Electroanalytical Detection of Cr(VI) and Cr(III) Ions Using a Novel Microbial Sensor

A microbial sensor, namely carbon paste electrode (CPE) modified with Citrobacter freundii (Cf–CPE) has been developed for the detection of hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium present in aqueous samples using voltammetry, an electroanalytical technique. The biosensor developed, demonstrated about a twofold higher performance as compared to the bare CPE for the chosen ions. Using cyclic voltammetry and by employing the fabricated Cf–CPE, the lowest limit of detection (LLOD) of 1x10⁻⁴ M and 5x10⁻⁴ M for Cr(VI) and Cr(III) ions respectively could be achieved. By adopting the Differential Pulse Cathodic Stripping Voltammetric technique, the LLOD could be further improved to 1x10⁻⁹ M and 1x10⁻⁷ M for Cr(VI) and Cr(III) ions respectively using the biomodified electrodes. The reactions occurring at the electrode surface‐chromium solution interface and the mechanisms of biosorption of chromium species onto the biosensor are discussed. The stability and utility of the developed biosensor for the analysis of Cr(VI) and Cr(III) ions in chromite mine water samples has been evaluated.     

Voltammetric behavior of sulfadimetoxol using square-wave and adsorptive stripping square-wave techniques

The voltammetric behavior of sulfadimetoxol (SDX) was studied by square-wave techniques, leading to two methods for its determination in aqueous samples and veterinary formulations. The application of the square-wave mode shows the determination of SDX between 1 × 10⁻⁷ M and 2 × 10⁻⁶ M at −0.60 V and for the stripping voltammetry of adsorbed SDX with an accumulation step of 15 s proved to be more sensitive, yielding signals five times larger than those obtained without the accumulation. The determination of SDX was done between 2 × 10⁻⁸ M and 5 × 10⁻⁷ M by stripping mode. The relative standard deviations obtained for concentration levels of SDX as low as 3 × 10⁻⁷ M with square-wave was 3.4 % (n = 8) and for 2 × 10⁻⁷ M with stripping square-wave was 3.1 % (n = 8). The methods were satisfactorily applied for determining SDX in four veterinary products.     

Voltammetric Analysis of Oxymetazoline Hydrochloride at Zeolite – Modified Carbon Paste Electrode in Micellar Medium

Simple, sensitive, accurate and inexpensive differential pulse (DPV) and square wave (SWV) voltammetric methods utilizing zeolite modified carbon paste electrode (ZMCPE) were developed for the determination of Oxymetazoline hydrochloride (OXM) in nasal drops. Various experimental parameters were optimized using cyclic voltammetry (CV). Calibration curves were linear over the concentration ranges 9.8×10⁻⁸–3.6×10⁻⁶ M and 9.8×10⁻⁶–9×10⁻⁵ M for DPV and SWV, respectively. The DPV method showed a limit of detection (LOD) of 1.04×10⁻⁷ M. The method was applied for the determination of OXM in pharmaceutical formulation with an average recovery of 101.18 % (%RSD=0.41, n=9).     

Multi-length scale wear damage mechanisms of ultra-high molecular weight polyethylene nanocomposites

Ultra-high molecular weight polyethylene (UHMWPE) is reinforced with 1–3 wt % sliver (Ag) nanoparticles and zinc oxide (ZnO) micro-rods, and tensile strength as well as wear resistance of the samples is evaluated. Tensile strength was observed to increase with Ag and ZnO reinforcement up to 18% for 1 wt % ZnO and 1 wt % Ag, but in case of 3 wt % ZnO and 3 wt % Ag + 3 wt % ZnO, it decreases marginally by 4% when compared with neat polymer. The sliding wear rate for 1 wt % Ag + 1 wt % ZnO and 3 wt % Ag + 3 wt % ZnO decreases from 9.54 × 10⁻⁵ mm³ (neat polymer) to 7.49 × 10⁻⁵ mm³ and 5.65 × 10⁻⁵mm³, respectively, showing the synergistic effect of Ag and ZnO reinforcement. In scratch testing, minimum damage is obtained in 1 wt % ZnO reinforced polymer. On one hand, where micro-scratch damage is resisted by harder ZnO, whereas on the other hand, pin on disc wear (repeated surface damage) is protected by softer Ag tribolayer. The improved tensile strength (up to 9.7%) and wear resistance with synergistic addition of Ag and ZnO (both 1 wt %) opens a window in the development of bearing surface biomaterials providing improved longevity and durability, thus, may reduce the chances of revision surgery.     

