Interference Of Ascorbic Acid Research Articles

Ultrasensitive and reliable dopamine sensor based on polythionine/AuNPs composites

Polythionine/AuNPs (PTh/AuNPs) composites were facilely synthesized through a one-pot synthesis method for the first time and used to modify glass carbon electrode (GCE) for constructing a highly sensitive and selective electrochemical sensor for dopamine (DA) assay. The prepared PTh/AuNPs was detailedly characterized by FTIR, UV–vis, TEM, EDX and AFM. Compared with pure polythionine, the prepared PTh/AuNPs exhibited more enhanced electron transfer property, higher electroactive areas and more efficiently electrocatalytical activity for DA. The prepared sensor could detect DA in the wide linear range from 7.5 to 320nmolL−1 with a detection limit of 2.8nmolL−1 (S/N=3). The sensor could favorably avoid the interference of glucose, ascorbic acid, uric acid, ethanol and bovine serum albumin in the detecting process of DA. Furthermore, the sensor was successfully applied to detect DA in human serum with standard addition method.

Amperometric Biosensor for Choline Based on Gold Screen‐Printed Electrode Modified with Electrochemically‐Deposited Silica Biocomposite

AbstractA mediator‐free choline biosensor was developed using the electrochemically assisted sol‐gel deposition on gold screen‐printed electrodes. The addition of 12 mM of cationic surfactant CTAB in silica sol allowed enhancing the stability of the sensor. The modified electrode demonstrated catalytic activity and stable amperometric response to choline for over 3 weeks of exploitation with the sensitivity of 6 µA mM−1 and LOD of 6 µM. The interference of ascorbic acid was reduced by pretreating the analyzed solution with MnO2 powder. The application of the sensor with the purpose of identifying choline in the baby milk demonstrated satisfactory metrological characteristics.

Electrocatalytic oxidation of NADH at low overpotential using nanoporous poly(3,4)-ethylenedioxythiophene modified glassy carbon electrode

Nanoporous-poly(3,4)ethylenedioxythiophene (PEDOT) modified glassy carbon electrode (GCE) significantly lowers the overpotential and shows high resistance against fouling while oxidizing β-nicotinamide adenine dinucleotide (NADH). The electrocatalytic behaviour of nanoporous-PEDOT modified GCE was studied using cyclic voltammetry in 0.1M phosphate buffer solution (pH 7.0) containing 5mM NADH. Studies revealed that nanoporous-PEDOT/GCE exhibited strong electrocatalytic activity on the oxidation of NADH with a decreased overpotential of about 0.318V as compared to a bare GCE. In addition, chronoamperometric measurements were studied to understand the electron transfer kinetics of nanoporous-PEDOT/GCE which revealed an average diffusion co-efficient (D) and apparent rate constant (k) of 1.56×10−6cm2s−1 and 1.09×102M−1s−1, respectively. Sensitivity of nanoporous-PEDOT/GCE is measured by amperometric method which showed linear variation in the concentration range between 5 and 45μM at an applied overpotential of 0.5V. Limit of detection (LOD) and sensitivity are found to be 3.8μM and 0.026μA/μM, respectively. While quantifying the sensitivity of the electrode, it is found that the electrode surface fouling towards NADH oxidation decreased to an extent of 85%. Interference study is examined in the presence of ascorbic acid (AA) where a peak separation of more than 0.370V is observed between AA and NADH. Thus, nanoporous-PEDOT/GCE provides a simple platform for the oxidation of NADH at low overpotential with high resistance against fouling and without AA interference.

