Electrochemical behaviour of some neuroleptics: Haloperidol and its derivatives

The electrochemical characteristics of Haloperidol and related compounds, representative neuroleptics of the butyrophenone family, have been investigated as a function of pH and concentration by direct-current, alternating-current and differential-pulse polarography and cyclic voltammetry at a hanging mercury drop electrode. A single cathodic wave representing an irreversible two-electron reduction is obtained, and its half-wave potential differs from that characteristic of aromatic ketone reduction. Adsorption processes disturb the wave behaviour and an adsorption prewave is observed at high concentrations. Quantitative measurements were successful in the concentration range 1 x 10(-4)-1 x 10(-6)M (0.4 mg/l.), the lower concentration representing the detection limit by differential-pulse polarography.     

Polarographic determination of total iron content using a Fe(2+/3+)-Methylthymol Blue-NO2- system.

In the buffer solution of NH3-NH4Cl (pH = 8.5, 0.04 mol l(-1)), iron-Methylthymol Blue (MTB) can produce a sensitive polarographic wave at -1.10 V (vs. SCE) in the NaNO2. The peak current is linear with the concentration of the iron in the range of 3 x 10(-8)-5 x 10(-6) mol l(-1), and the detection limit is 1 x 10(-8) mol l(-1). By studying the characteristics of the wave and the electrode reaction mechanism, we can prove that the catalytic wave is an adsorption wave and that the peak current comes from the reduction of Fe(II). The molar ratio of iron to ligand was found to be 1:1. Adsorption particles are neutral molecules, the saturated adsorption quantity of the complex on the mercury electrode is 1.92 x 10(-9) mol cm(-2), according with the Frumkin isothermal formula. In the experiments, the adsorption coefficient (beta) is 4.05 x 10(5); the adsorption factor (gamma) is 0.70: the electron transfer number (n) is 2; the free energy (deltaG(o)) is 31.99 kJ mol(-1); the transfer coefficient of the irreversible adsorption is 0.42-0.45; and the reaction velocity constant (Ks) is 1.35 s(-1). This method, whose result is satisfying, can be applied to the detection of trace total iron contents in medicinal products.     

Polargraphic adsorptive waves of alkaline-earth metal complexes with thymolphthalexone

Sensitive derivative polarographic adsorption waves have been observed for alkaline-earth metal-TP complexes in 0.15M potassium hydroxide containing 3 x 10(-5)M thymolphthalexone (TP). The limit of detection for calcium, strontium and barium was 7.5 x 10(-7)M and for magnesium 4.0 x 10(-6)M. The proposed method has been used successfully for determining trace amounts of calcium in natural waters and hair samples. The composition of the complex has been shown to be 1:1 alkaline-earth metal:TP and various experiments have confirmed that the wave is an adsorption wave. The reaction mechanism has been studied by a number of methods.     

The polarographic and voltammetric behaviour of the copper(II) mitoxantrone complex and its analytical application

The polarographic and voltammetric behaviour of the copper(II)-mitoxantrone complex have been studied. A well-defined linear sweep voltammetric peak was obtained at -0.275 V (vs. Ag AgCl ) or -0.325 V (vs. SCE) in ammonia-ammonium chloride (20 mmoll(-1), pH 9.0). The characteristics of the peak have been examined in detail. The experimental results show that the reduction of the copper(II) mitoxantrone complex is irreversible and the peak displays adsorption characteristics at the dropping mercury electrode. A mechanism is proposed for the reduction of the complex, comprising one-electron reduction of the copper(II) of the complex, is reduced directly in the complex form. A single-sweep oscillopolarographic method was develped for the determination of copper(II). The peak current is proportional to the concentration over the range 5 x 10(-8)-2 x 10(-5) mol l(-1). The method reported here has the advantage that the interference of many common metal ions is small.     

