Stripping Voltammetric Method Research Articles

Multiwall Carbon Nanotubes/Spherical Glassy Carbon as Environmentally Friendly Adsorption Materials Utilized in Adsorptive Stripping Voltammetry for the Determination of Trace Amounts of Ga(III).

This work presents a proposal for an adsorptive stripping voltammetric (AdSV) method for gallium(III) determination at an eco-friendly multiwall carbon nanotube/spherical glassy carbon (MWCNT/SGC) electrode modified with a lead film. The operational factors influencing the sensitivity of the AdSV procedure were thoroughly investigated, and their most favorable values were chosen (0.1 mol L-1 acetate buffer solution pH = 5.6; 7 × 10-5 mol L-1 Pb(II); 2 × 10-4 mol L-1 cupferron; potential/time of lead film formation: -1.9 V/30 s; potential/time of Ga(III)-cupferron adsorption: -0.75 V/30 s). The newly developed MWCNT/SGCE has proven to be a competitive substrate to the glassy carbon electrode to create a lead film electrode, since it allows the determination of gallium in a wider range of concentrations from 3 × 10-9 to 4 × 10-7 mol L-1 with a lower limit of detection equal to 9.5 × 10-10 mol L-1. The elaborated procedure has been shown to be highly selective and insensitive to the presence of an even 100-fold excess of most of the ions commonly found in environmental waters. The MWCNT/SGC sensor, which can maintain >95% of its original response after 70 days of use, has been successfully applied for the detection of gallium in water samples with the relative standard deviation (RSD) ranging from 4.5% to 6.2% (n = 3) and recoveries in the range from 95.3% to 104.9%.

2 in 1 versus 1 plus 1 – Outcomes of the transformation of adsorptive stripping method for the Ni2+ and Co2+ determination

AbstractDue to the similar chemical properties of Ni2+ and Co2+, several dozens of adsorptive stripping voltammetric (AdSV) methods have been developed for their simultaneous determination. The question was would there be some benefits if a stripping method made for simultaneous determination of Ni2+ and Co2+ will be optimized for the determination of only one of them (Ni2+). It was found that the optimized method has for an order of magnitude lower LOQ (1.89×10−10 M), an order of magnitude lower influence of Co2+, and the applicability of one calibration line for four orders of magnitude of Ni2+ concentration. The influence of some common anions and cations has been examined. The developed method was successfully applied for nickel content determination in real samples. The suitability of the developed method for the determination of Co2+ from the same solution in the second run, upon optimizations of deposition potential and time, was also explored. The LOQ obtained for Co2+ (3.61×10−11 M) is almost two orders of magnitude lower than LOQ of the method for simultaneous determination of both cations and, its LOD and LOQ are among few lowest obtained by AdSV methods for Co2+ determination. The developed method for Ni2+ and Co2+ determination from the same solution in two successive runs has significantly better analytical performances than the starting method for their simultaneous determination in one run.

A square-wave anodic stripping voltammetric method for determining carbendazim in pineapple and orange juices without sample pre-treatment

Carbendazim is a fungicide used for pest control in fruit crops. However, carbendazim is dangerous to human health and the environment, requiring monitoring by appropriate analytical methods. For this, a square-wave anodic stripping voltammetric method was developed for the first time for determining carbendazim in orange and pineapple juices. As a sensor, the proposed method uses a carbon paste electrode modified with cobalt phthalocyanine. The optimized voltammetric parameters were: rest time = 5 s, pulse amplitude = 30 mV, potential increment = 1.0 mV, frequency = 20 s−1, potential window ranging from + 0.6 to + 1.1 V, peak potential (+0.90 V) and deposition time = 45 s. The method presented a linear response (r2 = 0.994, n = 8, limits of detection = 0.57 nmol L−1) from 49.7 to 384.6 nmol L−1 carbendazim, good reproducibility (relative standard deviation = 2.4 %) and accuracy (recovery rates = 93.3–107.9 %). The proposed method is superior to other methods reported in the literature because the preparation of the sensor is faster, as well as being simple, sensitive, selective, low-cost, high-frequency analysis, and eco-friendly as it does not use any sample pre-treatment (sonication, centrifugation, filtration, pre-concentration, dilution and/or extraction with organic solvents).

