Differential pulse adsorptive stripping voltammetric determination of nickel and cobalt in high purity aluminium

A sensitive method for the simultaneous determination of trace amounts of nickel and cobalt in pure aluminium has been described using differential pulse adsorptive stripping voltammetry (DPASV) by adsorptive accumulation of the dimethyl glyoxime (DMG) complex on the hanging mercury drop electrode (HMDE). As supporting electrolyte 0.1 mol/l ammonia buffer, pH 9.0, containing ammonium citrate and 5×10^–4 mol/l DMG has been used. The determination limit obtained has been as low as 0.5 g/g for Ni and 0.2 g/g for Co (using about 100 mg sample) with a relative standard deviation of 13% and 22%, respectively.     

Differential pulse voltammetric determination of benznidazole loaded in nanostructured lipid carriers and urine**

Benznidazole (BZN) is the first-choice drug for treating Chagas disease (CD). However, it is not ideal for this purpose as it is highly toxic and has irregular pharmacokinetics due to factors such as its low aqueous solubility. These factors necessitate the development of reliable and effective alternative methods for the analytical determination of BZN in biological and pharmaceutical samples. In this context, we present a new electroanalytical method for quantifying BZN using differential pulse voltammetry (DPV) and a glassy carbon electrode (GCE). This method was applied to urine and a pharmaceutical formulation of BZN incorporated into nanostructured lipid carriers (NLC-BZN). The proposed method provided a linear analytical range of 1.00–10.6 μmol L⁻¹ (R=0.999), with a detection limit of 0.044 μmol L⁻¹ and a quantification limit of 0.13 μmol L⁻¹. The relative standard deviation of the intra-day and inter-day precision was below 2.50 %. Through interference studies, the methodology proved to be selective for BZN, because there was no significant potential interference in any of the samples. The recovery tests showed that the accuracy was within the limits recommended in the literature. Therefore, the developed DPV/GCE method can be successfully applied as an alternative method for detecting BZN in NLC-BZN pharmaceutical formulations and human urine.     

Differential pulse voltammetric determination of trace rotenone using molecularly imprinted polymer microspheres

A new voltammetric method for the determination of rotenone is described. It is based on the reduction of an electroactive derivative of rotenone on the surface of an electrode. Rotenone in water was pre-concentrated using a new type of molecularly imprinted polymer microspheres and can react with hydrazine chloride to produce the electroactive derivative. The experimental conditions were discussed. Under optimum conditions, it was found that the peak potential (Ep) of the derivative of rotenone is ?1.02 V (vs. Ag/AgCl). Using the proposed procedure rotenone can be determined in the range 0.2–400 μg L^?1. The detection limit for rotenone is 0.1 μg L^?1 and the relative standard deviation for 100 μg L^?1 rotenone is 1.99 %. The method was applied to the determination of rotenone in water samples with satisfactory results.     

Differential pulse voltammetric simultaneous determination of noradrenalin and acetaminophen using a hematoxylin biosensor

A highly efficient noradrenalin (NA) biosensor was fabricated on the basis of hematoxylin electrodeposited on a glassy carbon electrode, GCE. The cyclic voltammetric responses of the hematoxylin biosensor at various scan rates, which were obtained in a 0.25 mmol L⁻¹ NA solution, showed the characteristic shape typical of an EC_cat process. The kinetic parameters such as electron transfer coefficient, α, the catalytic electron transfer rate constant, k′, and the standard catalytic electron transfer rate constant, k⁰, for oxidation of NA at the hematoxylin biosensor surface were estimated using cyclic and RDE voltammetry. The peaks of differential pulse voltammetric (DPV) for NA and acetaminophen (AC) oxidation at the hematoxylin biosensor surface were clearly separated from each other when they co-exited in the physiological pH (pH 7.0). It was, therefore, possible to simultaneously determine NA and AC in the samples at a hematoxylin biosensor. Linear calibration curves were obtained for 5.0 × 10⁻¹ to 65.40 μmol L⁻¹ and 65.40-274.20 μmol L⁻¹ of NA, and for 12.00-59.10 μmol L⁻¹ and 59.10-261.70 μmol L⁻¹ of AC. The sensitivities of the biosensor to NA in the absence and presence of AC were found virtually the same, which indicates the fact that the electrocatalytic oxidation processes of NA are independent of AC and, therefore, simultaneous or independent measurements of the two analytes (NA and AC) are possible without any interference. The results of 16 successive measurements show an average voltammetric peak current of 1.13 ± 0.03 μA for an electrolyte solution containing 5.00 μmol L⁻¹ NA. The hematoxylin biosensor has been satisfactorily used for the determination of NA and AC in pharmaceutical formulations. The results obtained, using the biosensor, are in very good agreement with those declared in the label of pharmaceutical inhalation products.     