Single-sweep polarography of the copper(II)-3-hydroxy-1-p-sulphonatophenyl-3-phenyltriazene complex and its analytical applications

A polarographic investigation of the copper-3-hydroxy-1-p-sulphonatophenyl-3-phenyltriazene (HSPT) complex in 0.05 M sodium tetraborate medium is described and a simple and sensitive single-sweep polarographic method for the determination of trace amounts of copper in biological samples is proposed. The complex was shown to be Cu(HSPT)2 with log beta' = 11.38. The polarographic wave is caused by the reduction of copper(II) in the adsorbed complex to copper amalgam on the surface of a mercury electrode. The current peak is directly proportional to the concentration of copper in the range 8.0 x 10(-9)-4.0 x 10(-6) M and the detection limit is 5.0 x 10(-9) M.     

Determination of ketorolac in human serum by square wave adsorptive stripping voltammetry

The adsorption behavior of ketorolac on a hanging mercury drop electrode (HMDE) was explored by square-wave and cyclic voltammetry. The square wave voltammetric response of ketorolac depends on the parameters of the square wave voltammetry excitation signal as well as on the pH of the medium and the accumulation time. The drug was accumulated at HMDE and a well-defined peak was obtained at -1.41 V versus. Ag/AgCl (saturated KCl) in acetate buffer of pH 5.0. A square-wave adsorptive stripping voltammetric method for the quantitative determination of ketorolac was developed. The linear concentration range was 1x10(-10)-1x10(-8) when using 300 s accumulation at -0.8 V. The detection limit of ketorolac was 1.0x10 (-11)M . The precision was excellent with relative standard deviation of 3.85% at concentration of 5x10 (-8)M after 60 s accumulation time. Applicability to serum samples was illustrated. A detection limit of 14 ng per ml of serum was obtained.     

舒乐安定吸附伏安法的研究

Jimenez曾研究了舒乐安定的性质,但灵敏度较低,本文提出了测定痕量舒乐安定的吸附伏安法,在0.1 mol/L NH_3-NH_4Cl溶液(pH 9.3)中,富集电位—0.80 V(us. Ag/AgCl)得一灵敏的舒乐安定还原峰,Ep=—1.05 V,i_p与舒乐安定浓度在3.0×10~(-9)～5.0×10~(-6) mol/L范围内呈线性关系,检测限达1.0×10~(-9)mol/L,并用于试样的测定,用循环伏安法和恒电     

Adsorptive stripping voltammetry determination of molybdenum(VI) in water and soil

A differential pulse stripping voltammetry method for the trace determination of molybdenum(VI) in water and soil has been developed. In 0.048M oxalic acid and 6 x 10(-5)M Toluidine Blue (pH 1.8) solution, Mo(V), the reduction product of Mo(VI) in the sample solution, can form a ternary complex, which can be concentrated by adsorption on a static mercury drop electrode at -0.1 V (vs. Ag/AgCl). The adsorbed complex gives a well-defined cathodic stripping current peak at -0.30 V, which can be used for determining Mo(VI) in the range 5 x 10(-10)-7 x 10(-9)M, with a detection limit of 1 x 10(-10)M (4 min accumulation). The method is also selective. Most of the common ions do not interfere but Sn(IV) and large amounts of Cu(2+), Ag(+) and Au(3+) affect the determination.     

Differential pulse polarographic determination of ofloxacin in pharmaceuticals and biological fluids

A sensitive method is described for the determination of ofloxacin in its pure form, dosage forms and biological fluids. The proposed method depends upon the polarographic activity of ofloxacin in Britton Robinson buffers, whereby a well-defined cathodic wave is produced over the pH range 4.1-10.3. The wave was characterized as being irreversible, diffusion-controlled with limited adsorption properties. The current-concentration relationship was found to be rectilinear over the range 5x10(-5)-5x10(-4) M and 1x10(-5)-5x10(-4) M using the DC(t) and DPP modes respectively, with a minimum detectability (S/N=3) of 3x10(-7) M. The proposed method was successfully applied to the determination of ofloxacin in tablets and biological fluids. The results obtained were found to be in agreement with those obtained by a reference method.     

