Fast Fourier transformation with continuous cyclic voltammetry at an Au microelectrode for the determination of morphine in a flow injection system

For the fast morphine monitoring in flow injection systems a highly sensitive method is being introduced in this work. The fast Fourier transformation with continuous cyclic voltammetry (FFTCV) in a flowing solution as a detection system was applied for the prompt morphine monitoring. Here it should be stressed that this technique is simple, precise, accurate, time saving and economical. This research includes the observation of the effects of various parameters on the sensitivity of the detection system. Eventually, it was concluded that the best condition was obtained within the pH value of 2, scan rate value of 40 V s⁻¹, accumulation potential of 400 mV and accumulation time of 0.6 s.In detail, the noteworthy advantages which this method illustrates in comparison with other reported methods are the following; no necessity for the oxygen removal from the test solution, a sub-nano molar detection limit and the fast determination of any such compound in a wide variety of chromatographic methods.The method proved to be linear over the concentration range of 285-305,300 pg mL⁻¹ (r = 0.999) with a detection limit and a quantitation limit of 95.5 and 285 pg mL⁻¹, respectively. Consequently, the method illustrates the requisite accuracy, sensitivity, precision and selectivity to assay morphine in its tablets and biological fluids.     

Fast Fourier Continuous Cyclic Voltammetry at Gold Ultramicroelectrode in Flowing Solution for Determination of Ultra Trace Amounts of Penicillin G

In this work, for the first time a fast continuous cyclic voltammetry was used as a highly sensitive detection method for Penicillin G in a flow‐injection system. A special computer‐based numerical calculation method (using Fast Fourier Transformation) is introduced here for enhancing the analyte signal and noise reduction. During the measurements, the potential waveform (consists of potential steps for cleaning, stripping and potential ramp) was continuously applied on an Au disk microelectrode (with a radius 12.5 μm in radius). The stripping time was less than 200 ms. Effects of rest potential, sweep rate, and delay time on the sensitivity of the method were investigated. The limit of detection of the method was 1.0 × 10^?11 M. The detection limit of the method is 660 times lower than the most sensitive reported method. The relative standard deviation of the method at 1.0×10^?7 M of Penicillin G was 2.7% for 10 runs.     

Development a New Method for the Determination of Chloropromazine in Trace Amounts by Fast Fourier Continuous Cyclic Voltammetry at an Au Microelectrode in a Flowing System

In this study a new technique has been developed for the determination of chloropromazine in flow‐injection systems. The technique, named fast Fourier transformation continuous cyclic voltammetry (FFTCV), basically illustrates the benefits of sensitivity, selectivity, simplicity and low detection limit. It is also important to refer to the positive points, presented only by the use of this technique. Firstly, it is no longer necessary to remove the oxygen from the test solution. Furthermore, the quick determination of any such compound in many chromatographic methods is possible. Thirdly, the corresponding detection limit is of sub‐nanomolar level. Additionally, a special computer based numerical method is also introduced for the calculation of the analyte signal and noise reduction. The electrode response was calculated in accordance with the partial and total charge exchanges on the electrode surface, after the background current subtraction from that of noise. The integration range of currents was set for all the potential scan ranges, including oxidation and reduction of Au surface electrode, to obtain a sensitive determination. The performed experiments aimed at measuring the effects of different parameters on the method sensitivity. In the end of these measurements, it was concluded that the method was linear for the concentration range of 0.32–31900 pg/mL (r = 0.996) with a limit of detection and quantitation 0.1 and 0.32 pg/mL, respectively. For the achievement of these optimum results, the parameter values were set to 100 V/s for the scan rate, 0.4 s for accumulation time, 800 mV for accumulation potential and 2 for the pH.     

Monitoring of Anti Cancer Drug Letrozole by Fast Fourier Transform Continuous Cyclic Voltammetry at Gold Microelectrode

A continuous cyclic voltammetric study of letrozole at gold microelectrode was carried out. The drug in phosphate buffer (pH 2.0) is adsorbed at ?200 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 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^?10 mol/L (r=0.9975) with a limit of detection and quantitation 0.08 nmol/L and 0.15 nmol/L, respectively. The method has the requisite accuracy, sensitivity, precision and selectivity to assay letrozol in tablets. The influences of pH of eluent, accumulation potential, sweep rate, and accumulation time on the determination of the letrozol were considered.     

A novel method for fast determination of vitamin B6 by fast continuous cyclic voltammetry

In this work a novel method for the determination of Vitamin B6 in flow-injection systems has been developed. The fast Fourier transform continuous cyclic voltammetry (FFTCV) at gold microelectrode in flowing solution system was used for determination of Vitamin B6. This method is rapid, simple and highly sensitive procedures allowing the determination of Vitamin B6 in pharmaceutical analysis. The effects of various parameters on the sensitivity of the method were investigated. The best performance was obtained with the pH value of 2, scan rate value of 30 V/s, accumulation potential of 200 mV and accumulation time of 0.3 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 sub-nanomolar detection limit, and finally 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 (12.5 μm in radius) in a continuous way. The detection limit of the method for Vitamin B6 was 2.8 pg/ml. The relative standard deviation of the method at 2.1% was 8 runs. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 2, pp. 173–181. The text was submitted by the authors in English.     