Direct Determination of Trace Dopamine in an Ascorbic Acid Solution at a Bare Glassy Carbon Electrode Using Differential Pulse Voltammetry

It is difficult to monitor dopamine (DA) accurately with a bare glassy carbon electrode because of the interference of ascorbic acid (AA). In this paper, a method for the determination of DA in an AA solution using differential pulse voltammetry was established. Because AA loses its electrochemical activity after being oxidized, hydrogen peroxide was used to oxidize AA, and the interference of AA was completely eliminated. As a result, trace DA could be directly determined in the AA solution with a bare glassy carbon electrode. When trace DA was determined in a 1.0 mmol L−1 AA solution, there was a wide linear range from 3.0×10−8 mol L−1 to 1.0×10−5 mol L−1. The application of this method was demonstrated by the selective measurement of DA in an injection without pretreatment.

Evaluation of two glucose meters and interference corrections for screening neonatal hypoglycemia.

Many neonatal intensive care and maternal units still use self-monitoring of blood glucose (SMBG) devices as a tool to aid diagnosis despite the introduction of point-of-care testing (POCT) devices, which are known to have higher accuracy. We evaluated the performance of two glucose meters, the StatStrip (Nova Biomedical), a POCT device, and the Medisafe Mini (Terumo), an SMBG device, to detect hypoglycemia in neonates. In addition, we evaluated the interference of hematocrit, acetaminophen and ascorbic acid. Whole blood samples were drawn from neonates who were at risk of hypoglycemia and analyzed with the StatStrip and Medisafe Mini. The results were further confirmed with blood gas analyzers ABL825 and BM6050. To evaluate the interference of hematocrit, acetaminophen and ascorbic acid, concentrated solutions of glucose and interfering substances were gravimetrically prepared and analyzed. Among the 222 blood samples analyzed, results from the StatStrip were more closely aligned to those of the ABL825 at all levels of glucose than the Medisafe Mini. StatStrip appears to be unaffected by hematocrit, ascorbic acid or acetaminophen. We recommend its use in neonates in hospital. Further studies are required to identify other interference effects.

Selective recognition of 5-hydroxytryptamine and dopamine on a multi-walled carbon nanotube-chitosan hybrid film-modified microelectrode array.

It is difficult to determine dopamine (DA) and 5-hydroxytryptamine (5-HT) accurately because of the interference of ascorbic acid (AA) in vitro, which has a high concentration and can be oxidized at a potential close to DA and 5-HT at a conventional electrode, combined with the overlapping voltammetric signal of DA and 5-HT at a bare electrode. Herein, chitosan (CS) was used as a stabilizing matrix by electrochemical reaction, and multi-walled carbon nanotubes (MWCNTs) were modified onto the microelectrode array (MEA). The CS-MWCNT hybrid film-modified MEA was quite effective at simultaneously recognizing these species in a mixture and resolved the overlapping anodic peaks of AA, DA and 5-HT into three well-defined oxidation peaks in differential pulse voltammetry (DPV) at −80 mV, 105 mV and 300 mV (versus Ag|AgCl), respectively. The linear responses were obtained in the range of 5 × 10−6 M to 2 × 10−4 M for DA (r = 0.996) and in the range of 1 × 10−5 M to 3 × 10−4 M for 5-HT (r = 0.999) using the DPV under the presence of a single substance. While DA coexisted with 5-HT in the interference of 3 × 10−4 M AA, the linear responses were obtained in the range of 1 × 10−5 M to 3 × 10−4 M for selective molecular recognition of DA (r = 0.997) and 5-HT (r = 0.997) using the DPV. Therefore, this proposed MEA was successfully used for selective molecular recognition and determination of DA and 5-HT using the DPV, which has a potential application for real-time determination in vitro experiments.

Dispersive micro-solid-phase extraction of dopamine, epinephrine and norepinephrine from biological samples based on green deep eutectic solvents and Fe3O4@MIL-100 (Fe) core–shell nanoparticles grafted with pyrocatechol

DA, EP and NE were determined without interference of ascorbic acid using grafted Fe3O4@MIL-100 (Fe) NPs and a green solvent.

