A lead(II) ion selective electrode via a metal complex of poly(hydroxamic acid)

A new lead(II) electrode has been constructed with poly(hydroxamic acid) (PHXA) as the active material and silicone rubber as the supporting material. The electrode gave near Nerstian response over the concentration range 4 × 10⁻⁵−1 × 10⁻²M lead(II). The detection limit of the electrode is approximately 4 × 10⁻⁶M and the electrode works well in the pH range 4.5–6.0. The response time was 50–120 sec over the whole concentration range and the electrode has a working life of at least 4 weeks. Iron(III) severely poisoned the electrode membrane. Nickel(II) and mercury(II) gave very strong interference compared to copper(II), silver(I), cobalt(II), sodium(I), potassium(I), zinc(II) and cadmium(II) which gave some or little interference. Values determined with atomic absorption (AAS) and a commercial lead(II) electrode were in good agreement with those measured with the lead(II) electrode reported here.     

Determination of Ag(I) with chemically modified carbon paste electrode based on 2,3-dicyano 1,4-naphthoquinone

The utility of carbon paste modified with 2,3-dicyano 1,4-naphthoquinone (CYNQ) for the voltammetric determination of Ag(I) is demonstrated. The method is based on the formation of Ag(I) complex with CYNQ by accumulation from the aqueous solution to the electrode surface without an applied potential. Using the medium exchange technique, the electrode was transferred to another media followed by linear-scan voltammetric measurements. The reduction peak of the Ag(I)-CYNQ complex was observed at +0.22 V (vs. SCE). The silver response is studied with respect to paste composition, pH of the measurement solution, reproducibility, interference and other variables. A detection limit of 5 × 10⁻⁸M was obtained and the calibration curve was linear over the range 1 × 10⁻⁶−8 × 10⁻⁵M.     

Direct determination of sub-nanomolar levels of zinc in sea-water by cathodic stripping voltammetry

A novel technique for the determination of nanomolar levels of zinc in aqueous solution is presented. The zinc complex with ammonium pyrrolidine dithiocarbamate is adsorbed on a hanging mercury-drop electrode and the reduction current of zinc is measured by voltammetry. The detection limit for zinc is 3 × 10⁻¹¹M, with 10-min collection time. A procedure is suggested for the simultaneous determination of Ni and Zn in a single sample.     

Catalytic-adsorptive stripping voltammetric measurements of hydrazines

Hydrazine compounds can be determined by voltammetry, based on their hydrogen catalytic wave in formaldehyde-platinum-sulphuric acid media. Adsorption of the platinum-formazone complex on the hanging mercury drop electrode enhances the sensitivity, allowing convenient measurement of micromolar and submillimolar concentrations of simple hydrazines. The selectivity is better than that of conventional (anodic) measurements of hydrazines, as oxidizable compounds do not interfere. The sensitivity is also greatly improved. The hydrazine response is evaluated with respect to preconcentration time, concentration dependence, platinum and formaldehyde concentrations, reproducibility and other variables. The relative standard deviation (at 2 × 10⁻⁵M) is 1.6%.     

Studies on potentiometric stripping analysis

Theoretical and experimental investigations have been made on the method of potentiometric stripping analysis. By solving Fick's second law of diffusion for the metal in the amalgam, it was found that τ = C⁰_Rl/k[Ox], where τ is the elapsed time, l is the thickness of the mercury film, C⁰_R is the concentration of the metal in the amalgam, [Ox] is the concentration of the oxidant in the solution and k is a constant. Since C⁰_R is proportional to the concentration of that particular ion in the solution under given pre-electrolysis conditions, the relations given by the equation above can all be verified experimentally. The equation of the potential—time curve and the effect of complex formation on the elapsed time were also investigated and discussed. In the absence of complexation reactions in the solution and with proper control of the concentration of the oxidant, the lowest limit of detection for Pb was found to be 10⁻¹²M for a 4-min pre-electrolysis, with dissolved oxygen as oxidant.     

