Application of Electro Analytical in Trace Metals Determinations: Environmental and Industrial Samples

Trace elements determination in industrial and environmental samples are of high economic and environmental impact, and attractive area of research for many scientists. Modern electrochemical techniques are powerful and versatile analytical techniques that offer high sensitivity, accuracy, and precision as well as large linear dynamic range, with relatively low-cost instrumentation. After developing more sensitive pulse methods, the electro analytical studies are more regularly used on industrial, and environmental applications. However, electro analytical techniques can easily solve many problems of the trace metals determinations with a high degree of accuracy, precision, sensitivity, and selectivity employing this approach. Some of the most useful electro analytical techniques are based on the concept of continuously changing the applied potentials to the electrodesolution interface and the resulting measured current (Kissinger and Heineman 1996; J Wang 2006; Smyth and Vos 1992; Ozkan, Uslu and Aboul-Enein 2003; Bard and Faulkner 2001; Kellner et al. 2004; Hart 1990) [1]. Most of the chemical compounds were found to be as electrochemically active [1], During the past years, there has been extraordinary acceleration of progress in the discovery, synthesis, sensitive electrochemical analysis [2-9]. The aim of the present review is to give industrial, biological, and environmental applications used for each mode of electro analysis techniques, namely, cyclic, linear sweep, square wave and stripping voltametric techniques. An attempt was made to choose some readily available publications describing some advances in methodology and applications.

Modern electroanalytical methods show a remarkable sensitivity, broad scope and very low quantitation limit. Different electroanalytical methods, especially stripping analysis, widely used for the trace metals determination in environmental, industrial and in biological samples. Various stripping techniques were used for the determination of 30 trace elements [10-75].

Square-wave voltammetric determination of eight elements viz. Cd(II), Pb(II), Cu(II), Zn(II), Co(II), Ni(II), Cr(VI), and Mo(VI) in soil and indoor-airborne particulate matter has been examined and optimized [2]. It was found that the square-wave anodic stripping voltammetry is the conventional technique for the determination of Zn(II), Cd(II), Pb(II), and Cu(II), but square wave adsorptive cathodic stripping voltammetric method is used for the determination of Co(II), Ni(II), Mo(VI) and Cr(VI). The detection limits of these metal ions were 0.03, 0.4, 0.04, 0.1, 0.15, 0.05, 0.2, and 3.2ug/kg for Cd(II), Pb(II), Cu(II), Zn(II), Co(II), Ni(II), Cr(VI), and Mo(VI), respectively. A method was described for the determination of selenium in soils and plants by Differential Pulse Cathodic-Stripping Voltammetry (DPCSV) at a hanging mercurydrop electrode [21]. An ultrasensitive adsorptive catalytic stripping (voltammetric and potentiometric) procedure for determining trace levels of chromium in the presence of cup Ferron is described [22]. A preconcentration time of 1min results in a detection limit of 1.0ngL–1. The stripping potentiometric scheme allows convenient measurements of chromium in the presence of dissolved oxygen. The identical stripping response for Cr(III) and Cr(VI) solutions makes the method applicable to the measurement of the total chromium content. The simultaneous determination of chromium and uranium is illustrated. The merits of the proposed procedure are demonstrated by the analysis of soil and groundwater samples. A differential pulse stripping voltammetry method for the trace determination of Mo(VI) in water and soil has been developed [23]. The suggested procedure can be used for determining Mo(VI) in the range 5×10−10 to 7×10−9M, with a detection limit of 1×10−10M (4min accumulation). Direct and simultaneous voltammetric analysis of heavy metals in tap water samples at Assiut city was developed [24]. Tap water samples are analyzed to determine the total content of Cd(II), Cu(II), Pb(II) and Zn(II) by Differential Pulse Anodic Stripping Voltammetry (DPASV) while Ni(II) and Co(II) are determined by a new simple Differential Pulse Adsorptive Stripping Voltammetry (DPAdSV), using Dimethylglyoxime (DMG) as the complexing agent. This method uses sodium sulfite as the supporting electrolyte, which facilitates the removal of oxygen interference without the traditional necessity of purging with inert gas. Graphite Electrodes Modified by 8-hydroxyquinolines exhibited an affinity to chelating Cu(II) forming a Cu(II) complex, which was employed for Cu(II) trace analysis [25]. A differential pulse voltammetry, combined with a preconcentrating-stripping process and a standard addition method was used for the analysis. A detection limit for trace copper determination in water, such as 5.1×10-9molL-1, was obtained. Catalytic adsorptive stripping voltammetry determination of ultra-trace amount of Mo(VI) is proposed [26]. The method is based on adsorptive accumulation of the Mo(VI)-Pyrocatechol Violet (PCV) complex on to a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation Mo(VI) can be determined in the range 1×10-3-100.0ngmL-1 with a limit of detection of 0.2pgmL-1. The procedure was applied to the determination of Mo(VI) in mineral water and some analytical grade substances with satisfactory results. Differential pulse adsorptive cathodic stripping voltammetric method has been developed for trace determination of Mo(VI) in presence of alizarin red S as complexing agent [27]. The peak current is proportional to the concentration of Mo(VI) over the concentration range of 1-25ppb with a detection limit of 0.25ppb. The method has been applied to the determination of Mo(VI) in water samples.
