Cathodic adsorptive stripping square-wave voltammetry of the anti-inflammatory drug meloxicam

The adsorptive behavior of the anti-inflammatory drug meloxicam was studied by cyclic, differentia-pulse and square-wave voltammetry on a hanging mercury drop electrode (HMDE). The drug was accumulated at HMDE and a well-defined stripping peak current was obtained at -1.42 V vs. Ag/AgCl (saturated KCl) electrode in acetate buffer solution (pH 5.0). A voltammetric procedure was developed for the determination of meloxicam using square-wave cathodic adsorptive stripping voltammetry (SW-CASV). The optimum working conditions for the determination of the drug were established. The analysis of meloxicam in human plasma was carried out satisfactorily.     

Determination of selenium in sea water by adsorptive cathodic stripping voltammetry

A procedure is presented for determining Se(IV) and total dissolved Se in sea water using cathodic stripping voltammetry in the presence of added copper. Experiments using cyclic voltammetry indicate that the preconcentration step consists in adsorption of a Cu(I)₂Se complex species on the hanging mercury drop electrode. The optimized analytical conditions include a copper concentration of 40 μM and a solution pH of 1.6. Differential pulse modulation is used. Interference caused by organic surface-active substances present in natural waters in eliminated by UV photolysis of the sample. Cadmium interferes with the determination of Se only when present at a concentration 100 times higher than normal. UV photolysis at pH ≈ 8 is used to convert Se(VI), which is the electroactive species. The response is linear for Se concentrations between 0 and 200 nM. The limit of detection is 0.01 nM Se when a deposition time of 15 min is used.     

Ceramic composite electrode for the determination of selenium(IV) by stripping voltammetry

A ceramic composite electrode for the determination of selenium(IV) was manufactured using solgel and screen-printing technologies. This electrode exhibits a higher sensitivity and selectivity in comparison with the other studied carbon-containing electrodes. The effect of the type and amount of graphite powder, modifier, catalyst, and pore-forming agent on the properties of the ceramic composite electrode was investigated. It was found that an increase in the pore size in the electrode reduced the selectivity of selenium(IV) determination. The calibration plot was linear over the range 0.1–20 μg/L at an accumulation time of 10 s. The relative standard deviation for the determination of 1.0 and 0.05 μg/L of selenium(IV) (n = 5) was 3% and 8%, respectively. The detection limit of selenium(IV) was 0.02 μg/L at an accumulation time of 90 s. The results of selenium(IV) determination in natural and mineral waters are presented.     

Cathodic adsorptive stripping voltammetry of 6-thiopurine in absence and presence of some metal ions

Summary Cathodic stripping voltammetry of an adsorbed 6-thiopurine at HMDE was investigated in solutions of varying pH. A rapid and sensitive differential pulse voltammetric method was selected for its trace determination. A method has also been developed for the determination of 6-thiopurine in presence of Cu(II), due to the strong adsorption of the Cu-6-thiopurine complex at the surface of the HMDE and subsequent reduction of the surface-bound complex. A detection limit of 9.9×10^–9 mol/l was achieved in presence of Cu(II) and the slope of the straight line was seven times the slope in absence of Cu(II). Cathodic adsorptive stripping (CAS) voltammetry of 6-thiopurine in presence of Ni(II), Pb(II), Cd(II), and Fe(III) was also investigated. The influence of several operational parameters has been considered. Statistical analysis of the calibration curve data is included.     

Cathodic stripping voltammetry of 2-mercaptoethanol

The behaviour of 2-mercaptoethanol at a hanging mercury drop electrode by cathodic stripping voltammetry (c.s.v.) is studied. The stripping curves are recorded by three scanning modes: rapid-scan direct-current, differential-pulse and fundamental harmonic alternating-current polarography. Under the recommended conditions, pre-electrolysis is done at a potential of 0.0 V vs. Ag/AgCl for 3 min in a medium of pH 6.7 or 8 (Britton-Robinson buffer). Then after 1 min, stripping is done at a scan rate of 6.6 mV s^?1 preferably in the differential-pulse mode. The stripping peak at about ?0.4 V is used to determine 2-mercaptoethanol within the concentration range 3 × 10^?8/2-8 × 10^?7 mol l^?1. Calibration functions are reported; the standard additions method is preferred near the limit of detection. The interferences of several organic compounds are described.     

