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.     

Ultra trace analysis of molybdenum by differential pulse polarography and adsorptive stripping voltammetry in the presence of 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone

Summary Different polarographic and voltammetric techniques for the determination of molybdenum at the trace level have been investigated. As a result, a new high-sensitivity procedure for the determination of molybdenum by adsorptive stripping voltammetry was developed. The method is based on the reaction of molybdenum(VI) with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid) to produce a complex which is absorbed onto mercury at –0.20 V (vs. Ag/AgCl, 3 mol/l KCl) from pH 2.7 solution. The cathodic stripping peak at –0.62 V can be used to determine molybdenum with a detection limit of 0.02 ng/ml after 5 min deposition time. The relative standard deviation for the determination of 0.1 ng/ml Mo after 5 min stirred collection was 6.6%. Interference from various inorganic ions and organic substances are reported. The method was applied to the determination of molybdenum traces in waters; interfering organic substances in polluted waters were destroyed by oxidative digestion in a microwave oven.     

Adsorptive stripping measurements of germanium(IV) in the presence of pyrogallol

The adsorptive stripping voltammetric determination of germanium(IV) based on the adsorptive accumulation of the germanium(IV)-pyrogallol complex on a hanging mercury drop electrode is reported. The reduction current of the adsorbed germanium complex is measured by differential-pulse cathodic stripping voltammetry. The peak potential is at -0.42 V vs. Ag AgCl (saturated KCL). The effects of various parameters (ligand concentration, supporting electrolytic composition and concentration, accumulation potential and collection time) on the response are discussed. With controlled accumulation for 3 min, the detection limit is 1.2 x 10(-9) M germanium. The relative standard deviation (at 1.2 x 10(-8) M germanium) is 3.6%. Possible interferences are evaluated. The applicability of the method to the determination of germanium(IV) in ore samples was also successfully carried out.     

Capillary electrophoretic determination of phosphate based on the formation of a Keggin-type [PMo12O40]3- complex.

Based on the formation of a Keggin-type [PMo12O40]3- complex, a sensitive capillary electrophoresis (CE) method was developed for the determination of P(V) with direct UV detection at 220 nm. A mixture of alpha- and beta-Keggin-type [PMo12O40]3- complexes was readily formed in a sample solution consisting of a trace amount of P(V), 2.5 mM Mo(VI), 0.050 M p-C6H3(CH3)-2-SO3H (XSA), and 60% v/v CH3CN. When a 0.05 M HCl and 60% v/v CH3CN solution was used as a migration electrolyte, the Keggin complexes exhibited a sharp and well-defined peak in the electropherogram. The peak area was linearly dependent on the P(V) concentration in the range of 5 x 10(-7)-5 x 10(-5) M; a detection limit of 1 x 10(-7) M was achieved. In comparison with indirect UV detection, the direct UV detection is about ten times more sensitive, because the Keggin complexes possess high molar absorptivities. The developed CE method was applied to the determination of P(V) in river water, and the results were in good agreement with those obtained by ion chromatography (IC) and colorimetry (COL) based on the formation of mixed-valence heteropoly blue species.     

Simultaneous capillary electrophoretic separation and detection of P(V) and As(V) As heteropoly-blue complexes

A capillary electrophoretic (CE) method was developed for the simultaneous determination of P(V) and As(V). A Mo(VI)-ascorbic acid reagent reacted with a mixture of trace amounts of P(V) and As(V) to form the corresponding heteropoly-blue complexes in 0.05 M acetate buffer (pH 3.5). When 0.05 M malonate buffer was used as a migration buffer, the peaks due to their migrations were well separated in the electropherogram, and the pre-column complex-formation reaction was applied to the simultaneous CE determination of P(V) and As(V) with direct UV detection at 220 nm. With the proposed method, the calibration curves were linear in the concentration range of 5 x 10(-7) - 1 x 10(-4) M, with a detection limit of 1 x 10(-7) M (a signal-to-noise ratio of 3). Interference from foreign ions was also discussed.     

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.     