Electrochemical determination of prolintane in pharmaceutical formulations and in human urine

The oxidative behavior of 1-[1-(phenylmethyl)butyl]pyrrolidine, prolintane, was studied at a glassy carbon electrode using linear-sweep and differential-pulse voltammetry. The oxidation process was shown to be irreversible using 0.04 M Britton–Robinson buffer and was diffusion-adsorption controlled. Two voltammetric methods were developed for the determination of prolintane using different techniques: linear-sweep and differential-pulse voltammetry. The peak current varied linearly with prolintane concentrations in the range of 1.0 × 10⁻⁵ −2.5 × 10⁻⁴ M, with a detection limit of 8.5 × 10⁻⁶ and 4.0 × 10⁻⁶ M, and with relative standard deviations of 2.1 % and 3.1 %, respectively. The methods were applied to commercial preparations, giving relative errors less than 3.1 % and relative standard deviations lower than 4.8 % (n = 10). Determination of prolintane (down to the 8.5 × 10⁻⁸ M level) can be performed by using a preconcentration step prior to the determination by differential-pulse voltammetry in 0.04 M Britton–Robinson buffer (pH 8.0) with preconcentration potential of 0.0 V. The detection limit was found to be 6.2 × 10⁻⁸ M (4 min preconcentration) and the relative standard deviation for 2.5 × 10⁻⁷ M prolintane (n = 5) was 4.6 %. Applicability to human urine analysis is illustrated (recovery 98 ± 2 %). Standard additions method can be used to determine prolintane in real samples of urine.     

Graphene Oxide/ZnO Nano Composite for Sensitive and Selective Electrochemical Sensing of Levodopa and Tyrosine Using Modified Graphite Screen Printed Electrode

Determination of levodopa and tyrosine as two important species for treatment of Parkinson's disease is described. A novel electrochemical sensor involving graphene oxide/ZnO nanorods (GR/ZnO) nano composite and the graphite screen‐printed electrodes (GSPE) was developed for the simultaneous detection of levodopa and tyrosine. The screen‐printed electrodes with several advantages, including low cost, versatility and miniaturization were employed. On the other hand, the graphene oxide/ZnO nanorods nano composite was casted on the surface of GSPE to obtain GR/ZnO/SPE. The proposed nano sensor has excellent performance such as high sensitivity, good selectivity and analytical application in real samples. The combination of graphene oxide/ZnO nanorods nano composite with the screen‐printed electrode is favorable for amplifying electrochemical signals. Under optimized conditions square wave voltammetry (SWV) exhibited linear dynamic ranges from 1.0×10^?6 to 1.0×10^?3 M and 1.0×10^?6 to 8.0×10^?4 M with detection limits of 4.5×10^?7 M and 3.4×10^?7 M for levodopa and tyrosine respectively.     

Continuous flow and flow injection stripping voltammetric determination of silver(I), mercury(II), and bismuth(III) at a bulk modified graphite tube electrode

The epoxy-impregnated graphite tube electrode bulk modified with 2-mercaptobenzoxazole, employed in a wall-jet configuration, was found to be useful for the continuous flow and flow injection stripping voltammetric determinations of Ag^I, Hg^II and Bi^III. For continuous flow, detection limits for Ag^I, Hg^II and Bi^III were 1.8 × 10⁻¹⁰ M, 1.9 × 10⁻⁹ M and 9.5 × 10⁻⁹ M, respectively (10 min accumulation, S/N = 3). Precisions for 5.00 × 10⁻⁹ M Ag^I, 1.00 × 10⁻⁸ M Hg^II and 1.00 × 10⁻⁷ M Bi^III were 10.5%, 5.77 % and 7.90% (relative standard deviations, n = 6), respectively. In the case of flow injection stripping, with a 500 μL injection loop, detection limits of 0.59 ng, 2.0 ng and 120 ng were obtained for Ag^I, Hg^II and Bi^III, respectively (S/N = 3). Selected metal ions, inorganic and organic substances were investigated for interferences. The electrode was tested with a certified sample and then applied to the determinations of the metal ions in a urine and a sea-water sample.     