Novel method for the determination of trace amounts of metformin in its pharmaceutical formulation by fast Fourier continuous cyclic voltametric technique at Au microelectrode in flowing solutions

An easy and fast Fourier transform continuous cyclic voltametric technique for monitoring of ultra trace amounts of metformin in a flow-injection system has been introduced in this work. The potential waveform, consisting of the potential steps for cleaning, stripping and potential ramp, was continuously applied on an Au disk microelectrode (12.5 μm in radius). The proposed detection method has some of advantages, the greatest 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. The detection limit for metformin was 43 pg/ml. The relative standard deviation (RSD) of the proposed technique at 5.0 × 10⁻⁷ M was 2.2% for 10 runs. The influences of pH of eluent, accumulation potential, sweep rate, and accumulation time on the determination of the metformin were considered. The proposed method was applied to the determination of metformin in a pharmaceutical preparation. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 10, pp. 1221–1230. The text was submitted by the authors in English.     

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.     

Preparation of Carbon Nanowall and Carbon Nanotube for Anode Material of Lithium-Ion Battery

Carbon nanowall (CNW) and carbon nanotube (CNT) were prepared as anode materials of lithium-ion batteries. To fabricate a lithium-ion battery, copper (Cu) foil was cleaned using an ultrasonic cleaner in a solvent such as trichloroethylene (TCE) and used as a substrate. CNW and CNT were synthesized on Cu foil using plasma-enhanced chemical vapor deposition (PECVD) and water dispersion, respectively. CNW and CNT were used as anode materials for the lithium-ion battery, while lithium hexafluorophosphate (LiPF₆) was used as an electrolyte to fabricate another lithium-ion battery. For the structural analysis of CNW and CNT, field emission scanning electron microscope (FE-SEM) and Raman spectroscopy analysis were performed. The Raman analysis showed that the carbon nanotube in composite material can compensate for the defects of the carbon nanowall. Cyclic voltammetry (CV) was employed for the electrochemical properties of lithium-ion batteries, fabricated by CNW and CNT, respectively. The specific capacity of CNW and CNT were calculated as 62.4 mAh/g and 49.54 mAh/g. The composite material with CNW and CNT having a specific capacity measured at 64.94 mAh/g, delivered the optimal performance.     

Nonlinear alignment of chromatograms by means of moving window fast Fourier transfrom cross‐correlation

The preprocessing of chromatograms is essential to modern chromatography for further qualitative and quantitative analysis, especially when chromatographic instruments are used for herb products analysis involving large number of samples. To accurately compare and analyze the obtained chromatograms, it is necessary to preprocess, especially align retention time shifts. Here moving window fast Fourier transform (FFT) cross‐correlation is introduced to perform nonlinear alignment of high‐throughput chromatograms. Since elution characteristics of chromatograms will produce local similarity in retention time shifts, moving window procedure seems to be a better substitute of segmentation steps. The retention time shifts can be calculated and accelerated by FFT cross‐correlation. The artifacts can be detected and eliminated from the retention time shifts profile since the continuity of moving window procedure. The proposed method is demonstrated in comparison with recursive alignment by FFT on chromatographic datasets from herb products analysis. It is shown that the proposed method can address nonlinear retention time shift problem in chromatograms with the simple moving window procedure, which will not introduce segments size optimization problem. In additional, the parameters are intuitive and easy to adjust, which makes it off‐the‐shelf toolbox for alignment of chromatograms.     

Simultaneous extraction and determination of trace amounts of diclofenac from whole blood using supported liquid membrane microextraction and fast Fourier transform voltammetry

A novel, simple, and inexpensive analytical technique based on flat sheet supported liquid membrane microextraction coupled with fast Fourier transform stripping cyclic voltammetry on a reduced graphene oxide carbon paste electrode was used for the extraction and online determination of diclofenac in whole blood. First, diclofenac was extracted from blood samples using a polytetrafluoroethylene membrane impregnated with 1‐octanol and then into an acceptor solution, subsequently it was oxidized on a carbon paste electrode modified with reduced graphene oxide nanosheets. The optimal values of the key parameters influencing the method were as follows: scan rate, 6 V/s; stripping potential, 200 mV; stripping time, 5 s; pH of the sample solution, 5; pH of the acceptor solution,7; and extraction time, 240 min. The calibration curves were plotted for the whole blood samples and the method was found to have a good linearity within the range of 1–25 μg/mL with a determination coefficient of 0.99. The limits of detection and quantification were 0.1 and 1.0 μg/mL, respectively. Using this coupled method, the extraction and determination were merged into one step. Accordingly, the speed of detection for sensitive determination of diclofenac in complex samples, such as blood, increased considerably.     