Platinum decorated multi-walled carbon nanotubes/Triton X-100 modified carbon paste electrode for the sensitive amperometric determination of Paracetamol

Enhanced sensitivity and electro-catalytic activity for the sensor was achieved by incorporating platinum decorated multi-walled carbon nanotubes (PtMWCNTs) into the carbon paste matrix and TritonX-100 (TX100) layered onto its surface. The modification of carbon paste electrode (CPE) using PtMWCNTs and TX100 was accomplished by employing bulk modification and drop cast methods, respectively. The electrochemical behaviour of Paracetamol (PA) at PtMWCNTs and TX100 modified CPE was investigated by cyclic voltammetry and amperometry. The electrode sensitivity for PA has shown significant variation on varying the amount of Pt nanoparticles on MWCNTs and the PtMWCNTs content in carbon paste matrix. The influence of variation of concentration, volume and time of adsorption of TX100 on the response of PA was investigated. The developed sensor was employed for the selective detection of PA using hydrodynamic amperometry at physiological pH in the presence of ascorbic acid (AA), dopamine (DA) and tryptophan (Trp). The surface morphology of the electrode was studied using FE-SEM images and the interface properties of bare and modified electrodes were investigated by electrochemical impedance spectroscopy. PtMWCNTs in combination with TX100 resulted in an impressive enhancement in the redox current with an analytical advantage of complete elimination of the interference of AA in the simultaneous determination of PA in a mixture. A lower detection limit of (17.71±2.03) nM (S/N=3) was achieved for PA. The modified electrode showed excellent reproducibility, long-term stability and antifouling effects. The practical analytical application was demonstrated by carrying out determination of PA in real samples.

Strong adsorption characteristics of a novel overoxidized poly(3,4-ethylenedioxythiophene) film and application for dopamine sensing

An overoxidized poly(3,4-ethylenedioxythiophene) film-modified screen-printed carbon electrodes (SPCE/PEDOTox) was prepared and characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and water contact angle techniques. The obtained film is a porous structure with highly abundant oxygen functionality. The SPCE/PEDOTox could adsorb cations strongly and perform catalytic oxidation of biomolecules. The potential-induced adsorption of dopamine was observed for SPCE/PEDOTox. A simple medium-exchange procedure was developed for the selective determination of dopamine by the use of the dopamine-adsorbed electrode. Under optimal differential pulse voltammetry (DPV), the proposed assay can be employed in the determination of submicromolar concentration of dopamine without the coexisting interferences of ascorbic acid (1000-fold) and uric acid (10-fold).

Simultaneous Determination of Dopamine in Presence of Ascorbic Acid with Fe-Ag CTAB Nanoparticles Carbon Paste Electrode

A novel electro-chemical method was designed to develop a simple, inexpensive, selective and sensitive electrochemical sensor by modifying carbon paste electrode for the simultaneous determination of dopamine (DA) without the interference of ascorbic acid (AA). Chemically modified carbon paste electrode was prepared by the incorporation of iron-silver bimetallic nanoparticles (Fe-AgNps/Fe-AgCTABMCPE) in presence of cationic surfactant Cetyltrimethyl ammonium Bromide (CTAB) was used for the surface modification and the properties of the modified electrode was studied by using the analytical techniques like cyclic voltammetry (CV), differential pulse voltammetry (DPV) and scanning electron microscope (SEM) image. The modified electrode showed a couple of distinct and well-defined redox peaks for DA and AA mixture, which was not observed with bare carbon paste electrode in 0.1 M phosphate buffer solution (PBS) of pH 7.0 with a scan rate of 50 mVs -1 . There was a good enhancement in redox peak current for DA by 3 folds when compared to bare carbon paste electrode. The anodic peak current vs. scan rate was found to be linear with a correlation coefficient of 0.9951 indicating that the reaction is a diffusion controlled process. The anodic peak current (Ipa) showed a linear relation with concentration of DA with a correlation coefficient of 0.9986 and the detection limit was found to be 3.52×10 -5 M. The detection limit of DA is 0.01 μM with a correlation coefficient of 0.9953 and AA is 0.4 μM with a correlation coefficient of 0.9952 respectively. Hence this chemically modified electrochemical sensor showed a reliable result for the voltammetric determination of AA in the presence of DA and it can be ideal for the practical application of DA in human blood serum and dopamine hydro chloride injection.

