I J P A C© Global Research Publications

* To whom correspondence be made:E-mail: seddiqueahmedfarag@yahoo.com

Cathodic Stripping Differential Pulse Voltammetric Determination ofPoly(8–Hydroxyquinoline) Matrix

Mohammed. M. Shahtaa*, bSeddique. M. Ahmedb and Mostafa M. Kamalb

aEnvironmental affairs Department, Assiut University Hospitals, Assiut, EgyptbChemistry Department, Faculty of Science, Assiut University, Assiut, 71516, Egypt

ABSTRACT: Cathodic stripping differential pulse voltammetric (CSDPV) procedure was successfully usedfor the determination of poly(8-roxyquinoline) (PHQ) matrix. The linearity range for the determination ofPHQ in the presence (1 mmolL-1) of copper (Cu(II) ion was found to be more sensitive ten times of magnitudehigher than the determination of PHQ alone. The lower detection limit was found to be as low as 10 nmolL-1.While, in the case for the determination of Cu(II) ion as a PHQ–Cu(II) chelate, the linearity range is (0 – 4µmolL-1). The determination of PHQ chain and/or Cu(II) ion was successfully applied in the presence ofvariety of anions, cations and in an insulating poly(vinyl alcohol) (PVA) matrix. The PVP matrix enhanced theabsorbability at the mercury electrode surface which caused increased in the peak high of the chelated Cu(II)

Keywords: Poly(8-Hydroxyquinoline), copper (II) ion, anions, cations, CSVD, PVA, PVP, determination

Vol. 8 • No. 3 • July-September 2013pp. 209-216

INTRODUCTION

Cathodic stripping voltammetry (CSV) of metalions is one commonly used of the main electrochemical stripping techniques, which issuppressing considering the potential benefit ofCSV, including high specificity, mercury free andoxygen insensitive analysis. CSV is effectively theelectrochemical inverse of ASV, where the analyteof interest is accumulated as an oxidizing specieson the electrode surface at positive potential, andthen quantified during the stripping step as theelectrode potential is swept cathodically. Often,CSV techniques also involve complexation of themetal ions of interest, and the use of a hangingmercury drop electrode (HMDE) (Zhang H., 1989;Zhang J., 1994). Various CSV methods for directlyanalyzing aqueous metal have also been developedpreviously (Viltchinskaia, 1995). These allmethods employ the technique of firstaccumulating metal from solution by electrodepositing (M2

n+On) on anodically on the workingelectrode and then stripping of the reduced Mn+

ions by sweeping the potential cathodically.

Cathodic stripping voltammetry has provedsuitable for a number of organic compound

including drugs as thiopurine and thiopyrimidinederivatives at hanging mercury dropping electrodewere investigated (Temerk, et al. 1992; 1993) insolutions of varying pH.

Although not exhaustive, the above listcontains the best of the recently developed CSVtechniques for metals determination, and this isalso evident in various review (Goyal, 2005;Esteban, 1994) with such a limited range ofapplications for CSV existing at, an investigationof new electrode materials and electrochemicaltechniques in this area is easily justified, in orderto extend the range of CSV – basedelectroanalytical techniques.

The Hanging Mercury Drop Electrode (HMDE)has been used as a model surface for thephysicochemical study of adsorption phenomenaof hydrophobic molecules such as aliphatic fattyacids (Ulrich, 1988), tri-n-butyl phosphate (Dogiæ,2003) and the study of fractal properties ofadsorbed linoleic acid (Risovic, 2001), to studysurface adsorption of mitomycin (Pérez, 2002), theinsecticide imidacloprid (Giannakopoulos, 2008).Also, HMDE was previously used to study themechanism of the reduction and breaking of theS–S bonds in proteins (Heyrovsky, 1994;Honeychurch, 1997), dithiocarbamate pesticides(Giannakopoulos; 2007) and cysteine (Stankovich,

