Polarographic study of acrolein and its determination by flow injection with amperometric detection at a mercury electrode

A study of the electrochemical behavior of acrolein at a dropping mercury electrode using different polarographic techniques is described. Theoretical studies of the reversibility of the wave of acrolein were carried out using two different polarographic techniques: direct current tast and differential pulse. Differential pulse polarography may be used to determine acrolein concentration in a Britton-Robinson buffer solution of pH 10 in the ranges 2 x 10(-7)10(-8) and 5 x 10(-8)-10(-4) mol dm(-3) and a coefficient of variation of 1.7% for a concentration of 10(-5)mol dm(-3). A flow injection method with amperometric detection at a potential of -1.4V using a mercury electrode is also described. Before each injection, any drop hanging from the tip of the capillary needs to be dislodged and a new electrode drop dispensed; three different drop sizes were tested. A linear relationship between peak intensity and acrolein concentration was obtained in the range 10(-5)-10(-7) mol dm(-3), with a detection limit of 9.8 x 10(-8) mol dm(-) 3 and a coefficient of variation of 2.9% for a 2 x 10(-7) mol dm(-3) concentration. Several organic and inorganic species were tested in order to ascertain whether they interfered with the signal for acrolein. The proposed methods were applied to the determination of acrolein in seawater samples.     

Voltammetric analysis of ceftazidime after preconcentration at various mercury and carbon electrodes: application to sub-ppb level determination in urine samples

The electrochemical behavior of ceftazidime (CFZ) at four different kinds of electrodes viz. static mercury drop electrode (SMDE), controlled growth mercury electrode (CGME), glassy carbon electrode (GCE) and carbon paste electrode (CPE) has been presented. Optimal operational parameters have been selected for the drug preconcentration and determination in aqueous medium. Down to 2x10(-10) M CFZ is achieved as detection limit at the CGME. Modification of the CPE with polyvinyl alcohol (PVA) enhances both the sensitivity and selectivity for the drug accumulation and, therefore, its determination at very low levels. Application of the proposed method for CFZ analysis in spiked urine samples or those taken after metabolism has been easily assessed. Down to 1x10(-9) M CFZ (0.695 ng ml(-1)) could be easily achieved in such samples.     

The analytical performance of direct current,normal pulse and differential pulse polarography with static mercury drop electrodes

The recently developed static mercury drop electrode (SMDE) provides a fundamentally new approach to electrodes for polarography. An analytical evaluation of the electrode is presented. For a range of electrode processes, current-sampled d.c. polarography at the SMDE is useful down to at least the 10^-7 M concentration level when short drop times and fast potential scan rates are used. The improvement in the limit of detection for d.c. polarography is therefore very substantial. Improvements in sensitivity associated with normal pulse and differential pulse polarography at the SMDE compared with the dropping mercury electrode (DME) are marginal. It is concluded that at the SMDE, the analytical performance and response characteristics of d.c., normal pulse and differential pulse polarography tend to converge.     

Electrochemical determination of 6-mercaptopurine at silver microdisk electrodes

The electrochemical behaviour of 6-mercaptopurine (6-MP) at a microdisk electrode is investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicate that 6-MP can be strongly adsorbed on the surface of the static mercury drop electrode (SMDE) and reacts with Ag+ ions which are produced at positive potentials. 6-MP yields a well-defined cathodic stripping signal during the negative scan at about -0.812 V (vs. SCE) in pH 9.0 phosphate buffer solution. The electrode has hence been used for the determination of 6-MP by differential pulse voltammetry (DPV). The linear range is between 2.0x10(-7) and 5.0x10(-5) mol/l, with the calculated detection limit (S/N=3) of 8.0x10(-8) mol/l. The relative standard deviation is 3.0% for eight successive determinations of 4.0x10(-5) mol/l 6-MP. The determination of 6-MP in tablets has also been carried out and satisfactory results have been obtained.     