Novel Designing of Chemically Modified Electrode (CME) of the Bio-MOF-1 for the Detection of Dopamine Based on Inhibition of [Ru(bpy)3]2+/DBAE System

Metal organic frameworks (MOFs) have attracted extensive attention in electrochemical research fields due to their high surface area and controlled porosity. Current study is design to investigate the ECL performance of the chemically modified electrode (CME) based on the bio-MOF-1, a porous zinc-adenine framework, which loaded ruthenium complex and employed for the detection of dopamine (DA). The composite material [Ru(bpy)₃]²⁺@bio-MOF-1 (Ru-bMOF) modified carbon glassy electrode (Ru-bMOF/GCE) exhibited an excellent ECL performance having a linear co-efficient response (R²=0.9968) for 2-(dibutyl amino) ethanol (DBAE), a classical ECL co-reactant was obtained over a concentration range of 1.0×10⁻⁹ M to 1.0×10⁻⁴ M in 0.10 M pH=6.0 phosphate buffer solution (PBS). Furthermore, DA was detected based on its inhibition effect on [Ru(bpy)₃]²⁺/DBAE system. Compared to traditional analytical methods, this method has various advantages such as simple electrode preparation, quick response, high reproducibility (RSD<2.0 %), low limit of detection (LOD=1.0×10⁻¹⁰ mol/L). This chemical investigated modified electrode had exploited potential for detection of DA.     

Adsorption voltammetry of nandrolone phenylpropionate

The electrochemical behavior of nandrolone phenylpropionate (NP) at a hanging mercury drop electrode (HMDE) was investigated. The adsorption phenomena were observed by linear sweep voltammetry in NaOH. The electrode reaction was found to be a totally irreversible reduction of the adsorbed NP. In 1 × 10⁻⁷ mol/L NaOH, the detection limit and the linear range are 5 × 10⁻¹⁰ and 8 × 10⁻¹⁰–5 × 10⁻⁷ mol/L, respectively. The relative standard deviation of the method is 1.6 % for 1.7 × 10⁻⁷ mol/L NP. The method was applied to the determination of NP in clinical ampuls.     

Nanomolar Determination of Methyldopa in the Presence of Large Amounts of Hydrochlorothiazide Using a Carbon Paste Electrode Modified with Graphene Oxide Nanosheets and 3‐(4′‐Amino‐3′‐hydroxy‐biphenyl‐4‐yl)‐acrylic Acid

A novel electrochemical sensor for sensitive detection of methyldopa at physiological pH was developed by the bulk modification of carbon paste electrode (CPE) with graphene oxide nanosheets and 3‐(4′‐amino‐3′‐hydroxy‐biphenyl‐4‐yl)‐acrylic acid (3,′AA). Applying square wave voltammetry (SWV), in phosphate buffer solution (PBS) of pH 7.0, the oxidation current increased linearly with two concentration intervals of methyldopa, one is 1.0×10^?8–1.0×10^?6 M and the other is 1.0×10^?6–4.5×10^?5 M. The detection limit (3σ) obtained by SWV was 9.0 nM. The modified electrode was successfully applied for simultaneous determination of methyldopa and hydrochlorothiazide. Finally, the proposed method was applied to the determination of methyldopa and hydrochlorothiazide in some real samples.     

