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A solution anode glow discharge (SAGD) was established as a miniaturized excitation source of atomic emission spectrometry (AES) for the detection of Cd in rhizosphere soil, carrot, and carrot leaf samples. The working conditions, such as electrolyte pH, discharge voltage, support electrolyte, solution flow rate, and discharge distance, were systematically optimized. The effect of 31 foreign ions on the Cd determination was investigated. In addition, the influences of matrix modifiers on the Cd signal intensity and interference elimination were examined in detail. The results showed that under the optimal operating parameters, the presence of Fe3+, Co2+, Pb2+, Cu2+, Cr3+, and Tl3+ ions at 30 mg/L causes severe depression effects for the detection of Cd, and adding ascorbic acid as a matrix modifier can reduce the matrix interference, improve sensitivity, and lower the limit of detection (LOD). The LOD of Cd is 4.4 μg/L, and power is below 8 W using SAGD without any matrix modifier. Compared with the solution cathode glow discharge–atomic emission spectrometry (SCGD-AES), the sensitivity is improved about 11-fold, and the power is consumed only about one-sixth. The analysis results of SAGD-AES are in agreement with the Cd-certified reference material and verification values measured by inductively coupled plasma atomic emission spectroscopy, suggesting that proposed method has high accuracy and reliability. [ABSTRACT FROM AUTHOR]

The hydroxyl radical is the most aggressive and dangerous product of incomplete oxygen reduction in a body, making its determination and the effect of various antioxidants on the inhibition of OH radicals a pertinent task. We propose an impedance sensor for the determination of hydroxyl radicals, based on a graphite electrode modified with electrochemically deposited gold and a self-assembled monolayer of N-acetyl-L-cysteine (NAC). The use of NAC ensures the high selectivity of the sensor, and employing non-Faradaic impedance as a method of recording the analytical signal ensures the limit of detection for OH radicals at the level 0.01 nM with a linearity range of detectable concentrations from 0.08 to 8 nM. The developed sensor has been successfully used to assess the activity of certain antioxidants (ascorbic acid, glutathione, coenzyme Q10) towards OH radicals. [ABSTRACT FROM AUTHOR]

The reactivity of coulometric titrants (bromine, iodine, and hexacyanoferrate(III) ions) with respect to the antioxidants (AOs) of beer is evaluated. It is shown that electrogenerated iodine interacts with ascorbic acid and sulfur-containing compounds, but does not oxidize phenolic AOs. The stoichiometric coefficients of reactions of phenolic AOs with electrogenerated bromine and hexacyanoferrate(III) ions are found. A comprehensive assessment of the antioxidant properties of beer is carried out through overall antioxidant parameters (total antioxidant capacity (TAC) according to the reaction with electrogenerated bromine, ferric reducing power (FRP) according to the reaction with electrogenerated hexacyanoferrate(III) ions, and oxidation by). Sixteen samples, differing in the type of fermentation, variety, and style, are considered. A statistically significant difference between the parameters for individual samples is shown. The TAC and FRP of beer correlate with the total concentration of phenolic compounds and antioxidant activity (r = 0.7175–0.8703 at rcrit = 0.4973), which confirms the correctness of the results obtained using coulometric titration. Differences in the overall antioxidant parameters of the top-fermented and bottom-fermented beers, as well as filtered and unfiltered light and dark beers, are statistically insignificant (p = 0.10–0.82). The change in the overall antioxidant parameters of beer during storage in air is evaluated. [ABSTRACT FROM AUTHOR]

A green flow injection spectrophotometric technique for the determination of ascorbic acid was described based on the redox and complexation reactions. Iron(III) was reduced to iron(II) by ascorbic acid with subsequent complexation reaction of remaining iron(III) with a natural reagent extracted from Areca catechu L. at pH 5.0 yielding a dark-blue color. Absorbance decreased with increasing ascorbic acid concentration. A linear range of 1–10 mg/L for ascorbic acid was obtained with r2 of 0.9986. Limit of detection and limit of quantification were 0.3 and 0.9 mg/L, respectively. Relative standard deviation was less than 5.0%. This method was utilized to quantify ascorbic acid in pharmaceuticals and soft drinks with a sampling rate of 40 h−1. Ascorbic acid contents of 96–100% in pharmaceutical samples were obtained, while recoveries for spiked ascorbic acid standard at 3 mg/L in soft drinks were 92–113%. [ABSTRACT FROM AUTHOR]