Separation of trans-1,2-cyclohexanediaminetetra-acetic acid chelates of bismuth(III), iron(III) and copper(II) by reversed-phase paired-ion chromatography

Trans-1,2-cyclohexanediaminetetra-acetic acid (DCTA) chelates of bismuth(III), iron(III) and copper(II) have been separated by two techniques using reversed-phase paired-ion chromatography. In one, the chelates in aqueous solution were separated within 20 min on a 6.0 × 300 mm ERC-ODS column with 10⁻²M tetrabutylammonium ion (TBA⁺) in methanoi-water mixture (45:55 v/v) as eluent. In the other, the metal ions in aqueous solution were separated within 10 min by direct injection into an ERC-ODS column with 10⁻²M TBA⁺/10⁻³M DCTA in methanoi-water mixture (40:60 v/v) as eluent.     

Voltammetric study of the interaction of ciprofloxacin-copper with nucleic acids and the determination of nucleic acids

The behavior of the ciprofloxacin (CPFX) complex with copper, Cu(II)L₂, at a mercury electrode has been investigated in borax–boric acid buffer. The adsorption phenomena were observed by linear sweep voltammetry. The mechanism of the electrode reaction was found to be reduction of Cu(II)L₂ adsorbed on the surface of the electrode by an irreversible charge transfer to metal amalgam, Cu(0)(Hg). In the presence of DNA, the formation of the electrochemically non-active complexes Cu(II)L₂–DNA results in the decrease of the equilibrium concentration of Cu(II)L₂ and its peak current. Under the optimum conditions, the decrease of the peak current is proportional to DNA concentration. The linear ranges are 6.67×10⁻⁸ to 1.20×10⁻⁵ g ml⁻¹ for calf thymus DNA (ctDNA), 3.30×10⁻⁸ to 2.33×10⁻⁶ g ml⁻¹ for fish sperm DNA (fsDNA) and 1.0×10⁻⁸ to 1.2×10⁻⁶ g ml⁻¹ for yeast RNA. The detection limits are 5.00×10⁻⁹, 3.00×10⁻⁹ and 2.50×10⁻⁹ g ml⁻¹, respectively. This method exhibits good recovery and high sensitivity.     

Electroreduction and determination of Pipril (Piperacillin) in both aqueous and biological samples

The electrochemical behavior of the relatively new antibacterial antibiotic Pipril (Piperacillin) at the dropping mercury electrode is investigated using both direct current polarography (DCP) and differential pulse polarography (DPP). At the hanging mercury electrode (HMDE), the reduction mechanism has been elucidated using cyclic voltammetric technique in the pH range from 2 to 10. The effect of some metal ions, e.g. Cu(II) and Pb(II) has been also tested. Determination of the drug using adsorptive stripping analysis was assessed in both aqueous and urine samples. The effect of the different experimental parameters affecting the drug determination, e.g. pH, supporting electrolyte nature, accumulation potential, accumulation time and other operational parameters are also mentioned. Detection limits of 5 × 10⁻⁹ and 1 × 10⁻⁸M Pipril in aqueous and urine samples, respectively, are achieved.     

5-[(p-Methyl-phenyl)azo]-8-aminoquinoline as a new reagent for trace determination of nickel by adsorptive cathodic stripping voltammetry

The synthesis of p-MPAQ and the electroanalytical chemical properties of the nickel(II)-p-MPAQ complex are reported in this paper. A sensitive adsorptive cathodic stripping procedure for trace nickel determination was developed. For a 3-min preconcentration time the detection limit is 3.0 × 10⁻¹¹M.     

Cathodic adsorptive stripping voltammetric behaviour of guanine in the presence of copper at the static mercury drop electrode

The cathodic adsorptive electrochemical behavior of guanine in the presence of some metal ions at the static mercury drop electrode was investigated. A 1.0×10⁻³ mol l⁻¹ NaOH or a 2.0×10⁻² mol l⁻¹ Hepes buffer at pH 8.0 solutions were used as supporting electrolytes. The reduction peak potential for guanine was found to be around −0.15 V, which is very close to the mercury reduction wave. A new peak appears at −0.60 V in the presence of copper or at −1.05 V in the presence of zinc. A square wave voltammetric procedure for electroanalytical determination of guanine in 2.0×10⁻² mol l⁻¹ Hepes buffer at pH 8.0 containing 1.6×10⁻⁵ mol l⁻¹of copper ions, was developed. An accumulation potential of −0.15 V during 270 s for the prior adsorption of guanine at the electrode surface was used. The response of the system was found to be linear in the range of guanine concentration from 6.62×10⁻⁸ to 1.32×10⁻⁷ mol l⁻¹ and the detection limit was 7.0×10⁻⁹ mol l⁻¹. The influence of DNA bases such as adenine, cytosine and thymine was also examined. Cyclic voltammetry was used to characterize the interfacial and redox mechanism.     

