evaluate effects of interferences, the mean and standard deviation (n = 3) for each peak height of the metals were calculated, the latter being expressed as relative standard deviation. Repeatability of the method was evaluated through this relative standard deviation of replicate measurements of a solution (within-run precision) between run-precision is reproducibility that has been investigated by running standards in different days.

The detection limit (LD= k x Sy/x /m) was calculated by the analytical calibration function of each element in the different matrix, according to Miller and Miller [45], here k = 3, 'Sy/x' is the residual standard deviation of the regression line and 'm' is the slope of the calibration graph. The quantification limit (LOQ) was calculated through the same equation as for the detection limit. However the value of k was taken as 10 [46].

Accuracy of analysis have been assessed by running Certified Reference Material (CRM) NIST standard 1573(Tomato leaves), NBS SRM 1675 (River sediment) has been run for all types of analysis employed in this study. A good agreement has been found between results and certified values i.e. the % recoveries are ranging in 95-105%.

Application on Real Samples From Karachi Coast

The analytical procedure, established on the standard reference material, was used for samples of mangrove, sediment and shrimp, collected along the coastline of Karachi coast of Indus Delta. It is well known that the complete mineralization of the sample is the most important requirement for accurate voltammetric analysis. The result showed the well- defined peaks in the voltammogram as shown in (Fig. 1-5).

The results of the present study portray a complex interaction between different parameters that control metal fluxes in the natural environment. The nature of these effects depends upon the metal involved. Metals were found to exhibit high variability in their concentration at different localities ever marked for this study (Fig. 15). Field observations revealed that these locations pertaining to mangrove swamps received sewage discharges from domestic premises, restaurants, and fish and shrimp ponds and also from dyeing industries, indicating anthropogenic inputs. Results showed that the concentrations of metals are low in mangrove as compared to the sediments (Table-2). The low concentration of heavy metals in mangrove may be related to the less availability of metals in the soil.

The results revealed that the concentration of metals are higher in Port Qasim and Korangi Creek areas which may be due to industrial installations like thermal power plant, Pakistan steel mill and that their drainage are the contributors to the pollution. Less contamination were observed in Sandspit as there is no major industrial unit in this vicinity. The results of this study also provide valuable information about the metal content in shrimps from different sampling sites of Karachi coast. This can be considered as a bio-indicator of the environmental contamination in this area by estimating the bioavailability of metals to the marine biota. Moreover, these results can also be used to test the chemical quality of the marine food, in order to evaluate the possible risk associated with their consumption by humans.

Experimental

Apparatus

Metrohm VA 747 was used for voltammetric measurement. That was equipped with hanging mercury dropping electrode (HMDE). This electrode can be used for ASV, adsorptive stripping voltammetry ADSV and dropping mercury electrode (DME), as working electrode for differential pulse polarography. As reference electrode Ag/AgCl (saturated) (in 3 mM KCl) was used while platinum was used as auxiliary electrode throughout the analysis. The voltammetric cell was kept at 25 oC +- 2.0 oC throughout the study.

Reagents and Reference Solution

All solutions were prepared with deionized water (Millipore(tm), MilliQ(tm)) and all the reagents were of supra pure grade. Aqueous stock solutions of the analyzed metals are prepared by dilution of the respective standard 1000 mg/L solution (BDH (tm), U.K, and Merck (tm)). In order to ascertain reliability of the results standard reference material chosen for the analysis are NBS SRM 1675 (tm) (River sediment) and NBS SRM 1573 (tm) (Tomato leaves).

Sample Preparation

The samples of mangrove, shrimp and sediment samples were collected from different sites of Karachi coastal sites of Pakistan as shown in (Fig. 15).

Samples were dried in oven at 60-80 oC and subsequently grinded. 2 g of grinded samples were digested at 90 oC in (1:3) mixture of HClO4 and HNO3. The resultant suspension was filtered followed by triplicate washing of residues with deionized water. The filtrate and washing thus collected were finally diluted to 50 ml in a volumetric flask [33].

