Britton-Robinson Buffer pH Research Articles

Voltammetric and flow amperometric determination of drug guaifenesin in pharmaceutical and biological samples using screen-printed sensor with boron doped diamond electrode

New voltammetric and flow amperometric methods for the determination of guaifenesin (GFE) using a perspective screen-printed sensor (SPE) with boron-doped diamond electrode (BDDE) were developed. The electrochemical oxidation of GFE was studied on the surface of the oxygen-terminated BDDE of the sensor. The GFE provided two irreversible anodic signals at a potential of 1.0 and 1.1 V (vs. Ag|AgCl|KCl sat.) in Britton-Robinson buffer (pH 2), which was chosen as the supporting electrolyte for all measurements. First, a voltammetric method based on differential pulse voltammetry was developed and a low detection limit (LOD = 41 nmol L−1), a wide linear dynamic range (LDR = 0.1–155 μmol L−1), and a good recovery in the analysis of model and pharmaceutical samples (RSD <3.0 %) were obtained. In addition, this sensor demonstrated excellent sensitivity and reproducibility in the analysis of biological samples (RSD <3.2 %), where the analysis took place in a drop of serum (50 μL) without pretreatment and additional electrolyte. Subsequently, SP/BDDE was incorporated into a flow-through 3D printed electrochemical cell and a flow injection analysis method with electrochemical detection (FIA-ED) was developed, resulting in excellent analytical parameters (LOD = 86 nmol L−1, LDR = 0.1–50 μmol L−1). Moreover, the mechanism of electrochemical oxidation of GFE was proposed based on calculations of HOMO spatial distribution and spectroelectrochemical measurements focused on IR identification of intermediates and products.

Solid Bismuth Drop Electrode – A New Tool for Voltammetric Determination of Electrochemically Reducible Organic Compounds

Solid bismuth drop electrode (SBiDE) is a new working electrode commercially available on the Czech market from 2020 by the company Metrohm. The aim of this work was to verify the applicability of the SBiDE in the voltammetric determination of a model organic substance. According to the available information, this is the very first published work on this topic. Metronidazole (an antibiotic used to treat diseases caused by both Gram-positive and Gram-negative anaerobic bacteria) was chosen in this study as a model drug representing electrochemically reducible biologically active compounds. Under optimum conditions (Britton-Robinson buffer of pH 12.0 used as the supporting electrolyte and no electrochemical regeneration of the working electrode surface), a linear calibration dependence of metronidazole was recorded in the concentration range from 1 to 600 μmol L–1, with the limits of detection (LOD) and quantification (LOQ) of 0.41 μmol L–1 and 1.4 μmol L–1, respectively. The newly developed differential pulse voltammetric (DPV) method has also been successfully applied in the determination of metronidazole in various dosage forms.

Silver Nanoparticle-Embedded Hydrogels for Electrochemical Sensing of Sulfamethoxazole Residues in Meat.

A disposable electrochemical sensor based on silver nanoparticle-embedded cellulose hydrogel composites was developed for sensitive detection of sulfamethoxazole residues in meat samples. Scanning electron microscopy confirmed the porous structure of the cellulose matrix anchored with 20-50 nm silver nanoparticles (AgNPs). Fourier transform infrared spectroscopy and X-ray diffraction verified that the metallic AgNPs coordinated with the amorphous cellulose chains. At an optimum 0.5% loading, the nanocomposite sensor showed a peak-to-peak separation of 150 mV, diffusion-controlled charge transfer kinetics, and an electron transfer coefficient of 0.6 using a ferro/ferricyanide redox probe. Square-wave voltammetry was applied for sensing sulfamethoxazole based on its two-electron oxidation peak at 0.72 V vs. Ag/AgCl in Britton-Robinson buffer of pH 7.0. A linear detection range of 0.1-100 μM sulfamethoxazole was obtained with a sensitivity of 0.752 μA/μM and limit of detection of 0.04 μM. Successful recovery between 86 and 92% and less than 6% RSD was achieved from spiked meat samples. The key benefits of the proposed disposable sensor include facile fabrication, an antifouling surface, and a reliable quantification ability, meeting regulatory limits. This research demonstrates the potential of novel cellulose-silver nanocomposite materials towards developing rapid, low-cost electroanalytical devices for decentralized on-site screening of veterinary drug residues to ensure food safety.