Polarographic study of a triazolobenzodiazepine: Estazolam

Summary The polarographic behaviour of 8-chloro-6-phenyl-4H-s-triazolo(4,3-a)-(1,4)-benzodiazepine (estazolam) was studied in the pH range 3–10. The reduction process is irreversible and the current is diffusion-controlled. The linear relationship between current and estazolam concentration permits its polarographic determination in the range 3.4·10^–7–1.0·10^–4 M. The detection limit was 1.7·10^–7 M. The reproducibility of the method in terms of its relative standard deviation was 1.00% and 1.14% using ten determinations at the 2.4·10^–5 M and 3.4·10^–6 M levels respectively.

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Polarographische Untersuchung des Triazolbenzodiazepins Estazolam

     

Determination of lomefloxacin, an antibacterial drug, in pharmaceutical preparations based on its polarographic catalytic wave in the presence of 2-iodoacetamide.

In a 0.125 mol/L phosphate (pH 6.6)/2.5 x 10(-4) mol/L 2-iodoacetamide solution, lomefloxacin yields a response of a polarographic catalytic current. The second-order derivative peak current of the catalytic wave of lomefloxacin is proportional to its concentration in the range of 1.0 x 10(-8)-1.0 x 10(-6) mol/L (r = 0.998). The sensitivity of the catalytic wave is 25-times higher than that of the corresponding reduction wave for 5.0 x 10(-7) mol/L lomefloxacin. The proposed method was applied to the determination of lomefloxacin in pharmaceutical preparations. The polarographic reduction wave is ascribed to a one-electron reduction of the C=C bond of lomefloxacin zwitterion accompanied by an acid-base equilibrium. The catalytic wave should be caused by regeneration of the lomefloxacin molecule at electrode surface due to the one-electron reduction product being further oxidized by electroreductive intermediate products of 2-iodoacetamide.     

A polarographic and coulometric study of the iron(III)-Solochrome Violet RS system

Experimental results are presented which clearly illustrate the kinetic character of the polarographic waves/peaks of the iron(III)-Solochrome Violet RS (SVRS) complex formed at pH 4.7. Even in the presence of an excess of iron(III), at the 10(-3)M level of SVRS only half of the azo-dye wave is displaced to more negative potentials. At lower concentrations (e.g., 10(-6)M), however, a larger fraction is displaced. The undisplaced wave/peak corresponds to reduction of free dye dissociated from the complex, whereas the displaced wave/peak corresponds to the reduction of the complexed dye directly. The temperature coefficient for the undisplaced peak is 12%/deg at the 10(-5)M level, indicating that the height of this peak is controlled, at least in part, by the rate of dissociation of the iron(III) complex. The rate of increase of the total limiting current produced by reduction of the complex and of the free dye dissociated from it, becomes less at higher concentrations and is an indication of adsorption occurring at the dropping mercury electrode. In the controlled-potential coulometric reduction of the complex at a mercury-pool cathode at pH 4.7, the SVRS is reduced completely in a four-electron reaction at a potential only slightly more negative than that for the reduction of the free dye, indicating that the dye is dissociated from the complex and then reduced at this potential; the iron(III) is reduced simultaneously to iron(II). In view of the kinetic nature of the polarographic waves of the SVRS-iron(III) complex, care must be taken in using SVRS as a reagent for the polarographic determination of iron(III).     

Studies of the interaction between Aloe-emodin and DNA and preparation of DNA biosensor for detection of PML-RARalpha fusion gene in acute promyelocytic leukemia

The interaction of Aloe-emodin (AE) with salmon sperm DNA in 0.1M Tris-HCl buffer (pH 4.4) and at the DNA-modified glassy carbon electrode (GCE) was systemically studied with voltammetry and ultraviolet-visible (UV-vis) spectroscopy. AE had excellent electrochemical activity on the GCE with a couple of redox peaks. We propose that AE can intercalate into DNA strands forming a nonelectroactive complex, which results in the decrease of the reduction peak current of AE. The Langmuir adsorption constants of AE at ss- and dsDNA/GCE were (2.1+/-0.4)x10(5) and (2.7+/-0.2)x10(5)M(-1), respectively. The difference between AE at ss- and dsDNA has been used for the preparation of a sequence-specific DNA electrochemical biosensor for detection of PML-RARalpha fusion gene in acute promyelocytic leukemia (APL) with a detection limit of 6.7x10(-8)M and a linear range from 1.5x10(-8) to 1.5x10(-7)M. The selectivity of ssDNA-modified electrode was also described.     

