Fast Monitoring of Nano‐Molar Level of Gentamycin by Fast Fourier Transform Continuous Cyclic Voltammetry in Flowing Solution

Abstract

A novel method for the determination of gentamycin in flow‐injection systems has been developed in this work. The principal advantages of this method are that it is rapid, simple, and possesses low detection limit. Some investigations were also done to find the effects of various parameters on the sensitivity of the proposed method. The conditions producing the performance were the pH value of 2, the scan rate value of 350 V/s, accumulation potential of (100 mV), and accumulation time of 0.9 s. Some of the advantages of the proposed method are: the removal of oxygen from the test solution is not required anymore, the detection limit of the method is sub‐nanomolar, and finally, the method is fast enough for determination of such compounds, in a wide variety of chromatographic methods. We also introduce a special computer‐based numerical method for calculation of the analyte signal and noise reduction. After subtracting the background current from noise, the electrode response was calculated, based on partial and total charge exchanges at the electrode surface. The integration range of currents was set for all the potential scan ranges, including oxidation and reduction of the Au surface electrode, to obtain a sensitive determination. The waveform potential was continuously applied on an Au disk microelectrode (12.5 µm in radius). Detention limit of the method for gentamycin was found to be 1.0×10^?9 M. For 10 runs, the relative standard deviation of the method at 1.0×10^?7 M was 2.1%.     

Monitoring of Methyldopa by Fast Fourier Transform Continuous Cyclic Voltammetry at Gold Microelectrode

A continuous cyclic voltammetric study of methyldopa at gold micro electrode was carried out. The drug in phosphate buffer (pH 2.0) is adsorpted at 400 mV, giving rise to change in the current of well-defined oxidation peak of gold in the flow injection system. The proposed detection method has some of advantages, the greatest one of which are as follows: first, it is no more necessary to remove oxygen from the analyte solution and second, this is a very fast and appropriate technique for determination of the drug compound in a wide variety of chromatographic analysis methods. Signal-to-noise ratio has significantly increased by application of discrete Fast Fourier transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. Also in this work some parameters such as sweep rate, eluent pH, and accumulation time and potential were optimized. The linear concentration range was of 1.0×10－7—1.0×10－11 mol•L－1 (r＝0.9975) with a limit of detection and quantitation 0.004 nmol•L－1 and 0.03 nmol•L－1, respectively. The method has the requisite accuracy, sensitivity, precision and selectivity to assay methyldopa in tablets. The influences of pH of eluent, accumulation potential, sweep rate, and accumulation time on the determination of the methyldopa were considered.     

Subsecond FFT‐adsorptive Voltammetric Technique as a Novel Method for Subnano Level Monitoring of Piroxicam in its Tablets and Bulk Form at Au Microelectrode in Flowing Solutions

Abstract

In this work a novel method for the determination of piroxicam in flow‐injection systems has been developed. A system using fast Fourier transform continuous cyclic voltammetry (FFTCV), at a gold microelectrode in flowing solution, was used for determining piroxicam in its pharmaceutical formulations. The developed technique is very simple, precise, accurate, time saving, and economical, compared to all of the previously reported methods. The effects of various parameters on the sensitivity of the method were investigated. The best performance was obtained with a pH value of 2, scan rate value of 40 V/s, accumulation potential of (400) mV, and accumulation time of 0.4 s. The proposed method has some advantages over other reported methods, such as, no need for the removal of oxygen from the test solution, a picomolar detection limit, and finally that the method is fast enough for the determination of any such compound, in a wide variety of chromatographic methods. To obtain a sensitive determination, the integration range of currents was set for all the potential scan ranges, including oxidation and reduction of the Au surface electrode, while performing the measurements. The potential waveform, consisting of the potential steps for cleaning, accumulation, and potential ramp of analyte, was applied on an Au disk microelectrode (with a 12.5 µm in radius) in a continuous way. The method was linear over the concentration range of 1.5–364000 pg/ml (r=0.998) with a limit of detection and quantitation of 0.33 and 1.5 pg/ml, respectively. The method has the requisite accuracy, sensitivity, precision, and selectivity to assay piroxicam in tablets.     

Application of the Bismuth Film Electrode for Catalytic Adsorptive Stripping Potentiometric Determination of Cobalt in Dimethylglyoxime‐Nitrite System

Abstract

The application of bismuth film electrodes to the determination of cobalt by constant current adsorptive stripping potentiometry with exploitation of a catalytic effect is presented. The addition of NaNO₂ to the solution containing ammonia buffer and dimethylglyoxime results in a 25‐fold enhancement of the adsorptive stripping potentiometric cobalt signal. Several key parameters of the potentiometric stripping mode were optimized, including the composition of the supporting electrolyte, the stripping current, the accumulation potential, and the accumulation time. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=1.4% for a Co concentration of 2 µg L^?1), low detection limit (0.07 µg L^?1), and good linearity (up to 10 µg L^?1, R²=0.998) with a deposition time of 60 s and a stripping current of 10 µA. The method enables the determination of Co in the presence of high excesses of Ni or Zn.     

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.