Voltammetric determination of genotoxic 4‐nitroindane at a mercury meniscus modified silver solid amalgam electrode

AbstractA silver solid amalgam electrode modified with mercury meniscus (m‐AgSAE) was used as a non‐toxic replacement of mercury electrodes in the voltammetric determination of genotoxic environmental pollutant 4‐nitroindane (4‐NI). The m‐AgSAE was used to characterize of the overall electrode process during the 4‐NI conversion using cyclic voltammetry (CV), and it was shown that the electrochemical reduction of 4‐NI is an irreversible process controlled by both diffusion and adsorption. Techniques of direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at the m‐AgSAE were optimized for the development of a method for the sensitive determination of 4‐NI. The application of the more convenient DPV method was proven on authentic drinking and river water samples. Limits of quantification (LQs) obtained under the following optimal conditions were 0.1 μmol L−1 for DCV at the m‐AgSAE (Britton‐Robinson (BR) buffer pH 5.0–methanol (1 : 1); regeneration potentials E1,reg=−200 mV, E2,reg=−1100 mV) and 0.1 μmol L−1 for DPV at the m‐AgSAE (BR buffer pH 9.0–methanol (1 : 1); regeneration potentials E1,reg=−300 mV, E2,reg=−1300 mV). An attempt to decrease the LQ of the 4‐NI determination by differential pulse adsorptive stripping voltammetry at the m‐AgSAE was not successful. The LQs for DPV at the m‐AgSAE in authentic samples of drinking and river water were 1.0 μmol L−1 and 2.0 μmol L−1 (BR buffer pH 9.0–drinking or river water (1 : 9); regeneration potentials E1,reg=−300 mV, E2,reg=−1300 mV), respectively.

A highly selective nickel-aluminum layered double hydroxide nanostructures based electrochemical sensor for detection of pentachlorophenol

With the widespread use of pesticides, environmental pollution has elevated to a top priority for humans. The pentachlorophenol (PCP) is one of the most dangerous chlorophenols, employed as pesticides, fungicides, and wood preservatives. In the current study, a nickel-aluminum layered double hydroxide modified glassy carbon electrode (Ni-Al-LDH@GCE) was used to build a straight forward, environmentally friendly, and accurate electrochemical sensor for the measurement of PCP. The fabricated Ni-Al-LDH was principally assessed using a variety of characterization methods to confirm its functionalities, morphology, porosity and crytallanity. The proposed Ni-Al-LDH@GCE sensor was also characterized electrochemically for the evaluation of its conductivity using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The linear dynamic range of the developed ultra-sensitive Ni-Al-LDH@GCE based electrochemical method was found as 0.05 to 50 µM at a scan rate of 50 mV/s in Britton-Robinson buffer of pH 6 for PCP. The limit of detection (LOD) and limit of quanitification (LOQ) of electrochemical sensor for PCP were determined as 0.004 μM and 0.0132 μM, respectively. The sensor's analytical suitability was evaluated using real water samples that showed the acceptable recovery values.

Voltammetric analysis of mephenoxalone drug in pharmaceutical and biological samples using novel screen-printed sensor with boron-doped diamond electrode