Electrochemical behavior of zopiclone

The electrochemical properties of zopiclone, an anxiolytic and hypnotic drug, have been investigated by different techniques. The compound is reduced in two 2-electron steps in the pH range 0-12. The first step, which corresponds to the reduction of the pyrazine ring, is reversible in acidic and neutral solutions. Strong adsorption phenomena accompany the reduction process in acidic and neutral media. Zopiclone can be quantitatively measured over the entire pH range using DC polarography. However, the use of differential pulse and square-wave modes for quantitative measurements is more limited due to a slope modification in the current-concentration relationship. Adsorptive stripping voltammetry can be applied to the determination of low levels of the drug at pH 9, but only short deposition times may be used because large amounts of material accumulated under stirring conditions due to fast adsorption kinetics are rapidly released from the electrode surface. Detection limits are 1 x 10(-7)M and 2 x 10(-10)M for polarography and adsorptive stripping voltammetry, respectively. Only the first wave is of analytical interest for both techniques.     

8—氮鸟嘌呤的极谱伏安行为

用循环伏安法（ＣＶ）、电流采样极诸法（ＳＣＰ，即ＴＡＳＴ）、常规脉冲极谱法（ＮＰＰ）、微分脉冲极谱法（ＤＰＰ）、线性扫描伏安法（ＬＳＶ）、Ｏｓｔｅｒｙｏｕｎｇ方波伏安法（ＯＳＷＶ）和计时库仑法（ＣＣ）等电化学技术研究了抗癌药物８－氮鸟嘌呤（８－ａｚａｇｕａｎｉｎｅ，ｇｕａｎａｚｏｌｏ，简称８－ＡＧ）的极谱伏安行为．在 ０． １ｍｏｌ／Ｌ Ｈ２ＳＯ４底液中，８－ＡＧ有一良好的还原峰，峰电位（Ｅｐ）在－０． ９５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ，下同）附近，８－ＡＧ浓度在４×１０－６～８×１０－４ｍｏｌ／Ｌ范围内．峰高与浓度有良好的线性关系，线性相关系数ｒ＝０．９９９９～０．９９１０，检出限为１× １０－６ｍｏｌ／Ｌ．实验证明了该峰具有吸附性．本文提出了电极反应机理，它包括：酸性介质中８－ＡＧ的质子化、质子化的８－ＡＧ在汞电极上吸附以及完全不可逆的两电子还原过程．同时用量子化学计算方法（全略微分重叠法即ＣＮＤＯ／２）对８－ＡＧ和鸟嘌呤的各原子的净电荷以及Ｗｉｂｅｒｇ键级进行了计算，从理论上解释了８－ＡＧ的电化学还原机理。     

Voltammetric determination of tinidazole using a glassy carbon electrode modified with single-wall carbon nanotubes.

An electrochemical method based on a single-wall carbon nanotubes (SWNTs) film-coated glassy carbon electrode (GCE) was described for the determination of tinidazole. In a 0.1 M Britton-Robinson buffer with a pH of 10.0, tinidazole yields a very sensitive and well-defined reduction peak at -0.78 V (vs. SCE) on a SWNTs-modified GCE. Compared with that on a bare GCE, the reduction peak of tinidazole increases significantly on the modified GCE. Thus, all of the experimental parameters were optimized and a sensitive voltammetric method is proposed for tinidazole determination. It is found that the reduction peak current is proportional to the concentration of tinidazole over the range from 5 x 10(-8) to 4 x 10(-5) M, and that the detection limit is 1 x 10(-8) M at 3 min open-circuit accumulation. This new analysis method was demonstrated with tinidazole drugs.     