We found the conditions for the micellar extraction of active components from spices using 0.1 M Brij® 35 as an extractant and intensifying the process with ultrasonic treatment. A single extraction for 10 min ensures the maximum recovery of active components. The raw material-to-extractant ratio varies widely depending on the type of the spice. To characterize the extracts obtained, the Ce(IV)-based reducing capacity was used, based on the interaction of the extract components with electrogenerated Ce(IV). Using ascorbic acid as an example, we proved that the Brij® 35 micellar medium does not affect the current efficiency of the coulometric titrant. Stoichiometric coefficients of several biologically active compounds with electrogenerated Ce(IV) were determined. The Ce(IV)-based reducing capacity of 20 spices was determined. The results were compared with total antioxidant parameters. [ABSTRACT FROM AUTHOR]

We developed a method for the selective and sensitive voltammetric determination of ascorbic and oxalic acids. A screen-printed electrode, modified by gold–palladium bimetallic system and exhibiting catalytic activity in the electrooxidation of the organic acids under consideration, was used as a detector. The difference between the potentials of oxidation peaks of these compounds was 400–500 mV. The proposed method enables an in situ voltammetric determination of ascorbic and oxalic acids in citrus fruits and orange juices without sample preparation. The results of the voltammetric determination are comparable with the data of iodometry and permanganometry, which are the recommended methods for the analysis of fruit juices. [ABSTRACT FROM AUTHOR]

The present study suggested three different highly sensitive luminescent systems based on the employment of silver nanoparticles (NPs), copper oxide nanoparticles and gold nanoparticles in the presence of micellar medium sodium dodecyl sulfate (SDS) for the detection of ascorbic acid in some fruit juices. The fluorescence spectral behavior of ascorbic acid was detected at λem of 420 nm after λex at 350 nm in the presence of acetate buffer (pH 3). Under optimized experimental conditions, the suggested spectroflourimetric systems displayed excellent linearity over concentration ranges of 1.0 × 10–9–1.0 × 10–2, 1.0 × 10–7–1.0 × 10–3 and 1.0 × 10–6–1.0 × 10–3 M with lower limits of detection of 1.0 × 10–10, 5 × 10–8 and 5 × 10–7 M for SDS−AgNPs, SDS−CuONPs and SDS−AuNPs systems, respectively. The suggested approaches were successfully used to detect ascorbic acid in its bulk powder and in some commercial fruit juices. [ABSTRACT FROM AUTHOR]

We proposed a method for the selective and highly sensitive amperometric determination of dopamine and adrenaline in the presence of ascorbic and uric acids in a flow-injection system. Screen-printed electrodes modified with palladium nanoparticles, exhibiting catalytic activity in the electrooxidation of catecholamines, were used as a detector. The difference between the oxidation peak potentials of these compounds is 200 mV. A linear bilogarithmic dependence of the analytical signal on the concentration of dopamine and adrenaline is observed in the ranges from 5 × 10–12 to 5 × 10–8 M and from 1 × 10–9 to 1 × 10–5 M, respectively. For simultaneous two-component analysis, screen-printed electrodes with two working electrodes were used, that is, dual screen-printed electrodes modified with palladium nanoparticles, which enable two substances to be determined simultaneously at two different potentials. The proposed method for the joint flow-injection amperometric determination of dopamine and adrenaline using a modified dual screen-printed electrode was tested in the analysis of urine. [ABSTRACT FROM AUTHOR]

A liquid chromatography−mass spectrometry method was developed for the simultaneous quantitation of (2R,3R)-Dihydromyricetin and Myricetin in rat plasma samples to facilitate analysis of samples collected after administration of SenDeng-4 medicine. The plasma was subjected to protein precipitation with HCl (containing 10% ascorbic acid) and analyzed using electrospray ionization mass spectrometry in selected ion monitoring mode with Paeoniflorin as an internal standard. Good linearity for the two compounds was observed. The intra- and inter-day precision of analysis was <10% for each compound. The present method was suitable for determining (2R,3R)-Dihydromyricetin and Myricetin in rat plasma after intravenous administration of SenDeng-4 to rats with sufficient sensitivity. [ABSTRACT FROM AUTHOR]