A novel screen-printed sensor (SPE) with boron-doped diamond electrode (BDDE) for determination of a muscle relaxant and mild anxiolytic mephenoxalone (MNL) was developed. The sensor utilizes the electrochemical oxidation of MNL, which was firstly studied in aqueous solution using oxygen terminated BDDE. MNL provided an irreversible anodic signal at a potential of + 1380 mV (vs. Ag/AgCl/KCl sat.) over a wide pH range. Britton-Robinson buffer (pH 9) was selected as a suitable electrolyte and the square-wave voltammetric method (SWV) was developed. The low detection limit (55 nmol L–1), wide linear dynamic range (0.1–30 µmol L−1), and good recovery in the analysis of model and pharmaceutical samples (RSD < 1.77%) were attained. Subsequently, the new method was successfully transferred to SPE, which can find application in point-of-care testing. These sensors proved excellent sensitivity and reproducibility in the analysis of biological samples (RSD < 4.94%) without pretreatment and no need of electrolyte. Based on gas chromatography with mass spectrometry (GC-MS) analysis of preparative electrolysis products, a mechanism of the electrochemical oxidation of MNL was proposed, describing the oxidative cleavage of the alkoxybenzene ring. These results were supported with HOMO spatial distribution calculations and atomic charges calculations for arising radical cations, and with spectroelectrochemical measurements.

Effect of Magnesium Chloride in Supporting Electrolyte for Enhancing Sensitive and Selective Electrochemical Sensor: An Approach for Anti-Rheumatic Sulfasalazine Detection

In this work, an electroanalytical evaluation for voltammetric sensing of the anti-rheumatic sulfasalazine (SSZ) at an unmodified screen-printed graphene electrode (SPGE) is demonstrated. By using the differential pulse (DPV) technique, the SSZ produced a well-defined peak of around −0.3 V (vs Ag AgCl−1) in Britton-Robinson (BR) buffer pH 4. Supporting electrolytes, pH, and salts all significantly impact SSZ reduction. Therefore, their impact on the working solutions was assessed. We discovered that using a mixture of Britton–Robinson (BR) buffer with pH 4 and MgCl2 as a supporting electrolyte can enhance SSZ sensitivity by approximately 1.7 times while simultaneously increasing detection selectivity. Under optimal conditions, the proposed assay demonstrated the ultrasensitive determination of SSZ with a broad linear detection range from 0.01 to 100 μM and a low detection limit of 4.7 nM (S/N = 3). To demonstrate the impact of the proposed method, the sensor has been successfully applied for the quantitative determination of SSZ in pharmaceutical, urine, and artificial serum sample. Therefore, this approach could offer simplicity, and rapidity, and serve as an alternative to the SSZ detection in practical applications.

Advanced electrochemical platform for simple and rapid quantification of tannic acid in beverages using batch injection analysis with amperometric detection

In this work, an advanced electrochemical platform was developed for the simple, rapid and sensitive determination of the polyphenolic compound tannic acid in various beverages using the combination of batch injection analysis with amperometric detection on a screen-printed carbon electrode. Several experimental parameters (pH of supporting electrolyte, detection potential, dispensing rate, injected volume, stirring) were consistently evaluated. The most favorable analytical performance in terms of sensitivity, selectivity, repeatability and sampling frequency was obtained in Britton-Robinson buffer pH 5.0 at a detection potential of +0.6 V vs. Ag/AgCl, a dispensing rate of 204 µL/s and an injected volume of 80 µL under stirring condition (1500 r.p.m.). The presented platform has advantages for routine analysis including portable and small-scale experimental setup, low sample consumption (∼100 µL), simple sample preparation (dilution in supporting electrolyte), high sampling frequency (180 injections per hour), low limit of detection (80 nM) and suitable precision (RSD = 4.2% for 10 μM tannic acid, n = 20). The applicability of the method was verified by analyzing several beverage samples (tea, wine) in spike-recovery assay with the recovery values for tannic acid ranging from 94 to 101 %.