A new sensitive method for the spectrophotometric determination of molybdenum using 3-hydroxy-2-(2'-thienyl)-4H-chromen-4-one

A spectrophotometric method has been developed for the determination of Molybdenum (VI) using 3-hydroxy-2-(2'-thienyl)-4H-chromen-4-one as a complexing agent. The complex formed was dissolved in water in the presence of Triton X-100 and exhibits an absorption maximum at 410 nm. A large number of metal ions like Co(II), Ni(II), Mn(II), Cr(III), Zn(II), Cu(II), Hg(II), Bi(III), Fe(II), Fe(III), Zr(IV), V(V) can be tolerated at an appreciable concentrations. Molar absorptivity and Sandell's sensitivity of the method is 2.80 x 10(5) l mol-1cm-1 and 3.42 x 10(-4) micrograms cm-2, respectively. Beer's law is obeyed in the concentration range of 0.01-0.4 ppm Mo(VI). Aliquots containing 0.2 ppm of Mo(VI) give a mean absorbance of 0.56 with a relative standard deviation of 1.3%.     

Use of N-benzyl-2-naphthohydroxamic acid as a highly selective reagent for solvent extraction and spectrophotometric determination of vanadium(V)

N-Benzyl-2-naphthohydroxamic acid extracts vanadium(V) selectively and quantitatively into chloroform from 2-8.5M hydrochloric acid in the presence of Mo(VI), Zr(IV) and Ce(IV). The extraction takes place quickly and gives a stable reddish-violet extract which shows an absorption maximum at 505 nm with molar absorptivity of (5.34 +/- 0.05) x 10(3) 1.mole(-1).cm(-1). The optimum range for the determination is 2.2-7.4 ppm of vanadium(V) in the final solution. The method has been used for the determination of vanadium in steels.     

Adsorptive stripping voltammetric behaviour of copper complexes of some heterocyclic azo compounds

Controlled adsorptive accumulation of copper complexed with TAN, TAC, TAR and TAM (heterocyclic azo-compounds) on a static mercury drop electrode provides the basis for the direct stripping measurement of this element in the nanomolar concentration level. The ligand TAN exhibited great sensitivity and better separation of the peak current of the ligand in relation to the complex. The reduction current of adsorbed complex ions of copper is measured by linear scan cathodic stripping voltammetry, preceded by a period of accumulation of a few minutes. The peak potential is at approximately -0.37 V vs. Ag/AgCl. Optimal experimental parameters were found to be a TAN concentration of 1 x 10(-5)M, an accumulation potential of -0.22 V, and a solution pH of 3.7 (acetate buffer). The detection limit is 0.8nM after a 5-min accumulation with a stirred solution, and the response is linear up to 50 mug/l. Many common cations and anions do not interfere in the determination of copper. The interference of titanium is eliminated by addition of fluoride ion. Results are reported for a fresh water sample.     

Electroreduction of molybdenum(VI) at a prehydrogenated platinum electrode

The use of hydrogenated platinum electrodes allows observation of the electroreduction of some oxygenated ions, which is otherwise masked by the reduction of the hydrogen ion. The present paper deals with the reduction of molybdenum(VI) at a prehydrogenated platinum electrode in acid solutions. The experimental conditions for the electrode hydrogenation process are the following: 90 min at a cathodic current density of about 7 A/cm(2) for microelectrodes with an area of 0.02-0.03 cm(2); about 120 min at a current density of 1.5-2 A/cm(2) for microelectrodes with an area of 0.25-0.35 cm(2). The reduction of molybdenum(VI) in 0.8-1.6M H(2)SO(4) occurs in two consecutive steps: the more cathodic wave [Mo(V) to Mo(III)] is for the most part masked by the reduction of the solvent; the less cathodic wave [Mo(VI) to Mo(V)] takes place at E(1 2 ) values of about +0.07 V, is well shaped, diffusion-controlled and usable for the determination of molybdenum down to 4 x 10(-5)M or 6 x 10(-5)M if a rotating disk electrode is used. Interferences from diverse ions have been studied. A generalization of the effect of electrode hydrogenation on the reduction of those oxygenated ions so far studied [i.e., vanadium(IV), uranium(VI) and molybdenum(VI)] is presented.     