1977; Florence, 1979), using Cathodic StrippingVoltammetry. HMDE has been employed for theanalytical determination of the redox states ofphosphonic acid derivatives, amino-(4-dihydroxyphenyl) methyl phosphonic acid, and 3-(3,4-dihydroxyphenyl)-alanine (Dopa) by cyclicvoltammetry (CV). The theoretical electrochemicalaspects of Cathodic Stripping Voltammetry (CSV)have been applied for the adsorption ofmonophenols (Gasowska, 2002) and polyphenols(Giannakopoulos, 2011; Oliveira Brett, 2002;Ghica, 2005) on a HMDE and a glassy carbon mini-electrode respectively.

The electrochemical interfacial adsorption ofa series of polyphenolic molecules (i.e.polyhydroxybenzoic acids) at the Hanging MercuryDrop Electrode (HMDE)–electrolyte interfaceswere investigated using Square Wave-AdsorptionCathodic Stripping Voltammetry (SW-AdCSV) atpH7.5. Polyhydroxybenzoic acids bearing one 4-hydroxybenzoic acid, two 3,4-dihydroxybenzoicacid (protocatechuic) or three 3,4,5-trihydroxybenzoic acid (gallic) OH-groups atpositions C3, C4 and C5 on the benzene ring werestudied. The complex interfacial electrochemicalbehaviour of these molecules has beendeconvoluted to (i) adsorption evens and (ii) redoxformations at the HMDE interface. The approachpresented is based on the comparative analysis ofthe SW-AdCSV signals in conjunction with themolecular structure of the molecules. Accordingly,theoretical calculations, involving nonlinear-fit,resulted in the identification of the interfacialreaction mechanism of adsorbed gallic acid on theHMDE (Giannakopoulos, 2012).

A differential pulse voltammetric (DPV)procedure is proposed by chemically modifiedelectrode (CMEs) with an immobilized complexingagent or ion exchanger have been widely used intrace metal analysis and many other researchareas owing to their easy fabrication and goodperformance. High sensitivity is also attainedowing to the analyte pre- concentration that occursat the electrode surface (Liu, 2001).

Song et al., (Song, 1997), had been determinedpoly (vinyl alcohol) (PVA) by adsorptive strippingvoltammetric technique based on its Cu(II)complexes at pH 11.0 using carbonate buffersolution. They found the adsorptive peak of PVA– Cu(II) has a potential of (– 0.125 V). However,several limitations were reported in the

application of mercury electrodes in the followingsolutions such as their poor mechanical stabilityand the dissolution of mercury at low potentialsand higher pH, which resulted in their inadequacyin the detection of highly conjugated electroactivepolymer (Erdgodv, 1997).

The electrochemical behavior of 8–hydroxyquinoline (8–HQ) and its derivatives at thedropping mercury electrode (DME) show acathodic reduction peak, corresponding to thereduction of the quinolic azomethine group(Kamal, 1989). This peak is often located at morenegative potential and close to the potential of thebackground discharge.

The polarographic behavior of poly (8-hydroxyquinoline) PHQ shows a cathodicreduction peak similar to the reduction peak ofthe monomer (8–HQ). However, in case of thepolymeric form PHQ, the reduction peak is intenseto some extent and clearly resolved from thebackground discharge current.(Kamal, 2002). Thecoordination polymers based on PHQ complexedwith some metal ions using several techniqueshave been characterized. Moreover, The insertionof Al(III) ion into poly(8-hydroxyquinoline) matrixinstead of some metal ions has been proposed andcharacterized (Ahmed, 2003; Kamal, 2009).

EXPERIMENTAL

8–Hydroxyquinoline (8–HQ) was obtained fromAldrich (chemical co.,US.). ploy (vinyl alcohol)(PVA; Mwt =2.2x104 ;degree of hydrolysis, 88% )was purchased from chemical co., Japan).