Polarographic Measurements

Before subjecting the digested solutions to polarographic analysis, these samples were diluted with 10 ml of double deionized water. Subsequently 0.2 ml H3PO4 (85%), 2 ml of 5-sulphosalicylic acid and appropriate volume of 25% NH3 was added to adjust the pH to 9.5 for the analysis of Co+2, Ni+2, Zn+2 and Fe+2 [34].

Anodic Stripping Analysis

Anodic stripping voltammetry was used to determine Cd2+, Pb2+, Cu2+ and Mn2+. For this purpose 10 ml digested solutions were mixed with 5 ml of oxalate buffer before running for Cd2+, Pb2+ and Cu2+ [ 35]. For the analysis of Mn2+, another 10 ml of the digested sample was mixed with 250 (mu)L NH3, 50 (mu)L of borate buffer and 50-(mu)L of 100 ppm Zn2+ standards. The pH of solutions has been adjusted to 9.5-10 for the further analysis [36].

Adsorptive Stripping Measurements

For Cr6+ determination, 10 ml digested sample were mixed with 10 (mu)L ethylene diamine, 150 (mu)L acetic acid, 200 (mu)L ammonia solution was added with NaOH to adjust the pH of the solution to 6.2 +- 0.1 [37].

Polarographic and stripping voltammetric methods were applied according to instrumental conditions mentioned in (Table-1). Quantitative results were obtained by standard addition method. Appropriate aliquots of the standard solutions of the analyzed metals were added and the concentrations were evaluated.

Table-1: The parameters for the recorded voltammogram.

Metal ions###Cd2+, Cu2+, Pb2+###Mn2+###Cr6+###Ni2+, Co2+, Fe2+, Zn2+

Method###ASV###ASV###DPADSV###Polg

Working Electrode###HMDE###HMDE###HMDE###DME

Stirrer Speed(rpm)###2000###2000###2000###2000

Mode###DP###DP###DP###DP

Purge time (s)###300###300###300###300

Pulse Amplitude (mV)###50###-75###-50###-30

Deposition Potential (mV) -800###-1700###-1000###-800

Deposition Time (s)###60###90###60###80

Equilibration time (s)###10###5###10###10

Start potential (mV)###-800###-1620###-1000###-800

End potential (mV)###0###-1250###-1500###-1500

Voltage step (mV)###6###4###10###6

Voltage step time (s)###0.15###0.50###0.30###0.40

Sweep rate (mV/s)###40###8###33.33###15

###Cd2+ -600###Bi -990

Peak potential (mV) Cu2+ -140###Mn2+ -1470 Cr6+ -1250 Co2+ -1060

###Pb2+ -410###Fe2+ -1440

###Zn2= -1200

ASV: Anodic stripping voltammetry Polg: polarography

DPCSV: Differential pulse adsorptive stripping voltammetry pm: rotation per minute

HMDE: Hanging mercury dropping electrode DME: Dropping mercury electrode

Table- 2: Metal concentrations (mu)g/g +-S.D in mangrove, sediment and shrimps by using different techniques

Sample###Pb(ASV)###Cn(ASV)###Cd(ASV)###Mn (ASV)###Cr(ADSV)###Ni(Pol)###Co(Pol)###Fe(Pol)###Zn(pol)

Id

###20.751###9.752###0.182###178.502###10.253###81.252###5.252###510.502###11.752

PQ(M)###+- 0.62###+- 0.252###+-0.022###+-1.545###+-0.652###+-4.563###+-0.783###+-3.842###+-2.502

###31.802###20.753###0.155###755.255###42.500###88.953###14.852###635.003###30.254