Simultaneous determination of sulfite and phosphate in wine by means of immobilized enzyme reactions and amperometric detection in a flow-injection system

A flow-injection system is proposed for the simultaneous determination of sulfite and phosphate in wine. A sulfite oxidase immobilized reactor and purine nucleoside phosphorylase-xanthine oxidase co-immobilized reactor are incorporated at fixed positions (parallel configuration) in the flow line, which is based on the splitting of the flow after sample injection and subsequent confluence. A poly(1,2-diaminobenzene)-coated platinum electrode is used as an amperometric detector to detect selectively hydrogen peroxide generated enzymatically in the enzyme reactors, without any interference from oxidizable species and proteins present in wine. Because each channel has a different residence time, two peaks are obtained. The first peak corresponds to sulfite and the second peak to phosphate. The peak current is linearly related to the concentrations of sulfite between 1 × 10⁻⁵ and 2 × 10⁻³M and phosphate between 2 × 10⁻⁵ and 5 × 10⁻³M. The simultaneous determination of sulfite and phosphate in wine can be performed at a rate of 30 samples/hr with satisfactory precision (less than 1.2% RSD) and no pretreatment except for the sample dilution.     

Potentiometric titration of sulphate, sulphite and dithionate mixtures, with use of a lead ion-selective electrode

Simple methods are described for the analysis of sulphate, sulphite and dithionate mixtures by potentiometric titration with lead perchlorate (and use of a lead ion-selective electrode). The error and precision are both about 2–5% for the sulphate concentration range 3 × 10⁻³ −6 × 10⁻⁴M. The sulphur content in fuels derived from refuse was determined by potentiometric titration after bomb-combustion and the results compared favourably with those from the standard BaSO₄ gravimetric method.     

Application of lead film electrode for simultaneous adsorptive stripping voltammetric determination of Ni(II) and Co(II) as their nioxime complexes

An adsorptive stripping voltammetric (AdSV) procedure for simultaneous determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent at an in situ plated lead film electrode was described. The Co(II) signal was enhanced by exploitation of the catalytic process in the presence of nitrite. Ni(II) and Co(II) signals are better separated than in the case of bismuth film electrodes. Calibration graphs for an accumulation time of 120 s are linear from 1 × 10⁻⁹ to 1 × 10⁻⁷ mol L⁻¹ and from 1 × 10⁻¹⁰ to 5 × 10⁻⁹ mol L⁻¹ for Ni(II) and Co(II), respectively. The proposed procedure was applied for Ni(II) and Co(II) determination in water certified reference materials.     

Photometric determination of micro amounts of thiosulphate by means of its cyanolysis with lanthanum(III) as catalyst

Lanthanum(III) has been found to catalyse the reaction of thiosulphate with cyanide. The effects of pH, reaction time and temperature, amount of cyanide and lanthanum, and order of addition of reagents have been investigated. Temperature has little effect in the range 10–30°, but at both 35° and 40° the rate is noticeably faster. Reaction is complete at room temperature in 1.5 hr at pH 9.3–9.6, and in 3 hr at pH 9.1–9.6. The method can be applied to the determination of 1.0 × 10⁻⁵−6.0 × 10⁻⁴M thiosulphate, with a relative standard deviation of 0.3% for 4 × 10⁻⁴M thiosulphate.     

Electrochemical study of carminomycin at solid electrodes

The electrochemical behaviour of carminomycin at carbon-paste, glassy-carbon and composite carbon—polymer electrodes has been compared. Three electroactive sites on the molecule have been identified. Two sites are involved in the oxidation processes, the first corresponding to the hydroquinone structure in the C-6/C-11 positions, the second attributed to the C-4 phenolic function. Applying a negative-going scan allows reduction of the quinone moiety in the C-5/C-12 positions. Both the quinone and hydroquinone functions exhibit quasi-reversible electrochemical reactions in acidic medium, becoming irreversible in alkaline solution. Adsorption phenomena accompany both the oxidation and reduction processes, primarily in neutral and alkaline media. The adsorption can be decreased by using the composite electrode, which is less sensitive to surface phenomena. This working electrode is proposed as the most suitable for the determination of carminomycin at pH 1. A linear calibration plot can be obtained over the range 1 × 10⁻⁶-1 × 10⁻⁴M, with a limit of detection of 6 × 10⁻⁸M.     