A copper nitrate Cu(NO3)2 was obtained fromchemically pure of Merck. All Materials employedin the present study were of analytical reagentproducts from their Analar grade nitrate salts(BDH): Cu(NO3)2.3H2O, Ni(NO3)2.6H2O, Co(NO3)2,CaCl2, MgCl2.6H2O, NH4Fe(SO4)2.12H2O,Al2(SO4)3.16H2O, ZnSO4.7H2O, Cd(NO3)2.4H2O,and Pb(NO3)2.

Cathodic stripping differential pulsevoltammetric (CSDPV) measurements werecarried out with a PAR model 303A hangingmercury electrode (HMDE) and a PAR model 305magnetic stirrer. Voltamograms were recorded onadvanced X–Y recorder model RE0089 afterautomated deareation of the electrolyzed solutions.

The pH measurements were made usingJenway 3305 pH-meter accurate to ± 0.01 pH unit

with glass calomel electrode assembly. The pH-meter was standardized against pH values 4.0 and10.0 buffers (prepared by dissolving buffercapsules in definite amount of second deionizedwater).

Magnetic stirrer Jenway 1000 was used forstirring the solutions.

The cell used for the voltammetric studies is athermostated PAR cell equipped with a threeelectrodes system. This system contained ahanging mercury drop electrode (HMDE) as theworking electrode, Ag / AgCl, Saturated KCl asthe reference electrode and platinum wire as acounter electrode. The surface area of the hangingmercury drop electrode was 1.2 x10-2 cm2.

2.3- Preparation of Solutions

Poly(8-Hydroxyquinoline), PHQ, was preparedbased on the homo-oxidative polymerizationtechnique of the corresponding monomer, 8-HQ(Kamal, 2002; Ahmed, 2003).

A solution of copper (II) was prepared bydissolving a known amount of chemically pure Cu(NO3)2 (Merk) in twice–distilled deionized waterand was standardized complexometrically (Vogel,1989). Solutions (1 mmol L-1) of the metal solutionsof anions such as CO3

-2 , NO3-1 , SO4

-2, B4O7-2, PO4

-3,CH3COO-1 were prepared from their Analar gradesodium salts.

A modified universal buffer series derived fromthat of Britton ( Britton, 1952) was prepared. Theconstituents of this series of buffer were preparedas follow:-

(a) A solution of 0.4 M of each phosphoric andacetic acids were prepared by accuratedilution of the A.R.concentrated acids.

(b) A solution of 0.4 M boric acid was obtainedby dissolving the appropriate weight of there crystallized acid in bi distilled water.

(c) A stock acid mixture was prepared bymixing equal volumes of the three acids ina large bottle. The total molarity of the acidmixture was thus mentioned at 0.4 mol L-1.

A series of buffer solutions (pH 3–12) wereprepared as follow: 150 ml of the acid mixture wasplaced in a 250 ml measuring flask followed bythe appropriate volume of 0.4 M NaOH solutionwith stirring and measuring pH values.

10 ml of the supporting electrolyte (universalbuffer containing 15% ethanol) was placed in theelectrolysis cell, followed by an appropriate volumeof the solution of the depolarizer. The solution wasdeareated by passing a slow stream of purenitrogen through it for 20 minutes. Sequentialaddition of mM stock solution of the investigatedcompound of PHQ or metal nitrates were used.

Metal ions such as Cu(II), Ni(II), Co(II), andFe(III) were prepared by dissolving a knownamount of chemically pure metal nitrate (Merck)in twice-distilled deionized water and werestandardized complexometrically (Vogel, 1989).The working standard solutions in the synthseswere prepared in 10-ml volumetric flasks inaqueous ethanol (60% ethanol). The solutions werethen diluted to an appropriate volume with doublydistilled water. Solutions of the anions; e.g., Cl-,Br-, I-, NO3

-, PO43-, B4O7

-, SO42-, CH3COO-, CO3

2-,HCO3

-, C6H5COO-, citrate, and tartarate, wereprepared from their Analar grade sodium salts.

