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.     

Trace measurements of tetracyclines using adsorptive stripping voltammetry

The surface-active properties of tetracycline antibiotics are exploited for developing a sensitive adsorptive stripping method for trace measurements of these compounds. Controlled interfacial accumulation at the h.m.d.e. permits convenient quantitation at the submicromolar and nanomolar concentration levels. With 210 s accumulation, the method provides 28, 27, 26 and 23 signal enhancements for tetracycline hydrochloride, oxytetracycline, chlortetracycline and doxycycline, respectively. The adsorptive stripping response is evaluated with respect to accumulation time and potential, stripping mode, concentration dependence, electrolyte and pH, and other variables. Detection limits are 6 × 10⁻¹⁰ M for doxycycline, 1 × 10⁻⁹ M for oxytetracycline and chlortetracycline, and 2 × 10⁻⁹ M for tetracycline hydrochloride with 300 s accumulation. The reproducibility of the determination (at the 1 × 10⁻⁷ M level) expressed in terms of relative standard deviation, ranges from 0.8 to 2.0%.     

Trace measurements of the antineoplastic agent methotrexate by adsorptive stripping voltammetry

An extremely sensitive voltammetric method is presented for trace measurement of the cancer chemotherapy drug methotrexate. The method is based on controlled adsorptive preconcentration of methotrexate on the hanging mercury-drop electrode, followed by voltammetric determination of the surface species. Cyclic voltammetry was used to explore the interfacial behaviour. The adsorptive stripping response was evaluated with respect to preconcentration time and potential, pH, concentration dependence, stripping mode, possible interferences, and other variables. The detection limit found was 2 x 10(-9)M (5-min preconcentration), the response was linear, and the relative standard deviation (at the 1.6 x 10(-7)M level) 2.2%. Sensitive adsorptive stripping measurements were also obtained by use of a carbon-paste disk electrode. Applicability to urine analysis is illustrated.     

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 determination of molybdenum by adsorptive cathodic stripping voltammetry

Molybdenum is determined by adsorptive cathodic stripping voltammetry in 0.15 M nitric acid solution containing 15 μM 2′,3,4′,5,7-pentahydroxyflavone (morin) as a ligand. In this medium, molybdenum is preconcentrated on a hanging mercury drop electrode and stripped cathodically in square-wave voltammetry mode, with a peak potential of -350 mV vs. Ag/AgCl (saturated KCl). The effect of various parameters (ligand concentration, supporting electrolyte composition, accumulation potential and collection time) on the sensitivity and linear range of the calibration curve are discussed. With controlled accumulation for 1 min, the detection limit (3σ) was 0.45 ng ml^?1 molybdenum and the calibration curve is linear up to 70 ng ml^?1. The procedure is applied to the determination of molybdenum in real samples with satisfactory results.     

Trace determination of yttrium and some heavy rare-earths by adsorptive stripping voltammetry

The interfacial and redox behaviour of rare-earth chelates with Solochrome Violet RS are exploited for developing a sensitive adsorptive stripping procedure. Yttrium and heavy rare earths such as dysprosium, holmium and ytterbrium can thus be measured at ng ml levels and below, by controlled adsorptive accumulation of the metal chelate at the hanging mercury drop electrode, followed by voltammetric measurement of the surface species. With a 3-min preconcentration time, the detection limit ranges from 5 x 10(-10) to 1.4 x 10(-9)M. The relative standard deviation at the 7 ng ml level ranges from 4 to 7%. A separation method is required to differentiate between the individual rare-earth metals.     

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 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 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%.     

Highly sensitive and selective measurements of cobalt by catalytic adsorptive cathodic stripping voltammetry

A very sensitive and selective catalytic adsorptive cathodic stripping procedure for trace measurements of cobalt is presented. The method is based on adsorptive accumulation of the cobalt-MTB (methyl thymol blue) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by nitrite. The optimum conditions for the analysis of cobalt include pH 9.0 (ammonia buffer), 2.0 μM methyl thymol blue, 0.8 M sodium nitrite and an accumulation potential of −0.5 V (versus Ag/AgCl). The peak current is proportional to the concentration of cobalt over the entire concentration range tested (0.02–500 ng ml⁻¹) with a detection limit of 0.005 ng ml⁻¹ for an accumulation time of 60 s. The method was applied to determination of cobalt in a mineral water sample and some analytical grade salts with satisfactory results.     