Development of a voltammetric method for the determination of iron(III) in Zn-Fe alloy galvanic baths

A square wave voltammetric method with a static mercury drop electrode (SMDE) was developed for the quantitative determination of iron (III) in Zn-Fe alloy galvanic baths. Real alloy bath samples were analyzed by the standard addition method and recovery tests were carried out. 0.50 mol L-1 sodium citrate (pH 6.0) or 0.20 mol L-1 oxalic acid (pH 4.0) were applied as supporting electrolytes resulting in both cases in a peak potential of about -0.20 V vs. AgIAgCl (saturated KCl). The iron (III) concentration in the alloy bath was 9.0 x 10(-4) mol L-1. A good correlation (r = 0.9999) was achieved between the iron (III) concentration and the peak current in the electrolytes studied, with linear response ranges from 1.0 x 10(-6) to 1.2 x 10(-4) mol L-1. Interference levels for some metals such as copper (II), lead (II), chromium (III) and manganese (II) that can hinder the Zn-Fe alloy deposition were evaluated; only copper (II) interferes seriously.     

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.     

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.     

Differential pulse anodic stripping voltammetry of lead (lI) benzoylacetonate in chloroform: Application to the analysis of free-lead gasoline and gas oil samples

The voltammetric characteristics of lead(II) benzoylacetonate in chloroform at the mercury electrode are investigated. The conditions for nearly reversible reduction of lead(II) were optimized. Anodic stripping voltammetry for the determination of trace-lead was developed using differential pulse technique to strip amalgamed lead from hanging mercury drop electrode. The experimental conditions, such as scanning rate of electrode potential and deposition time of lead were optimized. The calibration graph was linear over concentration range 5x10(-8)-10(-6) M of lead(II). The detection limit was 2.5x10(-9) and the relative standard deviation for the determination of 4x10(-7) M Pb(II) was 2%. Preceded by decomposition of organolead compounds with concentrated nitric acid, then ashing at 300 degrees C and a solvent extraction of Pb(II) benzoylacetonate in chloroform, the suitability of the proposed method for the determination of lead in free-lead gasoline and gas oil was demonstrated as a typical example of application.     

Determination of aluminium in tree samples by cathodic adsorptive stripping voltammetry

This paper presents a method of determination of aluminium in tree samples (wood, leaves, roots) based on the cathodic adsorptive stripping voltammetry. Al(III) complexed with alizarin S was determined by ASV method using a hanging mercury drop electrode. Optimal conditions were found to be: accumulation time 30-90 s, accumulation potential - 0.70 V versus SCE, supporting electrolyte 0.1 M ammonia-ammonium chloride buffer at pH 8.2 and concentration of alizarin 1 x 10(-5) M. The response of the system, a linear current-concentration relationship was observed up to 8 x 10(-6) M. The developed method has been tested by analysing international reference materials (BCR 62 Olive leaves and BCR 101 spruce needles).     

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.     

Polarographic determination of fluoride using the adsorption wave of the Ce(III)-alizarin complexone-fluoride complex

A very sensitive electrochemical method for trace measurement of fluoride in water is discussed. The complex of cerium(III) with alizarin complexone (ALC) and fluoride ion is adsorbed at the dropping mercury electrode. In cathodic sweeps, the peak height is directly proportional to the concentration of fluoride over the range 8 x 10(-8)-5 x 10(-6)M (1.5 x 10(-9)-9.5 x 10(-8) g/ml), and the detection limit is 5 x 10(-8)M (9.5 x 10(-10) g/ml). The proposed method was applied to the determination of fluoride in water.     

