Adsorptive stripping voltammetry of a fentanyl derivative at a mercury electrode

In a supporting electrolyte of NaOH, a pair of cathodic and anodic peaks of N,N'-diphenyl-N,N'-bis(1-phenylmethyl-4-piperidinyl)-ethanediamide (DBPPE) is found by cyclic voltammetry at a Hg electrode. The cathodic and anodic peak potentials are -1.53 and -1.46 V (vs. Ag/AgCl), respectively. The cathodic peak shows adsorptive characteristics when the concentration of DBPPE is low and the preconcentration time is long. The adsorbed species is most probably the DBPPE neutral molecule. The method for measuring trace amount of DBPPE by adsorptive stripping voltammetry is established and the detection limit can reach 5 x 10(-9)M with a 6-min preconcentration.     

Quantification of terbutaline in pharmaceutical formulation and human serum by adsorptive stripping voltammetry at a glassy carbon electrode

The electrochemical oxidative behavior of terbutaline at the glassy carbon electrode was studied in a series of the Britton-Robinson buffer of pH 2--11. Cyclic and square-wave voltammograms of terbutaline at the pH values 相似文献   

Voltammetric measurement of haloperidol following adsorptive accumulation at glassy-carbon electrodes

A sensitive stripping voltammetric method is reported for trace measurement of the psychotherapeutic drug haloperidol. The method is based on adsorptive preconcentration of haloperidol on the glassy-carbon electrode in an open circuit, followed by medium exchange and voltammetric determination of surface species. Cyclic voltammetry was used to explore the adsorptive behaviour and the results obtained suggest that the adsorption of haloperidol corresponds to the Frumkin-type isotherm. The adsorptive stripping response was evaluated with respect to stripping mode, electrolyte. pH, preconcentration time, concentration dependence, possible interference and other variables. The detection limit was 1.3 x 10(-9)M (10 min preconcentration) and the response was linear. The relative standard deviation (at the 1.3 x 10(-6)M level) was 2.3%. Applicability to a patient's urine sample is illustrated.     

Stripping voltammetric determination of traces of catechol compounds preceded by adsorptive accumulation of metal complexes

Catechol compounds are quantified by controlled adsorptive accumulation of their metal complexes onto a hanging mercury drop electrode followed by stripping voltammetry. By using tin(IV) as a redox marker for quantifying the surface-bound species, selectivity can be improved relative to conventional oxidative methods; dopamine can be quantified in the presence of ascorbic acid. The method allows measurements of micromolar levels of catechol, dopamine, l-dopa, 3,4-dihydroxyphenylacetic acid and caffeic acid. The adsorptive stripping response is evaluated with respect to preconcentration time and potential, tin(IV) and analyte concentrations, stripping mode, reproducibility and possible interferences. Analogously, solochrome violet RS and dimethylglyoxime can be quantified after accumulation of their iron(III) and nickel(II) complexes, respectively. Detection limits are 7×10^?9 M for solochrome violet RS and 5×10^?8 M for caffeic acid (1- and 5-min preconcentration, respectively).     

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 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.     

Determination of folic acid by adsorptive stripping voltammetry at the static mercury drop electrode

Folic acid can be determined at nanomolar concentrations by controlled adsorptive accumulation of folic acid on a static mercury drop electrode held at ?0.3 V vs. Ag/AgCl followed by reduction of the surface species. In 0.1 M sulfuric acid, a cathodic scan gives peaks at ?0.47 v and ?0.75 V vs. Ag/Agcl; the latter peak provides greater sensitivity. Differential-pulse stripping is shown to be superior to normal-pulse and d.c. stripping. After a 5-min preconcentration, the detection limit is about 1 × 10^?10 M folic acid. The adsorptive stripping response is evaluated with respect to concentration dependence, preconcentration time and potential, solution acidity and the presence of gelatin and bromide. The relative standard deviation at the 5 × 10^?8 M level is 1.2%. This method is applied to the determination of folic acid in pharmaceutical tablets.     

Square-wave adsorptive cathodic stripping voltammetric determination of anti-inflammatory indomethacin drug in tablets and human serum at a mercury electrode

Indomethacin is a non-steroidal anti-inflammatory drug possessing anti-pyretic and analgesic properties. A fully validated square-wave adsorptive cathodic stripping voltammetric procedure is described for determination of indomethacin. The procedure was based on the reduction of the C=O double bond of the drug molecule in Britton-Robinson buffer (pH 4) after its preconcentration onto the mercury electrode surface. The optimized conditions of the procedure were: frequency 120 Hz, scan increment 10 mV, pulse amplitude 50 mV, preconcentration potential -0.9 V (vs. Ag/AgCl/KCl(s)) and preconcentration time 90 s. The proposed procedure was successfully applied for determination of the drug in tablets and human serum with good recoveries. The limits of detection in bulk form and human serum were 6.7 x 10(-10) mol L(-1) and 8.1 x 10(-10) mol L(-1), respectively.     