Determination of molybdenum in the presence of 2-(2-benzothiazolylazo)-p-cresol by catalytic-adsorptive stripping voltammetry

The adsorptive collection of the molybdenum (VI) complexed with 2-(2-benzothiazolylazo)-p-cresol (BTAC) coupled with the catalytic current of the adsorbed complex at a static mercury drop electrode yields an ultrasensitive voltammetric procedure for the determination of molybdenum. Optimal experimental conditions were: a stirred acetate buffer 0.2 M (pH 3.5) as supporting electrolyte, a BTAC concentration of 1.0 x 10(-6) M as ligand, and a concentration of 0.1 M potassium nitrate as the oxidizing agent. In addition, a preconcentration potential of -0.080 V vs Ag/AgCl (3 M KCl), equilibration time of 15 s, a frequency of 30 Hz, a scan increment of 2 mV, a pulse amplitude of 0.050 mV, and a drop area of 0.032 cm2 were used. The cyclic voltammogram was recorded using a staircase wave with a scan rate of 100 mV/s. The forward scan starts at the initial potential of -0.080 V and is reversed at -0.90 V. Using the catalytic current at approximately -0.55 V the response to the Mo(VI) was found to be linear over a concentration range of 1.0-10.0 microg/L. The limit of detection is as low as 6.2 x 10(-10) M with 4 min of preconcentration time. The possible interference of other trace ions was investigated. The merits of this procedure are demonstrated using of reference samples.     

Voltammetric determination of phosphonate ion as a heteropoly complex

A simple voltammetric method for the determination of phosphonate ion is described. A 12-molybdodiphosphonate complex is formed in a 50mM Mo(VI)-0.5M HCl-70% (v/v) CH(3)CN system containing phosphonate ion. The yellow heteropolyanion undergoes apparent two-step reductions at a glassy carbon electrode. The voltammetric reduction currents depend linearly on the phosphonate concentration in the range 1 x 10(-5)-1 x 10(-3)M.     

Simultaneous determination of phosphonate, phosphate, and diphosphate by capillary electrophoresis using in-capillary complexation with Mo(VI)

This study describes the simultaneous determination of phosphonate, phosphate, and diphosphate by CE with direct UV detection, based on in-capillary complexation with Mo(VI). When a mixture of phosphonate, phosphate, and diphosphate was injected into a capillary containing 3.0 mM Mo(VI), 0.05 M malonate buffer (pH 3.0) and 45% v/v CH3CN, three well-defined peaks, due to the migration of the corresponding polyoxomolybdate anions, were separated. The respective calibration graphs were linear in the concentration range of 2 x 10(-6)-2 x 10(-4) M for phosphonate, 1 x 10(-6)-5 x 10(-5) M for phosphate, and 1 x 10(-6)-2 x 10(-4) M for diphosphate; the correlation coefficients were better than 0.9990. The present CE method is successfully applied to the simultaneous determination of phosphonate, phosphate, and diphosphate in tap water.     

Simultaneous voltammetric determination of molybdenum and copper by adsorption cathodic differential pulse stripping method using a principal component artificial neural network

An adsorption differential pulse stripping method for the simultaneous determination of molybdenum and copper based on the formation of their complexes with cupferron (benzene, N-hydroxy-N-nitroso) is proposed. The optimum experimental conditions were obtained 0.010 mM cupferron, pH 3.0, accumulation potential of -0.15 V versus Ag/AgCl, accumulation time of 60 s, scan rate of 10 mV s(-1) and pulse height of 50 mV. Molybdenum and copper peak currents were observed at -0.16 and +0.02 V, respectively. A principal component artificial neural network (PC-ANN) was utilized for the analysis of the voltammogram data. A three layer back-propagation network was used with sigmoidal transfer function for the hidden and the output layers. The linear dynamic ranges were 5.0-60.0 and 0.1-20.0 ng ml(-1) for Cu(II) and Mo(VI), respectively. The detection limit was 0.06 ng ml(-1) for Mo(VI) and 0.20 ng ml(-1) for Cu(II). The capability of the method for the analysis of real samples was evaluated by the determination of molybdenum and copper in river water, tap water, and alloy.     