2.4. Procedure for the CSVD of PHQ Matrix

The differential pulse cathodic strippingvoltammetry (DPCSV)were carried out at: scanrate 5 mVs-1, modulation amplitude 100 mV,deposition time 120 sec., plus 15 sec quiescentperiod. All measurements were performed at 22±0.5 oC. Nitrogen was bubbled through the solutionin the cell for 20 min. to remove oxygen to anundetectable level, and the correspondingvoltammetric curves were recorded.

RESULTS AND DISCUSSION

CSDPV of PHQ at Different pH Value

The chathodic stripping differential plusevoltammetric (CSDPV) behavior of PHQ matrixat the hanging mercury dropping electrode(HMDE) in various pH media was shown in Fig.1. In acidic and neutral media (pH < 7.10), thereduction response of the adsorbed PHQ was notobserved and the cathodic reduction peak iscompletely overlapped with the backgrounddischarge. This behavior is due to the highlycatalytic effect of the adsorbed PHQ molecules onthe hydrogen ion (H+) discharge potential.However, In alkaline media (pH > 7.1), thevoltammograms display a relatively weak signalat the negatively charged electrode potential (Ep= –1.55 V, pH 11.20) which is highly affected bythe background discharge. Under these conditions

the DPCSV peak of PHQ can not be used as asensitive signal for its analytical determinationof PHQ chain using such technique.

It was observed that the more sensitiveCSDPV signal for the reduction of PHQ–Cu(II)matrix observed at pH 7.10 and the peak heightdecreases with increasing or decreasing the pH.This signal is strongly Cu(II) and/or PHQconcentration dependent. Hence, pH 7.10 is chosenas the optimum pH medium for the tracedetermination of Cu(II) and/or PHQ matrix.

Effect of operating parameters

3.3.1- Effect of alcohol percentage on the CSDPVof PHQ – Cu(II) system

The CSDPV of PHQ–Cu(II) system at pH 7.1 wasrecorded in solutions containing different ethanolpercent. The maximum response of the chelatedCu(II) peak is recorded at 15 % ethanol. Withincreasing or decreasing the ethanol percent, thesignal decreased by about 10 – 20 %. This behavioris due to the solubility effect at lower ethanolpercent as well as at higher percentage, ethanolmay be compete with the adsorption of the PHQ–Cu(II) system. Therefore, 15 % ethanol at pH 7.1was used in our subsequent experiments.

3.3.2. Effect of Scan Rate

The effect of scan rate on the CSDPV peak of thechelated PHQ–Cu(II) system was investigated atpH = 7.1 containing 15% ethanol, tacc. 120 sec., Ei= 0.0 V, and pulse amplitude 100 mV. The peakheight increases by 15% with increasing the scanrate from 2 to 5 mV s-1. At higher scan rates 10and 20 mV s-1 the peak height decreased. Then,the scan rate 5 mV s-1 was selected as an optimumone for the analytical determination of Cu(II) and/or PHQ experiments

Effect of Pulse Amplitud

The pulse amplitude dependence of the ip of theCSDPV peak height of complexed Cu(II) increaseswith changing the pulse amplitude from 25 to 100mV. At pulse amplitude 100 mV the peak heightis 200 % of the height at 50 mV and the peakpotential slightly shifted to less negative value.

