Angela de Luca Rebello Wagener

Precipitation-dissolution system for silver preconcentration and determination by flow injection flame atomic absorption spectrometry.

In this paper, flame atomic absorption spectrometry was used for the determination of silver in various materials. The proposed preconcentration method is based on the continuous precipitation of silver as p-dimethylaminobenzilidene-rhodanine (PDBR) complex and dissolution of the precipitate with potassium cyanide. EDTA was added to the sample solution to mask large concentrations of Fe(III), Ni(II), Cu(II), Zn(II), Pb(II), Co(II) and Al(III). An enhancement factor of 20 was obtained for a preconcentration time of 3 min, resulting in a sampling frequency of 16 h(-1). The detection limit (3sigma) in the sample solution was 5 ngml(-1). The relative standard deviation at 30 ngml(-1) level was 4.7%. Analytical results obtained for alloy, biological reference material and ore samples analyzed were in good agreement with the certified values and comparable to those obtained with other techniques.

Cathodic adsorptive stripping voltammetric behaviour of guanine in the presence of copper at the static mercury drop electrode

The cathodic adsorptive electrochemical behavior of guanine in the presence of some metal ions at the static mercury drop electrode was investigated. A 1.0x10(-3) mol l(-1) NaOH or a 2.0x10(-2) mol l(-1) Hepes buffer at pH 8.0 solutions were used as supporting electrolytes. The reduction peak potential for guanine was found to be around -0.15 V, which is very close to the mercury reduction wave. A new peak appears at -0.60 V in the presence of copper or at -1.05 V in the presence of zinc. A square wave voltammetric procedure for electroanalytical determination of guanine in 2.0x10(-2) mol l(-1) Hepes buffer at pH 8.0 containing 1.6x10(-5) mol l(-1)of copper ions, was developed. An accumulation potential of -0.15 V during 270 s for the prior adsorption of guanine at the electrode surface was used. The response of the system was found to be linear in the range of guanine concentration from 6.62x10(-8) to 1.32x10(-7) mol l(-1) and the detection limit was 7.0x10(-9) mol l(-1). The influence of DNA bases such as adenine, cytosine and thymine was also examined. Cyclic voltammetry was used to characterize the interfacial and redox mechanism.

Turbidimetric determination of sulphate in waters employing flow injection and lead sulphate formation

Abstract An analytical flow-injection procedure based on PbSO4 colloidal formation is proposed as a turbidimetric determination of sulphate in natural waters. Ethanol-water was used as a medium in order to improve the sensibility of the method. Both chemical and flow variables as well as interfering species were studied. A detection limit of 0.3 μg SO2−4 ml−1 was found, and the analytical range (according to Beers law) was 2–20 μg SO2−4 ml−1. The precision was better than 3% R.S.D. and the sample throughput was ca. 35 h−1. The method, when compared with a standard methodology, gave good results when applied to water analysis.

Adsorptive stripping voltammetric behavior of adenosine triphosphate (ATP) in presence of copper at the mercury film electrode

Abstract A stripping method for the determination of adenosine triphosphate (ATP) in presence of copper at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of ATP‐copper at thin‐film mercury electrode followed by linear DC or cyclic voltammetry scan measurement of the surface species. Optimum experimental conditions were found to be the use of a 1×10−3 M NaOH solution, an accumulation potential of −0.40 V and a scan rate of 200 mV · s−1. The response of ATP‐copper is linear over the concentration range 0.2–1.2 ppm. For an accumulation time of 30 min, the detection limit was found to be 14 ppb (2.5×10−8 M). The more convenient relation to measuring the ATP in presence of metals, adenine and amino acids were also investigated.

Adsorptive Stripping Voltammetric Behavior of Acridine Orange at the Static Mercury Drop Electrode

Abstract The electrochemical behavior of acridine orange was investigated as to allow the development of a stripping method for the determination of acridine orange at the sub‐micromolar concentration level. The optimized reaction is based on controlled adsorptive accumulation of acridine orange at the static mercury drop electrode followed by differential pulse measurement of the surface species. The adsorptive stripping response is evaluated with respect to the concentration dependence, the preconcentration time and potential, the presence of reacting ions, EDTA, ssDNA and other variables. Best results were obtained using 1.0×10−3 mol L−1 sodium hydroxide solution as the supporting electrolyte. Compared to the response of solution‐phase voltammetry, a signal enhancement factor of about 7 is observed when using 90 s preconcentration. The standard deviation at the 2.5×10−6 mol L−1 level (0.284 µA) is ±0.019 µA and the detection limit equals 1.0×10−8 mol L−1.