Voltammetric determination of organic UV filters by carbon paste electrodes modified with pyridinium-based ionic liquids

The rapid and sensitive voltammetric determination of organic UV filters benzophenone-3 (BP-3) and avobenzone (AVO) was performed by an ionic liquid carbon paste electrode (IL-CPE). Namely, the synthesized pyridinium-based ILs, 1-butyl-3-methylpyridinium chloride ([N–C4–3C1Py]Cl) and 1-ethoxyethyl-3-methylpyridinium chloride ([N–C2OC2–3C1Py]Cl) were compared as bulk CPE modifiers for BP-3 determination. [N–C4–3C1Py]Cl-CPE showed more favorable interactions with the target analyte, and it was tested for AVO determination, too. Cyclic voltammetric (CV) studies suggested that the irreversible electrode reaction is adsorption controlled in the case of both UV filters. Also, the square-wave adsorptive stripping voltammetric (SW-AdSV) method was optimized for quantifying selected UV filters. In the model solutions, the linear calibration curve was obtained by the SW-AdSV method in the concentration range from 0.05 to 0.89 μg mL−1 at pH 3.0 for BP-3 (Eacc = −0.7 V, tacc = 100 s), and from 0.05 to 1.77 μg mL−1 at pH 11.98 for AVO (Eacc = 0.2 V, tacc = 100 s). The evaluated limit of detection (LOD) was 0.015 μg mL−1 in both cases, while the relative standard deviation (RSD) was lower than 1.5%. The affordable IL-based voltammetric sensor fulfills the main requirements for application in real samples due to an adequate selectivity towards selected analytes in the presence of interferents usually found in swimming pool water. Therefore, the BP-3 and AVO were quantified in a swimming pool water matrix with good repeatability and recovery. The obtained results demonstrate an excellent potential of the IL-CPEs, especially of the [N–C4–3C1Py]Cl-CPE, for determining selected UV filters in various real samples.

An Electrochemical Sensor for the Determination of Trace Concentrations of Cadmium, Based on Spherical Glassy Carbon and Nanotubes.

The practical application of a novel, eco-friendly electrochemical sensor based on low-dimensional structures, spherical glassy carbon microparticles, and multiwall carbon nanotubes is described. This sensor, modified with a bismuth film, was used for the determination of Cd(II) by the anodic stripping voltammetric method. The instrumental and chemical factors influencing the sensitivity of the procedure were thoroughly investigated and their most favorable values were selected (acetate buffer solution pH = 3 ± 0.1; 0.15 mmol L-1 Bi(III); activation potential/time: -2 V/3 s; accumulation potential/time: -0.9 V/50 s). Under the selected conditions, the method exhibited linearity in the range of 2 × 10-9 to 2 × 10-7 mol L-1 Cd(II) with a detection limit of 6.2 × 10-10 mol L-1 Cd(II). The results obtained also showed that the application of the sensor for Cd(II) detection did not experience any significant interference in the presence of a number of foreign ions. The applicability of this procedure was evaluated using TM-25.5 Environmental Matrix Reference Material and SPS-WW1 Waste Water Certified Reference Material as well as river water samples through addition and recovery tests.