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.     

Trace metal speciation by adsorptive stripping voltammetry of metal chelates of solochrome violet RS

Adsorptive stripping voltammetry has become one of the most sensitive methods for trace metal determinations. The growing application of the method to natural water systems prompted an investigation into the fraction of the metal concentration that contributes to the adsorptive stripping response. Recent procedures for trace measurement of iron, titanium and gallium, based on chelation with solochrome violet RS (SVRS) are coupled to systematic ligand competition experiments. Tannic acid, EDTA, NTA, glycine, cysteine, carbonate and chloride ions are used as model natural ligands. It is shown that adsorptive stripping voltammetry measures the free ion and metal displaced from complexes by the “analytical” ligand. The exact fraction of the metal measured thus depends on the thermodynamic stability of the metal-SVRS chelate (compared to that of natural complexes), and on the relative concentrations of the competing ligands. The method offers possible distinction between metal complexes, based on their thermodynamic stabilities. The use ofa large excess of the “analytical” ligand can lead to measurement of the total metal content. Implications of these results relative to the use of this procedure for studying the speciation of trace elements in natural waters are discussed.     

Ultrasensitive and selective measurements of tin by adsorptive stripping voltammetry of the tin-tropolone complex

Trace levels of tin can be determined by voltammetry after controlled adsorptive preconcentration of the tin-tropolone complex on a hanging mercury drop electrode. The resulting adsorptive stripping procedure offers better sensitivity and selectivity than conventional stripping methods for tin. Optimal conditions include 4 x 10(-6)M tropolone in a stirred acetate buffer (pH 4.0), a preconcentration potential of -0.40 V, and differential-pulse stripping. For an 8-min preconcentration period, the detection limit is 2.3 x 10(-10)M (28 ng/l.). Linear calibration plots of i(p)vs. C are obtained at low concentrations, with linear plots of 1/i(p)vs. 1/C at high concentrations. The relative standard deviation (at the 6-mug/1. level) is 2.6%. The response is not affected by the presence of lead, cadmium, indium and thallium, which commonly interfere severely in analogous anodic stripping measurements. Results are reported for river and orange-juice samples.     

Cathodic stripping voltammetry and adsorptive stripping voltammetry of selenium(IV)

Cathodic stripping voltammetry of selenium(IV) in 0.1 M hydrochloric acid media yielded a nonlinear calibration graph for the concentration range 10^?9?10^?8 M. In this concentration range, adsorptive stripping voltammetry based on adsorption of the selenium/3,3′-diaminobenzidine complex on the surface of the hanging mercury drop electrode at the deposition potential of +0.05 V (vs. SCE) is more convenient. A linear calibration graph is obtained for selenium concentrations of 3×10^?9?3×10?8 M, with an accumulation time of 300 s.     

Trace analysis by anodic stripping voltammetry

Summary An anodic stripping voltammetric method for the determination of zinc in silicates is described and discussed. The method is sensitive and is not affected by interferences resulting from varying sample composition.

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Zusammenfassung Ein Verfahren zur Bestimmung von Zink in Silicaten mit Hilfe der anodischen Amalgamvoltammetrie wird beschrieben und diskutiert. Das Verfahren ist empfindlich und wird durch verschiedenartige Zusammensetzung der Probe nicht beeinflußt.

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Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.

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This work was performed under the sponsorship of the U.S.National Bureau of Standards. Reproduction of this article, with the customary credit to the source, is permitted.     

Determination of alprazolam in serum by adsorptive stripping voltammetry

The surface-active properties of alprazolam at a hanging mercury drop electrode allow their sensitive determination by differential-pulse adsorptive stripping voltammetry. Detection limits are 0.07 ng/ml for accumulation in water (accumulation time 240 s) and 0.3 ng/ml for accumulation in serum extract (accumulation time 30 s). Coefficients of variation at 5 ng/ml (10 determinations) were typically <2%.