A highly sensitive enzyme-induced metallization-based electrochemical signal amplification strategy was developed based on the integration of the enzyme-induced metallization reaction, Au nanoparticles (AuNPs)-induced silver deposition, chemically modified electrode and highly sensitive stripping voltammetry detection. The presence of alkaline phosphatase (ALP) catalyzed ascorbic acid 2-phosphate into ascorbic acid, which reduced Ag+ to Ag0 on the surface of the AuNPs/multi-walled carbon nanotubes/polyethyleneimine/glassy carbon electrode (AuNPs/MWNTs/PEI/GCE). As a result, the enzyme-generated product was accumulated on the surface of the AuNPs/MWNTs/PEI/GCE by means of silver deposition via this signal amplification strategy, which enhanced the detection signal dramatically. Amounts as low as 1 × 10–8 U/mL (corresponding to 10 aM) ALP can be detected using this strategy, which is about 4−7 orders of magnitude more sensitive than with other reported methods for ALP determination. In addition, this strategy can be applied to ALP detection in real complex samples, which shows great potential in the early diagnosis of diseases. [ABSTRACT FROM AUTHOR]

A simple, economical and selective method employing ion pair dispersive liquid−liquid microextraction (DLLME) coupled with spectrophotometric determination of carbamazepine (CBZ) in pharmaceutical preparations and biological samples was developed. The method is based on reduction of Mo(VI) to Mo(V) using a combination of ammonium thiocyanate and ascorbic acid in acidic medium to form a red binary Mo(V) thiocyanate complex. After addition of CBZ to the complex, extraction of the formed CBZ−Mo(V)−(SCN)6 was performed using a mixture of methylene chloride and methanol. Then, the measurement of target complex was performed at the wavelength of 470 nm. The important extraction parameters affecting the efficiency of DLLME were studied and optimized in detail. At the optimum conditions, the linear range was 0.02–0.2 µg/mL. Moreover, the limits of detection and quantification were 0.01 and 0.04 µg/mL, respectively. High enrichment factor was obtained (118). Good recoveries at 0.06, 0.15 and 0.2 µg/mL ranging from 93 to 102% were achieved. The proposed method was successfully applied to the determination of CBZ in pharmaceutical formulations and biological samples. [ABSTRACT FROM AUTHOR]

The antioxidant capacity (AOC) of water–alcohol tinctures of medicinal plant materials, vitamins, and vitamin complexes was investigated. The accuracy indicators for determining the antioxidant capacity of these samples are found; the accuracy of the measurement results is examined using a sample of ascorbic acid with a known concentration of the main component. The relative measurement error of the antioxidant capacity of herbal and synthetic medications does not exceed 10%. [ABSTRACT FROM AUTHOR]

A glassy carbon electrode has been modified by electrochemical polymerization of dianix yellow along with multi-walled carbon nanotubes (MWCNTs) and utilized for the selective determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA). Atomic force microscopy and scanning electron microscopy images were obtained to compare the surface morphology and topography of the bare and modified electrodes. Also, the electrochemical activities of DA, AA, and UA on the bare and modified electrodes were evaluated with the use of cyclic, linear sweep and differential pulse voltammetry (DPV). Large peak separation, good sensitivity, and stability allow to apply the poly-dianix yellow/MWCNTs modified electrode for the determination of DA individually and in the presence of AA and UA. The DPV data showed the linearity of DA, AA, and UA peak currents in the concentrations ranges of 7–2500 nM, 5–110 µM, and 0.100–7.500 µM with the detection limits of 6.1, 99 and 8.9 nM, respectively. The proposed electrode was applied for the quantification of dopamine in human blood serum samples. [ABSTRACT FROM AUTHOR]

The results of complex studies of a possibility of the rapid analysis of solutions using a spectroscopic system based on a hollow-core photonic-crystal fiber are presented. Pharmaceutical preparations of vitamins B and C from various manufacturers were selected as test samples. The transformation of the transmission spectra of the fiber after filling hollow channels with an analyte solution was observed in the wavelength region of 350-1100 nm, depending on the type of the vitamin, producer, and concentration. Comparative quantitative estimates of the sensitivity, resolution, and error in determining the concentration of solutions are given. To increase the functionality of the spectroscopic system, it is suggested to use known chemometric methods and algorithms. [ABSTRACT FROM AUTHOR]