Automatic adsorptive stripping voltammetry at thin-mercury film electrodes (TMFE)

A procedure for the automated on-line determination of nickel in aquatic samples was developed. It is based upon adsorptive stripping voltammetry of the dimethylglyoxime complex at a thin-mercury film electrode (TMFE) on glassy carbon substrate. The severe problem of reproducibly renewing the TMFE was solved by the choice of an appropriate electrolyte and a special potential program. With the developed procedure automatic on-line nickel determinations are possible over extended periods of time with standard deviations not higher than 5% and down to 1.3 ppb nickel.Dedicated to Professor Dr. W. Fresenius on the occasion of his 80th birthday     

Determination of palladium by adsorptive stripping voltammetry

 Adsorptive accumulation of the Pd(II) complex with dimethylglyoxime was evaluated for stripping voltammetry with respect to different parameters. The sensitivity of the method and the linearity between the peak current and the concentration of Pd(II) depends on the ionic strength, the electrode area, the preconcentration time, the transport rate to the electrode, and the potential scan rate. The most appropriate medium was 0.1 mol/L acetate buffer between pH 3.5 and 4. Using 2 min of preconcentration at a 2.6 mm² electrode and the differential pulse mode, a detection limit of 0.05 μg/L Pd was achieved for liquid samples and 50 ng/g for solid samples. Different aqueous and solid samples were analysed and the recovery from biological and inorganic materials investigated. Received: 29 February 1996/Revised: 29 July 1996/Accepted: 1 August 1996     

Determination of azinphos-methyl by adsorptive stripping voltammetry

A very sensitive electrochemical stripping procedure for azinphos-methyl (Guthion) is reported. Accumulation is achieved by adsorption of the compound on a hanging mercury drop electrode. The adsorptive stripping response was evaluated with respect to accumulation time and potential, concentration dependence, electrolyte and other variables. The determination limit is 0.2 ng ml^?1 after 300 s accumulation and 0.4 ng ml^?1 after 180 s accumulation. The procedure was applied to spiked river water.     

Determination of uranium by adsorptive stripping voltammetry

A voltammetric method for the determination of uranium in natural waters in the concentration range from 0.4 μg 1⁻¹ to 0.2 mg 1⁻¹ is described. The method is based on adsorptive accumulation of the uranium(VI)—pyrocatechol complex on the hanging mercury drop electrode followed by the reduction of the absorbed complex.     

Determination of gallium by adsorptive stripping voltammetry

A procedure for the determination of gallium by differential pulse adsorptive stripping voltammetry (DPADSV), using different complexing agents (ammonium pyrrolidine dithiocarbamate (APDC), pyrocatechol violet (PCV) and diethyldithiocarbamate (DDTC)), has been optimized. The selection of the experimental conditions was made using experimental design methodology. Under these conditions, the calibration was made and the detection limit was determined for each gallium-ligand complex. A robust regression method was applied which allowed the elimination of anomalous points. The detection limit, with α=β=0.05, for gallium-APDC complex was 5.0×10⁻⁸ mol dm⁻³, for gallium-PCV complex was 9.9×10⁻⁹ mol dm⁻³, and the lowest detection limit (1.3×10⁻⁹ mol dm⁻³) was obtained with DDTC. For this reason, DDTC was selected for the determination of the gallium concentration in a certificate sample and in a spiked tap water sample. The linear dynamic range for gallium-APDC complex was from 5.0×10⁻⁸ to 2.7×10⁻⁷ mol dm⁻³, for gallium-PCV complex was from 5.0×10⁻⁹ to 4.8×10⁻⁷ mol dm⁻³, and for gallium-DDTC complex was from 1.0×10⁻⁹ to 2.1×10⁻⁷ mol dm⁻³.     

Determination of trichlorobiphenyl by adsorptive stripping voltammetry

Trichlorobiphenyl is determined in the concentration range 0.004–1 mg l^?1 by adsorptive stripping voltammetry at a hanging mercury drop electrode. Preconcentration is achieved by adsorption at a potential of ?0.40 (V (vs. Ag/AgCl), and desorption at ?1.10 V. Biphenyl interferes with the determination only when present in 5-fold molar amounts compared to trichlorophenyl. The interference of DDT is eliminated by prior treatment of the sample solution with sulphuric acid. The method was applied for the analysis of waste and natural waters, the relative standard deviation being <5%.     