Carbon paste electrode modified with diacetyldioxime used for the simultaneous determination of Pb(II) and Cd(II) [28]. Calibration graphs were linear in the concentration ranges of 1.0x10-7-1.5x10- 5mol/L (Pb(II)) and 2.5x10-7-2.5x10-5mol/L (Cd(II)), respectively. For 5min preconcentration, detection limits of 1x10-8mol/L (Pb(II)) and 4x10-8mol/L (Cd(II)) were obtained. The diacetyldioxime modified carbon paste electrode was applied to the determination of Pb(II) and Cd(II) in water samples. Electrochemical method is described for the determination of inorganic arsenic in water at the μg/L level, applicable in the laboratory and in the field, based on differential pulse cathodic stripping voltammetry [29]. Determination of total AS is performed by reducing As(V) to As(III) using sodium meta-bisulfite/sodium thiosulfate reagent stabilized with ascorbic acid. As(V) is quantified by difference The detection limit was 0.5μg/L with a linear range from 4.5 to 180μg/L. Adsorptive stripping voltammetric determination of Pb(II) in presence of 2,2′-dipyridyl–2,4-dioxybenzoic acid molecular complex was proposed [30]. The compounds formed by Pb(II) and 2,2′-dipyridyl–2,4-Dioxybenzoic Acid Molecular Complex (DDOB) are adsorbed on the mercury electrode. Linear dependence between the current and Pb(II) concentration in the solution was observed in the range 1.2×10−8-3.5×10 diffusion. This method natural waters. −7M Pb(II), for accumulation time 60s and stationary was applied for the determination of the Pb(II) in the anodic stripping voltammetric method with a mercury thin film electrode is reported for the establishment of baseline concentrations of Cd(II), Pb(II) and Cu(II) in natural waters [31]. A voltammetric method based on chelate adsorption at the hanging mercury electrode is described for the simultaneous determination of Cu(II), Pb(II), Cd(II), Ni(II) and Co(II) by adsorptive stripping voltammetry using quercetin as complexing agent [32] The method was applied successfully for the simultaneous determination of the five metals in tap water samples. Differential pulse anodic stripping voltammetry was used for the determination of Zn(II), Cd(II), Pb(II) and Cu(II) in the underground water [33]. The trace elements levels found are in the ranges 0.01-0.37, 1.27-49.5, 0.41-29.8 and 0.13- 98.09ug/L for Cd(II), Cu(II), Pb(II) and Zn(II), respectively. The method was applied with satisfactory results for the determination of these metals in underground water samples.
Adsorptive cathodic stripping voltammetric determination of Mo(VI) in synthetic solutions and environmental samples was proposed [34]. This method is based on controlled adsorptive preconcentration of Mo(VI) species on the Hanging Mercury Drop Electrode (HMDE) using mixtures of nitrate and phosphate as supporting electrolytes. The method used is Cathodic Linear Sweep Stripping Voltammetry (CLSSV). The detection limit found was 1×10- 8M using 120s. as accumulation time. This method has been applied for the determination of Mo(VI) in environmental samples; e.g., soil, natural water and indoor airborne particulate. Determination of iron in seawater using cathodic stripping voltammetry preceded by adsorptive collection with the hanging mercury drop electrode [35]. The detection limit for the determination of iron in seawater of pH 6.9 was 6×10−10M in the presence of 4×10−4M catechol and after a collection period of 3 minutes. The peak current increased linearly with the metal concentration up to about 5×10−8M, but the linear range could be increased by using a shorter collection period. Direct determination of sub-nanomolar levels of Zn(II) in seawater by cathodic stripping voltammetry is presented [36]. The zinc complex with ammonium pyrrolidine dithiocarbonate is adsorbed on a hanging mercury drop electrode and the reduction current of zinc is measured by voltammetry. The detection limit for Zn(II) is 3×10−11M, with 10-min collection time. Dissolved Al(III) in seawater and freshwater is determined by cathodic stripping voltammetry preceded by adsorptive collection of complex ions with 1,2-Dihydroxyanthraquinone-3-Sulphonic Acid (DASA) on the hanging mercury drop electrode [37]. Direct determination of dissolved Co(II) and Ni(II) in seawater by differential pulse cathodic stripping voltammetry preceded by adsorptive collection of cyclohexane-1,2-dione dioxime complexes [38]. Detection limit for Co(II) and Ni(II) depend upon reagent blanks and are 6pM and 0.45nM, respectively, for 15-min adsorption periods.