The adsorption of vanadium(V) and 8-hydroxyquinoline-5-sulfonic acid ( HQS) on polyacrylonitrile fiber disks filled with an AV-17 ( PANV-AV-17) anion exchanger is studied by diffuse reflection spectroscopy. Vanadium(V) at pH 5-7 is adsorbed on PANV-AV-17; when a HQS solution is applied to the disk, a yellowish green complex compound formed, which changed color to almost black after the treatment of the disk with a HCl solution. The presence of sulfo groups in the HQS molecule ensures the preconcentration of the reagent on PANV-AV-17 disks with the registration of an analytical signal after the treatment of the disk with NaVO and 0.1 M HCl solutions. A linear dependence of the analytical signal is observed in the HQS concentration range of 1-10 μg/mL. The presence of 20-fold amounts (by weight) of 8-hydroxyquinoline ( HOQ) does not interfere with the determination. When ascorbic acid is applied to the disk with a vanadium(V)-HQS-HCl complex, the color changes from black to green. A test method for the determination of ascorbic acid is proposed. 8-Hydroxyquinoline can be determined by the intrinsic color of the adsorbate on PANV-KU-2 in the range of concentrations of HOQ solution in two drops 5-100 μg. [ABSTRACT FROM AUTHOR]

Deposited cobalt microparticales ( Co-MPs) film onto the platinum disk electrode has been successfully used as a new amperometric sensor for the determination of ascorbic acid ( AA). AA is detected by surface catalyzed oxidation involving cobalt(III) oxyhydroxides in alkaline solution. The Co-MPs/Pt electrode exhibits a high electrocatalytic activity toward the AA oxidation. The diffusion coefficient of AA (6.09 × 10 cm/s) and the catalytic rate constant ( k = 6.27 × 10 Ms) have been determined using electrochemical approaches. The amperometric response of the modified electrode is linear against the AA concentration in the range (0.01-0.48 mM). The sensor displays the best activity with a high response signal, a good sensitivity of 74.3 μA/mM, a low detection limit of 2.5 μM (signal/noise = 3) and a fast response time (<3 s). Moreover, the reproducibility, selectivity and applicability of this biosensor are satisfactorily evaluated. [ABSTRACT FROM AUTHOR]

The silver doped poly(L-arginine)-modified glassy carbon electrode was prepared by electropolymerization. Cyclic voltammetry and electrochemical impedance spectroscopy were used to study the electrochemical properties of the modified electrode. The modified electrode exhibits good electrocatalytic activity for the oxidation of vitamin B ( VB), vitamin C ( VC) and vitamin B ( VB). Under optimal conditions, VB, VC and VB are oxidized at-0.298, 0.317 and 1.058 V, respectively, at the modified electrode using linear sweep voltammetry method. The linear ranges for VB, VC and VB are 1.0 × 10-2.3 × 10, 5.0 × 10-4.0 × 10 and 1.0 × 10-3.0 × 10 M, respectively, and the detection limits are 8 × 10, 3 × 10 and 5 × 10 M. The modified electrode has been successfully applied to simultaneous determination VB, VC and VB in multivitamin tablets with satisfactory results. [ABSTRACT FROM AUTHOR]

Three sample preparation methods (wet grinding followed by centrifugation, ultrasonic-assisted extraction and microwave-assisted solvent extraction) for extracting ascorbic acid ( AA) from parsley, dill and celery were evaluated. AA was extracted into 8% aqueous solutions of acetic acid, metaphosphoric acid and trichloroacetic acid, respectively. An efficient and precise high-performance liquid chromatography method was used for detecting AA. The best extraction technique was ultrasonic-assisted extraction, and acetic acid was the best extractant. A new and original pulse microwave-extraction procedure for AA extraction was also developed. Ascorbate from the plant extracts obtained was quantified and the linearity, precision, recovery, limit of detection ( LOD) and limit of quantification ( LOQ) were studied. LOD and LOQ were 0.2 and 0.22 mg/L for the established method, respectively. The mean recovery ranged from 90.7 to 102.3% with higher variation in the case of celery. Parsley contains the highest amount of ascorbic acid (264 mg AA/100 g of fresh plant), followed by dill (121 mg AA/100 g of fresh plant) and celery (103 mg AA/100 g of fresh plant). [ABSTRACT FROM AUTHOR]