Screen-printed electrochemical sensors for label-free potentiometric and impedimetric detection of human serum albumin

Herein, two electrochemical methods based on potentiometric and impedimetric transductions were presented for albumin targeting, employing screen-printed platforms (SPEs) to make easy and cost-effective sensors with good detection merits. The SPEs incorporated ion-to-electron multi-walled carbon nanotubes (MWCNTs) transducer. Sensors were constructed using either tridodecyl methyl-ammonium chloride (TDMACl) (sensor I) or aliquate 336S (sensor II) in plasticized polymeric matrices of carboxylated poly (vinyl chloride) (PVC-COOH). Analytical performances of the sensors were evaluated using the above-mentioned electrochemical techniques. For potentiometric assay, constructed sensors responded to albumin with −81.7 ± 1.7 (r² = 0.9986) and −146.2 ± 2.3 mV/decade (r² = 0.9991) slopes over the linearity range 1.5 μM–1.5 mM with 0.8 and 1.0 μM detection limits for respective TDMAC- and aliquate-based sensors. Interference study showed apparent selectivity for both sensors. Impedimetric assays were performed at pH = 7.5 in 10 mM PBS buffer solution with a 0.02 M [Fe(CN)₆]^−3/−4 redox-active electrolyte. Sensors achieved detection limits of 4.3 × 10⁻⁸ and 1.8 × 10⁻⁷ M over the linear ranges of 5.2×10⁻⁸–1.0×10⁻⁴ M and 1.4×10⁻⁶–1.4×10⁻³ M, with 0.09 ± 0.004 and 0.168 ± 0.009 log Ω/decade slopes for sensors based on TDMAC and aliquate, respectively. These sensors are characterized with simple construction, high sensitivity and selectivity, fast response time, single-use, and cost-effectiveness. The methods were successfully applied to albumin assessment in different biological fluids.     

Application of a Nanosensor Based on MWCNT‐Sodium Dodecyl Sulphate Modified Electrode for the Analysis of a Novel Drug,Alpha‐Hydrazinonitroalkene in Human Blood Serum

The sensitivity enhancing properties of sodium dodecyl sulphate (SDS) and multi‐walled carbon nanotubes (MWCNTs) were associated to construct a nanosensor based on carbon paste electrode (CPE) by adopting drop cast method. The drop cast method makes use of minimum modifier and the entire modified surface of the sensor is available for the analyte. Surface characterization of the electrodes was carried out using FE‐SEM and EDX. EIS was used for the electrochemical characterization. We report for the first time the electrochemical analysis based on the oxidation of the ‐OH group of a novel drug, alpha‐hydrazinonitroalkene ( I ) which was found to have antibacterial and antimicrobial properties. The electron transfer kinetic parameters such as the charge transfer coefficient α and heterogeneous rate constant k′ were calculated and they have been found to be 0.64 and 9.62 × 10⁻² cm s⁻¹ respectively. The linear response ranges for ( I ) obtained at this sensor are 1.0 × 10⁻⁷ M − 7.0 × 10⁻⁷ M and 1.0 × 10⁻⁶ M – 4.5 × 10⁻⁵ M with a detection limit of (7.03 ± 0.41) × 10⁻⁸ M (S/N=3). The interference study suggested that the sensor was free from 1000‐fold excess of UA in the determination of ( I ). It was important to note that the sensor completely eliminated Ascorbic acid (AA) signal which offered a significant analytical advantage for the determination of the drug at this sensor. The practical usefulness of the modified sensor was demonstrated by the analysis of ( I ) in blood serum.     

Carboxylic Acid f-MWCNT/Graphite and Safranin O/Graphite Based Voltammetric Sensors for Norfloxacin Detection

A well-established electrode modifier, i. e., carboxylic acid (CA) functionalized-multiwalled carbon nanotubes (f-MWCNT), and a less explored safranin O (SFO) were fabricated on cuboidal graphite electrodes to develop two different voltammetric sensors for norfloxacin‘s electrochemical detection. The developed CA f-MWCNT/graphite electrode and SFO/graphite showed a linear range of 3.10×10⁻⁷ to 3.13×10⁻⁵ M and 2.50×10⁻⁸ to 4.06×10⁻⁷ M with a limit of detection of 1.60×10⁻⁸ and 4.80×10⁻⁹ M, respectively. The practical applicability was tested in the spiked hospital wastewater, milk, and orange juice. It showed that the SFO could be a potential modifier for rapid, simple, and sensitive voltammetric detection of norfloxacin.     