Complex ions of Mo(V1) with 8-hydroxyqulnoilne (oxine) are shown to adsorb onto the hanging mercury drop electrode [39]. This property forms the basis of a sensitive electrochemical technique by which dissolved Mo(VI) in seawater can be determined directly. The peak current-Mo(VI) concentration relationship is linear up to 3x10-7M; the detection limit is 4nM. Procedures are presented to determine simultaneously Cu(II), Pb(II) and Cd(II) in seawater by differential pulse cathodic stripping voltammetry preceded by adsorptive collection of complexes with 8-hydroxyquinoline (oxine) onto a Hanging Mercury Drop Electrode (HMDE) [40]. The limits of detection for a 1 min stirred adsorption time are 0.12nM Cd(II), 0.3nM Pb(II) and 0.24nM Cu(II). A sensitive stripping voltammetric procedure for determining titanium is described [41]. There is a linear relationship between the preconcentration time and peak height at low surface coverages. With a 5min preconcentration period the detection limit is 7×10−10M. The merits of the described procedure are demonstrated in the analysis of sea, river and rain waters. Ti(IV) dissolved in sea water can be determined using adsorptive cathodic stripping voltammetry in the presence of mandelic acid [42]. The sensitivity of the voltammetric technique was thus improved by a factor of 20, and the limit of detection was lowered to 7pM with 60s adsorption, sufficiently low to determine Ti(IV) in water of oceanic origin. Direct electrochemical determination of dissolved vanadium in seawater by cathodic stripping voltammetry with the hanging mercury drop electrode [43]. Polarographic measurements showed that catechol complexes of V(V) adsorb onto the hanging mercury drop electrode. This property forms the basis of a sensitive electrochemical technique by which dissolved vanadium in seawater can be determined directly. The limit of detection is 0.3nM vanadium after a 2-min collection with a stirred solution, which is decreased further to 0.1nM after a 15-min collection. A procedure for the direct determination of iodide in seawater is described [11]. Using cathodic stripping square wave voltammetry, it is possible to determine low and subnanomolar levels of iodide in seawater, freshwater, and brackish water. The minimum detection limit is 0.1- 0.2nM (12 parts per trillion) at a 180-s deposition time.

A highly sensitive and selective stripping voltammetric procedure for the determination of uranium (VI) based on the adsorption properties of dioxouranium (II)-phathalate complexes onto hanging mercury drop electrode was developed [12]. The reduction current of adsorbed complex ions of U(VI) was measured by both linear sweep (LSCSV) and Differential Pulse Cathodic Stripping Voltammetry (DPCSV). As low as 2x10-9moL dm-3 (0.5ug/L) and 2x10-8moldm-3 (4.8ug/L) with accumulation time 240 and 120s using DPCSV and LSCSV, respectively, have been determined successfully. The application of this method was tested in the determination of uranium in super-phosphate fertilizer. Application of orthogonal functions to differential pulse voltammetric analysis was suggested [13].
The study was extended to Differential Pulse Cathodic Stripping Voltammetry (DPCSV) for the simultaneous determination of tin and lead. The stripping voltammetric analysis data processed by orthogonal functions and the first-derivative (1D) methods were successfully applied to the simultaneous determination of both metals in canned soft drinks. Differential Pulse Cathodic Stripping Voltammetry (DPCSV) was used to determine ultra-trace platinum in gasoline after wick bold combustion and subsequent UV digestion [14]. Cathodic stripping voltammetry combined with the Osteryoung square-wave mode at the glassy carbon electrode gave rise to both sensitivity and selectivity of the determination of manganese in some industrial samples [15]. The detection limit with 5 min accumulation is 0.022ug/L. Simultaneous determination of manganese in presence of Cu(II), Pb(II) and Zn(II) could be easily done using anodic stripping voltammetry at pH 4. Bismuth film electrodes were prepared ex-situ by pulsed potential electrodeposition. The analytical performances of these electrodes for adsorptive cathodic stripping voltammetry of nickel were evaluated in nondeaerated solutions using dimethylglyoxime as complexing agent [16]. Linear calibration curves were obtained for Ni+2 concentrations ranging from 1x10-8-1x10-7molL-1 and from 1x10-7-1x10-6molL-1 with relative standard deviations of 5% (n=15) at 1x10-7molL-1 level. The analytical methodology was successfully applied to monitor Ni+2 content in industrial electrolytic baths, ground water and tap water.
Differential Pulse Cathodic Stripping Voltammetry (DPCSV) and Linear Sweep Cathodic Stripping Voltammetry (LSCSV) were used for the determination of trace amounts Cr(VI) ions in neutral phosphate media [17]. Detection limit was 5x10-9molL-1 and 1x10- 9molL-1 using LSCSV and DPCSV, respectively. Differential pulse cathodic and anodic stripping voltammetry were applied for the determination f trace ions Cd(II), Co(II), Cu(II), Pb(II), Mn(II), Ni(II) and Zn(II) which are found in different grades of common salt as contaminants [19]. A procedure for the determination of lead in paints by differential-pulse anodic-stripping voltammetry is presented [44]. Differential pulse anodic stripping voltammetry with a hanging mercury drop electrode has been used for the determination of trace amounts of Cu(II), Cd(II), Pb(II) and Zn(II) ions in white cane sugar [45,46]. Trace amounts of Zn(II), Cd(II) and Pb(II) were determined in refined beet sugar by Differential Pulse Anodic Stripping Voltammetry (DPASV) at a hanging mercury drop electrode [47].