PQ(S)###+-0.783###+-0.383###+-0.032###+-10.953###+-0.653###+-7.852###+-3.251###+-7.852###+-3.253

###16.510###0.072###130.000###5.852###80.500###10.000###220.841###13.910

###6.252+-0.772

KC(M)###+-0.483###+-0.005###+-5.452###+-0.071###+-0.883###+-1.113###+-4.233###+-0.983

###426.000

###22.254###20.454###0.202###488.583###22.255###75.000###9.502###30.503

###+-

KC(S)###+-0.222###+-2.542###+-0.021###+-10.583###+-1.633###+-3.953###+-1.472###+-0.583

###10.000

###21.583###0.112###102.502###9.502###108.952###9.003###198.852###18.853

###9.543+-1.552

SP(M)###+-1.992###+-0.041###+-2.777###+-1.475###+-3.563###+-2.312###+-1.293###+-2.451

###296.002

###25.354###15.484###0.133###383.254###22.003###76.774###13.853###27.000

SP(S)###+-0.890###+-2.950###+-0.042###+-8.982###+-2.482###+-3.572###+- 2.104###+-2.310

###13.544

###19.912###0.273###85.485###11.953###50.501###8.555###658.253###36.003

###8.853+-0.654

M(LF)###+-1.654###+-0.002###+-3.182###+-0.690###+-2.000###+-2.586###+-9.542###+-0.324

###27.502###20.502###0.127###72.003###14.501###60.002###13.654###175.253###30.953

Kiddi

###+-5.204###+-1.777###+-0.005###+-2.512###+-0.792###+-5.212###+-1.523###+-5.982###+-4.441

###18.843###15.953###0.092###34.503###18.000###52.253###9.582###107.852###25.253

Patash

###+-2.412###+-2.452###+-0.003###+-1.622###+-3.212###+-1.982###+-1.483###+-9.873###+-1.782

Table- 3: Validation parameters.

Parameters###Cd2+###Cu2+###Pb2+###Mn2+###Cr6+###Ni2+###Co2+###Fe2+###Zn2+

Regression/ linearity###0.999###0.999###0.999###0.988###0.992###0.999###0.999###0.982###0.998

Sensitivity

nA ml (mu)g-1###5.264###1.886###2.901###0.416###5.359###1.932###5.636###2.151###7.46

Limit of Detection (mu)g/g###0.229853###0.38253###0.093119###0.048998###0.032415###0.832###1.897728###0.182455###5.0609

Limit of Quantification (mu)g/g###0.574632###0.956325###0.232798###0.122496###0.081038###2.08###4.74432###0.456138###12.65225

Reproducibility (mu)g/g###0.8675###1.5375###0.3625###0.435###0.1875###0.4###0.32###0.08125###1.625

Repeatability###0.0694###0.123###0.029###0.0348###0.015###0.032###0.0256###0.0065###0.13

(mu)g/g

Conclusions

The study addressed the analytical compatibility of voltammetric techniques for difficult and complex matrixes. It is concluded that voltammetry is a valuable analytical procedure highly applicable to the characterization of metals in the aquatic environment. Because of its freedom from reagents contamination and its ability to distinguish between complexes and free metal ions, the method is considered very useful in studying the role of trace metals in biologically mediated reactions in aquatic ecosystems. The speed and selectivity of voltammetric methods facilitate the study of the metal-binding ability by ligand of natural or manmade origin. It can be concluded that, if the supporting electrolyte is accurately chosen, voltammetry together with the standard addition method is certainly a valid analytical method (good selectivity and, especially, sensitivity) for simultaneously determining elements in the real samples.

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1Department of Chemistry, University of Karachi- Karachi 75270 Pakistan., 2Jinnah University for Women. Nazimabad- Karachi 74600 Pakistan., erum_zahir@hotmail.com
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Author:Zahir, Erum; Naqvi, Iftikhar Imam; Mohiuddin, Shaikh
Publication:Journal of the Chemical Society of Pakistan
Article Type:Report
Geographic Code:9PAKI
Date:Dec 31, 2012
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