Differential pulse voltammetric determination of uranium in low concentration streams

A differential pulse voltammetric method has been successfully used for the determination of uranium in low concentration streams of a uranium plant. The method gives a precision of about 13% to 7% in the range of 300 ppb to 15 ppm. The accuracy of the results was ascertained by comparing the values with those obtained by a spectrophotometric method. The method is simple, fast, sensitive, fairly accurate and does not require a preconcentration step.     

Rapid analysis of L-dopa in urine samples using gold nanoelectrode ensembles

This work describes the application of a three-dimensional gold nanoelectrode ensembles (GNEE) for monitoring l-dopa in standards and human urine samples using flow injection analysis (FIA) with amperometric detection. Analytical results reveal that the GNEE exhibited better electrocatalytic activity than a gold disk or glassy carbon electrode. Under optimal conditions of l-dopa analysis at GNEE, the calibration plot has a linear range of 5-300 ng/mL with a coefficient of variation (CV) of 3.1% in pH 7.0 phosphate buffer saline (PBS, pH 7.0). The detection limit was 3.0 ng/mL for FIA. The high precision and sensitivity of GNEE provides a feasible means of directly determining l-dopa in urine samples.     

Sensitive adsorptive stripping voltammetric procedure of Imatinib determination in spiked urine samples using solid lead microelectrode

This article reports for the first time the application of solid lead microelectrode for organic compound determination. The proposed sensor was used for anticancer drug Imatinib quantification by adsorptive stripping voltammetry. Procedure of Imatinib determination was developed utilizing advantages ensured by solid lead microelectrode: reusability and durability for a long period of time and its ecological character as compared to film electrodes. The detection limit of Imatinib determination was calculated to be 1.9 × 10⁻¹⁰ mol L⁻¹. The analytical usability of the developed procedure was confirmed by acceptable recoveries of Imatinib determination in spiked urine samples.     

Differential pulse voltammetric determination of tin in the presence of noble metals

A voltammetric method for the determination of tin is proposed to minimise interferences from noble metals that are commonly encountered with other analytical techniques. Strong distortions of voltammetric peaks are observed in the presence of platinum. On the basis of a full investigation, the formation of an intermediate Sn(II)–Pt mixed chloro-complex at the electrode surface is identified as being responsible for the platinum interference, as it competes with the normal Sn(IV)→Sn(0)_Hg reduction. The use of a higher scan rate prevents the relatively low reaction kinetics and thus gets rid of this interference. No problems are encountered with other noble metals such as Pd, Ir, Re, Rh and Ru when using the modified method, although a baseline subtraction is necessary for the latter one. The proposed method is validated with real Pt–Sn catalysts.     

Voltammetric behavior of some fluorinated quinolone antibacterial agents and their differential pulse voltammetric determination in drug formulations and urine samples using a β-cyclodextrin-modified carbon-paste electrode

A voltammetric determination of ofloxacin (OF), norfloxacin (NF), gatifloxacin (GF), and lomefloxacin (LF) at a β-cyclodextrin-modified carbon-paste electrode (CDMCPE) is described. A large increase in the peak currents was observed in cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of OF, NF, GF, and LF at CDMCPE compared with a bare carbon-paste electrode (CPE). These increases in the peak currents were attributed to the complex formation of the quinone group of the drugs with β-cyclodextrin. CV studies indicate that the process is irreversible and adsorption-controlled. The experimental parameters which influence the peak current responses of OF, NF, GF, and LF were studied. The reduction peak currents of OF, NF, GF, and LF change linearly over the common concentration range from 3.2 × 10⁻⁸ to 2 × 10⁻⁵ M, with a common correlation coefficient and limit of detection of 0.9995 and 2.4 × 10⁻⁸ M, respectively, in pH 4.0 Britton-Robinson (BR) buffer at an accumulation time of 160 s. The interference of metal ions in the peak current response was also studied. The modified electrode exhibited good sensitivity and stability. The proposed method was applied to the determination of OF, NF, GF, and LF in both commercially available drugs and spiked human urine samples. The text was submitted by the authors in English.     