Titanium and silicon-titanium xerogels have been obtained and it has been demonstrated that titanium(IV) incorporated into the xerogel matrix can participate in complexation reactions with ascorbic, gallic, ferulic, and caffeic acids and also rutin, quercetin, and dihydroquercetin present in aqueous solutions. In the case of dihydroquercetin 1 min of contact has been sufficient for achieving the equilibrium; the other compounds required 7-10 min. The stability constants of titanium(IV) complexes incorporated into xerogels reduced in the order dihydroquercetin > gallic acid > ascorbic acid > quercetin > caffeic acid > rutin. The procedures have been developed for solid-phase spectrophotometric determination of ascorbic, gallic, ferulic, caffeic acid as well as rutin, quercetin, and dihydroquercetin. The accuracy of the procedure has been examined by the standard addition method. The procedures for the determination of dihydroquercetin and ascorbic acid have been applied to the analysis of pharmaceutical preparations. [ABSTRACT FROM AUTHOR]

A simple and sensitive spectrophotometric method for the determination of L-ascorbic acid with leuco crystal violet is proposed. The determination is based on the oxidation of analyte by potassium iodate. The colourless oxidation products were formed in the quantity equivalent to iodide ions. The iodide ions react with the excess of iodate ions in acidic medium, to form free iodine which oxidized leuco crystal violet ( LCV) to the liberated crystal violet ( CV) dye, showing maximum absorption at 588 nm. The absorbance was measured at pH of 4.1-4.2 in 1 cm cuvettes. Beer's law was obeyed in the concentration range 0.5-4.0 μg/mL. The molar absorptivity of the coloured compound is 4.14 × 10 L/mol cm for L-ascorbic acid. The analytical parameters were optimized and the method was successfully applied to the determination of L-ascorbic acid in pharmaceuticals. The results were compared with those obtained by methods proposed in Polish Standard. [ABSTRACT FROM AUTHOR]

glassy carbon electrode was modified with electropolymerized film of diphenylamine sulfonic acid ( DPASA). Electropolymerization was performed by cyclic voltammetry in 0.1 M KCl solution. The modified electrode showed an excellent electrocatalytic effect towards oxidation of dopamine ( DA) and ascorbic acid ( AA). Electrostatic interaction between the negatively charged poly(DPASA) film and either cationic DA species or anionic AA species favorably contributed to the redox response of DA and AA. Anodic peaks of DA and AA in their mixture were well separated by ca 168 and −11.8 mV. The proposed modified electrode was utilized for selective determination of dopamine in the concentration range of 5.0 × 10-2.0 × 10 M in the presence of high concentration of ascorbic acid. Detection limit was 6.5 × 10 M. [ABSTRACT FROM AUTHOR]

In this paper, the silver doped poly (L-glutamic acid) modified glassy carbon electrode (PLG-Ag/GCE) was fabricated through an electrochemical immobilization. The modified electrode was used for simultaneous determination of uric acid ( UA) and ascorbic acid ( AA) in 0.1 M phosphate buffer solutions (PBS). The cyclic voltammetric signals of UA and AA were well separated with a potential difference of 396 mV in pH 3.0 phosphate buffer solution. The linear calibration curves were obtained in the concentration range 5.00 × 10-1.00 × 10 M for UA and 8.00 × 10-5.00 × 10 M for AA with the detection limits of 3 × 10 M and 4 × 10 M, respectively. The relative standard deviations were 1.3 and 1.0% for the determinations of UA and AA for 20 continuous measurements. The signal was highly stable and reproducible. This method was successfully applied to the determination of UA in human urine samples. [ABSTRACT FROM AUTHOR]

procedure is developed for the photometric determination of ascorbic acid in drug preparations. It is based on the rapid and highly selective reaction of ascorbic acid with a novel reagent, the guanidinium salt of 1-bismuto-11-molybdophosphoric heteropolyacid. The detection limit for ascorbic acid in stepwise injection analysis makes 15 mg/L, and the duration of single analysis, 5 min. [ABSTRACT FROM AUTHOR]