THE METAL IONS CONCENTRATION DETERMINING IN THE SOLUTIONS USING VOLTAMMETRIC ANALYZER

Ion exchange materials are successfully used for solution of a number of practical problems, such as production processes waste-free technology creation, industrial wastewater treatment, rational natural resources and environmental protection use. The Physicochemical and sorption characteristics study is needed for the determination of ion exchangers application promising areas, however chemical research methods are laborious, and atomic absorption spectroscopy is not always available. The purpose of this work is to find and use available methods, which do not require complex technological equipment for metal ions concentration determining in the solutions. Methodology. Stripping voltammetric determination of metal ions by addition method has been used to determine the equilibrium concentrations of metal ions in the solutions. Results and discussion. The non-ferrous metal ions concentration determining methods have been developed and used on the voltammetric analyzer «Ecotest BA», which is a real economical alternative to expensive methods of analysis. Stripping voltammograms of samples, which contain cadmium and copper, zinc, lead cations; vanadate ion, molybdate ion were constructed. The ions concentrations in the equilibrium solutions after sorption are calculated. Conclusion. The stripping voltammetric method is convenient for studying the sorption and ion-exchange materials complexing properties; it and also allows to determine several metals without their preliminary separation resorting.

Recent development of eco-friendly nanocomposite carbon paste electrode for voltammetric determination of Cd(II) in real samples

Using eco-friendly, cheap, and available adsorbents is promising for the determination of metal ions. So, this study focuses on the modification of graphite reinforcement carbon paste electrode (GRCPE) with mango seed kernel (MSK) for voltammetric determination of Cd(II). Moreover, to increase the surface area of this adsorbent, it was prepared in nanosized that formed nanoparticles of mango seed kernel (MSK-NPs). The developed nanocomposite electrode of carbon paste electrode modified with nanoparticles of mango seed kernel (MSK-NPs@GRCPE) was characterized using Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM). The effect of pH, buffer solution, and supporting electrolyte as experimental conditions were optimized through differential pulse adsorptive anodic stripping voltammetric method (DPAdASV). Britton-Robinson buffer pH = 3.9 at Eacc = – 1400 mV, tacc = 30 s, pulse width = 10 ms and sampling time = 8 ms were the optimum conditions for determination of Cd(II). The LOD and LOQ of MSK-NPs@GRCPE were calculated at 5.44 × 10–9 and 1.65 × 10–8 M, respectively. Compared with bare graphite reinforcement carbon paste electrode (BGRCPE), the nanocomposite MSK-NPs@GRCPE has a lower detection limit, indicating that the presence of MSK-NPs could greatly improve the response to Cd(II). The practical applicability of the electrode was verified by the determination of Cd(II) in chocolate and white rice samples. The results show high selectivity and sensitivity for Cd(II) in real samples.Graphical abstract

Arsenic (III) detection with underpotential deposition on gold

We report a new, sensitive stripping voltammetric method for the detection of As(III) in aqueous solution using either a gold macroelectrode or a gold nanoparticle-modified glassy carbon electrode (GCE) based on the underpotential deposition (UPD) of As ad-atoms. The pre-concentration step deposits and accumulates As ad-atoms onto gold and is followed by a potential sweep to strip the ad-atoms with no interference from Cu(II) or Cl- at either electrode. Linear responses were found for the range 0.01 μM to 0.1 μM or 0.005 μM to 0.1 μM at gold macroelectrodes and gold nanoparticle-modified electrodes, respectively. The visually clearly discernable signals recorded at 0.005 μM (0.4 ppb) on gold nanoparticle-modified electrodes suggests that this method has practical value given the WHO limit of 0.13 μM (10 ppb) for drinking water.

Analytical Comparison of Cefadroxil Determination by Square Wave Adsorptive Stripping Voltammetric and Spectrophotometric Methods