The procedure was applied to the determination of toxic elements in commercial beet sugar samples and levels of metals below 35mgkg-1 Pb(II), 80mgkg-1 Zn(II) and 10mgkg-1 Cd(II) were found. Determination of heavy metals (Cu(II), Cd(II), Pb(II) and Zn(II)) in concentrated refined sugar and raw syrups with differential pulse polarography and anodic stripping voltammetry was described [48]. Using differential pulse polarography, trace determinations down to 10-7M were measured. But using anodic stripping voltammetry at a mercury film electrode, it was found that the refined sugar of alimentary grade contained: 57 Cu(II), 34 Zn(II), 1 Cd(II), and 6 Pb(II) μg/kg of dry sugar. Anodic stripping voltammetry with a hanging mercury drop electrode was used for the determination of trace amounts of Zn(II), Pb(II) and Cu(II) in sugar cane spirit from different sources: commercial, oak-cask matured and home-made [49]. Experiments have been carried out to assess the potential of differential pulse voltammetry and potential stripping analysis for determining Pb(II), Cu(II) and Cd(II) directly in dissolved honey samples [50]. Se(IV) is determined by differential pulse anodic stripping voltammetry using gold electrodes [51]. A wide linear response range 0.5-291ng mL-1, was obtained using a 5.0mm diameter gold electrode.
Mo(VI) is determined by anodic stripping voltammetry using a carbon paste electrode modified in situ with Cetyltrimethylammonium Bromide (CTAB) [52]. Differential Pulse Anodic Stripping Voltammetry exploiting the reoxidation signal is used for the determination of trace levels of molybdenum(VI). Linearity between current and concentration exists for a range of 0.5-500μgL−1. Mo(VI) with proper preconcentration times; the limit of detection is 0.04μgL−1 with an accumulation period of 10min. A chemically modified carbon paste electrode was developed for the determination of silver by incorporating the strong acid ionexchanger into a conventional graphite-Nujol oil paste using by square wave anodic stripping voltammetry [53]. For 5 minutes of accumulation, the linear range was from 1.62μgL−1 to 0.8mgL −1 with a detection limit of 0.27μgL−1. Another type of chemically modified carbon paste electrode was suggested for the determination of silver [54]. Using differential pulse stripping voltammetry, the appropriate calibration graph for Ag(I) was obtained between 5x10- 7M and 1.5x10-6M and detection limit was 2x10-7M. Determination of lead and antimony in firearm discharge residues on hands by anodic stripping voltammetry using a mercury-coated graphite electrode are established [55]. Anodic stripping voltammetric determination of trace amounts of titanium has been studied using glassy carbon electrode modified with Thymol Blue (TB) [56]. The method has been successfully applied to determine titanium in two standard reference material portland cement samples, then to portland cement and cement clinker.
A voltammetric method has been used for the determination of the contents of toxic heavy metals in domestic waste and in compost produced from it [57]. Cu(II), Pb(II), Zn(II) and Cd(II) were determined in wet-digested samples of domestic waste, compost produced of that waste and in compost mixed with sewage sludge by anodic stripping voltammetry. An indirect voltammetric method is described for determination of cyanide ions and hydrogen cyanide, using the effect of cyanide on cathodic adsorptive stripping peak height of Cu-adenine using mercury electrode [58]. The detection limit was obtained as 1x10-8M for 60s accumulation time. The method was applied to the determination of cyanide in various industrial waste waters such as electroplating waste water and also for determination of hydrogen cyanide in air samples. Simultaneous determination of Cu(II), Zn(II) and Pb(II) by adsorptive stripping voltammetry in the presence of morin was suggested [59].
With an accumulation time of 60s, the peak currents are proportional to the concentration of copper, lead and zinc over the 1-60, 0.3-80 and 1-70ng/mL range with detection limits of 0.06, 0.08 and 0.06ng/mL, respectively. The procedure was applied to the simultaneous determination of Cu(II), Zn(II) and Pb(II) in some real and synthetic artificial real samples. Ni(II) and Co(II) have been determined simultaneously by means of Adsorptive Cathodic Stripping Voltammetry (AdCSV) in a computerized flow injection system [60].The selectivity of the method was demonstrated for the analysis of high purity iron. A voltammetric method is presented for the determination of trace levels of Cr(VI) in the presence of cupferron as ligand [61]. This method based on using Square Wave Adsorptive Stripping Voltammetry (SWAdSV) in conjunction with the electrochemical batch injection analysis technique at mercury thin-film electrodes. An analytical method has been developed for the determination of dissolved chromium at concentrations less than 2μg/L in PWR coolant by differential-pulse adsorptive stripping voltammetry at a hanging mercury drop electrode [62].
Mo(VI) has been determined by differential-pulse adsorptive stripping voltammetry in a pH 2 phosphate buffer utilising the strong adsorption of 12-molybdophosphoric acid at a hanging mercury drop electrode [63]. Calibration graphs are rectilinear up to the 7x10–7M Mo(VI). A clearly defined stripping peak was observed at the 5.6x10–9M level with 2 min accumulation. Adsorptive stripping voltammetry at a static mercury drop electrode for the determination of Al(III) and Fe(III) in portland cement has been employed [64]. An analytical procedure for the determination of Fe(III) and total iron in wines based on adsorptive stripping voltammetry is described [19]. Fe(III) was determined by using Solochrome Violet Red as chelating agent while catechol was used for the determination of the total iron content.