Adsorptive stripping voltammetric properties of fentanyl at Hg electrode

Cyclic voltammetry shows that in a supporting electrolyte of NaOH, fentanyl (FENT) has a pair of cathodic and anodic peaks at Hg electrode. The peak potentials, E(pc) and E(pa), are -1.47 and -1.44 V (vs. Ag/AgCl), respectively. Fentanyl can be adsorbed on Hg surface, so the cathodic peak shows adsorptive properties. The adsorptive characteristics of fentanyl are explored in detail with various methods. The adsorbed species is considered to be fentanyl neutral molecule. The method for measuring trace amount of fentanyl by adsorptive stripping voltammetry is established. Under the optimised condition, the detection limit may reach 5 x 10(-8)M with a 10-min preconcentration.     

Adsorptive behavior and electrochemical determination of the anti-fungal agent ketoconazole

The adsorptive properties and electrochemical behavior of ketoconazole, an oral anti-fungal agent, are demonstrated at a glassy carbon electrode. The adsorption of the compound obeys the Frumkin isotherm with an interaction factor (alpha) of 0.985 and adsorptive coefficient (beta) of 1.98 x 10(6) L mol(-1). The Gibbs energy of adsorption (deltaG) is -3.59 x 10(4) J mol(-1) at 25 degrees C. A very sensitive electroanalytical method has been developed for determination of the drug with a detection limit of 4.0 x 10(-11) mol L(-1). Relationships between stripping current and concentration of ketoconazole were linear in the range 10(-6)-10(-10) mol L(-1) with different preconcentration periods. The method has been used to measure the ketoconazole content of tablets.     

Adsorptive preconcentration for voltammetric measurements of trace levels of zirconium

This paper describes an electrochemical stripping procedure for ultratrace measurements of zirconium, in which preconcentration is achieved by the adsorption of a zirconium-Solochrome Violet RS complex onto a hanging mercury drop electrode. Cyclic voltammetry was used to characterize the interfacial and redox behaviour. For a 10-min preconcentration time, the detection limit found was 2.3 x 10(-10)M. Optimal experimental conditions were found to be use of a stirred acetate buffer (pH 4.6) solution with Solochrome Violet RS concentration 1.5 x 10(-6)M, a preconcentration potential of -0.3 V and linear scan mode. A 60-fold enhancement of the response is obtained following 5-min preconcentration. With preconcentration for 60 sec, calibration plots for zirconium are linear for the 1.1 x 10(-8)-1.1 x 10(-7)M range. The relative standard deviation at 5.5 x 10(-8)M is 1.7%. Possible interferences by surface-active organic materials and other trace metals have been investigated. Zirconium added to a sea-water sample at the 10 ng/ml level was readily determined.     

Differential pulse adsorptive stripping voltammetric determination of dinoseb and dinoterb at a modified electrode.

A sensitive adsorptive stripping voltammetric method for the determination of dinitrophenolic herbicides, dinoseb (DSB) and dinoterb (DTB) at a bare carbon paste electrode (CPE) and a clay modified carbon paste electrode (CMCPE) was developed. A systematic study of various experimental conditions, such as the pH, accumulation variables and composition of a modifier on the adsorptive stripping response, were examined by using differential pulse voltammetry. A significant improvement was observed in the sensitivity by using the present method with CMCPE. When CMCPE was used, a linear response was obtained over the concentration range 2 x 10(-10) to 3 x 10(-7) M and 6 x 10(-10) to 6 x 10(-7) M with lower detection limits of 1 x 10(-10) M and 5.4 x 10(-10) M for dinoseb and dinoterb, respectively, at an accumulation time of 100 s. The interference from other herbicides and ions on the stripping signals of both compounds was also evaluated. The described method was applied to estimate of the dinoseb and dinoterb in environmental samples.     

Determination of secnidazole in urine by adsorptive stripping voltammetry

Cyclic voltammetry was used to explore the adsorption behavior of secnidazole on a hanging mercury drop electrode (HMDE). The effects of various operational parameters on the accumulation behavior of the adsorbed species were tested. Thus, a sensitive stripping voltammetry procedure for the determination of secnidazole with an adsorptive accumulation on the surface of HMDE has been developed. Measurements were taken by differential-pulse voltammetry after determination of the optimum conditions. The linear concentration range was 1 x 10(-8)-1 x 10(-7) s when using a 120 s preconcentration at -0.1 V vs. Ag/AgCl in acetate buffer of pH 4.0. The detection limit of secnidazole was 5 x 10(-9) M. The precision, expressed by the coefficient of variation, was 2.5% (n = 10) at a concentration of 1 x 10(-7) m. The method was successfully applied to the analysis of secnidazole in urine.     

Study on the determination of metronidazole in human serum by adsorptive stripping voltammetry

In Britton-Robinson buffer, metronidazole is preconcentrated on a HMDE at 0.0 V (vs. AgAgCl). An adsorptive stripping peak is observed at -0.62 V. The response is linear from 1 x 10(-8) to 1 x 10(-6)M with 1.5 min accumulation. The method has been successfully applied to the determination of metronidazole in human serum and formulations.     

Cyclopentanone thiosemicarbazone, a new complexing agent for copper determination in biological samples by adsorptive stripping voltammetry.