The goal of this research is to verify the proposed nano-silver amalgam paste electrode (Ag-nano-SPE) method to compare with a spectrophotometric technique based on derivatization with potassium periodate (KIO4 ), 2,4-dinitrophenyl hydrazine (DNP) and sodium hydroxide (NaOH) for the estimation of cefadroxil (CFDL) by square wave adsorptive stripping voltammetry (SWAV). The different parameters of both methods were optimized in detail separately and then compared their efficiency, selectivity, sensitivity and applications. The SWAV produced a reduction peak with a precise definition at -0.160 V while measuring CFDL in 0.04 molL-1 Britton–Robinson buffer at pH 4, accumulation potential (0.5 V), accumulation time (10 sec), and with stirring rate of 200 rpm. Whereas, the CFDL was measured at 515 nm (λmax) by UVVisible spectrophotometer after the derivatization by using 1.5 mL of 0.5 mM DNP, 1.5 mL of 6.52 mM KIO4 and 0.5 mL of 10 M NaOH solution at room temperature. The linear response for CFDL was found using the SWAV and spectrophotometric techniques along a linear dynamic range from 0.033 - 0.304 and 0.051 - 1.376 µM, respectively. However, the precision, detection limit and quantification limit of SWAV for CFDL in the samples and standards significantly lower (p <0.01) as compared to spectrophotometric method. This indicates that the SWAV is more sensitive and selective than the spectrophotometric technique for regular CFDL analysis.

ПОРІВНЯЛЬНА ХАРАКТЕРИСТИКА ЕФЕКТИВНОСТІ ЕЛЕКТРОХІМІЧНИХ МЕТОДІВ ДОСЛІДЖЕННЯ ВМІСТУ ВАЖКИХ МЕТАЛІВ У СТІЧНИХ ВОДАХ

Сompare the various modern electrochemical research methods effectiveness used to determine the heavy metals concentration in waste water, based on the literature data. Methodology. Analysis of literature data on the possibilities, advantages and disadvantages of voltammetric, potentiometric, coulometric and conductometric methods for the heavy metals content studying in waste water. Findings. The electrochemical methods are the most common methods for analyzing the composition of waste water. Among their advantages, it should be noted high selectivity, low concentration registration limit (up to 10-10 M for stripping voltammetric methods), simplicity in execution, absence of preliminary long-term samples preparation for analysis, the ability to microvolumes measure without samples destroying and automation of the process for continuous metals concentrations determination in waste water treatment, relatively inexpensive equipment, the ability to determine the concentration of several metal ions in a mixture. Originality. The studies have shown that most often the concentration of heavy metals in waste water determine with the using of the different modifications of voltammetric research methods (polarography and varieties of stripping voltammetry) and potentiometric research methods in particular with highly sensitive and specific ion-selective indicator electrodes. Practical value. The theoretical material on modern electrochemical methods for the heavy metal ions content determining in waste water is generalized.

Voltammetric determination of a fluoroquinolone antibiotic based on multilayer reduced graphene oxide sensor prepared directly, promptly by electrochemically expanding graphite electrode surface

ABSTRACT Ciprofloxacin (Cip), a fluoroquinolone antibiotic, was determined by linear sweep adsorptive stripping voltammetric method using multilayer reduced graphene oxide electrode (m-rGO). The m-rGO electrode was fabricated directly, simply and promptly from graphite platform by potentiostatic technique without further modification. The produced electrode exhibited excellent performance for ciprofloxacin (Cip) determination with a much higher signal of Cip than that on the initial graphite electrode (13.4 times). This dominance of the m-rGO electrode resulted from the large electrochemically active surface area, electrochemical catalysis, suitable functional groups on the electrode surface. Experimental conditions such as the electrode fabrication time, the supporting solution, and accumulation time were optimised to obtain the Cip highest signal. A Cip analytical method established under the optimal conditions had a good linear relationship between the Cip signal with its concentration range from 0.5 to 20 µM (R2 = 0.9953). The method showed a low detection limit (LOD = 0.078 µM), satisfactory reproducibility (RSD = 1.50%), and high accuracy. Cip concentration in a spiked lake water sample determined by the proposed method with acceptable precision (RSD = 5.59%) and trueness (recovery = 94.2–106.3%) was comparable with LC-MS/MS method.