It has been found that the analytical signal from copper(II), cadmium(II), and zinc(II) in alternating-current stripping voltammetry in the presence of ascorbic acid ( AA) increases only for copper(II) ions, which have significant oxidative potential. It is associated with the appearance of a catalytic current of the reducer in stripping voltammetry, where the reducer is AA. A scheme has been proposed for this process. The rate constant has been calculated for the chemical reduction of copper(I) ions, electrochemically produced in the diffusion layer as a result of the electrochemical oxidation of copper atoms, with AA. A procedure has been developed for the determination of copper in model solutions using the catalytic current of AA; the limit of copper detection is 0.01 μg/L, which is one order lower than the one achieved without AA. [ABSTRACT FROM AUTHOR]

A new method for the determination of traces of iron was developed based on its catalytic effect on the oxidation reaction of dibromo- p-sulfonic acid-arsenazo ( DBS-arsenazo, DBS-ASA) by potassium bromate in a 5.0 × 10−3 M sulfuric acid medium. The optimum experimental conditions for the determination of iron using iron(III)-dibromo- p-sulfonic acid-arsenazo, ( DBS-ASA)-potassium bromate-ascorbic acid system and its kinetic spectrophotometric properties were studied. The absorbance difference (Δ A) is linearly related with the concentration of iron(III) over the range of 0.20–6.0 ng/mL at the maximum absorption wavelength of 520 nm and described by the equation: Δ A = 0.133 c (ng/mL) — 0.0133 with a regression coefficient of 0.9966. The detection limit of the method is 0.17 ng/mL. The method has been successfully used in the determination of traces of iron in potato samples. The obtained results agree with those of atomic absorption spectrometry. [ABSTRACT FROM AUTHOR]

Natural macromolecular compounds, humic acids ( HA), have been used to form gas-sensitive layers of piezoelectric resonance gravimetric sensors. HA have been extracted from humus using alkaline extraction and purified by electrodialysis through ion-exchange membranes. Species have been deposited onto the electrode surface of piezoelectric quartz resonators by air-spraying their aqueous solutions, the layer thickness being 100–200 nm. In determining ammonia with the sensor obtained on the basis of purified HA species, the detection limit is ∼10 mg/m3. Gas-sensitive layers on the basis of humic acids are more stable as compared to the conventionally used gas-sensitive layers based on pyridoxine hydrochloride or ascorbic acid. [ABSTRACT FROM AUTHOR]

An investigation of UV spectroscopic methods, i.e. absorbance, 1st and 2nd derivative spectra for the determination of simvastatin in tablet formulations has been undertaken. This work investigated the possible difficulties that might arise due to the presence of UV absorbing excipients and likely presence of degradation products in such assays. We have demonstrated that the presence of ascorbic acid as an excipient causes interference with simple absorbance measurements leading to a gross over-determination of the simvastatin. 1st and 2nd derivative methods appear to eliminate this problem. We have also shown that the degradation product of simvastatin, i.e. simvastatin β-hydroxy acid, having an almost identical spectrum to the parent drug, may cause problems in the UV spectroscopic determination of the drug in degraded samples. [ABSTRACT FROM AUTHOR]

The effect of the immobilization of 2,6-dichlorophenolindophenol ( DCIP) on a polymethacrylate matrix on its redox and acid-base properties was studied. The ionization constant and formal redox potentials of the immobilized DCIP were determined by solid-phase spectrophotometry. It was shown that the acidity constant and the formal potentials of DCIP decreased upon the immobilization in the polymethacrylate matrix. The results of studying the interaction of ascorbic acid with immobilized DCIP are presented. [ABSTRACT FROM AUTHOR]

A procedure was developed for determining water-soluble vitamins B and vitamin C in premixes, biologically active supplements, and combined feed by reversed-phase HPLC using sodium heptanesulfonate as an ion-pair reagent. A procedure was proposed for purifying a combined food extract by solid-phase extraction on a column packed with a Sep-Pak C18 adsorbent. The stability of ascorbic acid and riboflavin in aqueous solutions with different pH values was studied. [ABSTRACT FROM AUTHOR]

A sensitive and selective electrochemical method for the determination of norepinephrine using a poly (Evans Blue) film-modified glassy carbon electrode was developed. The polymer film-modified electrode shows excellent electrocatalytic activity toward the oxidation of norepinephrine ( NE) in phosphate buffer solution (pH 5.0). The linear range of 5.0 × 10−7–1.8 × 10−5 M and detection limit of 3.5 × 10−8 M were observed for the determination of NE in pH 5.0 phosphate buffer solutions. The interference studies showed that the modified electrode had excellent selectivity for the determination of NE in the presence of large excess of ascorbic acid ( AA) and uric acid ( UA). The differences of the oxidation peak potentials for NE-AA and NE-UA were about 175 and 172 mV, respectively. The resolution is large enough to determine AA, NE and UA individually. This work provides a simple and easy approach to selective detection of NE in the presence of AA and UA in physiological samples. [ABSTRACT FROM AUTHOR]

