Arnaldo Aguiar Castro

Ultratrace determination of adenine in the presence of copper by adsorptive stripping voltammetry.

An electrochemical stripping procedure for ultra-trace measurements of adenine is described based on the adsorption of the adenine-copper complex on a static mercury drop electrode. Cyclic voltammetry was used to characterize the interfacial and redox behavior. Optimum experimental conditions were found when using a 0.005 M NaOH solution containing 0.4 ppm of copper, an accumulation potential of -0.30 V, a scan rate of 100 mV s(-1) and a linear scan mode. There is a linear response to adenine concentration in the range of 0.1-1.0 ppb and the detection limit for 6 min accumulation time was of 4.0 ppt (3.0x10(-11) M). Proper conditions for measuring the adenine in presence of guanine, thymine and cytosine were also investigated. The method was applied for the determination of adenine in a sample of single-stranded calf thymus DNA.

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.

ADSORPTIVE VOLTAMMETRIC BEHAVIOR OF ADENINE IN PRESENCE OF GUANINE AND SOME TRACE ELEMENTS AT THE STATIC MERCURY DROP ELECTRODE

An electrochemical stripping procedure is described for trace measurements of adenine by adsorption on a static mercury drop electrode. Cyclic voltammetry was used to characterize the interfacial and redox behavior. Optimum experimental conditions were found when using a 0.001 M NaOH solution, initial potential of + 0.01 V, scan rate of 5 mV s−1 and linear scan mode. The response of free adenine is linear over the concentration range 0.25–1.25 ppm. Linear scan voltammetry, without accumulation yields a detection limit of 55 ppb adenine. Proper conditions were tested to measuring adenine in presence of guanine, acridine orange, copper, zinc and ssDNA.

Adsorptive voltammetric behavior of thymine in presence of guanine at the static mercury drop electrode

An electrochemical stripping procedure for trace measurements of thymine is described by adsorption on a static mercury drop electrode. Cyclic voltammetry was used to characterize the interfacial and redox behavior. Optimum experimental conditions were found to be the use of a 0.005M NaOH solution, an initial potential of −0.08 V, a scan rate of 100 mV.s−1 and a linear scan mode. The response of free thymine is linear over the concentration range 0.1–0.5 ppm. Linear scan voltammetry, without acumulation time yields a detection limit of 62 ppb thymine. Acridine orange and copper were also investigated for measuring thymine in the presence of guanine.

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.

Determination of the antiretroviral drug nevirapine in diluted alkaline electrolyte by adsorptive stripping voltammetry at the mercury film electrode.

: This paper describes a stripping method for the determination of nevirapine at the submicromolar concentration levels. The method is based on controlled adsorptive accumulation of nevirapine at thin-film mercury electrode, followed by a linear cyclic scan voltammetry measurement of the surface species. Optimal experimental conditions include a 2.0 x 10(-3) mol L(-1) NaOH solution (supporting electrolyte), an accumulation potential of -0.20 V, and a scan rate of 100 mV s(-1). The response of nevirapine is linear over the concentration range 0.01-0.14 ppm. For an accumulation time of 6 minutes, the detection limit was found to be 0.87 ppb (3.0 x 10(-9) mol L(-1)). More convenient methods to measure the nevirapine in presence of the efavirenz, acyclovir, didanosine, indinavir, nelfinavir, saquinavir, lamivudine, zidovudine and metals ions were also investigated. The utility of this method is demonstrated by the presence of nevirapine together with ATP or DNA.

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.