Arsenic (III) Detection with Underpotential Deposition and Anodic Stripping Voltammetry

AbstractWe report a stripping voltammetric method for the detection of aqueous As(III) using a Pt macroelectrode or a Pt nanoparticle‐modified glassy carbon electrode (GCE) which, novelly, is based on the underpotential deposition of As atoms. The method consists of a pre‐concentration reductive step to accumulate As ad‐atoms onto Pt, followed by linear sweep voltammetry (LSV). It is shown that the stripping peak of As ad‐atoms improves the response at low concentrations of As(III) as compared to analogous measurements using the deposition of bulk As. No interference was seen from Cu(II) at realistic concentrations although high concentrations of chloride inhibited the deposition of the ad‐atoms. A linear response was found for the concentration range 0.05 to 1 μM As(III) at both types of electrode with a visually clear signal recorded at 0.05 μM (4 ppb), suggesting that this method has practical value noting the WHO limit of 0.13 μM (10 ppb) for safe drinking water.

Nimesulide Determination on Carbon Black-Nafion Modified Glassy Carbon Electrode by Means of Adsorptive Stripping Voltammetry

Adsorptive Stripping Voltammetric method for Nimesulide (NIM) determination was developed. As a working electrode, glassy carbon electrode (GCE) modified with carbon black and Nafion (CB-Nafion GCE) was used. All measurements were carried out in 0.1 M acetate buffer (pH 4.6). Conducted experiments allowed to optimize differential pulse voltammetry (DPV) instrumental parameters: sampling and waiting time ts = tw = 10 ms, step potential Es = 4 mV, and pulse amplitude ΔE = 50 mV. The best results were obtained for preconcentration potential and time equal to 400 mV and 20 s, respectively. Limit of detection was calculated and was equal to 0.14 µM for 20-s preconcentration time and 0.06 µM for 40-s preconcentration time. In order to prove the applicability of the developed method, concentration of nimesulide in pharmaceutical products was determined. Calculated recoveries were in the range 94–99%, which indicates that the method might be assumed as accurate. Coefficient of variation was equal to 5.0% (n = 7, NIM concentration 1 µM) Obtained results of NIM determination were in good agreement with the content declared by producers.

Voltammetric study of itraconazole an antifungal drug at glassy carbon electrode in acidic medium: A simple plus cost-effective detection method

In this study, the electro-oxidative behaviour and determination of itraconazole at a glassy carbon electrode have been investigated using cyclic voltammetry, differential pulse anodic stripping voltammetry (DPASV), and square wave anodic stripping voltammetric (SWASV) techniques, under different experimental conditions. The voltammetric peak current for the oxidation of itraconazole has been analyzed at different pH, scan rate and concentrations. The voltammograms have exhibited irreversible oxidation of ITRA in B.R. buffer of pH 3.0. The oxidation of itraconazole gives a well-defined irreversible peak at glassy carbon electrode vs. Ag/AgCl as reference electrode. The oxidation process is adsorption controlled. A linear response has been obtained between 26.7×10–6 to 152.8×10–6 M in non-aqueous media for all the techniques. The analyzed square wave anodic voltammetric and differential pulse anodic stripping voltammetric methods show limit of detection at 27.28 µM and 65.16 µM respectively. Ultimately, the proposed validated method has been effectively applied for the determination of the antifungal drug which is commercially available in solid form.

Multivariate optimization of a novel electrode film architecture containing gold nanoparticle-decorated activated charcoal for voltammetric determination of levodopa levels in pre-therapeutic phase of Parkinson`s disease

