Highly sensitive and simultaneous electrochemical determinations of non-steroidal anti-inflammatory drugs in water using nanostructured carbon-based paste electrodes.

Simple and fast simultaneous quantifications in water of anti-inflammatory drugs, which belong to the emerging pollutants, represents a great challenge for water quality control. The development of electrochemical methods to meet the simultaneous and concomitant detection requirements depends mainly on the electrode material. The fullerene­carbon nanofiber (FULL/CNF) and graphene­carbon nanotubes (GR/CNT) paste electrodes as sensing elements were employed for the first time for the determination of diclofenac (DCF), naproxen (NPX) and ibuprofen (IBP) simultaneously and concomitantly. The comparative morphostructural and electrochemical characterizations of both electrodes were achieved by scanning electron microscopy (SEM) and cyclic voltammetry (CV). Differential-pulsed voltammetry (DPV), chronoamperometry (CA) and multiple-pulsed amperometry (MPA) were used for detection tests. FULL/CNF electrode was suitable to develop a simultaneous DPV-based detection methodology that allowed reaching the lowest limit of detections of 0.230 nM for DCF, 0.310 nM for NPX and 0.180 nM for IBP. GR/CNT electrode did not provide stability for DPV-based detection, but the lowest limits of detection of 0.149 nM for DCF, 0.809 nM for NPX and 0.640 nM for IBP were achieved by MPA-based methodology. Both electrodes, linked to specific detection technique, showed good reproducibility, stability and ability to measure DCF, NPX and IBP simultaneously in aqueous solution. The satisfactory results achieved by analysis of real surface water sample (Bega River, Timisoara city, Romania) indicated that the proposed voltammetric and amperometric methodologies using both electrodes have great potential for practical applications in analysis of different water samples.

Graphene Quantum Dots and Cu(I) Liquid Crystal for Advanced Electrochemical Detection of Doxorubicine in Aqueous Solutions.

Two paste electrodes based on graphene quantum dots and carbon nanotubes (GRQD/CNT) and one modified with a homoleptic liquid crystalline Cu(I) based coordination complex (Cu/GRQD/CNT) were obtained and morphostructurally and electrochemically characterized in comparison with simple CNT electrode (CNT) for doxorubicine (DOX) detection in aqueous solutions. GRQD/CNT showed the best electroanalytical performance by differential pulse voltammetry technique (DPV). Moreover, applying a preconcentration step prior to detection stage, the lowest limit of detection (1 ng/L) and the highest sensitivity (216,105 µA/mg·L-1) in comparison with reported literature data were obtained. Cu/GRQD/CNT showed good results using multiple pulse amperometry technique (MPA) and a favorable shifting of the potential detection to mitigate potential interferences. Both GRQD-based paste electrodes have a great potential for practical utility in DOX determination in water at trace concentration levels, using GRQD/CNT with DPV and in pharmaceuticals formulations using Cu/GRQD/CNT with MPA.

CuBi2O4 Synthesis, Characterization, and Application in Sensitive Amperometric/Voltammetric Detection of Amoxicillin in Aqueous Solutions.

CuBi2O4 synthesized by thermolysis of a new Bi(III)-Cu(II) oxalate coordination compound, namely Bi2Cu(C2O4)4·0.25H2O, was tested through its integration within carbon nanofiber paste electrode, namely CuBi/carbon nanofiber (CNF), for the electrochemical detection of amoxicillin (AMX) in the aqueous solution. Thermal analysis and IR spectroscopy were used to characterize a CuBi2O4 precursor to optimize the synthesis conditions. The copper bismuth oxide obtained after a heating treatment of the precursor at 700 °C/1 h was investigated by an X-ray diffraction and scanning electron microscopy. The electrochemical behavior of CuBi/CNF in comparison with CNF paste electrode showed the electrocatalytic activity of CuBi2O4 toward amoxicillin detection. Two potential detections, with one at the potential value of +0.540 V/saturated calomel electrode (SCE) and the other at the potential value of -1.000 V/SCE, were identified by cyclic voltammetry, which were exploited to develop the enhanced voltammetric and/or amperometric detection protocols. Better electroanalytical performance for AMX detection was achieved for CuBi/CNF using differential-pulsed and square-wave voltammetries than others reported in the literature. Very nice results obtained through anodic and cathodic currents recorded at +0.750 V/SCE and -1.000 V/SCE in the same time period using a pseudo multiple-pulsed amperometry technique showed the great potential of the CuBi/CNF paste electrode for practical applications in amoxicillin detection in aqueous solutions.