Graphene and gold nanoparticle-based bionanocomposite for the voltammetric determination of bisphenol A in (micro)plastics

The monitoring of endocrine disruptors in the environment is one of the main strategies in the investigation of potential risks associated with exposure to these chemicals. Bisphenol A is one of the most prevalent endocrine-disrupting compounds and is prone to leaching out from polycarbonate plastic in both freshwater and marine environments. Additionally, microplastics also can leach out bisphenol A during their fragmentation in the water environment. In the quest for a highly sensitive sensor to determine bisphenol A in different matrices, an innovative bionanocomposite material has been achieved. This material is composed of gold nanoparticles and graphene, and was synthesized using a green approach that utilized guava (Psidium guajava) extract for reduction, stabilization, and dispersion purposes. Transmission electron microscopy images revealed well-spread gold nanoparticles with an average diameter of 31 nm on laminated graphene sheets in the composite material. An electrochemical sensor was developed by depositing the bionanocomposite onto a glassy carbon surface, which displayed remarkable responsiveness towards bisphenol A. Experimental conditions such as the amount of graphene, extract: water ratio of bionanocomposite and pH of the supporting electrolyte were optimized to improve the electrochemical performance. The modified electrode displayed a marked improvement in current responses for the oxidation of bisphenol A as compared to the uncovered glassy carbon electrode. A calibration plot was established for bisphenol A in 0.1 mol L−1 Britton-Robinson buffer (pH 4.0), and the detection limit was determined to equal to 15.0 nmol L−1. Recovery data from 92 to 109% were obtained in (micro)plastics samples using the electrochemical sensor and were compared with UV–vis spectrometry, demonstrating its successful application with accurate responses.

Carbon Fiber Paper Sensor for Determination of Trimethoprim Antibiotic in Fish Samples.

The increase in anthropogenic pollution raises serious concerns regarding contamination of water bodies and aquatic species with potential implications on human health. Pharmaceutical compounds are a type of contaminants of emerging concern that are increasingly consumed and, thus, being frequently found in the aquatic environment. In this sense, an electrochemical sensor based on an unmodified and untreated carbon fiber paper (CPS-carbon paper sensor) was simply employed for the analysis of trimethoprim antibiotic in fish samples. First, the analytical conditions were thoroughly optimized in order for the CPS to achieve maximum performance in trimethoprim determination. Therefore, an electrolyte (0.1 M Britton-Robinson buffer) pH of 7 was selected and for square wave voltammetry parameters, optimum values of amplitude, frequency and step potential corresponded to 0.02 V, 50 Hz, and 0.015 V, respectively, whereas the deposition of analyte occurred at +0.7 V for 60 s. In these optimum conditions, the obtained liner range (0.05 to 2 µM), sensitivity (48.8 µA µM-1 cm-2), and LOD (0.065 µM) competes favorably with the commonly used GCE-based sensors or BDD electrodes that employ nanostructuration or are more expensive. The CPS was then applied for trimethoprim determination in fish samples after employing a solid phase extraction procedure based on QuEChERS salts, resulting in recoveries of 105.9 ± 1.8% by the standard addition method.

Electrode Based on the MWCNTs and Electropolymerized Thymolphthalein for the Voltammetric Determination of Total Isopropylmethylphenols in Spices.

Isopropylmethylphenols, namely thymol and carvacrol, are natural phenolic monoterpenoids with a wide spectrum of bioactivity making them applicable in the cosmetic, pharmaceutical, and food industry. The dose-dependent antioxidant properties of isopropylmethylphenols require their quantification in real samples. Glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and electropolymerized thymolphthalein has been developed for the sensitive quantification of isopropylmethylphenols. Conditions of thymolphthalein electropolymerization (monomer concentration, number of cycles, and electrolysis parameters) providing the best response to thymol have been found. Scanning electron microscopy and electrochemical methods confirm the effectivity of the electrode developed. The linear dynamic ranges of 0.050-25 and 25-100 µM for thymol and 0.10-10 and 10-100 µM for carvacrol with detection limits of 0.037 and 0.063 µM, respectively, have been achieved in differential pulse mode in Britton-Robinson buffer pH 2.0. The selectivity of the isopropylmethylphenols response in the presence of typical interferences (inorganic ions, saccharides, ascorbic acid) and other phenolics (caffeic, chlorogenic, gallic and rosmarinic acids, and quercetin) is a significant advantage over other electrochemical methods. The electrode has been used in the analysis of oregano and thyme spices. Total isopropylmethylphenols contents have been evaluated after a single sonication-assisted extraction with methanol.