• Activated charcoal (AC) is a low cost alternative material for electroanalysis. • A robust modified electrode is developed by immobilizing gold nanoparticle-decorated activated charcoal (AuNPs-AC) film. • A Doehlert matrix design experiment is used to optimize the electrode performance. • The AuNPs-AC based sensor presents enhanced response toward an antiparkinsonian drug sensing • The voltammetric method was successfully applied for levodopa determination in biological and environmental samples. Levodopa analysis is important to monitor progress of patients in Parkinson's disease, as well as to determine the treatment directions. In this way, the development of an electrochemical sensor based on a glassy carbon electrode modified with gold nanoparticles supported in activated charcoal with an epichlorohydrin-reticulated chitosan film was carried out under the assistance of a Doehlert matrix design experiment. The resulting electrode was subjected to a series of characterization techniques, including scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, for morphological analysis, as well as electrochemical impedance spectroscopy and cyclic voltammetry for electrochemical characterization. The active surface presented response for electrocatalytic oxidation of levodopa with high current response at reduced potential, which was applied, along with a square-wave adsorptive anodic stripping voltammetric methodology, for analysis of levodopa in different samples, presenting a three order of magnitude linear concentration range (50.0 nmol L −1 to 10.0 µmol L −1 ), low detection limit of 8.2 nmol L −1 , good recovery analysis of spiked samples with low signal deviation under the presence of interfering species, and good accuracy front a comparative methodology. Schematic representation of experimental steps followed for determination of levodopa levels in pre-therapeutic phase of Parkinson`s disease by a square-wave adsorptive anodic stripping voltammetric method.

Potential Diagnostic Significance of Salivary Copper Determination in Breast Cancer Patients: A Pilot Study.

Determination of the copper content in the saliva of breast cancer patients was carried out to assess the potential diagnostic and prognostic value. The malignant group included 75 breast cancer patients; the benign group included 87 patients with fibroadenomas; and the control group included 20 volunteers without breast pathology. All participants had 1 ml of saliva collected prior to treatment. The determination of copper in saliva was carried out by the stripping voltammetric method. Overall survival was assessed using the Kaplan-Meier method with the presentation of survival curves and the calculation of the significance of differences by Log-rank. The average copper content in the saliva of breast cancer patients is 49.3% higher than in patients with fibroadenomas and 60.4% higher than in volunteers without breast pathologies. Within the group of breast cancer patients, the content of copper in saliva is heterogeneous, which limits the possibilities of using this indicator for diagnostic purposes. The copper content increases when comparing the initial stages and locally widespread (+ 22.4%) and then sharply increases by 3.5 times at the T3-4N0-2M0 stage. For HER2-positive breast cancer, the copper content in saliva is 51.9% higher than for HER2-negative, a similar pattern was observed for luminal A and B breast cancer subtypes. The content of copper in saliva less than 1.14 mg/l is a prognostically unfavorable sign, while the relative risk of dying from breast cancer more than doubles. Thus, the content of copper in saliva can be used in clinical practice for planning treatment tactics.

Square‐wave Anodic Stripping Voltammetric Method for Novelty Detection of Bismuth Extracted by Aqueous Two‐phase Systems

AbstractIn this work, a voltammetric sensor was used to monitor the concentration of bismuth extracted from an eutectic alloy of BiSn by aqueous two‐phase system. This strategy is a sustainable and economically viable way of recovering bismuth from secondary sources. In the aqueous two‐phase system (ATPS), biodegradable and non‐toxic constituents dispersed in water (major constituent) are used. For monitoring the extraction, bismuth was determined in the upper phase of the aqueous two‐phase system, which is rich in L35 copolymer, that causes attenuation of the electrochemical signal (anodic peak current). The electrode and operational parameters of the square‐wave anodic stripping voltammetry (SWASV) were evaluated according to the deposition and stripping processes of the bismuth on the surface of the carbon paste electrode (CPE). It was observed a similarity between the electrochemical response of the bismuth extracted by ATPS and with the standard solution of bismuth. The proposed method shows a linear range of 1.29–8.94 μmol L−1, limit of detection (1.07 μmol L−1) and limit of quantification (3.57 μmol L−1) and good precision (RSD%=2.27 %). This method was validated by comparing the results with Flame Atomic Absorption Spectroscopy (FAAS), using statistical tests to verify precision and accuracy. In conclusion, using a voltammetric sensor to monitor the concentration of bismuth extracted by ATPS proved to be an efficient method, in agreement with the concentrations of the referenced method.