Electrochemical Method for Ease Determination of Sodium Diclofenac Trace Levels in Water Using Graphene-Multi-Walled Carbon Nanotubes Paste Electrode.

Sodium diclofenac (DCF) presence reported in water use cycle at various concentrations including trace levels necessitates continuous development of advanced analytical method for its determination. In this work, ease electrochemical methods for DCF determination based on voltammetric and amperometric techniques were proposed using a simple combination of graphene with multi-walled carbon nanotubes as paste electrode. Integration of the graphene with multi-walled carbon nanotubes enlarged the electroactive surface area of the electrode and implicitly enhanced the electrochemical response for DCF determination. On the basis of the sorption autocatalytic effect manifested at low concentration of DCF, we found that the preconcentration step applied prior to differential-pulsed voltammetry (DPV) and multiple-pulsed amperometry (MPA) allowed for the enhancement of the electroanalytical performance of the DCF electrochemical detections, which were validated by testing in tap water. The lowest limit of detection (LOD) of 1.40 ng·L-1 was found using preconcentration prior to DPV under optimized operating conditions, which is better than that reached by other carbon-based electrodes reported in the literature.

Enhanced Electrochemical Response of Diclofenac at a Fullerene⁻Carbon Nanofiber Paste Electrode.

The requirements of the Water Framework Directive to monitor diclofenac (DCF) concentration in surface water impose the need to find advanced fast and simple analysis methods. Direct voltammetric/amperometric methods could represent efficient and practical solutions. Fullerene⁻carbon nanofibers in paraffin oil as a paste electrode (F⁻CNF) was easily obtained by simple mixing and tested for DCF detection using voltammetric and amperometric techniques. The lowest limit of detection of 0.9 nM was achieved by applying square-wave voltammetry operated under step potential (SP) of 2 mV, modulation amplitude (MA) of 10 mV, and frequency of 25 Hz, and the best sensitivity was achieved by four-level multiple pulsed amperometry (MPA) that allowed in situ reactivation of the F⁻CNF electrode. The selection of the method must take into account the environmental quality standard (EQS), imposed through the "watchlist" of the Water Framework Directive as 0.1 µg·L-1 DCF. A good improvement of the electroanalytical parameters for DCF detection on the F⁻CNF electrode was achieved by applying the preconcentration step for 30 min before the detection step, which assured about 30 times better sensitivity, recommending its application for the monitoring of trace levels of DCF. The electrochemical behavior of F⁻CNF as a pseudomicroelectrode array makes it suitable for practical application in the in situ and real-time monitoring of DCF concentrations in water.

Simultaneous Voltammetric Detection of Carbaryl and Paraquat Pesticides on Graphene-Modified Boron-Doped Diamond Electrode.

Monitoring of pesticide residues in food, beverages, and the environment requires fast, versatile, and sensitive analyzing methods. Direct electrochemical detection of pesticides could represent an efficient solution. Adequate electrode material, electrochemical technique, and optimal operation parameters define the detection method for practical application. In this study, cyclic voltammetric and differential pulse voltammetric techniques were used in order to individually and simultaneously detect two pesticides, i.e., carbaryl (CR) and paraquat (PQ), from an acetate buffer solution and also from natural apple juice. A graphene-modified boron-doped diamond electrode, denoted BDDGR, was obtained and successfully applied in the simultaneous detection of CR and PQ pesticides, using the differential pulse voltammetric technique with remarkable electroanalytical parameters in terms of sensitivity: 33.27 μA μM −1 cm −2 for CR and 31.83 μA μM −1 cm −2 for PQ. These outstanding results obtained in the acetate buffer supporting electrolyte allowed us to simultaneously detect the targeted pesticides in natural apple juice.

Electrochemical Selective and Simultaneous Detection of Diclofenac and Ibuprofen in Aqueous Solution Using HKUST-1 Metal-Organic Framework-Carbon Nanofiber Composite Electrode.