Voltammetric Sensor Based on the Poly(p-aminobenzoic Acid) for the Simultaneous Quantification of Aromatic Aldehydes as Markers of Cognac and Brandy Quality.

Cognac and brandy quality control is an actual topic in food analysis. Aromatic aldehydes, particularly syringaldehyde and vanillin, are one of the markers used for these purposes. Therefore, simple and express methods for their simultaneous determination are required. The voltammetric sensor based on the layer-by-layer combination of multi-walled carbon nanotubes (MWCNTs) and electropolymerized p-aminobenzoic acid (p-ABA) provides full resolution of the syringaldehyde and vanillin oxidation peaks. Optimized conditions of p-ABA electropolymerization (100 µM monomer in Britton-Robinson buffer pH 2.0, twenty cycles in the polarization window of -0.5 to 2.0 V with a potential scan rate of 100 mV·s-1) were found. The poly(p-ABA)-based electrode was characterized by scanning electron microscopy (SEM), cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Electrooxidation of syringaldehyde and vanillin is an irreversible two-electron diffusion-controlled process. In the differential pulse mode, the sensor allows quantification of aromatic aldehydes in the ranges of 0.075-7.5 and 7.5-100 µM for syringaldehyde and 0.50-7.5 and 7.5-100 µM for vanillin with the detection limits of 0.018 and 0.19 µM, respectively. The sensor was applied to cognac and brandy samples and compared to chromatography.

Rapid and straightforward electrochemical approach for the determination of the toxic food azo dye tartrazine using sensors based on silver solid amalgam

The research paper reports for the first time the investigation of the electrochemical reduction of the synthetic food azo dye tartrazine (TZ) on three different types of silver solid amalgam electrodes (AgSAEs), in particular, the polished one (p-AgSAE), covered by mercury film (f-AgSAE) or by mercury meniscus (m-AgSAE), and the comparison with dropping mercury electrode. The highest reduction peak of TZ on AgSEAs was obtained in the Britton-Robinson buffer (pH 3.4). It was shown that the accumulation step can considerably increase the peak height of TZ reduction. Two adsorptive stripping voltammetric techniques, the linear sweep (LS-AdSV) and the differential pulse (DP-AdSV), were used to develop the simple, rapid, and sensitive methods for the determination of TZ based on its reduction on the working AgSAE. The results showed that all three AgSAEs can be applied for electroanalysis of TZ, however, the best limit of detection (0.078 μmol L−1) and the limit of quantification (0.24 μmol L−1) were obtained for m-AgSAE using LS-AdSV. The developed procedures were successfully applied for TZ determination in soft drink, succade, and veterinary drug using a standard addition method. Therefore, the AgSAEs have been demonstrated to be beneficial electrochemical tools for food products’ quality and safety monitoring.

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

Facile Electrochemical Sensor for Sensitive and Selective Determination of Guaifenesin, Phenylephrine and Paracetamol on Electrochemically Pretreated Pencil Graphite Electrode.

Guaifenesin (GFS), phenylephrine (PHE) and paracetamol (PAR), drugs used in combination for the relief of cold and flu symptoms, were determined at electrochemically pretreated pencil graphite electrode. Differential pulse voltammetry (DPV) was used for the first time for the concomitant determination of the target compounds based on the electro-oxidation of PAR at 0.43 V, PHE at 0.74 V and GFS at 1.14 V in Britton–Robinson buffer pH 6.0. Under optimized experimental conditions, two linear ranges were obtained for PAR (2.50 × 10−6 M–1.00 × 10−5 M and 1.00 × 10−5 M–1.00 × 10−4 M) and for PHE and GFS linearity was proved between 5.00 × 10−6 M–2.00 × 10−4 M and 2.50 × 10−6 M–2.00 × 10−4 M, respectively. The detection limits were 8.12 × 10−7 M for PAR, 1.80 × 10−6 M for PHE and 8.29 × 10−7 M for GFS. The selective and sensitive DPV method and the electrochemically treated electrode were employed for simultaneous analysis of the analytes in pharmaceutical samples with good recoveries.