Nonelectroactive recognition: Monitoring of perphenazine by its subsecond adsorption on an Au microelectrode by the fast fourier transform continuous cyclic voltammetric technique (FFTCCV)

A novel method for determining perphenazine in flow-injection systems has been developed in this work. The method was successfully applied for fast determination of perphenazine in its pharmaceutical formulations. Being very simple, precise, accurate, time-saving, and economical, this method has many advantages compared to all of the previously reported methods. Some investigations were also performed to find the effects of various parameters on the sensitivity of the proposed method. The conditions responsible for the performance were a pH value of 2, a scan rate value of 30 V/s, an accumulation potential of 500 mV, and an accumulation time of 0.8 s. Some of the advantages of the proposed method are as follows: the removal of oxygen from the test solution is not required anymore, the detection limit of the method is subnanomolar, and finally, the method is fast enough to determine such compounds in a wide variety of chromatographic methods. We also introduce a special computer-based numerical method to calculate the analyte signal and noise reduction. After subtraction of 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 (a radius of 12.5 μm). The detention limit of the method for perphenazine was 15 pg/ml. For eight runs, the relative standard deviation of the method at 1.1 × 10⁻⁸ M was 2.1%. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 9, pp. 1093–1102. The text was submitted by the authors in English.     

Multi-walled carbon nanotube paste electrode for selective voltammetric detection of isoniazid

A multi-walled carbon nanotube paste electrode (MWCPE) is prepared as an electrochemical sensor with high sensitivity and selectivity in responding to isoniazid. The electrochemical oxidation of isoniazid is investigated in buffered solution by cyclic and differential pulse voltammetry. The electrode is shown to be very effective for the detection of isoniazid in the presence of other biological reductant compounds. The electrochemical oxidation of cysteine, due to the high overvoltage, is completely stopped at the surface of MWCPE. The electrode exhibits a very good resolution between the voltammetric peak of isoniazid and the peaks of ascorbic acid (AA) and dopamine (DA). A resolution of more than 450 mV between the anodic peak potentials makes the MWCPE suitable for simultaneous detection of isoniazid in the presence of AA or DA in clinical and pharmaceutical preparations. Differential pulse voltammetry (DPV) is applied as a sensitive method for the determination of isoniazid. The linear range in these determinations is 1 × 10⁻⁶–1 × 10⁻³ M for isoniazid and the detection limit is 5 × 10⁻⁷ M. The electrode was applied to the simultaneous determinations in isoniazid and AA mixtures and also, isoniazid and DA mixture over a wide concentration range. The slope variation for the calibration curves of isoniazid (RSD) was less than 4.5% (based on ten measurements over a period of three months).     

功能化多壁碳纳米管的光电性质

表面光电压谱;循环伏安;金刚石薄膜电极;功能化多壁碳纳米管的光电性质     

循环伏安法测定维生素B6

循环伏安法测定维生素B6;多壁碳纳米管;修饰玻碳电极;循环伏安法     

Efficient strategy for quality control of screen-printed carbon ink disposable sensor electrodes based on simultaneous evaluation of resistance,capacitance and Faradaic current by Fourier transform AC voltammetry

Two types of mass-produced, screen-printed carbon ink-based macrodisc electrodes suitable for routine sensing applications have been fabricated. Microscopic examination of these carbon ink electrode surfaces reveals that their surfaces are both rough and highly heterogeneous, consisting of random arrays of carbon particles of different sizes, as well as binder. Consequently, they may suffer from a lack of reproducibility in their performance because of variable resistance, capacitance or electroactive area. Use of a Fourier transform AC voltammetric protocol involving application of periodic waveform obtained from summation of five sine waves of variable frequency enabled resistance and capacitance, as well as DC and AC Faradaic currents associated with the model processes or (where FcMeOH is ferrocene methanol) to be assessed from a single experiment. Such data, which may be obtained rapidly via this approach, are highly suitable for quality control assessment.     

Robust alignment of chromatograms by statistically analyzing the shifts matrix generated by moving window fast Fourier transform cross‐correlation

Retention time shift is one of the most challenging problems during the preprocessing of massive chromatographic datasets. Here, an improved version of the moving window fast Fourier transform cross‐correlation algorithm is presented to perform nonlinear and robust alignment of chromatograms by analyzing the shifts matrix generated by moving window procedure. The shifts matrix in retention time can be estimated by fast Fourier transform cross‐correlation with a moving window procedure. The refined shift of each scan point can be obtained by calculating the mode of corresponding column of the shifts matrix. This version is simple, but more effective and robust than the previously published moving window fast Fourier transform cross‐correlation method. It can handle nonlinear retention time shift robustly if proper window size has been selected. The window size is the only one parameter needed to adjust and optimize. The properties of the proposed method are investigated by comparison with the previous moving window fast Fourier transform cross‐correlation and recursive alignment by fast Fourier transform using chromatographic datasets. The pattern recognition results of a gas chromatography mass spectrometry dataset of metabolic syndrome can be improved significantly after preprocessing by this method. Furthermore, the proposed method is available as an open source package at https://github.com/zmzhang/MWFFT2 .     