The effect of accumulating time (dipping time)(tacc) on the maximum response of the CSDPV ofthe chelated Cu(II) was examined using theconcentration of 2.0 µmolL-1 of PHQ (Fig. 3). Thepeak height increases with increasing the pre-concentration time. This behavior is consistentwith a process that is limited by adsorption of the

Figure 2: CSDPV behavior of (1 molL-1) of Cu(II) ion and (2mmolL-1) of PHQ at different pH value foruniversal buffer solutions, containing 20 %Ethanol, tacc 120 sec.; pulse amplitude 100 mV andscan rate 10 mV / sec

Figure 1: CSDPV behavior of 10 mmolL-1 PHQ at differentpH value for universal buffer solutions containing20 % Ethanol, tacc, 120 sec.; pulse amplitude 100mV and scan rate 10 mV/sec

investigated system. At higher accumulation time(t > 180 sec) the electrode surface becomesaturated, since, the peak current reaches aconstant value at adsorption longer than 120 sec.,which was used in our subsequent experiments.

hanging mercury dropping electrode (HMDE) inacidic media displays a very weak signal atnegatively charged electrode potential. Theweakness and broadness of the CSDPV of PHQ isdue to the weak adsorption and accumulation ofthe investigated compound on the electrodesurface at such negative potential. This fact couldbe explained by the repulsion between thenegatively charged electrode surface and the bi-electron system of the adsorbed and accumulatedspecies leading to formation of the less stableadsorptive layer. It is well known that the step ofthe adsorption and accumulation is a prerequisitestep for application of the stripping analysistechnique. The above results indicate that thecathodic adsorptive stripping differential pulsevoltammetric (CSDPV) technique is not sensitivetechnique for the direct determination of PHQmatrix.

The cathodic stripping differential pulsevoltammetric (CSDPV) behavior of PHQ chelateswith copper ion [PHQ – Cu(II) matrix] wasrecorded over a wide pH range (1.4–11.25) asshown in (Fig. 2). This behavior shows a verysharp, sensitive and resolved cathodic reductionpeak at potential – 0.45 V (pH-dependent). Thispeak corresponding to the reduction of the chelatedCu(II) ion of the strongly adsorbed andaccumulated PHQ–Cu(II) matrix at the droppingmercury electrode surface. The optimum solutionand operation conditions for determination ofCu(II) and PHQ matrix at HMDE using CSDPVtechnique were studied and recorded as follows:pH 7.10, alcohol percentage 15 %, pulse amplitude100 mV, scan rate 5 mVs-1, deposition time 120sec., and starting potential 0.0 V. The sensitivityof the CSDPV signal of the PHQ–Cu(II) matrixare fully investigated by variation of concentrationof PHQ on 1 (µmolL-1) of Cu(II) shown in (Fig. 4).The variation of the peak height of CSDPVresponse with the concentration of PHQ is linearly,and the linearity range for determination of PHQin the presence (1 µmolL-1) of Cu(II) is the range(0.01 – 0.2 µmolL-1).

It should be mentioned that, under theoptimum conditions for determination of PHQ byusing CSDPV, the detection limit was 1x10-8molL-1. While, in the case of determination ofCu(II) as PHQ–Cu(II), the linearity range fordetermination of Cu(II) in presence of (10 µmolL-1) of PHQ is the range (0 – 4 µmolL-1), and thedetection limit was 1x10-7 molL-1 .

Figure 3: CSDPV-voltammograms of PHQ – Cu(II) chelate[2.0 : 1.0 mmolL-1 ] at different acc. time, pH 7.01,scan rate 5 mV sec and pulse

Effect of Accumulation Potential

The dependence of the height of the CSDPV peakof PHQ–Cu(II) on the pre-concentration potentialwas studied at pH 7.01 in the potential range +0.05 V and – 0.1 V. The peak height at potentialsmore negative or more positive than 0.0 V is almostconstant. This behavior indicates that themaximum accumulation of the neutral form ofPHQ – Cu(II) complex at the mercury electrodesurface is observed at 0.0 V. The accumulationpotential was adopted at 0.0 V for the strippinganalysis experiments.