The catalytic activities of gold, palladium, and rhodium particles and their binary systems electrodeposited on the surface of a glassy-carbon electrode in the oxidation of dopamine and ascorbic acid are compared. As compared to individual noble metals, the Au-Pd binary system exhibits a higher catalytic activity that manifests itself in a multiple increase in the oxidation current of the mediator and in a decrease in the oxidation potential of the substrate. It is found that dopamine and ascorbic acid can be simultaneously determined by voltammetry at an electrode modified with the Au-Pd binary system. The catalytic currents of substrate oxidation are linear functions of the concentrations in the ranges from (1 × 10−3 to 1 × 10−7) M for dopamine and from (5 × 10−3 to 1 × 10−6) M for ascorbic acid. [ABSTRACT FROM AUTHOR]

The interaction of iron(II) with 2,2′-dipyridyl and 1,10-phenanthroline immobilized in a polymethacrylate matrix was studied. The optimum conditions of the complexation of iron(II) with the immobilized reagents and the chemical analytical properties of the complexes in the polymethacrylate matrix were determined. A sorption-spectrophotometric procedure was developed for the determination of iron(II) and the total of iron(II, III) after the reduction of iron(III) by ascorbic acid. The procedure with 2,2′-dipyridyl was used for the analysis of samples of tap, well, and mineral water and a solution of glucose. [ABSTRACT FROM AUTHOR]

In this study, a very simple spectrophotometric method for the simultaneous determination of citric and ascorbic acid based on the reaction of these acids with a copper(II)-ammonia complex is presented. The Cu2+-NH3 complex (with λmax = 600 nm) was decomposed by citrate ion and formed a Cu2+-citrate complex (with λmax = 740 nm). On the other hand, during the reaction of ascorbic acid with copper(II)-ammonia complex, ascorbic acid is oxidized and the copper(II)-ammonia complex is reduced to the copper(I)-ammonia complex and the absorbance decreases to 600 nm. Although there is a spectral overlap between the absorbance spectra of complexes Cu2+-NH3 and Cu2+-citrate, they have been simultaneously determined using an artificial neural network (ANN). The absorbances at 600 and 740 nm were used as the input layer. The ANN architectures were different for citric and ascorbic acid. The output of the citric acid ANN architecture was used as an input node for the ascorbic acid ANN architecture. This modification improves the capability of the ascorbic acid ANN model for the prediction of ascorbic acid concentrations. The dynamic ranges for citric and ascorbic acid were 1.0–125.0 and 1.0–35.0 mM, respectively. Finally, the proposed method was successfully applied to the determination of citric and ascorbic acids in vitamin C tablets and some powdered drink mixes. [ABSTRACT FROM AUTHOR]

The stability of ascorbic acid is studied in dependence on the pH of its aqueous solution. It is shown that itenhances in acidic and weakly alkaline media and upon the addition of acetonitrile. The stabilizing effect of ethanol is considerably lower. Processes occurring in aqueous and aqueous-organic solutions of ascorbic acid are considered and the results obtained are explained. These data are important for the development of analytical procedures and can be used in the chemical and pharmaceutical industries for improving the stability of preparations containing ascorbic acid. [ABSTRACT FROM AUTHOR]

The optimum conditions of the complexation of cobalt with nitroso-R salt in the presence of and without ascorbic acid were found. Molar coefficients of chromaticity functions of the complexes were calculated, and it was demonstrated that cobalt(II) and cobalt(III) complexes can be distinguished only with the use of chromaticity functions, whereas their optical characteristics are nearly the same. For practical purposes, it is better to introduce ascorbic acid and to obtain the kinetically inert complex of cobalt(III) with nitroso-R salt. [ABSTRACT FROM AUTHOR]