Differential pulse polarography of some benzodiazepines and their determination in urine

A differential pulse polarographic method has been applied to the determination of diazepam, oxazepam, nitrazepam and flurazepam down to 2 x 10(-7)M (0.14 mug/ml). The method can also be used with biological materials such as urine, without prior extraction. Only a 2-ml volume of urine is necessary.     

Differential pulse adsorptive stripping voltammetric determination of methotrexate using a functionalized carbon nanotubes-modified glassy carbon electrode

A glassy carbon electrode (GC) containing multiwalled functionalized carbon nanotubes (MWCNTs) immobilized within a dihexadecylhydrogenphosphate film (DHP) is proposed as a nanostructured platform for determination of methotrexate (MTX) concentration (a drug used in cancer treatment) using differential pulse adsorptive stripping voltammetry (DPAdSV). The voltammograms for a MTX solution using MWCNTs-DHP/GC electrode presented an oxidation peak potential at 0.98 V vs. Ag/AgCl (3.0 mol L^?1 KCl) in a 0.1 mol L^?1 sulphuric acid. The apparent heterogeneous electron transfer rate constant of 0.46 s^?1 was calculated. The recovery area of 2.62×10^?9 mol cm² was also obtained. Under the optimal experimental conditions, the analytical curve was linear in the MTX concentration range from 5.0×10^?8 to 5.0×10^?6 mol L^?1, with a detection limit of 3.3×10^?8 mol L^?1. The MWCNTs-DHP/GC electrode can be easily prepared and was applied for the determination of MTX in pharmaceutical formulations, with results similar to those obtained using a high-performance liquid chromatography comparative method.      

Differential pulse stripping voltammetric determination of heavy metals simultaneously using new polymer modified glassy carbon electrodes

Seven novel polymer modified glassy carbon electrodes have been developed for the analysis of metals of zinc, cadmium, lead, arsenic and copper in formulated samples of waters and industrial wastewater samples by differential pulse stripping voltammetry. Very good responses have been observed for all the metals with all the modified electrodes employed. However, the poly(3,4-ethylenedioxythiophene) modified electrode has resulted in very low detection limits. An independent atomic absorption spectroscopic analysis of the industrial wastewater sample was carried out and the results are compared.     

Differential pulse polarographic determination of thiol flotation collectors and sulphide in waters

Thiol collectors and sulphide can be determined together by differential pulse polarography. Ethyl xanthate, diethyl dithiophosphate, and diphenyl dithiophosphate have been determined in concentrations from 10 muM to 2 mM, and sulphide from 1 muM to 0.5 mM. The method is reliable and rapid; however, the exact behaviour of the thiol collectors must be known since the pattern of current peaks changes as the concentration increases. This method has been used in the study of sulphide mineral flotation and could be utilized at full-scale flotation plants.     

Differential pulse polarographic determination of inorganic and organic arsenic in natural waters

Summary As(III), As(V) and organic arsenic in water are determined by differential pulse polarography. As (III) is directly determined in 2M HCl as supporting electrolyte. Total inorganic arsenic [As (III) + As(V)] is measured after reduction of electro-inactive As(V) with sodium sulphite. Total arsenic is determined after oxidative treatment of the water residue with potassium permanganate and magnesium nitrate, and reduction of arsenic with sodium sulphite. Organic arsenic is evaluated by difference. The efficiency of the whole procedure is 78–80% and its detection limit is 1g/l. The relative standard deviation is better than ±1.5% at 50g/l. Interferences due to heavy metals are overcome by removing them by anionexchange or pre-electrolysis with a mercury cathode.

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Differential-puls-polarograpbische Bestimmung von anorganischem und organischem Arsen in natürlichen Wässern

Zusammenfassung As (III), As(V) und organisches Arsen in Wässern wurden differentialpuls-polarographisch bestimmt. As (III) wurde direkt in 2 M HCl als Trägerelektrolyt bestimmt. Das anorganische Gesamtarsen [As(III) und As(V)] wurde nach Reduktion des elektro-inaktiven As(V) mit Natriumsulfit gemessen. Nach der oxydativen Behandlung des Wasserrückstandes mit KMnO₄ und Magnesiumnitrat und nach Reduktion des Arsens mit Natriumsulfit wurde das Gesamtarsen bestimmt, und das organisch gebundene Arsen durch Differenzbildung ermittelt. Die Ausbeute des gesamten Verfahrens beträgt 78–80%, seine Erfassungsgrenze 1g/l Die relative Standardabweichung ist besser als ±1,5% bei 50g/l. Störungen durch Schwermetalle werden entweder durch deren Entfernung mittels Anionen-austauscher oder durch vorhergehende Elektrolyse mit einer Quecksilberelektrode beseitigt.