Determination of PHQ as PHQ–Cu(II) Matrix

The catodic stripping differential pulsevoltammetric (CSDPV) behavior of the PHQ at the

Effect of Interfering Ions on PHQ–Cu(II)Chelates

The effects of interference of cations, anions,organic additive and/or insulating matrix on theresponse of the peak height of the DPCSV of thechelated Cu(II) with PHQ matrix were examined.The recovery percentage (%) of the peak height onrelative to the peak height of (1 µmolL-1) of Cu(II)and (2 µmolL-1) of PHQ was recorded and plottedas in (Fig. 5). It was found that, In the presence of1.0 and 10.0 µmolL-1 mixture of K(I), Na(I), Ca(II),Ba(II), Mg(II), Mn(II), Pb(II), Cd(II), Co(II), Ni(II),and Zn(II), the peak height decreases by 6.25%and 9.37% respectively. The results indicated thatthe degree of the recovery of PHQ in 0.1 µM ofPHQ–Cu(II) system is in the range of 90.63 and93.75% in presence that metals ions mixture. Thedegree of recovery of 0.1 µmolL-1 PHQ–Cu(II)system in the presence of 100 µM mixture ofCHCOO-, BO4

2-, PO43-, SO4

2-, NO3-, and CO3

2- isabout 98.65%. This result refers that all of theseanions does not competitor with the adsorpabilityof the investigated species at the mercury electrode

surface. Addition of 10 and 100 µmolL-1 of glutaricacid, as an example for amino acids, to 0.1 µmolL-1 of PHQ–Cu(II) system the response current dueto the reduction of Cu(II) chelated is decreasedabout 2.13%

Figure 4: CSDPV-voltammograms of: (1) universal buffersolution at pH 7.12; (2) 1 + 1 mmolL-1 of Cu(II)ion and different concentration of PHQ withoutstirring, tacc 120 sec., scan rate 5 m V / sec., andpulse amplitude 100 m V. Figure 5: Effect of interfering ions individually by recovery

percentage (%) on relative to 1 µmolL-1 of Cu(II)ion and 2 µmolL-1 of PHQ at universal buffersolutions, pH 7.02, tacc 120 sec., scan rate 5 m V /sec., and pulse amplitude 100 m V

Rec

over

y pe

rcen

tage

(%)

100 99 9893

91

24

Although the addition of amino acid (1000times), the degree of PHQ recovery is about 97.61%. It is interesting to note that the addition ofTriton X-100 does not highly affected on thecathodic reduction peak height (ip) of the chelatedCu(II) ion, whereas the degree of the recoveryabout 97.25%. However, in the presence of EDTA(10 mmolL-1), the ip of the chelated Cu(II) signalis almost diminishes and the degree of the recoveryof PHQ is ~ 24.14 %. This dramatic effect is due tothe very strong chelating efficiency of EDTAtowards Cu(II) than PHQ matrix.

Effect of Insulating Matrix

In the presence of insulating matrix such as poly(vinyl alcohol) (PVA) in the concentration range10 ~100 µmolL-1, the degree of the recovery ofPHQ–Cu(II) system (0.10 : 0.05 µmolL-1) wasfound to be closed 93 %, as shown in (Fig. 6) andpeak potential of the CSDPV peak of the chelated

Cu(II) is almost constants in the presence of PVAmatrix. While, in presence of poly (vinylpyrrolidine) (PVP) with the concentration (100µmol L-1) the reduction peak height (ip) of chelatedCu(II) with PHQ was higher than the reductionpeak height (ip) of PHQ–Cu(II) system alone. Thismeans that the PVP matrix enhanced theabsorbability at the mercury electrode surfacewhich caused increased in the peak high ofchelated Cu(II), The calibration plot of reductionpeak height (ip / mA) was increased with increasingthe PHQ concentration.

AcknowledgementsThe authors would like to thank the members of the ChemistryDepartment, Faculty of Science, Assiut University, Egypt, fortheir encouragement.