Simultaneous determination of acetaminophen,dopamine and ascorbic acid using a PbS nanoparticles Schiff base-modified carbon paste electrode

A highly sensitive method was investigated for the simultaneous determination of acetaminophen (AC), dopamine (DA), and ascorbic acid (AA) using a PbS nanoparticles Schiff base-modified carbon paste electrode (PSNSB/CPE). Differential pulse voltammetry peak currents of AC, DA and AA increased linearly with their concentrations within the ranges of 3.30 × 10⁻⁸–1.58 × 10⁻⁴ M, 5.0 × 10⁻⁸–1.2 × 10⁻⁴ M and 2.50 × 10⁻⁶–1.05 × 10⁻³ M, respectively, and the detection limits for AC, DA and AA were 5.36 × 10⁻⁹, 2.45 × 10⁻⁹ and 1.86 × 10⁻⁸ M, respectively. The peak potentials recorded in a phosphate buffer solution (PBS) of pH 4.6 were 0.672, 0.390, and 0.168 V (vs Ag/AgCl) for AC, DA and AA, respectively. The modified electrode was used for the determination of AC, DA, and AA simultaneously in real and synthetic samples.     

Chemical Modified Carbon Paste Electrode for Potentiometric Determination of Mo(VI) and its Application in Food Analysis and Agriculture Fertilizers

Since to the best of our knowledge, there is no potentiometric sensors based on carbon paste electrodes were proposed for the potentiometric determination of molybdenum(VI) ion. In this study, 2,2′-(propane-1,3-diylbis(oxy))dibenzoic acid (PBODBA) was synthesized and used as modifier in the fabrication of carbon paste electrode (CPE) for the quantification of molybdenum(VI). The developed electrodes I and II showed hexavalent Nernstian response of 9.80±0.05 and 9.90±0.08 mV decade⁻¹ over the concentration ranges of 1.0×10⁻⁷–1.0×10⁻³ and 1.0×10⁻⁸–1.0×10⁻³ mol L⁻¹, respectively. The electrodes showed good selectivity for Mo(VI). The modified electrodes were applied for the determination of Mo(VI) concentration in masscuaje agricultural fertilizer and spiked juice extractions containing several metals.     

Incorporation of Tetrazolium Blue (TB)/Gold Nanoparticles (GNPs) into Carbon Paste Electrode: Application as an Electrochemical Sensor for the Sensitive and Selective Determination of Sotalol in Micellar Medium

The electrochemical oxidation of Sotalol (SOT) based on Tetrazolium Blue (TB)/gold nanoparticles (GNPs)‐modified carbon paste electrodes (CPE) have been studied in the presence of sodium lauryl sulphate (SLS). Cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques have all been utilized within this study. GNPs and TB have a synergetic effect‐giving rise to highly improved electrochemical responses and provide an advantageous platform for the basis of an electrochemical sensor with excellent performance. The experimental parameters, electrodeposition time, pH and scan rate have all been examined and optimized. The sensing of SOT via DPV is found to exhibit a wide linear dynamic range of 1.0×10⁻⁷–7.5×10⁻⁴ M in pH 2. LOD and LOQ were calculated and found to correspond to 2.5×10⁻⁸ M and 8.3×10⁻⁸ M, respectively. The suggested sensor has been used successfully for SOT determination in pharmaceutical samples and human urine as real samples. Satisfactory recoveries of analyte from these samples are demonstrated indicating that the suggested sensor is highly suitable for clinical analysis, quality control and a routine determination of SOT in pharmaceutical formulations.     