Investigations on adsorption potentiometry-part VIII. Determination of ultratrace copper in food by derivative adsorption chronopotentiometry

An electroanalytical method, based on derivative chronopotentiometry of the copper complex with 4-[(4-diethylamino-2-hydroxyphenyl) azo]-5-hydroxy-naphthalene-2,7-disulphonic acid (Beryllon III) accumulated on the surface of a hanging mercury drop electrode, for determining trace copper in food has been developed. The dependence of the peak height of reduction of the copper complex on the preconcentration time and preconcentration potential are discussed. Optimum experimental conditions include 0.01 M HOAc, 0.01M NaOAc, 1.0 x 10(-6) Beryllon III and a preconcentration potential of 0.10 V (vs. SCE). Under these conditions the detection limit and the linear range are 4 x 10(-11)M and 6 x 10(-11) -4 x 10(-7)M, respectively. The method was applied to samples of digested rice.     

Voltammetric detection of sulfonamides at a poly(3-methylthiophene) electrode

Detection of sulfonamide compounds in a mixture of standards at a poly(3-methylthiophene) coated on glassy carbon (GC) electrode is reported. The polymer, poly(3-methylthiophene), was electrochemically synthesized at a GC rotating disk-working electrode versus Ag/AgCl using cyclic voltammetry (+0.5 to +2.0 V). Square wave voltammetry (SQWV) with cathodic reduction (0 to -4.0 V) was used for the detection of seven sulfonamide compounds in a mixture. The working concentration ranges (curvilinear) established for different compounds in Britton-Robinson (BR) buffer (pH 6.26), were: 5.0x10(-6)-3.2x10(-3) M sulfamerazine, 5.0x10(-6)-3.2x10(-3) M sulfadiazine, 7.5x10(-7)-3.2x10(-4) M sulfasalazine, 9.0x10(-7)-5.0x10(-4) M sulfamethazine, 6.5x10(-8)-3.5.0x10(-5) M sulfamethoxazole, 9.7x10(-8)-5.0x10(-5) M sulfathiazole, and 9.0x10(-8)-3.2x10(-5) M 5-sulfaminouracil. Detection limits were calculated as: 3.9x10(-6) M for sulfamerazine; 4.0x10(-6) M sulfadiazine; 2.5x10(-7) M sulfasalazine; 3.7x10(-7) M sulfamethazine; 4.0x10(-8) M sulfamethoxazole; 6.4x10(-8) M sulfathiazole and 6.0x10(-9) M 5-sulfaminouracil. The data suggests a potential application of the poly(3-methylthiophene) (P3MT) electrode for determination of sulfonamides in veterinary and other applications.     

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.     

Simultaneous square-wave voltammetric determination of acetazolamide and theophylline in pharmaceutical formulations

Simple, rapid, sensitive and low cost voltammetric method for simultaneous determination of acetazolamide and theophylline in pharmaceutical formulations, was developed using a static mercury drop electrode (SMDE). Well-defined voltammetric peaks were obtained at–0.87 and–1.33 V for acetazolamide and–0.21 V (vs. Ag/AgCl) for theophylline in Britton–Robinson (B–R) buffer (pH 2.4). The reduction peak currents are found to be linearly dependent on the concentration for the both drugs. Calibration graphs were obtained over the concentration range 1.98 × 10^–6 to 5.94 × 10^–5 M and 2.0 × 10^–5 to 5.6 × 10^–4 M for acetazolamide and theophylline, respectively. The limits of detection (LOD) and quantitation (LOQ) of the procedure were also presented. Factors such as, pH of supporting electrolyte, equilibrium time, frequency, scan rate and pulse height were optimized. The validated voltammetric method was successfully applied for simultaneous determinations of the two drugs. The procedure does not require any sample pretreatment or timeconsuming separation steps.     