In this study, the detection protocols for the individual, selective, and simultaneous determination of ibuprofen (IBP) and diclofenac (DCF) in aqueous solutions have been developed using HKUST-1 metal-organic framework-carbon nanofiber composite (HKUST-CNF) electrode. The morphological and electrical characterization of modified composite electrode prepared by film casting was studied by scanning electronic microscopy and four-point-probe methods. The electrochemical characterization of the electrode by cyclic voltammetry (CV) was considered the reference basis for the optimization of the operating conditions for chronoamperometry (CA) and multiple-pulsed amperometry (MPA). This electrode exhibited the possibility to selectively detect IBP and DCF by simple switching the detection potential using CA. However, the MPA operated under optimum working conditions of four potential levels selected based on CV shape in relation to the potential value, pulse time, and potential level number, and order allowed the selective/simultaneous detection of IBP and DCF characterized by the enhanced detection performance. For this application, the HKUST-CNF electrode exhibited a good stability and reproducibility of the results was achieved.

Non-invasive assessment of liver fibrosis in chronic viral hepatitis.

BACKGROUND: Hyaluronic acid (HA), ASAT to Platelet Ratio Index (APRI), ASAT/ALAT ratio, Fibrosis 4 score (FIB4) and FibroScan were studied as non-invasive markers of liver fibrosis (F) in chronic viral hepatitis B (CHB) and C (CHC), in an attempt to avoid the complications of liver puncture biopsy, considered the gold standard in the evaluation of F. The aim of our research was to study whether HA, APRI, ASAT/ALAT ratio, FIB4 and FibroScan are useful non-invasive markers in predicting severe F in Romanian patients. PATIENTS AND METHODS: This was a prospective multicenter transversal and observational study, which included 76 patients with CHB/CHC. The independent effect of studied markers was tested using multiple binary logistic regression. RESULTS: In patients with CHB and CHC, the APRI cut-off value for F4 was 0·70 ng/mL (Se = 77%, Sp = 78%), the FIB4 cut-off value was 2·01 (Se = 77%, Sp = 69%), and the FibroScan cut-off value was 13·15 (Se = 92%, Sp = 88%). For patients with CHB/CHC, there was a significant linear positive correlation between F and HA (r = 0·42, P = 0·001), FibroScan (r = 0·67, P < 0·001), APRI (r = 0·46, P < 0·001) and FIB4 (r = 0·51, P < 0·001). Considering age, sex and body mass index as possible confounding factors or covariates in multivariable logistic modelling, FibroScan was the unique test that able to significantly highlight the presence of F4 score in CHB/CHC patients (P = 0·009) while FIB4 test seems to have a tendency to statistical significance. CONCLUSION: FibroScan, APRI and FIB4 are useful non-invasive tests for the evaluation of F4 in patients with CHB and CHC.

Simultaneous Voltammetric/Amperometric Determination of Sulfide and Nitrite in Water at BDD Electrode.

This work reported new voltammetric/amperometric-based protocols using a commercial boron-doped diamond (BDD) electrode for simple and fast simultaneous detection of sulfide and nitrite from water. Square-wave voltammetry operated under the optimized working conditions of 0.01 V step potential, 0.5 V modulation amplitude and 10 Hz frequency allowed achieving the best electroanalytical parameters for the simultaneous detection of nitrite and sulfide. For practical in-field detection applications, the multiple-pulsed amperometry technique was operated under optimized conditions, i.e., -0.5 V/SCE for a duration of 0.3 s as conditioning step, +0.85 V/SCE for a duration of 3 s that assure the sulfide oxidation and +1.25 V/SCE for a duration of 0.3 s, where the nitrite oxidation occurred, which allowed the simultaneously detection of sulfide and nitrite without interference between them. Good accuracy was found for this protocol in comparison with standardized methods for each anion. Also, no interference effect was found for the cation and anion species, which are common in the water matrix.

Serum hyaluronic acid in chronic viral hepatitis B and C: a biomarker for assessing liver fibrosis in chronic hemodialysis patients.