Synthesis of polyanthranilic acid-Au nanocomposites by emulsion polymerization: development of dopamine sensor

Polyanthranilic acid (PANA) and polyanthranilic acid-gold (PANA-Au) nanocomposites have been synthesized through emulsion polymerization technique. Use of gold chloride as an oxidant for anthranilic acid not only provides a new route for chemical synthesis of PANA, but also explores a facile method for the formation of nanocomposites. Emulsion polymerization helps in slowing down kinetics of polymerization in comparison to one-phase polymerization and thereby induces formation of monodispersed, both pure and Au nanoparticles, embedded PANA sphere. Reaction progress of nanocomposite formation is studied by UV-Vis spectroscopy for 0–24 h. PANA-Au nanocomposites are characterized by SEM, equipped with EDS, TGA, FT-IR, XRD and electrochemical techniques. XRD of nanocomposites depicts the amorphous nature of polymer and crystalline nature of Au with crystallite size of ~ 24 nm. Differential pulse voltammetry has shown the electro-active nature of PANA. The nanocomposites with improved thermal properties show good dispersion in common organic solvents, and it can be explored for application in interference-free dopamine sensors with sensitivity 12.5 μA/mM. Acidic group (−COOH) on the polymer makes the sensor free from ascorbic acid interference.

Total Soluble Phenolic Compounds Quantification Is Not As Simple As It Seems

Despite the important role of total soluble phenolic compounds (TSPC) in plant and human health, a large number of studies that have evaluated the TSPC in food matrices did not consider possible interfering compounds such as soluble sugars, ascorbic acid (AA), and other reducing compounds in the Folin-Ciocalteu (F-C) quantification method. Thus, the present study describes steps for the optimization of a methodology to extract the TSPC using banana leaves as an example. In addition, the method was tested using ascorbate oxidase (AOX) as a tool to determine and emphasize the importance of the evaluation of AA interference in food products using orange juice as an example. The results showed that two extraction cycles with 80 % acetone and a posterior hexane extraction cycle to remove the excess of chlorophylls were able to obtain a good TSPC extraction yield from banana leaves without extracting compounds that may interfere with the F-C method. The methodology has proven to be accurate, precise, simple, rapid, and inexpensive. Additionally, an overestimation of the TSPC levels in AA-rich matrices was proven using orange juice as an example. Finally, it was demonstrated that the use of AOX could be a useful and simple tool to verify and reduce the AA interference. This work proves and emphasizes the importance of evaluating the yield of the extraction and interferences in the quantification of the TSPC in vegetal-derived foods, which are complex matrices that should be cautiously evaluated.

Electrocatalytic activity of core/shell magnetic nanocomposite

Electrically active magnetic nanocomposites (EAMNCs), Au nanoparticles/self-doped polyaniline@Fe3O4 (AuNPs/SPAN@Fe3O4) with well-defined core/shell structure, were first synthesized by a simple method. The morphology and composition of the as-synthesized AuNPs/SPAN@Fe3O4 nanocomposite have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT–IR), ultraviolet–visible (UV–Vis), X-ray powder diffraction (XRD), and thermogravimetric analysis (TGA). Horseradish peroxidase (HRP)–AuNPs/SPAN@Fe3O4 biocomposites were immobilized onto the surface of indium tin oxide (ITO) electrode to construct an amperometric hydrogen peroxide (H2O2) biosensor. The effects of HRP dosage, solution pH, and the working potential on the current response toward H2O2 reduction were optimized to obtain the maximal sensitivity. Under the optimal conditions, the proposed biosensor exhibited a linear calibration response in the range of 0.05 to 0.35mM and 0.35 to 1.85mM, with a detection limit of 0.01mM (signal-to-noise ratio=3). The modified electrode could virtually eliminate the interference of ascorbic acid (AA) and uric acid (UA) during the detection of H2O2. Furthermore, the biosensor was applied to detect H2O2 concentration in real samples, which showed acceptable accuracy with the traditional potassium permanganate titration.