Adsorptive stripping voltammetric determination of pipemidic acid in human urine

The electrochemical behaviour of pipemidic acid (8-ethyl-5,8-dihydro-5-oxo-2-(1-piperazinyl)-pyrido[2,3-d]pyrimidine-6- carboxylic acid), a well known antimicrobial agent used for urinary infections, was investigated by linear-sweep, differential-pulse and square-wave voltammetry at a hanging mercury drop electrode. Two reduction processes were observed in Britton-Robinson buffers at acid pH, whereas only one or two processes were observed in alkaline solutions, dependent on the pH of the buffer employed. Adsorptive effects were used to accumulate the drug on to the electrode. The adsorbed species were measured voltammetrically by using a cathodic process appearing at -0.76 V in 0.1 M HCIO4. Linear calibration graphs were obtained in the range 2.5 x 10(-9)-2.0 x 10(-7) M. A simple procedure of extraction was employed for the determination of the drug in urine samples.     

Adsorptive stripping voltammetric measurements of trace levels of uranium following chelation with mordant blue 9

The chelate of uranium with the azo dye Mordant Blue 9 is shown to be adsorbed and then reduced on the hanging mercury drop electrode. These properties have been exploited in developing a highly sensitive stripping voltammetric procedure for trace determination of uranium. With controlled adsorptive accumulation for 5 min, a detection limit near 2 x 10(-10)M uranium is obtained. Cyclic voltammetry has been used to characterize the interfacial and redox behaviour. The effect of various operational parameters on the stripping response is discussed. Experimental conditions include use of 1 x 10(-6)M Mordant Blue 9 in 0.05M acetate buffer (pH 6.5), an accumulation potential of -0.43 V, and a linear potential scan. The response is linear up to 1.2 x 10(-7)M uranium, and the relative standard deviation at 4.2 x 10(-8)M is 3.2%. The effects of possible interferences from organic surfactants or metal ions have been investigated.     

Poly(amidosulfonic acid) modified glassy carbon electrode for determination of isoniazid in pharmaceuticals

Amidosulfonic acid was electropolymerized by cyclic voltammetry onto the surface of glassy carbon electrode (GCE) to fabricate the chemically modified electrode, which showed high stability, good selectivity and reproducibility for determination of isoniazid. The modified electrode showed an excellent electrocatalytical effect on the oxidation of isoniazid. Under the optimum conditions, there was a good linear relationship between anodic peak current and isoniazid concentration in the range of 5.0 x 10(-8)- 1.0 x 10(-5) M, and a detection limit of 1.0 x 10(-8) M (S/N = 3) was obtained after 120 s at the accumulation potential of - 0.2 V (vs. SCE). This developed method had been applied to the direct determination of isoniazid in injection and tablet samples with satisfactory results.     

Preconcentration with chromatomembrane cell and adsorptive polarographic determination of fluorine in air

The present paper describes a procedure in which fluorine in the air was preconcentrated in a chromatomembrane cell and its content was determined by adsorptive polarography. In a pH 4.90 buffer solution the fluorine ion can form a ternary complex with La(III) and ALC. The complex can be adsorbed at the mercury electrode and yields a sensitive oscillopolarographic wave at -0.67 V, which can be sensitized by Triton X-100. Over the range 3.0x10(-8)-1.60x10(-6) M, the peak currents are linearly proportional to the concentration of the fluoride. The detection limit is 1.0x10(-8) M. First the fluorine in the air samples was preconcentrated in the chromatomembrane cells using 0.10 M NaOH solution, then its content was determined by complex-adsorptive polarography.     

Direct zinc determination in commercial sulphuric acid by dpasv. Comparison of rotating disc and stationary graphite electrodes

A striking gas technique employed made a direct Zn determination possible at extremely low pH in commercial acid solutions when a stationary impregnated graphite-based mercury film electrode was used. The original Zn(II) concentrations were determined quantitatively by differential pulse anodic stripping voltammetry on 0.5M and 1M sulphuric acid solutions by standard addition and were found to be 2 x 10(-8)M and 4.1 x 10(-8)M, respectively. The influence of mercury ion concentration, pulse amplitude, potential step and pulse repetition time on analytical data was studied and optimized. A rotating disc graphite electrode was also used as a working electrode and was found unreliable for this purpose as hydrogen bubbles were not removed effectively and blocked the working electrode surface.