A sensitive stripping voltammetric procedure for quantifying thorium is described [65]. The chelate of thorium with the azo dye mordant blue 9 is adsorbed on the hanging mercury drop electrode. The detection limit is 4x10−10M (4-min accumulation), a linear current-concentration relationship is observed up to 1.3x10−7M. Square Wave Adsorptive Stripping Voltammetric Method for the determination of Ti(IV) is described [66]. The method is based on Ti(IV) complexed with Hydroxynaphthol Blue (HNB) at the static mercury drop electrode. The limit of detection was found to be 0.18μg/L and the limit of determination to be 1.09μg/L, both using 30s of preconcentration time. Simultaneous determination of tin and lead by differential pulse polarography with addition of hyamine-2389 is described [67]. Calibration plots are linear up to 5x10−5M for tin and 1.3x10−4M for lead, with detection limits of 8.4x10−7M and 2.4x10−7M, respectively. Simple methods are proposed for the determination of tin in solders and canned fruit juices.
Traces of Fe(III) were determined by differential pulse polarography in solar-grade silicon [68]. Differential pulse polarography provides a detection limit of about 0.15μg g-1 with a precision of 1-2% and linear calibration graphs up to 0.5μgmL-1 Fe(III).
Differential pulse polarographic determination of Cr(VI) in semiconductor gallium arsenide based on the catalytic current produced by nitrate in the electrolytic reduction of the Cr(VI)- diethylenetriaminepentaacetate complex [69]. This method is suitable for determinations of Cr(VI) at levels as low as about 1μg g−1 with about 50mg of sample. Mo(VI) was determined in steel by differential-pulse polarography [70]. The method is applicable to the determination of molybdenum in the 0.001-5% of Mo(VI) range and good agreement is reported for a number of certified British Chemical Standard and commercial steels. Ternary mixtures of metals can be resolved by using the ratio derivative polarography without the need for any pre-separation step [71,72]. The method is based on the simultaneous use of the first derivative of ratios of polarograms and measurements of zero-crossing potentials. The method has been successfully applied for resolving ternary mixtures of Cu(II), Cd(II) and Ni(II), which have overlapped polarograms. The concentration ranges to be determined are 0.30-1.40mgL−1 for Cu(II), 0.90-4.50mgL−1 for Cd(II) and 0.20-1.20mgL−1 for Ni(II). An electrochemical method for the quantitative determination of boron in minerals and ceramic materials is described [73]. It is based on the abrasive attachment of mixtures of ZnO plus sample to modified graphite electrodes. A method for determining trace level of V(V) has been developed [74]. The reaction is the polarographic reduction of the bromate, catalyzed by this metal ion, in the presence of cupferron. A linear current-concentration relationship is observed between 2x10-8 and 3x10-7M, with a detection limit of 6x10-9M. The procedure is very selective and has been successfully applied to a certified steel sample.
Voltammetric determination of the iodide ion with a quinine copper(II) complex modified carbon paste electrode employing linear sweep and differential pulse voltammetry [75]. Using linear sweep voltammetry, a calibration curve was attained over the concentration ranges 1x10-4–2.5x10-6M of the iodide ion at deposition time of 10min, with the detection limit 1x10-6M. Using differential pulse voltammetry, linear response range for the iodide ion was between 10-6 and 10-8M, and the detection limit was 1x10- 8M. This method was evaluated by analyzing the iodide ion content in a commercial disinfectant.

The previous survey shows that the number of publications dealing with the application of some selected modern electrochemical techniques (voltammetric techniques) to determine trace metals in industrial, and environmental samples The importance of such applications increased steadily, and this due to the following advantages:
a) Voltammetry coupled with different separation methods such as (HPLC, Flow Injection (FI) and Capillary Electrophoresis (CE)) enhancing the analytical properties for complex mixtures in different compounds.
b) Only small volumes of samples are necessary, and short analysis time.
c) Electroanalytical stripping procedures have been developed for the measuring down to sub-μg/L level. d) These techniques have been developed for various cations, anions and organic molecules.
e) Elelctroanalytical techniques (specially stripping analysis) are well known as excellent procedures for the determination of trace chemical species.
f) The developed stripping voltammetric methods are simple, time saving, selective and more sensitive for the simultaneous determination of trace substances.
g) Electroanalytical methods especially square wave voltammetry is a very sensitive and rapid analytical method due to it is high scan rate in all cases where the reacting species is accumulated by adsorption on the electrode surface.

1. Bengi U, Sibel AO (2011) Electroanalytical methods for the determination of pharmaceuticals: A review of recent trends and developments. Analytical Letters 44(16): 2644-2702.
2. Farghaly OA, Ghandour MA (2005) Square-wave stripping voltammetry for direct determination of eight heavy metals in soil and indoor-airborne particulate matter. Environmental Research 97(3): 229-235.