     

Differential pulse cathodic stripping adsorption voltammetric determination of trace amounts of lead using factorial design for optimization

A sensitive cathodic stripping voltammetric method is developed for determination of lead(II), with adsorptive collection of complexes with Pyrogallol red (PGR) on to a hanging mercury drop electrode. After accumulation of the complex at −0.80 V vs. Ag/AgCl reference electrode, the potential is scanned in a negative direction from −0.20 to −0.50 V with differential pulse method. Then the reduction peak current for the lead(II)-PGR complex is measured at −0.39 V. The influence of reagent and instrumental variables was completely studied by factorial design analysis. The optimum analytical conditions for the determination of lead(II) were established. Under optimum conditions, lead(II) determined in the range of 0.1-30.0 ng ml⁻¹ with a limit of detection of 0.06 ng ml⁻¹. The method is successfully applied to determination of lead(II) in water sample.     

Optical molecular fluorescence determination of ultra-trace beryllium in occupational and environmental samples using highly alkaline conditions

Exposures to beryllium (Be), even at extremely low levels, can cause severe health effects in a percentage of those exposed; consequently, occupational exposure limits (OELs) promulgated for this element are the lowest established for any element. This work describes the advantages of using highly alkaline dye solutions for determination of Be in occupational hygiene and environmental samples by means of an optical molecular fluorescence technique after sample extraction in 1–3% (w?w^?1) aqueous ammonium bifluoride (NH₄HF₂). Improved attributes include the ability to further enhance the detection limits of Be in extraction solutions of high acidity with minimal dilution, which is particularly beneficial when NH₄HF₂ solutions of higher concentration are used for extraction of Be from soil samples. Significant improvements in Be method detection limits (MDLs) are obtained at levels manyfold below those reported previously for this methodology. Notably, MDLs for Be of <0.01 ng L^?1 /0.1 ng per sample have been attained, which are superior to MDLs routinely reported for this element by means of the most widely used ultra-trace elemental measurement technique, inductively coupled plasma mass spectrometry (ICP-MS). Very low MDLs for Be are essential in consideration of reductions in OELs for this element in workplace air by health organisations and regulatory agencies in the USA and internationally. Applications of enhanced Be measurements to air filter samples, surface wipe samples, soils and newly designed occupational air sampler inserts are illustrated.     

Differential pulse polarography of cadmium-and lead-urate and adsorptive stripping voltammetric determination of uric acid

The complex formation between uric acid and zinc, cadmium and lead ions has been investigated using differential pulse polarography in 0.01M NaNO(3). It is found that the complexes formed by Cd(II) and Pb(II) ions with uric acid have the stoichiometry of 1:2 and the logarithmic values of the apparent stability constant are 9.47 and 11.7, respectively. On the other hand, zinc(II) ions do not give any indication of complexation with uric acid. A sensitive voltammetric method is developed for the quantitative determination of uric acid. This method is based on controlled adsorptive preconcentration of uric acid on the hanging mercury drop electrode (HMDE), followed by tracing the voltammogram in the cathodic going potential scan. The modes used are direct current stripping voltammetry (DCSV) and differential pulse stripping voltammetry (DPSV). The detection limits found were 8 x 10(-9)M (quiescent period 15 sec) by DPSV and 1.6 x 10(-8)M by DCSV.     

A direct differential pulse anodic stripping voltammetric method for the determination of thallium in natural waters

A dual direct method for the ultratrace determination of thallium in natural waters by differential pulse anodic stripping voltamrnetry (d.p.a.s.v.) is presented. D.p.a.s.v. at the hanging mercury drop electrode and at the mercury film electrode is used in the concentration ranges 0.5–100 μg Tl l^-1, and 0.01–10 μg Tl l^-1, respectively. Quantification is aided by the technique of standard additions. The response of the method is optimized for typical natural surface water matrices. An intercomparison of thalium determinations performed by the two anodic stripping methods and electrothermal-atomization atomic absorption spectrometry on normal and thallium-spiked surface water samples demonstrates equivalent accuracy within the range where atomic absorption is applicable. The method appears free from serious interferences.