Fabrication of folic acid sensor based on the Cu doped SnO2 nanoparticles modified glassy carbon electrode

A novel folic acid biosensor has been fabricated using Cu doped SnO2 nanoparticles (NPs) synthesized by a simple microwave irradiation method. Powder XRD and TEM studies confirmed that both the pure and Cu doped SnO2 (Cu: 0, 10, 20wt%) crystallized in tetragonal rutile-type structure with spherical morphology. The average crystallite size of pure SnO2 was estimated to be around 16 nm. Upon doping, the crystallite sizes decreased to 9 nm and 5 nm for 10 and 20wt% Cu doped SnO2 respectively. XPS studies confirmed the electronic state of Sn and Cu to be 4+ and 2+ respectively. Cu (20wt%) doped SnO2 NPs are proved to be a good sensing element for the determination of folic acid (FA). Cu-SnO2 NPs (20wt%) modified glassy carbon electrode (GCE) exhibited the lowest detection limit of 0.024 nM over a wide folic acid concentration range of 1.0 × 10−10 to 6.7 × 10−5 M at physiological pH of 7.0. The fabricated sensor is highly selective towards the determination of FA even in the presence of a 100 fold excess of common interferent ascorbic acid. The sensor proved to be useful for the estimation of FA content in pharmaceutical sample with satisfactory recovery.

Selective Detection of Dopamine against Ascorbic Acid Interference Using 3D Carbon Interdigitated Electrode Arrays

3D carbon interdigitated electrode arrays (IDEAs) were fabricated using inexpensive conventional UV photolithography of SU8 with modified exposure and post exposure bake settings. SU8 patterns were pyrolyzed in an inert environment to obtain three-dimensional (3D) carbon IDEAs. In SU8 an IDEA with a digit width of 3µm, digit height of 6µm (aspect ratio of 2) and gap spacing of 0.8µm was achieved. The carbon sensor performance was investigated as a function of IDEA digit width/gap ratio and digit height under no flow and flow conditions. We demonstrated a gradual increase in redox amplification with an increase in IDEA digit width/gap ratio in the lower ratio range. At higher width/gap ratios, from 1.5 onwards, the amplification factor showed a much steeper increase. The highest amplification of 37 we obtained for a width/gap ratio of 2.45 for an electrode height of 0.95µm. Redox amplification increases significantly with increase in IDEA height. Redox amplification increased from a factor of 9 at 0.09µm digit height to a factor of 37 at 0.95µm height. The effect of potential sweep rate on redox amplification was also investigated. As the sweep rate was decreased from 50mV/s to 5mV/s, the collection efficiency increased from 0.92 to 0.97 whereas the amplification increased from 7 to 25. Under flow condition, the amplification decreases substantially as the recycling of the redox species is impeded by convection resulting in a drop in collection efficiency. The highest amplification of 37 dropped to 4 for the same electrode for a flow rate of 500nL/s.

Selective Detection of Dopamine against Ascorbic Acid Interference Using 3D Carbon Interdigitated Electrode Arrays

Three-Dimensional Carbon Interdigitated electrode arrays were fabricated using a single step 365 nm UV photolithography of a negative photoresist followed by pyrolysis under nitrogen flow. The sensor was applied to selectively detect dopamine via redox cycling in the presence of ascorbic acid under physiological conditions. The sensor didn’t require any chemical modification to achieve selectivity and low limit of detection i.e., 1.5 µM and a linearity range of 5-500 µM in the presence of 0.1 mM ascorbic acid.