3. Farghaly OA, Mohamed NA, Gahlan AA, El-Mottaleb MA (2008) Stability constants and voltammetric determination of ramipril in tablet and real urine samples. Indian Journal of Analytical Chemistry 7(5): 294-300.
4. Farghaly OA, Hazazi OA, Rabie EM, Khodari M (2008) Determination of some cephalosporins by adsorptive stripping voltammetry. International Journal of Electro Science 3: 1055-1064.
5. Jonathan EH, Sunyhik DA, Dongmei J, Luke LK, Andrew DB, et al. (2013) Reprint of proton uptake vs. redox driven release from metal–organic-frameworks: Alizarin red S reactivity in UMCM-1. Journal of Electroanalytical Chemistry 710: 2-9.
6. Almeida SAA, Montenegro MCBSM, Sales MGF (2013) New and low cost plastic membrane electrode with low detection limits for sulfadimethoxine determination in aquaculture waters. Journal of Electroanalytical Chemistry 709: 39-45.
7. Aaboubi O, Housni A (2012) Thermoelectrochemical study of silver electrodeposition from nitric and tartaric solutions. Journal of Electroanalytical Chemistry 677-680: 63-68.
8. Xinfeng C, Jinsheng Z, Chuansheng C, Yunzhi F, Xianxi Z (2012) Star-shaped conjugated systems derived from thienyl-derivatized poly(triphenylamine)s as active materials for electrochromic devices. Journal of Electroanalytical Chemistry 677-680: 24-30.
9. Yuzhi Li, Chao H, Haijun D, Liu W, Yingwei L, et al. (2013) Electrochemical behavior of metal–organic framework MIL-101 modified carbon paste electrode: An excellent candidate for electroanalysis. Journal of Electroanalytical Chemistry 709: 65-69.
10. Fiorucci AR, Cavalheiro ÉTG (2002) The use of carbon paste electrode in the direct voltammetric determination of tryptophan in pharmaceutical formulations. Journal of Pharmaceutical and Biomedical Analysis 28(5): 909-915.
11. Farghaly OA, Ghandour MA (1999) Cathodic adsorptive stripping voltammetric determination of uranium with potassium hydrogen phthalate. Talanta 49(1): 31-40.
12. Sabry SM, Wahbi AM (1999) Application of orthogonal functions to differential pulse voltammetric analysis: Simultaneous determination of tin and lead in soft drinks. Analytica Chimica Acta 401(1-2): 173-183.
13. Hoppstock K, Michulitz M (1997) Voltammetric determination of trace platinum in gasoline after Wickbold combustion. Anal Chim Acta 350(1-2): 135-140.
14. Abo El-Maali N, Abd El-Hady D (1998) Square-wave adsorptive stripping voltammetry at glassy carbon electrode for selective determination of manganese. Application to some industrial samples. Anal Chim Acta 370(2-3): 239-249.
15. Legeai S, Bios S, Vittori O (2006) A copper bismuth film electrode for adsorptive cathodic stripping analysis of trace nickel using square wave voltammetry. J Electroanal Chem 591(1): 93-98.
16. Ghandour MA, El-Shatoury SA, Ali AMM, Ahmed SM (1996) Adsorptive cathodic stripping voltammetric determination of hexavalent chromium. Anal Lett 29(8): 1431-1445.
17. Ali AMM (1999) Determination of trace metal ions in common salt by stripping voltammetry. J AOAC International 82(6): 1413-1418.
18. Lai PC, Fung KW (1978) Determination of lead in paint by differential-pulse anodic-stripping voltammetry. Analyst 103: 1244-1248.
19. Ghandour MA, Ali AMM, Farghaly OA, Khodari M (2001) Digestion-free determination of trace Cu, Cd, Pb, and Zn Ions in Egyptian cane sugar by differential pulse anodic stripping voltammetry. Chemical Papers 55(2): 91-99.
20. Karadakhi TM, Najib FM, Mohammed FA (1987) Determination of traces of Zn, Cd, Pb and Cu in white sugar by anodic stripping voltammetry and a modified oxygen-flask combustion technique. Talanta 34(12): 995-999.
21. Forbes S, Bound GP, West TS (1979) Determination of selenium in soils and plants by differential pulse cathodic-stripping voltammetry. Talanta 26(6): 473477.
22. Wang J, Lu J, Olsen K (1992) Measurement of ultratrace levels of chromium by adsorptive–catalytic stripping voltammetry in the presence of cupferron. Analyst 117(12): 1913-1917.
23. Zhao Z, Pei J, Zhang X, Zhou X (1990) Adsorptive stripping voltammetry determination of molybdenum(VI) in water and soil. Talanta 37(10): 1007-1010.
24. Farghaly OA (2003) Direct and simultaneous voltammetric analysis of heavy metals in tap water samples at Assiut city: An approach to improve the analysis time for nickel and cobalt determination at mercury film electrode. Microchem Journal 75(2): 119-131.
25. Sousa ER, Marques EP, Fernandes EN, Zhang J, Marques ALB (2006) Graphite electrodes modified by 8-Hydroxyquinolines and its application for the determination of copper in trace levels. J Braz Chem Soc 17(1): 177-183.