PURPOSE: Serum hyaluronic acid (sHA) is studied as a noninvasive marker of liver fibrosis (F) in chronic B and C viral hepatitis in general population but less in end-stage renal disease patients undergoing hemodialysis. METHODS: We evaluated sHA as a noninvasive biomarker of F in a multicenter prospective, transversal, and observational study which included 52 end-stage renal disease patients with chronic B (14) and C (38) viral hepatitis (age 55.57 ± 14.46 years, dialysis vintage 132.59 ± 86.02 months). RESULTS: Of the noninvasive tests analyzed, only sHA, APRI, and FIB4 index were able to differentiate patients with F1 (sHA p = 0.006; APRI p = 0.031; FIB4 p = 0.016). No statistically significant differences were found between sHA and APRI, ASAT/ALAT ratio, and FIB4 index in detecting F1 a (p > 0.02). sHA seemed to be more efficient than APRI, ASAT/ALAT ratio, and FIB4 index, having the highest estimated AUC value. The sHA threshold value for F1 was equal to 33.46 ng/mL, with the following estimated values of the performance indicators: Se 88.46 % and Sp 50 %. sHA was the only noninvasive test of the studied tests that could determine F2 (p = 0.002), with a threshold value of 80.24 ng/mL (Se 63 %, Sp 88 %), and F3 (p = 0.008), with a threshold value of 88.54 ng/mL (Se 60 %, Sp 84 %). None of the studied noninvasive tests could determine F4. CONCLUSIONS: In patients with chronic B and C viral hepatitis undergoing hemodialysis, sHA may be a useful biomarker for the liver fibrosis grades: F1-mild, F2-moderate, and F3-severe, but it does not differentiate between chronic hepatitis (F1-F3) and liver cirrhosis (F4).

Electrochemical detection and degradation of ibuprofen from water on multi-walled carbon nanotubes-epoxy composite electrode.

This work describes the electrochemical behaviour of ibuprofen on two types of multi-walled carbon nanotubes based composite electrodes, i.e., multi-walled carbon nanotubes-epoxy (MWCNT) and silver-modified zeolite-multi-walled carbon nanotubes-epoxy (AgZMWCNT) composites electrodes. The composite electrodes were obtained using two-roll mill procedure. SEM images of surfaces of the composites revealed a homogeneous distribution of the composite components within the epoxy matrix. AgZMWCNT composite electrode exhibited the better electrical conductivity and larger electroactive surface area. The electrochemical determination of ibuprofen (IBP) was achieved using AgZMWCNT by cyclic voltammetry, differential-pulsed voltammetry, square-wave voltammetry and chronoamperometry. The IBP degradation occurred on both composite electrodes under controlled electrolysis at 1.2 and 1.75 V vs. Ag/AgCl, and IBP concentration was determined comparatively by differential-pulsed voltammetry, under optimized conditions using AgZMWCNT electrode and UV-Vis spectrophotometry methods to determine the IBP degradation performance for each electrode. AgZMWCNT electrode exhibited a dual character allowing a double application in IBP degradation process and its control.

Electrochemical determination of pentachlorophenol in water on a multi-wall carbon nanotubes-epoxy composite electrode.

The aim of this study was the preparation, characterization, and application of a multi-wall carbon nanotubes-epoxy composite electrode (MWCNT-EP) with 25%, wt. MWCNTs loading for the voltammetric/amperometric determination of pentachlorophenol (PCP) in aqueous solutions. The structural and morphological aspects of the MWCNT-EP composite electrode were examined by scanning electron microscopy. The electrical properties were characterized by direct-current conductivity measurements in relation with the percolation threshold. The electrochemical behavior of PCP at the MWCNT-EP composite electrode was investigated using cyclic voltammetry in 0.1 M Na2SO4 supporting electrolyte in order to establish the parameters for amperometric/voltammetric determination of PCP. The linear dependence of current vs. PCP concentrations was reached in a wide concentration range from 0.2 to 12 µM PCP using cyclic voltammetry, differential-pulsed voltammetry, square-wave voltammetry, chronoamperometry, and multiple-pulsed amperometry techniques. The best electroanalytical performances of this composite electrode were achieved using a pre-concentration/square-wave voltammetric technique and also multiple-pulsed amperometry techniques envisaging the practical applications. The ease of preparation, high sensitivity, and stability of this composite electrode should open novel avenues and applications for fabricating robust sensors for detection of many important species.