Voltammetric study of the redox behaviour of the Hg(II)/Hg(I)/Hg system at a rotating metal-ring/glassy-carbon disc electrode

The reduction of Hg(II) at a glassy-carbon electrode in various electrolytes has been studied by rotating ring-disc voltammetry. Reduction proceeds directly to metallic mercury in a single 2-electron step. However, at the foot of the wave, and only during the first reduction sweep after pretreatment of the electrode surface, a small amount of Hg(I) species is detected at the ring. The appearance of an Hg(I) intermediate is most pronounced in sulphuric acid solution. The reduction of Hg(II) is found to proceed irreversibly and to be of first order. At sufficiently negative potentials the reduction is convective-diffusion controlled. Stripping voltammetric experiments indicate that the dissolution of mercury gives Hg(II) in complexing electrolytes. In non-complexing electrolytes the initially formed Hg(II) reacts with mercury atoms on the electrode surface to give Hg(I). During electrodissolution, two stripping peaks may be observed as a result of underpotential adsorption of mercury on glassy carbon. The difference in peak potential between the adsorption (mono) layer peak and the bulk mercury peak has been related to the difference in work functions of the deposit (mercury) and substrate (carbon). A rotating glassy-carbon electrode has been used for the anodic stripping determination of mercury. When an appropriate amount of a cation such as cadmium(II) or copper(II) is added to the test solution, mercury down to 2 x 10(-9)M (0.4 ng ml ) can be determined in acidified thiocyanate electrolyte with a relative standard deviation of about 22%.     

Enhanced electrochemical detection of ketorolac tromethamine at polypyrrole modified glassy carbon electrode.

A glassy carbon electrode modified with a coating of polypyrrole (Ppy) exhibited an attractive performance for the detection and determination of a non-steroidal and non-narcotic analgesic compound, ketorolac tromethamine (KT). Cyclic voltammetry, differential pulse and square wave voltammetry were used in a combined way to identify the electrochemical characteristics and to optimize the conditions for detection. For calibrating and estimating KT, square-wave voltammetry was mainly used. The drug shows a well-defined peak at -1.40 V vs. Ag/AgCl in the acetate buffer (pH 5.5). The existence of Ppy on the surface of the electrode gives higher electrochemical active sites at the electrode for the detection of KT and preconcentrate KT by adsorption. The square-wave stripping voltammetric response depends on the excitation signal and the accumulation time. The calibration curve is linear in the range 1 x 10(-11) to 1 x 10(-7) M with a detection limit of 1.0 x 10(-12) M. Applicability to serum samples was also demonstrated. A detection limit of 1.0 ng ml for serum was observed. Square-wave voltammetry shows superior performance over UV spectroscopy and other techniques.     

Differential pulse polarographic determination of trace selenium(IV) and molybdenum(VI) using the catalytic hydrogen wave

In the presence of selenium(IV) and molybdenum(VI) a new polarographic peak appears which corresponds to a hydrogen catalytic wave. By differential pulse polarography a single, sharp peak at about -1.1 V is obtained, allowing trace determination of selenium(IV) and molybdenum(VI) in the range 1x10(-6)-5.0x10(-9) M with a linear calibration and a detection limit of 1.5x10(-9) M. The optimum conditions are found to be 0.1 M KNO(3) and a pH of about 3.2 (Britton-Robinson buffer). There is no serious interference from some ions when present at 1.0-40 times that of molybdenum. At higher amounts of interfering ions the interference is eliminated by the addition of EDTA.     

Trace adsorptive voltammetric determination of antimony in hair

A very sensitive electrochemical procedure for trace determination of antimony is described. The complex of antimony with p-dimethyl-aminophenyl-fluorone (p-DMPF) is adsorbed on a hanging mercury drop electrode (HMDE), and the reduction current of the accumulated complex is measured by voltammetry. In linear sweep voltammetry, the reduction potential of the complex is more positive than that of the free dye. The peak height of the complex is proportional to the concentration of antimony in the range of 4.0 x 10(-9) to 4.0 x 10(-7) M, the detection limit is 1.0 x 10(-9) M Sb(III) for a 5 min preconcentration time. The relative standard error for the determination of 8.0 x 10(-8) M Sb(III) is 2.9%.