26. Zarei K, Atabati M, Ilkhani H (2006) Catalytic adsorptive stripping voltammetry determination of ultra trace amount of molybdenum using factorial design for optimization. Talanta 69(4): 816-821.
27. Jugade R, Joshi AP (2005) Trace determination of Mo(VI) by adsorptive cathodic stripping voltammetry. Acta Chim Slov 52(2): 145-148.
28. Hu C, Wu K, Dai X, Hu S (2003) Simultaneous determination of lead(II) and cadmium(II) at a diacetyldioxime modified carbon paste electrode by differential pulse stripping voltammetry. Talanta 60(1): 17-24.
29. He Y, Zheng Y, Ramnaraine M, Locke DC (2004) Differential pulse cathodic stripping voltammetric speciation of trace level inorganic arsenic compounds in natural water samples. Anal Chim Acta 511(1): 55-61.
30. Zayats GD, Meryan VT, Revenco MD, Chiugureanu DG (2002) Determination of the lead by adsorptive stripping voltammetry in the presence of 2,2′-Dipyridyl– 2,4-Dioxybenzoic acid molecular complex. Anal Lett 35(3): 577-584.
31. Poldoski JE, Glass GE (1978) Anodic stripping voltammetry at a mercury film electrode: Baseline concentrations of cadmium, lead, and copper in selected natural waters. Anal Chim Acta 101(1): 79-88.
32. Farghaly OA, Wadood HMA, Mohamed HA (2003) Simultaneous determination of copper, lead, cadmium, nickel and cobalt by adsorptive stripping voltammetry using quercetin as complexing agent. J Pharm Sci 17(1): 43-47.
33. Farghaly OA, Ali AMM, Ghandour MA (1999) Determination of zinc, cadmium, lead and copper ions in the underground water by differential pulse anodic stripping voltammetry. Egypt J Anal Chem 8: 70-83.
34. Ali AMM, Ghandour MA, El-Shatoury SA, Ahmed SM (2000) Adsorptive cathodic stripping voltammetric determination of molybdenum in synthetic solutions and environmental samples. Electroanalysis 12(2): 155-158.
35. Berg CMG, Huang ZQ (1984) Determination of iron in seawater using cathodic stripping voltammetry preceded by adsorptive collection with the hanging mercury drop electrode. J Electroanal Chem 177(1-2): 269-280.
36. Berg CMG (1984) Direct determination of sub-nanomolar levels of zinc in sea-water by cathodic stripping voltammetry. Talanta 31(12): 1069-1073.
37. Berg CMG, Murphy K, Riley JP (1986) The determination of aluminium in seawater and freshwater by cathodic stripping voltammetry. Anal Chim Acta 188: 177-185.
38. Donat JR, Bruland KW (1988) Direct determination of dissolved cobalt and nickel in seawater by differential pulse cathodic stripping voltammetry preceded by adsorptive collection of cyclohexane-1,2-dione dioxime complexes. Anal Chem 60(3): 240-244.
39. Berg CMG (1985) Direct determination of molybdenum in seawater by adsorption voltammetry. Anal Chem 57(8): 1532-1536.
40. Berg CMG (1986) Determination of copper, cadmium and lead in seawater by cathodic stripping voltammetry of complexes with 8-hydroxyquinoline. J Electroanal Chem 215(1-2): 111-121.
41. Wang J, Mahmoud JS (1986) Stripping voltammetry with adsorptive accumulation for trace measurements of titanium. J Electroanal Chem 208(2): 383-394.
42. Yokoi K, Berg CMG (1991) Determination of titanium in sea water using catalytic cathodic stripping voltammetry. Anal Chim Acta 245: 167-176.
43. Berg CMG, Huang ZQ (1984) Direct electrochemical determination of dissolved vanadium in seawater by cathodic stripping voltammetry with the hanging mercury drop electrode. Anal Chem 56(13): 2383-2386.
44. Luther GW, Swartz CB, Ullman WJ (1988) Direct determination of iodide in seawater by cathodic stripping square wave voltammetry. Anal Chem 60(17): 1721-1724.
45. Lai PC, Fung KW (1978) Determination of lead in paint by differential-pulse anodic-stripping voltammetry. Analyst 103(1233): 12441248.
46. Karadakhi TM, Najib FM, Mohammed FA (1987) Determination of traces of zinc cadmium lead and copper in white sugar by anodic stripping voltammetry and a modified oxygen flask combustion technique. Talanta 34(12): 995-1000.
47. Sancho D, Vega M, Debán L, Pardo R, Gonzáles G (1997) Determination of zinc, cadmium and lead in untreated sugar samples by anodic stripping voltammetry. Analyst 122: 727-730.
48. Khoulif Z, Jambon C, Chatelut M, Vittori O (1993) Determination of heavy metals in concentrated refined sugar and raw syrups with differential pulse polarography and anodic stripping voltammetry. Electroanalysis 5(4): 339-342.
49. Barbeira PJS, Mazo LH, Stradiotto NR (1995) Determination of trace amounts of zinc, lead and copper in sugar cane spirits by anodic stripping voltammetry. Analyst 120(6): 1647-1650.