Binder Free Modification of Glassy Carbon Electrode by Employing Reduced Graphene Oxide/ZnO Composite for Voltammetric Determination of Certain Nitroaromatics

Reduced Graphene oxide/ZnO nanoflowers ( rGO/ZnO‐NFs ) composite has been synthesized in‐situ using asymmetric Zn complex ( 1 ) as a single‐source molecular precursor (SSMP) with GO at 150 °C. The rGO/ZnO‐NFs composite was characterized by PXRD, UV‐vis, SEM, EDX mapping, TEM and SAED pattern to confirm its purity and morphology. The rGO/ZnO‐NFs composite shows uniform distribution of nanoflowers on graphene sheets. The modified glassy carbon electrode ( GCE ) was fabricated by drop wise layering of the rGO/ZnO‐NFs composite at the surface of the GCE without using binder. The binder free modified electrode ( GCE‐rGO/ZnO ) was explored for detection of nitroaromatics such as p‐nitro‐phenol ( p ‐NP ), 2,4‐dinitrophenol ( 2,4‐DNP ), 2,4‐dinitrotoluene ( 2,4‐DNT ) and 2,4,6‐trinitrophenol ( 2,4,6‐TNP ). The fabricated sensor showed remarkable response for the both toxicants and explosives. The LOD, sensitivity and linear range for the studied toxicants and explosives were found to be in a good range: p ‐NP= 0.93 μM, 240 μA mM⁻¹ cm⁻² and 0.2–0.9 mM; 2,4‐DNP= 6.2 μM, 203 μA mM⁻¹ cm⁻² and 0.1–0.9 mM; 2,4‐DNT= 10 μM, 371 μA mM⁻¹ cm⁻² and 0.2–0.9 mM; 2,4,6‐TNP= 16 μM, 514 μA mM⁻¹ cm⁻² and 0.2–0.9 mM, respectively.     

Organometallic complexes with biological molecules. XIV. Biological activity of dialkyl and trialkyltin(IV) [meso‐tetra(4‐carboxy‐ phenyl)porphinate] derivatives

The effects of several organotin(IV) meso‐tetra(4‐carboxyphenyl)porphinate] derivatives with the general formula (R₂Sn)₂TPPC and (R₃Sn)₄TPPC (R = Me, Bu, Ph) were tested in vivo on ascidian embryonic development. Embryos at the two‐cell stage were incubated in 1 × 10⁻⁵ or 1 × 10⁻⁷ M solutions of various compounds. The ligand, [meso‐tetra(4‐carboxyphenyl)porphine] (H₄TPPC) was toxic at 1 × 10⁻⁵ M , because development was blocked at an early gastrula stage, whereas 1 × 10⁻⁷ M H₄TPPC allowed the eggs to develop up to the larva stage. The most toxic among the tested compounds was tributyltin(IV) [meso‐tetra(4‐carboxyphenyl)porphinate], (Bu₃Sn)₄TPPC, since the fertilized eggs were unable to divide into two cells, even at a concentration of 1 × 10⁻⁷ M . To correlate this embryonic arrest with the metabolic pathway, and especially to understand why cellular organelles first underwent chemical damage, 10⁻⁵ and 10⁻⁷ M (Bu₃Sn)₄TPPC‐cultured fertilized eggs were tested for DNA, RNA, protein, glucose, lipid and ATP contents, comparing the values obtained with those of control culture fertilized egg contents. The higher concentration (1 × 10⁻⁵ M ) reduced the content of all the tested compounds, but the lower one (1 × 10⁻⁷ M ), even if still unable to allow cleavage, reduced only the lipids and the ATP contents. A hypothesis concerning initial damage to mitochondrial membrane is proposed. Copyright © 2000 John Wiley & Sons, Ltd.     

Development of an Electrochemical Sensor for Selective Determination of Dopamine Based on Molecularly Imprinted Poly(p-aminothiophenol) Polymeric Film

In this study, a molecularly imprinted electrochemical sensor (MIP/DA) was investigated for selective and sensitive determination of dopamine (DA) by electrochemical polymerization of p-aminothiophenol in the presence of DA on gold electrode. According to electrochemical behaviour of the sensor, gained through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), MIP/DA sensor showed distinctive electron transfer characteristics in comparison to the non-imprinted (NIP/DA) sensor. Besides the MIP/DA sensor showed high selectivity for dopamine through its analyte specific cavities. The sensor had a broad working range of 5.0×10⁻⁸–2.0×10⁻⁷ M with a limit of detection (LOD) of 1.8×10⁻⁸ M and the developed sensor was successfully applied for determination of dopamine in pharmaceutical samples.