Cathodic adsorptive stripping voltammetry of nickel complexed with hydroxynaphthol blue at a static mercury drop electrode

A new method is described for the determination of Ni based on the cathodic adsorptive stripping of Ni(II) complexed with hydroxynaphthol blue (HNB) at a static mercury drop electrode. Optimal conditions were found to be: accumulation potential -0.50 V (vs. Ag/AgCl); final potential -1.10 V; accumulation time 50 sec; scan rate 200 mV/sec; linear scan mode; filter 0.1 sec; supporting electrolyte acetic acid/acetate (0.25M, pH = 6.0) and concentration of HNB 3.3 x 10(-5)M. The response of the system was found to be linear in a range of Ni concentrations from 25 ppb to the detection limit. The detection limit was found to be 1.7 nM (0.10 ppb) with 2 mins of accumulation time. The effect of various potential interferences (including a variety of cations, anions and organic surfactants) were also studied. With the exception of Co, at less than equimolar concentrations no significant interferences were observed. Al was found to interfere at high concentrations with respect to Ni, but Al concentrations up to 1000 ppb may be masked by sodium citrate or sodium fluoride. The utility of the method is demonstrated by the recovery of Ni in a doped sample of commercial mineral water.     

Indirect determination of surfactants by adsorptive stripping voltammetry

The effect of some anionic, cationic and nonionic surface-active substances on the suppression of adsorptive accumulation of the bis(dimethylglyoximato)nickel(II) complex, Ni(DMG)₂, is described. Competitive adsorption of surfactants can be used to determine surfactants commonly used in commercial detergents. Triton X-100 shows the most pronounced effect on the peak height. The shape of the calibration curve depends on the concentration and on the adsorption potential. Highest sensitivity is obtained when equilibrium between Ni(DMG)² in solution and on the electrode surface is attained rapidly. Under these conditins, the detection limit is 1 μ 1^?1 Triton X-100. Calibrations are linear over 1–2 orders of magnitude.     

Cathodic stripping voltammetric determination of selenium(IV) at a thin-film mercury electrode in a thiocyanate-containing electrolyte

The well-known method for the determination of selenium(IV), which is based on the cathodic stripping voltammetry of copper(I) selenide, has been adapted for application at the thin-film mercury electrode on glassy carbon (TFME). Insufficient reproducibility and sensitivity have been overcome by using a 0.1 mol/L HClO₄ electrolyte solution containing 0.02 mol/L thiocyanate ions. Thiocyanate ions have been found to increase the peak height of the selenium response and shift it to more positive potentials. This behaviour is explained by an adsorption of SCN^– at the interface glassy carbon/Cu₂Se and its action as an electron transfer catalyst between glassy carbon and copper(I) selenide. A 3σ-detection limit of 75 ng/L Se^(IV) has been achieved. The relative standard deviation is 5.2% at 5 μg/L selenium(IV). The influence of cadmium(II), arsenic(III), zinc(II), iron(III) and lead(II) ions on the selenium response has been studied. In case of lead ions, a new signal occurred at more negative potentials than the reduction of Cu₂Se. This signal, which is probably due to the reduction of PbSe, can also be used for the determination of selenium(IV). Received: 13 November 1996 / Revised: 19 December 1996 / Accepted: 24 December 1996     

Trace measurement of dipyridamole by adsorptive stripping voltammetry

A sensitive adsorptive stripping voltammetric method for trace measurement of dipyridamole in alkaline solution is described. The method is based on the adsorptive accumulation of the drug at the hanging mercury drop electrode, followed by linear sweep voltammetric determination. The response is evaluated with respect to percentage of ethanol, preconcentration time and potential, and concentration of NaOH. The detection limit of 1.0 x 10(-9)M is obtained under optimized conditions with a 5-min preconcentration. Applicability to injection, tablets and urine analysis is illustrated.     

Trace measurements of colchicine by adsorptive stripping voltammetry

A highly sensitive voltammetric method for trace measurements of the alkaloid colchicine is described. The method is based on the controlled adsorptive accumulation of the drug at the hanging mercury drop electrode, followed by voltammetric determination of the surface species. The adsorptive stripping response is evaluated with respect to preconcentration time and potential, solution pH, voltammetric waveform and other variables. With a 10-min preconcentration, a detection limit of 1.3 x 10(-10)M is obtained. The relative standard deviation (at the 1 x 10(-7)M level) is 1.1%. Applicability to urine analysis is illustrated.