Non-enzymatic glucose sensors based on controllable nanoporous gold/copper oxide nanohybrids

A kind of dealloyed nanoporous gold (NPG)/ultrathin CuO film nanohybrid for non-enzymatic glucose sensing has been prepared by a simple, in-situ, time-saving and controllable two-step electrodeposition. The three-dimensional and bicontinuous nanoporous structure of the nanocomposites have been characterized by scanning electron microscope (SEM) and transmission electron microscopy (TEM), and the electrochemical tests have been estimated by cyclic voltammetry and single potential step chronoamperometry (SPSC). The optimal NPG/CuO electrode exhibits great electrocatalytic activity towards glucose oxidation and also shows obvious linear response to glucose up to 12mM with a high sensitivity of 374.0µAcm−2mM−1 and a good detection limit of 2.8µM (S/N=3), as well as strong tolerance against chloride poisoning and interference of ascorbic acid and uric acid.

Validated spectrophotometric methods for the evaluation of Oseltamivir counterfeit pharmaceutical capsules

Four rapid, reliable and economical spectrophotometric methods have been established for the quantitative determination of Oseltamivir phosphate (OST) without the interference of ascorbic acid (ASC) found in some of its counterfeit capsules. The first method involves the use of derivative spectrophotometry with the zero-crossing technique where OST was easily determined using its 1D (Δλ=3) at 219nm. The second method is based on a first-order derivative ratio spectrophotometry (1DD, Δλ=5) where 218nm was selected for its quantification, while the third method applies a more advanced spectrophotometric method based on the ratio difference spectrophotometry (RD) in which the difference in absorbance ratio was measured between 217 and 210nm. In the fourth method, difference spectrophotometric method (ΔA) is applied by subtracting absorbance at 252 from that at 263nm where the difference in absorbance was zero for ASC. The proposed methods were validated for linearity, accuracy, precision and selectivity. Synthetic mixtures of different proportions and commercial capsules were assayed by the proposed methods and the results revealed good accuracy and repeatability of the developed methods.

Determination of uric acid in human urine by eliminating ascorbic acid interference on copper(II)-polydopamine immobilized electrode surface

The polydopamine (PD) coating was spontaneously formed through simple immersion of glassy carbon (GC) electrode in a dilute aqueous solution of dopamine (DA) at acidic solution (pH=4.5) in the presence of Cu2+. Copper(II) ions were anchored on surface of GC electrode to prepare a PD-Cu(II) modified electrode. The morphology, composition and electrochemical properties of the PD-Cu(II) films were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray photoelectron spectroscopy, powder X-ray diffraction, electrochemical impedance spectroscopy and cyclic voltammetry. This modified electrode shows the extraordinary selectivity for electrochemical determination of uric acid (UA) without interference of high concentration of ascorbic acid (AA). Under coexistence of 5mM AA, the differential pulse voltammetry peak current of UA give linear response over the range of 0.06–1.68mM (R2= 0.9934) with detection limit of 24.6μM (S/N=3). Furthermore, the proposed sensor is ideal for the analysis of UA in human urine samples providing satisfactory results.

Photometric starch-iodine determination in plant materials as influenced by ascorbic acid. Critical remarks

Following the work of Sharma et al. (1990) on the interference of ascorbic acid (AA) with starch-iodine reaction, the present authors repeated it, giving a proper explanation of the influence of AA in this reaction. AA oxidizes iodine-iodide (I-KI) reagent which makes impossible to form the blue complex with starch. Three measures are suggested to overcome the interference of AA: 1) to titrate starch solution with I-KI reagent and thus work out an I-KI amount for development of blue coloration, 2) to remove from plant material AA (and other reducing soluble substances) by washing the material with cold water or ethanol, and 3) starch solution could be treated with alkali (pH about 9), which destroys AA in 15 minutes. After acidifying the solution and adding I-KI reagent the blue complex can be determined.