Determination of Cysteine in the Presence of Copper in Diluted Alkaline Electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film Electrode

Abstract A stripping method for the determination of cysteine in the presence of copper at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of cysteine at mercury film electrode followed by linear cyclic voltammetry scan measurement of the surface species. Optimum experimental conditions were found to be the use of a 1×10−3 M NaOH solution, an accumulation potential of −0.50 V and a scan rate of 200 mV. s−1. The response of cysteine is linear over the concentration range 0.04–0.20 ppm. For an accumulation time of 15 minutes, the detection limit was found to be 0.9 ppb (7.4×10−9 M). The more convenient relation to measuring the cysteine in presence of metals, and others amino acids were also investigated. The utility of the method is demonstrated by presence of casein and ATP.

Ultratrace Xanthine Determination in Diluted Alkaline Electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film Electrode

Abstract A stripping method for the determination of xanthine at the submicromolar concentration level is described. The method is based on controlled adsorptive accumulation of xanthine at a thin-film mercury electrode followed by a linear scan voltammetry measurement of the surface species. Optimum experimental conditions were found to be the use of a 5.0 × 10−3 M NaOH solution, an accumulation potential of 0.00 V, and a scan rate of 20 mV s−1. The response of xanthine is linear over the concentration range 20–140 ppb. For an accumulation time of 30 min, the detection limit was found to be 36 ppt (2.3 × 10−10 M). The more convenient relations for measuring xanthine in the presence of the metals, hypoxanthine, amino acids, and other nitrogenated bases were also investigated. The utility of the method is demonstrated by the presence of xanthine in adenosine-5′-triphosphate or DNA.

Histidine Determination in the Presence of Copper in Diluted Alkaline Electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film Electrode

Abstract A stripping method for the determination of histidine at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of histidine-copper complex at mercury film electrode followed by linear cyclic scan voltammetry measurement of the surface species. Optimum experimental conditions were found to be the use of a 1.0 × 10−3 M NaOH solution, an accumulation potential of − 0.20 V, and a linear scan rate of 200 mV sec−1. The response of histidine is linear over the concentration range 0.02–0.12 ppm. For an accumulation time of 20 min, the detection limit was found to be 0.5 ppb (3.2 × 10−9 M). The more convenient relation to measuring the histidine in the presence of metals, cysteine, tyrosine, and other amino acids was also investigated. The utility of the method is demonstrated by presence of casein, ATP, and ss DNA.

Cathodic Adsorptive Stripping Voltammetry of Cytosine and Guanine in Presence of Acridine Orange

Abstract A cathodic adsorptive electrochemical behavior of cytosine and guanine in the presence of acridine orange (DNA‐intercalating dye) at the static mercury drop electrode was investigated. Optimum experimental conditions were found to be the use of a 0.001 M NaOH solution with an acridine orange concentration of 2 ppm, an initial potential of −0.0 V, a scan rate of 10 mV s−1, and a linear scan mode. The more convenient relation to measuring the cytosine and guanine in the presence of acridine orange is 1:1:2. A new approach for improving the selectivity in analysis using copper and zinc as masking agents also was investigated. Cyclic voltammetry was used to characterize the interfacial and redox behavior.

Adsorptive Stripping Voltammetry of 9‐Phenanthrol in the Presence of Copper at the Static Mercury Drop Electrode—Basis for Quantitative Determination of PAH Metabolite in Biological Materials

Abstract The electrochemical behavior of 9‐phenanthrol in the presence of copper (II) at a static mercury drop electrode was investigated to provide the basis for development of an inexpensive, sensitive, and reliable method for determination of polycyclic aromatic hydrocarbon (PAH) metabolites in biological matrices. Optimum experimental conditions for analytical applications were obtained in 0.005 M NaOH solution using an accumulation potential of −0.25 V, a scan rate of 5 mV. s−1, a pulse height of 25 mV, and a differential pulse scan mode. The response of 9‐phenanthrol is linear over the concentration range 1.0–12.0 ppb. For an accumulation time of 5 minutes, the detection limit was found to be 0.2 ppb (1.03×10−9 M). The more convenient relation to measure the 9‐phenanthrol in the presence of copper and other metals was also investigated. The utility of the method was demonstrated by the presence of 9‐phenanthrol in samples of sea water and human urine. Cyclic voltammetry was used to characterize the interfacial and redox behavior.