A selective and sensitive stripping voltammetric method for the determination of trace amounts of copper(II) with cyclopentanone thiosemicarbazone (CPTSC) is presented. The method is based on the adsorptive accumulation of the resulting copper-CPTSC complex on a hanging mercury drop electrode, followed by the stripping voltammetric measurements at the reduction current of the adsorbed complex at -0.37 V vs. Ag/AgCl. The optimal conditions for the stripping analysis of copper include pH 9.3, deposition time of 120 s, and a deposition potential of -0.1 V (vs. Ag/AgCl). The peak current is linearly proportional to the copper concentration over a range 3.14 x 10(-9) M to 1.57 x 10(-6) M with a limit of detection of 1.57 x 10(-9) M. The technique has been applied to the determination of copper in biological samples, like urine and whole blood.     

Determination of trace thorium using catalytic-adsorptive stripping voltammetry of the thorium-cupferron complex

A sensitive stripping voltammetric procedure for trace measurement of thorium, based on the catalytic-adsorptive peak of the thorium-cupferron complex, is reported. Optimal experimental conditions include the use of 1mM BES buffer solution (pH 5.5), containing 20muM cupferron, an accumulation potential of -0.80 V (vs. Ag/AgCl), and a differential pulse potential scan. The resulting stripping procedure offers improved sensitivity over a previous stripping scheme for thorium. The limit of detection after 5 min preconcentration is 50 ng/l. (2 x 10(-10)M), the response is linear up to 8 x 10(-8)M, and the relative standard deviation at the 2.1 x 10(-8)M level is 4.4%. Possible interferences are evaluated.     

Subtractive differential pulse voltammetry following adsorptive accumulation of organic compounds

Subtractive differential pulse voltammetry following adsorptive preconcentration of organic compounds at solid electrodes is described. Different preconcentration periods are used, and the difference between the oxidation (stripping) currents is recorded. Background currents which are independent of the preconcentration period cancel out. Combining the enhanced peak current, due to the preconcentration step, with the background current correction of the subtractive mode, gives improved sensitivity and/or allows the use of shorter preconcentration periods. Chlorpromazine and dopamine have been used as test systems. A detection limit of around 1 x 10(-9)M has been obtained for chlorpromazine with a 10-min preconcentration period. Applicability to clinical samples is illustrated by the determination of chlorpromazine in whole blood and urine.     

Tensammetry with accumulation on the hanging mercury drop electrode : Part 4. The behaviour of oxyethylated alcohols (polyoxyethylene n-alkyl monoethers)

The behaviour of polydispereed oxyethylated alcohols having a well-defined n-alkyl radical is described. Surfactants 6-14, 10-10, 10-14, 18-14, 18-10 and 18-6 (the first number denotes the number of carbon atoms in the n-alkyl radical, and the second one the average number of oxyethylene subunits) were examined. The conditions included 5 or 10 min of adsorptive preconcentration of surfactants at concentrations lower than the c.m.c value. Only negative tensammetric peaks were examined. The relationships between the peak height and the preconcentration potential were investigated for potentials more negative than - 1.0 V vs. SCE. More hydrophilic surfactants (i.e., 6-14, 10-10 and 10-14) form one wide tensammetric peak. The relationship of this peak to the preconcentration potential is simple and is similar to the negative branch of the adsorption isotherm. More hydrophobic surfactants (i.e., 18-6, 18-10 and 18-14) form a narrow peak, caused by the monomer form of the surfactant. If the threshold concentration of surfactants 18-6 and 18-10 is exceeded, a second very narrow peak appears, which is caused by the premicellar form of the surfactant formed at concentrations lower than the c.m.c. The dependences of the peak height on the preconcentration potential for surfactants 18-6, 18-10 and 18-14 are complicated; each plot shows a maximum, but the curves greatly depend on the surfactant concentration, which makes the choice of preconcentration potential difficult. Within the 10-(30-50) μg l^?1 range of surfactant concentration, the plots of peak height vs. surfactant concentration are approximately linear. Results for the lowest concentrations are very imprecise because of strong adsorption of the surfactants on the surface of the cell.     

Adsorptive voltammetry and hydrolysis kinetics of loprazolam mesilate

Loprazolam is determined by square-wave adsorptive stripping voltammetry in 0.04M ammonium chloride at pH 4.0, with an accumulation potential of -0.25 V vs. Ag/AgCl/KCl(s), at which the nitro group is reduced to a hydroxylamine group, with adsorption of the product. Cathodic stripping results in reduction of the azomethine bond of the adsorbed product. With a deposition time of 120 sec the detection limit is 2.5 x 10(-10)M. The relative standard deviation is 1.7% for 5 x 10(-8)M loprazolam (60 sec deposition). Reversible hydrolysis of the azomethine group occurs in sulfuric or hydrochloric acid. The reaction is initially first-order, followed by an apparent second-order reaction. First-order rate constants and half-lives are reported for 0.1-1M sulfuric acid and 0.02M hydrochloric acid media and compared with the values for nitrazepam hydrolysis.     

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.