Square wave adsorptive stripping voltammetric determination of famotidine in urine

Electrochemical studies of famotidine were carried out using voltammetric techniques: cyclic voltammetry, linear sweep and square wave adsorptive stripping voltammetry. The dependence of the current on pH, buffer concentration, nature of the buffer, and scan rate was investigated. The best results for the determination of famotidine were obtained in MOPS buffer solution at pH 6.7. This electroanalytical procedure enabled to determine famotidine in the concentration range 1 × 10⁻⁹–4 × 10⁻⁸ mol L⁻¹ by linear sweep adsorptive stripping voltammetry (LS AdSV) and 5 × 10⁻¹⁰–6 × 10⁻⁸ mol L⁻¹ by square wave adsorptive stripping voltammetry (SW AdSV). Repeatability, precision and accuracy of the developed methods were checked. The detection and quantification limits were found to be 1.8 × 10⁻¹⁰ and 6.2 × 10⁻¹⁰ mol L⁻¹ for LS AdSV and 4.9 × 10⁻¹¹ and 1.6 × 10⁻¹⁰ mol L⁻¹ for SW AdSV, respectively. The method was applied for the determination of famotidine in urine.     

Polarographic determination of proguanil and chlorhexidine

The method is based on the cathodic wave obtained for chlorhexidine and proguanil in buffered aqueous dimethylformamide media. Concentrations up to 8 × 10⁻⁵ and 6 × 10⁻⁴M, respectively, can be determined. The difference in behaviour at various pH values or in the presence of surface-active agents, is useful for characterization of both biguanides.     

Selective potentiometric determination of Bi(III) with a coated-wire electrode

A bismuth-selective electrode based on the chlorobismuthate(III) salt of Aliquat 336 is described. The electrode gives nearly linear response in the bismuth concentration range 10⁻¹–10⁻⁴M. The optimum solution conditions for operation of the electrode have been determined together with possible interference effects. The application of the electrode to analysis of samples containing large amounts of other metals is illustrated by the determination of bismuth in pharmaceuticals. The electrode is shown to give results by direct potentiometry and the standard-addition method which differ from atomic-absorption results by not more than 2%.     

Simultaneous determination of selenium and lead in whole blood samples by differential pulse polarography

The polarographic reduction of lead in the presence of selenite gives rise to an additional peak corresponding to the reduction of lead (Pb) on adsorbed selenium (Se) on mercury at −0.33 V. The selenium and lead content can be determined using this peak by the addition of a known amount of one of these ions first and then the second ion. The linear domain range of lead is 5.0×10⁻⁷–2.0×10⁻⁵ M and for selenium 5.0×10⁻⁷–1.0×10⁻⁵ M. Using this method 4.90×10⁻⁷ M Se(IV) and 1.47×10⁻⁶ M Pb(II) in a synthetic sample could be determined with a relative error of +2.0% and 1.8%, respectively (n=4). A recovery test after acid digestion for a synthetic sample was 97% for selenium and 96.5% for lead. The method was applied to 1 ml of digested blood, and 328±23 μg l⁻¹ Se(IV) and 850±62 μg l⁻¹ Pb(II) could be determined with a 90% (n=5) confidence interval.     

Indirect determination of chloride and carbonate by reversed flow-injection analysis coupled with atomic-absorption spectrometry and in-line preconcentration by precipitation

Chloride and carbonate are determined indirectly by reversed flow-injection analysis with preconcentration by precipitation. The anions are precipitated in a Tygon tube containing glass beads and connected to an atomic-absorption spectrophotometer, and are then dissolved by suitable reagents. Chloride is precipitated as silver chloride, which is then dissolved with ammonia, sodium thiosulphate or potassium cyanide solution. Carbonate is precipitated as calcium carbonate, which is dissolved with hydrochloric acid. The response of the system has been optimized with respect to concentration, precipitation time, solution flow-rate and other AAS variables. Detection limits are 3 × 10⁻⁷ and 5 × 10⁻⁷M for chloride and carbonate, respectively, with thiosulphate and hydrochloric acid as the dissolution agents.