Flow Injection Analysis System Coupled to Chronoamperometry and Boron-Doped Diamond Electrode for Determination of Synthetic Hormones 17α-Ethinylestradiol and Cyproterone Acetate

Flow injection analysis with chronoamperometry detection using a cathodically pretreated boron-doped diamond electrode (CPT-BDDE) was employed to develop and optimize a novel method for the determination of the hormones 17-α-ethinylestradiol (EE2) and cyproterone acetate (CPA). The electrochemical properties of EE2 and CPA were evaluated by cyclic voltammetry and oxidation peaks were observed at 0.97 V and 1.60 V in 0.04 mol L−1 Britton-Robinson buffer (pH 2.0). Analytical curves were linear in the concentration range from 0.070 to 10.0 µmol L−1 for EE2 and 1.0 to 80.0 µmol L−1 for CPA with detection limits of 0.023 and 0.23 µmol L−1, respectively. The developed methods presented good precision and accuracy for EE2 and CPA quantification in commercial pharmaceutical samples. The obtained results were satisfactory and consistent compared with a reference high-performance liquid chromatography method at a confidence level of 95%. Furthermore, recovery studies carried out in synthetic urine and lake water show that these methods do not suffer any significant matrix interferences and are potentially applicable for the determination of these hormones in real samples. Thus, the developed procedure for EE2 and CPA determination are simple and fast, with an analytical frequency of ∼83 determinations per hour, and attractive for routine analysis.

Electrochemical paper-based analytical devices containing magnetite nanoparticles for the determination of vitamins B2 and B6

Disposable electrochemical paper-based analytical devices were developed from a conductive ink using graphite powder, automotive varnish and magnetite nanoparticles. The addition of magnetite nanoparticles in the conductive ink improved the sensitivity of the analytical devices. The devices were applied in the quantification of vitamins B2 (VB2) and B6 (VB6) in commercial dietary supplements. The characterization of the analytical devices was carried out by microscopy and electrochemical techniques. Square wave voltammetry (SWV) was used to study the electrochemical behavior of the vitamins and the experimental parameters were optimized (pH, supporting electrolyte and SWV parameters). The calibration plot for VB2 (−484 mV vs. graphite) was obtained in Britton-Robinson buffer (pH 2.0) in the range of 2.0 to 20.0 μmol L−1 with a detection limit of 0.25 µmol L−1. Similarly, for the VB6 (+675 mV vs. graphite), the calibration plot was obtained in McIlvaine buffer (pH 4.0) in the range of 0.2 to 2.0 mmol L−1 with a detection limit of 29.5 µmol L−1. The analytical devices were employed to determine VB2 and VB6 levels in B-complex supplements (capsules and sublingual liquid) and the results were compared with those provided by fluorescence spectrometry. The statistical analysis showed no considerable difference in terms of the precision and accuracy of the data obtained by both methods.

Simultaneous Determination of Amlodipine and Irbesartan in their Pharmaceutical Formulations by Square-Wave Voltammetry.