Theoretical description of a new analytical technique: comprehensive online multidimensional fast Fourier transform separations

Comprehensive multidimensional separations are today dominated by systems that are fundamentally limited to highly asymmetrical online separations sacrificing separation space, or to lengthy, time consuming offline separations. With the exception of pulse-modulated methods, separations have thus been limited to two dimensions. It is proposed that some of the limitations and shortcomings of these methods may be ameliorated or overcome by employing multi-dimensional detection whereby each analyte is effectively labelled in the frequency domain by a series of pulsed-injections, and a symmetrical, comprehensive online analysis performed with the resulting signal processed by sequential Fourier analysis. A semi-empirical computer model of this system was developed and its feasibility positively demonstrated in simulations of high-efficiency separations in two dimensions. Separations of higher dimensionality were shown to be possible but involved signal-processing challenges beyond the present work. By eliminating wrap-around effects and enabling the separation of physically unseparated peaks, the technique facilitates significant improvements in peak capacity per unit of analysis time as well as greatly improved signal to noise ratios. Because these comprehensive online multidimensional Fourier transform separations depend heavily upon the practical lifetime of imposed injection pulses, it is envisaged that this method will leverage emerging high-efficiency micro- and nanoscale separations technologies.     

Development of fast Fourier transform continuous cyclic voltammetry at Au microelectrode in flowing solutions as a novel method for sub-nanomolar monitoring of lidocaine in injection and biological fluids

In this work a novel method for the fast monitoring of lidocaine in flow-injection systems has been developed. The fast Fourier transform continuous cyclic voltammetry (FFTCV) at gold microelectrode in flowing solution system was used for determination of lidocaine in its pharmaceutical formulation. The presented technique was very simple, precise, accurate, time saving and economical, compared with all of the previously reported methods. The recommended technique demonstrated some advantages over other reported methods. Firstly, there was no need for the oxygen removal from the test solution. Secondly, a picomolar detection limit was achieved, and additionally, the method was fast enough for the determination of any such compound, in a wide variety of chromatographic methods. The method was linear across the concentration range of 240-1.1 × 10⁵ pg mL⁻¹ (r = 0.996) with a limit of detection and quantitation 117.3 and 240 pg mL⁻¹, respectively. As a conclusion this system offers the requisite accuracy, sensitivity, precision and selectivity to assay lidocaine in injections.     

Bias-current modulation technique of a radio-frequency glow discharge plasma for atomic emission analysis associated with a fast Fourier transform analyzer

A measuring method using a fast Fourier transform (FFT) analyzer is suggested to estimate the emission intensity from a radio-frequency (RF)-powered glow discharge plasma for atomic emission analysis. The FFT analyzer has an ability to disperse the components by frequency from an overall signal, and thus works as a selective detector in modulation spectroscopy. In the RF glow discharge plasma, a dc bias current can be introduced by connecting an external electric circuit with the discharge lamp, which predominantly enhances the emission intensities. Further, the bias current can be pulsated with a switching device to modulate the emission intensities, and then the modulated component was selectively detected with the FFT analyzer. This method greatly improved the data precision. The emission intensity of the Cu I 324.75-nm line in an Fe-based alloy sample containing 0.043 mass% Cu could be estimated with a relative standard deviation of 0.20%. The 3σ detection limits of Cu in Fe-based alloys could be obtained to be 2.3 × 10^− 6 mass% Cu for Cu I 324.75 nm and 6.8 × 10^− 6 mass% Cu for Cu I 327.40 nm.     

Electrochemical determination of sulfaguanidine using COOH-MWCNT coated GC electrode

The electrochemical behavior of sulfaguanidine was investigated in PBS buffer aqueous solutions. Cyclic voltammograms have shown that (1) the Sg provided a well-defined irreversible oxidation peak (2) the signal-to-background current ratio is 3 times higher at COOH-MWCNT coated GCE than that of bare GCE and (3) the modifying GCE surface by COOH-MWCNT led to a significant improvement (2.7 folds) of the electrochemical response. It has been shown that Sg oxidizes according to a diffusion-controlled mechanism. A linear calibration curve was obtained for the oxidation of Sg at 10–70 μM. The COOH-MWCNT coated GCE has also been successfully used for the determination of Sg in real samples.