References[1] Ahmed S.M., M.M. Shahata, & M.M. Kamal. (2003),

Spectrophotometric Studies of the Coordination PolymerBased on Poly (8–Hydroxyquinoline) Matrix. J. Inorg.Organometall. Polym. 13(3): 171- 192.

[2] Britton H.T.S., “Hydrogen Ions” Fourth Edition, (1952).

[3] Dogić R. & D. Krznariæ. (2003), Adsorption of Tri-n-ButylPhosphate (TBP) from NaClO4 Aqueous Solution on HgElectrode Adsorption of Tri-n-Butyl Phosphate (TBP) fromNaClO4 Aqueous Solution on Hg Electrode.Electroanalysis. 15: 312–318.

[4] Erdgodv G. & A. F. Karagozler. (1997), Investigation andcomparison of the electrochemical behavior of someorganic and biological molecules at various conductingpolymer electrodes. Talanta. 44: 2011-2018.

[5] Esteban M. & C. Arino. (1994), Expert system for thevoltammetric determination of trace metals: Part V.Methods for determining total iron, manganese(II),aluminium and titanium. Anal. Chim. Acta. 285: 377-389.

[6] Florence M. (1979), Cathodic stripping voltammetry: PartI. Determination of organic sulfur compounds, flavins andporphyrins at the sub-micromolar level. J. Electroanal.Chem. 97: 219-236.

[7] Gasowska B., M. Drag, K. Nowak, & P. Kafarski. (2002),Redox reaction between amino-(3,4-dihydroxyphenyl)methyl phosphonic acid anddopaquinone is responsible for the apparent inhibitoryeffect on tyrosinase. Eur. J. Biochem. 269: 4098–4104.

[8] Giannakopoulos E. & Y. Deligiannakis. (2007),Thermodynamics of Adsorption of Dithiocarbamates atthe Hanging Mercury Drop. Langmuir. 23: 2453–2462.

[9] Giannakopoulos E. & Y. Deligiannakis. (2011), Interfacialthermodynamics of gallic acid adsorption on a chargeablehydrophobic surface. J. Colloid Interface Sci. 358: 575-581.

[10] Giannakopoulos E. & Y. Deligiannakis and G. Salahas.(2012), Electrochemical interfacial adsorption mechanismof polyphenolic molecules onto Hanging Mercury DropElectrode surface (HMDE). J. Electroanal. Chem. 664:117-125.

[11] Giannakopoulos E., P. Stivajtakis & Y. Deligiannakis.(2008), Thermodynamics of Adsorption of Imidaclopridat Constant Charge Hydrophobic Surfaces:Physicochemical Aspects of Bioenvironmental Activity.Langmuir. 24: 3955–3959.

[12] Ghica M. E., & A. M. Oliveira Brett. (2005) ,Electrochemical Oxidation of Rutin. Electroanalysis. 17:313- 318.

[13] Goyal R. N. & A. Mittal, J. Sci. Ind. Res. (1993),Application of electroanalytical techniques in monitoringmetal-ions pollution in water - a review. J. Sci. Ind. Res.52: 607-623.

[14] Heyrovskyt M., P. Mader, V. Vesel., & M. Feduro. (1994),Influence of dissociation of tris(2,22 -bipyridyl)iron(II)cations on the time dependence of currents in clay-modified electrodes. J. Electroanal. Chem. 369: 53-58.

[15] Honeychurch M.J., (1997), The reduction of disulfidebonds in proteins at mercury electrodes. Bioelectrochem.Bioeenerg. 44 : 13-21.

Figure 6: CSDP-Voltammograms of: (1) universal buffersolution, pH 7.12, (2) 1 + 1 µmolL-1 of Cu(II) ion,(3) 2 + 100 mmolµ-1 of insulating matrix, PVP,and different concentration of PHQ withoutstirring, tacc 120 sec; scan rate 5 m V / sec., andpulse amplitude 100 m V

12

11

10

9

8

7

6

5

3

4

21

[16] Kamal M. M., A. M. Aly, M. S. El-Meligy & A. I. El-Said.(1989), Studies on Some Metal Chelates of 8-Hydroxy-Quinoline-5-Sulphonylhydrazide. Synth React InorgChem. 19: 557-569.