50. Li Y, Wahdat F, Neeb R (1995) Digestion-free determination of heavy metals (Pb, Cd, Cu) in honey using anodic stripping differential pulse voltammetry and potentiometric stripping analysis. Fresenius J Anal Chem 351: 678-682.
51. Pereira CF, Gonzaga FB, Guaritá-Santos AM, Souza De JR (2006) Determination of Se(IV) by anodic stripping voltammetry using gold electrodes made from recordable CDs. Talanta 69(4): 877-881.
52. Stadlober M, Kalcher K, Raber G (1997) A new method for the voltammetric determination of molybdenum(VI) using carbon paste electrodes modified in situ with cetyltrimethylammonium bromide. Anal Chim Acta 350(3): 319-328.
53. Gellon H, González PS, Fontan CA (2003) Square Wave anodic stripping determination of silver using a carbon paste electrode modified with a strong acid ion-exchanger. Anal Lett 36(13): 2749-2765.
54. Ha KS, Kim JH, Ha YS, Lee SS, Seo ML (2001) Anodic stripping voltammetric determination of silver(i) at a carbon paste electrode modified with S₂O₂-donor podand. Anal Lett 34(5): 675-686.
55. Konanur NK, VanLoon GW (1977) Determination of lead and antimony in firearm discharge residues on hands by anodic stripping voltammetry. Talanta 24(3) 184-187.
56. El-Maali NA (2001) Thymol blue coated glassy carbon electrode for selective determination of titanium. Anal Lett 34(1): 43-60.
57. Golimowski J, Tykarska A (1994) Voltammetric methods for the determination of heavy metals in domestic waste and compost produced from it. Fresenius J Anal Chem 349: 620-624.
58. Safavi A, Maleki N, Shahbaazi HR (2004) Indirect determination of cyanide ion and hydrogen cyanide by adsorptive stripping voltammetry at a mercury electrode. Anal Chim Acta 503(2): 213-221.
59. Shams E, Babaei A, Soltaninezhad M (2004) Simultaneous determination of copper, zinc and lead by adsorptive stripping voltammetry in the presence of morin. Anal Chim Acta 501(1): 119-124.
60. Economou A, Fielden PR (1998) Selective determination of Ni(II) and Co(II) by flow injection analysis and adsorptive cathodic stripping voltammetry on a wall jet mercury film electrode. Talanta 46(5): 1137-1146.
61. Christopher MAB, Filipe OMS, Neves CS (2003) Determination of Chromium(VI) by batch injection analysis and adsorptive stripping voltammetry. Anal Lett 36(5): 955-969.
62. Torrance K, Gatford C (1987) Determination of soluble chromium in simulated PWR coolant by differential-pulse adsorptive stripping voltammetry. Talanta 34(11): 939-944.
63. Fogg AG, Alonso RM, Jimenez RM (1988) Differential-pulse adsorptive stripping voltammetry of the psychotropic drugs triazolam and clotiazepam. Analyst 113(1): 27-30.
64. Abo El-Maali N, Temerk YM, M. Sh-Abd El-Aziz M (1997) Application of stripping voltammetry at a static mercury drop electrode for the determination of aluminium and iron in portland cement. Anal Chim Acta 353(2-3): 1-6.
65. Wang J, Mannino S (1989) Application of adsorptive stripping voltammetry to the speciation and determination of iron(III) and total iron in wines. Analyst 114(5): 643-645.
66. Wang J, Zadeii JM (1986) Stripping voltammetry of thorium based on adsorptive accumulation. Anal Chim Acta 188: 187-194.
67. Fraga ICS, Ohara AK, Farias PAM (2001) Square wave stripping voltammetry of titanium based on adsorptive accumulation of its Hydroxynaphthol Blue (Hnb) complex at the static mercury drop electrode. Anal Lett 34(1): 125-135.
68. Guinón JL, García-Antón (1985) Determination of tin and lead by differential pulse polarography with addition of hyamine-2389. J Anal Chim Acta 177: 225-229.
69. Ferri D, Buldini PL (1981) Differential pulse polarographic determination of traces of iron in solar-grade silicon. Anal Chim Acta 126: 247-251.
70. Lanza P, Taddia M (1984) The differential pulse polarographic determination of chromium in gallium arsenide. Anal Chim Acta 157: 37-44.
71. Lanza P, Ferri D, Buldini PL (1980) Differential-pulse polarographic determination of molybdenum in steel. Analyst 105: 379-385.
72. Ni Y (1998) Simultaneous determination of copper, cadmium and nickel by ratio derivative polarography. Talanta 47(1): 137-142.
73. Carbó AD, Ramos SS, Marco DJY, Moreno MM, Adelantado JVG, et al. (2004) Electrochemical determination of boron in minerals and ceramic materials. Anal Chim Acta 501(1): 103-111.
74. Barrado E, Alvarez V, Pardo R, Batanero PS (1991) Vanadium(V) determination through a catalytic polarographic method. Electroanalysis 3(7): 715-719.
75. Yeom JS, Won MS, Shim YB (1999) Voltammetric determination of the iodide ion with a quinine copper(II) complex modified carbon paste electrode. J Electroanal Chem 463(1): 16-23.