Hypertension is one of the most important health problems in the world and irbesartan and amlodipine are used in combination in various dosages for the treatment of high blood pressure. The aim of this study is to develop a fast, easy, sensitive, accurate, and precise squarewave voltammetry method for simultaneous determination of irbesartan and amlodipine besylate from pharmaceutical formulations at a hanging mercury drop electrode. In the applied method, since both active substances gave a peak at different potentials, no interference occurred between them. In optimization studies, Britton-Robinson buffer of pH 8.0 was chosen, in which the most appropriate peak shape and maximum peak current were observed. At the same time, as a result of instrumental parameter optimization to obtain reproducible results, 6 mV for scan increment, 30 mV for pulse amplitude, and 50 Hz for frequency were found suitable. As a result of the calibration studies of the optimized method, linear working ranges were determined as 1.00-13.08 μg mL-1 for irbesartan and 5.83-16.51 μg mL-1 for amlodipine besylate. Limit of detection and limit of quantitation values were respectively calculated as 0.63 and 1.00 μg mL-1 for irbesartan and 0.50 and 1.98 μg mL-1 for amlodipine besylate. The results of precision values (RSD) ranged from 0.67% to 2.31% for irbesartan and 0.65% to 1.49% for amlodipine besylate. Accuracy values were calculated as -0.15% to 1.63% for irbesartan and -0.07% to 3.78% for amlodipine besylate. The results obtained from the recovery studies ranged from 101.05% to 102.78% and from 98.88% to 102.20% for amlodipine besylate and irbesartan, respectively. After the validation studies of the developed method were carried out, it was successfully applied to pharmaceutical formulations containing these active substances.

Voltammetric determination of daminozide and its degradation product N,N-dimethylhydrazine using a boron-doped diamond electrode

• First study of direct oxidation of plant growth stimulator daminozide (DMZ) on BDDE. • Mechanism of the electrochemical oxidation of DMZ was proposed. • Sensitive direct voltammetric method for DMZ determination was developed. • Process of DMZ degradation product N , N -dimethylhydrazine (DMH) elimination was developed. • New method was successfully applied for determination of DMZ and DMH in real samples. • Isolation and concentration technique was also proposed. The simultaneous determination of growth regulator daminozide (DMZ) and its degradation product N , N -dimethylhydrazine (DMH) via their direct electrochemical oxidation was investigated for the first time and the mechanism of DMZ oxidation has been proposed. With regard to the very positive values of the oxidation potentials of both substances, a boron doped diamond electrode (BDDE) was used as the working electrode and Britton-Robinson buffer of pH 9 was applied as the suitable supporting electrolyte. First, a differential pulse voltammetric method for DMZ determination was developed, which provided a very low detection limit ( LOD = 4.56 × 10 −7 mol L −1 ). DMH could also be determined under the same experimental conditions ( LOD = 2.16 × 10 −7 mol L −1 ). The proposed extraction technique then allowed the determination of concentrations up to 50 times lower. In case of the mixture analysis, while the determination of DMH was not affected by the presence of DMZ, the results of the DMZ analysis were significantly influenced by the presence of its degradation product. Therefore, a method for removing DMH from a sample was also developed in this work. Finally, real samples of a commercially available pesticide preparation and spiked natural and rinsing waters were successfully analyzed.

Multi-Analyte Sensor Based on Pencil Graphite Electrode for Riboflavin and Pyridoxine Determination

Riboflavin (VB2) and pyridoxine (VB6) are two of the eight water-soluble B vitamins that play an essential role and are correlated in normal function of the body. In the present study, cyclic voltammetry demonstrated that in Britton-Robinson buffer (pH 5.00) VB2 undergoes a quasi-reversible electron transfer reaction and the oxidation of VB6 is irreversible, both electrochemical systems being diffusion controlled at the pencil graphite electrode (PGE) surface. Also, a sensitive and selective voltammetric procedure has been developed for the simultaneous determination of the two compounds using PGE and square wave voltammetry (SWV). Two well-defined oxidation peaks with a voltammetric separation of more than 1.10 V were obtained in Britton-Robinson buffer (pH 5.00). The SWV curves exhibited linear responses with riboflavin and pyridoxine concentrations. Thus, for VB2 two linear concentration ranges of 1.00 · 10−7–5.00 · 10−5 M and 5.00 · 10−5–7.50 · 10−4 M were obtained and in the case of VB6 the linear response was between 2.50 · 10−5 M and 2.50 · 10−3 M. The detection limits for VB2 and VB6 were 7.38 · 10−8 M and 1.10 · 10−5 M, respectively. The applicability of PGE was successfully proved for simultaneous determination of VB2 and VB6 in pharmaceutical tablets with good accuracy and precision.