Sensitive Differential Pulse Polarographic Determination of Molybdenum Using The New Catalytic System Mo(VI)‐Phenantroline‐Chlorate

It was found that in acidic chloride media the complex of Mo(VI) with 1,10‐phenantroline induces catalytic reduction of KClO₃. This catalytic effect can be utilized for sensitive differential pulse polarographic determination of Mo(VI) with a low detection limit of 2.9×10^?11 M (2.8 ng/L). The optimal Mo(VI) response was obtained at pH 2.8, in the presence of (6–12)×10^?5 M 1,10‐phenantroline and 2×10^?2 M KClO₃. The sensitivity was 1.73 nA/nM and the catalytic response was linear up to 7.5×10^?7 M Mo (VI). The interferences from inorganic ions and surface‐active substances were investigated. The results of the determination of Mo(VI) in CRM water sample showed good reproducibility (R.S.D. for standard solution is below 1.2% and for water samples is 8.9%) and accuracy of the elaborated catalytic polarographic method.     

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.     

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   

Capillary electrophoretic determination of Ga(III) based on the formation of a heteropolyoxomolybdate complex

A novel capillary electrophoretic (CE) method was developed for the determination of Ga(III). The so-called Anderson-type [GaMo6O24H6]3- complex was readily formed by the reaction of Mo(VI) with Ga(III) in 0.050 M monochloroacetate buffer (pH 2.0) and the precolumn complex-formation reaction was applied to the CE determination of Ga(III) with direct UV detection at 240 nm. The peak area was linearly dependent on the concentration of Ga(III) in the range of 5.0 x 10(-7)-5.0 x 10(-5) M. Owing to the high molar absorptivity of the Anderson anion, a detection limit of 2.0 x 10(-7) M (signal-to-noise ratio=3) was achieved. The advantage of the present method is that the presence of large excesses of Al(III) and In(III) does not cause interference.     

Square wave adsorptive stripping voltammetry of molybdenum(VI) in continuous flow at a wall-jet mercury film electrode sensor

An adsorptive stripping voltammetry method for the determination of traces of molybdenum(VI) in flowing solution at a wall-jet electrode sensor has been developed. After adsorption of a molybdenum complex on a wall-jet mercury film electrode, the complex is reduced by a square wave scan. More satisfactory results were obtained using 8-hydroxyquinoline as a complexing agent in nitrate medium than using Toluidine Blue in oxalic acid. Enhanced sensitivity was achieved by optimizing adsorption time and square wave parameter values. The detection limit of Mo(VI) was found to be at the nanomolar level. Interference of some other metallic species in the determination of nanomolar Mo(VI) was also investigated: Cu(II), Zn(II), Mn(II) do not interfere at 10 muM, whereas 1 muM FeEDTA(-) causes an increase in peak current. This iron interference was removed effectively with citric acid.     

Adsorptive stripping voltammetric determination of traces of molybdenum in natural water in the presence ofα-benzoinoxime

The electrochemical behavior of the molybdenum complex of -benzoinoxime was investigated using cyclic voltammetry and linear scan voltammetry, after adsorptive accumulation of the complex onto a hanging mercury drop electrode (HMDE). The signal corresponds to the reduction of molybdenum in the complex adsorbed at the HMDE surface. Under optimal conditions, the adsorptive stripping voltammetric procedure gave an extremely low detection limit of 0.1 nM (9.6ng/l) Mo(VI) following stirred accumulation for 5 min at 0.0 V (vs. Ag/AgCl). The reduction cur rent-[Mo(VI)] relationships were linear up to 25 and 100 nM. Repetitive determinations of 10 nM solutions gave relative standard deviations of 2.2 and 3.5%, for 1 and 5-min accumulation periods, respectively. Most of the ions investigated did not interfere with the determination of molybdenum, except for tungsten. Excellent selectivity against copper was observed. The proposed procedure was applied to the direct determination of molybdenum in natural water.