Silver-functionalized carbon nanofiber composite electrodes for ibuprofen detection.

The aim of this study is to prepare and characterize two types of silver-functionalized carbon nanofiber (CNF) composite electrodes, i.e., silver-decorated CNF-epoxy and silver-modified natural zeolite-CNF-epoxy composite electrodes suitable for ibuprofen detection in aqueous solution. Ag carbon nanotube composite electrode exhibited the best electroanalytical parameters through applying preconcentration/differential-pulsed voltammetry scheme.

Copper-decorated carbon nanotubes-based composite electrodes for nonenzymatic detection of glucose.

The aim of this study was to prepare three types of multiwall carbon nanotubes (CNT)-based composite electrodes and to modify their surface by copper electrodeposition for nonenzymatic oxidation and determination of glucose from aqueous solution. Copper-decorated multiwall carbon nanotubes composite electrode (Cu/CNT-epoxy) exhibited the highest sensitivity to glucose determination.

Non-enzymatic electrochemical detection of glycerol on boron-doped diamond electrode.

A non-enzymatic direct electrochemical glycerol detection method at a commercial boron-doped diamond (BDD) electrode in 0.1 M NaOH supporting electrolyte was developed. All the used electrochemical techniques proved useful features for the oxidation and direct amperometric determination of glycerol at a BDD electrode in 0.1 M NaOH aqueous solution. It was found that the direct electrooxidation of glycerol on the BDD electrode requires both adsorbed glycerol and hydroxyls at the electrode surface. Also, the sp(2) carbon did not allow enhancement of the glycerol oxidation process. The electronalytical sensitivity for the determination of glycerol at the BDD electrode ranged from 0.040 to 0.226 µA mM(-1) as a function of the technique used. The highest electroanalytical sensitivity for the determination of glycerol at the BDD electrode was reached in batch system amperometric quantification under stirring conditions. Performed recovery studies indicated that it is possible to determine glycerol in real samples, and the proposed batch system analysis-based methodology can be a valuable tool for practical glycerol analysis.

Voltammetric Detection of Urea on an Ag-Modified Zeolite-Expanded Graphite-Epoxy Composite Electrode.

In this paper, a modified expanded graphite composite electrode based on natural zeolitic volcanic tuff modified with silver (EG-Ag-Z-Epoxy) was developed. Cyclic voltammetry measurements revealed a reasonably fast electron transfer and a good stability of the electrode in 0.1 M NaOH supporting electrolyte. This modified electrode exhibited moderate electrocatalytic effect towards urea oxidation, allowing its determination in aqueous solution. The linear dependence of the current versus urea concentration was reached using square-wave voltammetry in the concentrations range of urea between 0.2 to 1.4 mM, with a relatively low limit of detection of 0.05 mM. A moderate enhancement of electroanalytical sensitivity for the determination of urea at EG-Ag-Z-Epoxy electrode was reached by applying a chemical preconcentration step prior to voltammetric/amperometric quantification.

Carbon-based Composite Electrodes: Preparation, Characterization and Application in Electroanalysis.

Electrodes based on carbon, i.e., expanded graphite (20%, wt.)-epoxy composite(20EG-Epoxy) and expanded graphite (20%, wt.)-polystyrene composite (20EG-PS) havebeen prepared, characterized using scanning electron microscopy (SEM) and cyclicvoltammetry (CV), and tested as anodic sensors. The electrodes exhibited good mechanicalresistance and low electrical resistances. Scan rate dependent cyclic voltammetry responsesat 20EG-Epoxy and 20EG-PS composite electrodes, which were exemplified for thiourea(TU), a toxic sulphur organic compound selected as testing target analyte in 0.1 M Na2SO4 supporting electrolyte, were investigated. The obtained voltammetric data were inaccordance with those for a random array of microelectrodes. The voltammetric andchronoamperometric detection results of TU in tap water samples, without a supplementaryaddition of supporting electrolyte, at 20EG-Epoxy electrode proved its use for directanalysis of environmental samples.