Highly Sensitive Levodopa Determination by Means of Adsorptive Stripping Voltammetry on Ruthenium Dioxide-Carbon Black-Nafion Modified Glassy Carbon Electrode.

A new, highly sensitive Adsorptive Stripping Voltammetric method for levodopa determination was developed. As a working electrode, the glassy carbon electrode (GCE) modified with carbon black (CB), RuO2·xH2O (RuO2) and Nafion was used (CB-RuO2-Nafion GCE). Levodopa signal obtained on the modified electrode was 12 times higher compared to GCE. During research, instrumental parameters were optimized: sampling time ts = 10 ms, waiting time tw = 10 ms, step potential Es = 5 mV and pulse amplitude ΔE = 50 mV. Preconcentration potential Eprec was equal to 0 mV. The best results were obtained in 0.025 M perchloric acid (approx. pH 1.4). Signal repeatability measured on the CB-RuO2-Nafion modified electrode for 0.2 µM of levodopa was equal to 2.1% (levodopa concentration 1 µM, n = 5). Linearity of the method was achieved in the concentration range from 1 to 8 µM. Limit of detection was equal to 17 nM. Recoveries calculated for pharmaceutical products and tap water measurements were in the range 102–105%, which confirms the accuracy of the developed. The applicability of the method was confirmed by analysis of pharmaceutical products and tap water samples. Based on obtained results, it might be concluded that the developed voltammetric method could be a useful tool in routine drug analysis.

Electro-reduction, Quantification and Pharmacokinetic Studies for the Anti-Hyperglycemic Drug Glibenclamide Using Stripping Voltammetric method: Development and Validation

The electrochemical behavior of anti-hyperglycemic (glibenclamide, GBC) was investigated and discussed at HMDE in Britton-Robinson universal buffer using cyclic voltammetry. Its voltammogram at pH values 6-11 displayed a quasi-reversible redox couple one-electron peak corresponding to a catalytic hydrogen process. Based on this voltammetric peak, a validated and sensitive SW-AdCS voltammetric method was depicted for determination of GBC in the bulk form, diabetic drug (Daonil 5 mg) and in human serum. The (LOD) of 6×10-9 M (2.964 ng mL1) and (LOQ) of 2×108 M (9.88 ng mL1) bulk GBC were achieved, respectively, While for protein-free GBC-spiked human serum were (LOD) of 1.5x10-8 M (7.41 ng mL-1) and limit of quantification (LOQ) of 5x10-8 M (24.7 ng mL-1), respectively. The described analytical method was utilized to estimate the pharmacokinetic parameters of GBC in plasma of hospitalized volunteers after the administration of a single oral dose of Daonil 5 mg (p  0.05).

Highly Sensitive Adsorptive Stripping Voltammetric Method for Sitagliptin Determination on Renewable Amalgam Film Electrode

Highly sensitive voltammetric method for sitagliptin (STG) determination was developed. As working electrode cyclic renewable amalgam film electrode Hg(Ag)FE was used (surface area 10.4 mm2). Application of Hg(Ag)FE allowed to improve sensitivity of the method in comparison with HMDE. Instrumental parameters were optimized and were as follow: waiting and sampling time tw = tp = 10 ms, step potential Es = 5 mV and pulse amplitude ΔE = 50 mV. Preconcentration step was carried out at the potential equal to −600 mV for 15 s. Supporting electrolyte was optimized: 0.025 M ammonium buffer (pH 8.2). Conducted calibration allowed to determine linear range: 20–140 nM and limit of detection LOD: 2.6 nM (1.3 ng ml−1) (20 s preconcentration time). Based on linear sweep voltammetry (LSV) measurements the possible mechanism of sitagliptin reduction has been proposed. The applicability of the method was confirmed by analysis of commercially available pharmaceutical product containing sitagliptin. Obtained results were in a good agreement with producer’s declaration. Calculated recoveries (102%–107%) proved the accuracy of the method. Signal repeatability expressed as RSD was equal to 3.2% (STG concentration 0.1 μM, n = 5).