[17] Kamal M.M., S.M. Ahmed, M.M. Shahata, & Y.M.Temerk. (2002), Differential Pulse Polarographic (DPP)of Poly (8–Hydroxyquinoline) Matrix. Anal. Bioanal.Chem. 372: 843 – 848.

[18] Kamal M. M., A. Y. Al-Sayed, S.M. Ahmed, A.E. Omran& M.M. Shahata. (2009), Cation exchange mobility onPoly(8-hydroxyquinoline) matrix. J. Inorg OrganometPolym 19: 501-506.

[19] Liu J., X. Wang, G. Chen. & S. Bi. (2001), Speciation ofaluminium(III) in natural waters using differential pulsevoltammetry with a Pyrocatechol Violet-modifiedelectrode. Analyst. 126: 1404-1408.

[20] Oliveira Brett , A.M. & M.E. Ghica. (2003) ,Electrochemical Oxidation of Quecetin. Electroanalysis.15: 1745- 1750.

[21] Pérez P., C. Teijeiro, & D. Marín. (2002), Study on theAdsorption Properties of the Drug Mitomycin C byStripping Voltammetry. 18: 1760–1763.

[22] Risovic D., B. Gašparovictÿ, & B. Cosovic. (2001), Fractaland Voltammetric Study of Linoleic Acid Adsorption atthe Mercury/Electrolyte Solution Interface. Langmuir. 17:1088–1095.

[23] Song M., H. Ma, Y. Huang, & S. Liang. (1997) ,Determination of poly(vinyl alcohol) by adsorptivestripping voltammetry based on its copper(II) complex.Anal. Chim. Acta. 338: 103–108.

[24] Stankovich M.T., & A.L. Bard. (1977), Theelectrochemistry of proteins and related substances: I.Cystine and cysteine at the mercury electrode. J.Electroanal. Chem. 75: 487-505.

[25] Temerk Y. M., M. M. Kamal, Z. A. Ahmed, M. E. Ahmed& M. S. Ibrahim. (1992), Adsorptive stripping analysis ofthiocytosine at the static mercury electrode surface.Fresenius J. Anal. Chem. 342: 601-605.

[26] Temerk Y. M., Z. A. Ahmed, M. E. Ahmed, M. S. Ibrahim& M. M. Kamal. (1993), Cathodic adsorptive strippingvoltammetry of 6-thiopurine in absence and presence ofsome metal ions. Fresenius J. Anal. Chem. 345: 733-736.

[27] Ulrich J.H. & W. Stumm. (1988), Adsorption of aliphaticfatty acids on aquatic interfaces. Comparison between twomodel surfaces: the mercury electrode and ́ -Al2O3 colloids.Environ. Sci. Technol. 22: 37–41.

[28] Viltchinskaia E. A., D. M. Zeigman, D. M. Garcia & P. F.Santos. (1995), The Effect of Organic Substances andElectrochemical Elimination of it for Cathodic StrippingVoltammetric Determination of Manganese (II) in NaturalWaters. Anal. Lett. 28: 1845-1863.

[29] Vogel A. I., Text book of quantitative inorganic analysis,5th edn. EIBS – Longman. London, (1989).

[30] Zhang H., R. Wollast, J. C. Vire & G. J. Wollast. (1989),Simultaneous determination of cobalt and nickel in seawater by adsorptive cathodic stripping square-wavevoltammetry . Analyst. 114: 1597-1602.

[31] Zhang J. Z. & F. J. Millero. Anal. Chim. Acta. (1994),Investigation of metal sulfide complexes in sea waterusing cathodic stripping square wave voltammetry. Anal.Chim. Acta. 284: 497–504.