The potentials of the anodic peak of ascorbic acid oxidation and the potential differences of anodic and cathodic peaks (Δ E p) of the hydroquinone/benzoquinone redox system at an electrode made of a graphite-epoxy composite are determined in weakly acidic and neutral supporting electrolytes by direct and cyclic voltammetry. The results obtained are compared with thermodynamic values and with the available values of these parameters at different solid electrodes for the above-mentioned redox systems. The effect of aging of the surface of electrodes made of graphite-epoxy composites on the potentials and peak currents of the anodic oxidation of ascorbic acid are studied. It is demonstrated that the regeneration of the electrode surface by mechanically cutting thin layers is important for reducing the δ E p value of the hydroquinone/benzoquinone redox system down to 28–30 mV in supporting electrolytes with pH 2.0 and 7.0. This value is typical of thermodynamically reversible electrode reactions involving two-electron transfer at 20–25°C. [ABSTRACT FROM AUTHOR]

Ascorbic acid is the most common electroactive biological compound found in some plant species (e.g., Citrus species, Rosa species). The electrochemical oxidation of ascorbic acid was investigated by cyclic, linear sweep, differential pulse (DPV), and square wave (SWV) voltammetry. For analytical purposes, a very well-resolved diffusion-controlled voltammetric peak was obtained in acetate buffer at pH 3.50 for DPV and SWV. The linear response was obtained in the range of 3.52–176.1 μg/mL with a detection limit of 0.88 μg/mL for DPV and 0.52 µg/mL for SWV. Based on this study, simple, rapid, selective, and sensitive voltammetric methods were developed for the determination of ascorbic acid in pharmaceutical dosage forms and Rosa species ( R. dumalis ssp. boissieri var. boissieri, R. canina, R. pulverulenta, R. heckeliana ssp. vanheurckiana, and R. montana subsp. woronowii). The results obtained are compared with the HPLC data. The developed methods enable the extracts to be analyzed without the necessity of any time-consuming separation. [ABSTRACT FROM AUTHOR]

The partial least squares (PLS) modeling method was used in the analysis of mixtures of ascorbic, citric, and tartaric acids by potentiometric titration. Binary mixtures of tartaric and citric acids, as well as ternary mixtures of tartaric, citric, and ascorbic acids, were titrated by sodium hydroxide pH-metrically. The linear relationship between the volumes of titrant and the concentrations of analytes was obtained by PLS regression. The designed model was then used to predict the concentrations of components in unknown samples. The practical utility of this method was demonstrated for the simultaneous determination of acids in binary and ternary mixture systems within concentration range from 4 × 10−4 to 2 × 10−3 M, and acceptable results were obtained. [ABSTRACT FROM AUTHOR]

A triiodide-selective electrode based on copper (II)-Schiff base complex as a membrane carrier is proposed. The electrode was prepared by incorporating the carrier into a plasticized polyvinylchloride (PVC) membrane and was directly coated on the surface of a graphite electrode. The obtained electrode showed a near Nernstian slope of 57.0 ± 0.4 mV/decade to I ions over an activity range of 1.0 × 10−5−1.0 × 10−1 M with a limit of detection of 4.8 × 10−6 M. The response time of the electrode was fast (5 s) and the electrode could be used for about 2 months without considerable divergence in response. The potentiometric selectivity coefficients were evaluated and displayed anti-Hofmeister behavior. The electrode was used as an indicator electrode in the potentiometric titration of the triiodide ion and in the determination of ascorbic acid in vitamin C tablets. [ABSTRACT FROM AUTHOR]

A method for forming a composite film on the surface of a graphite electrode is proposed. Conditions for detecting the maximum catalytic current under batch and flow conditions are determined. A procedure for the electrocatalytic determination of ascorbic acid at the graphite electrode modified with a polyaniline film containing palladium particles is proposed. The catalytic effect of this electrode manifests itself by a ∼300-mV decrease in the peak potential of ascorbic acid oxidation and by a multiple increase in the peak current of ascorbic acid oxidation as compared to the unmodified electrode. The linear dependence of the electrocatalytic response of the composite electrode on the concentration of ascorbic acid is observed down to 1 × 10−8 M and 2.5 nmol of ascorbic acid under batch and flow-injection analysis conditions, respectively. [ABSTRACT FROM AUTHOR]

It is shown that an optically transparent polymethacrylate matrix modified with 2,2′-dipyridyl and iron(III) can be used as a sensor for ascorbic acid. A procedure for the solid-phase spectrophotometric and visual determination of ascorbic acid in model solutions and juices using this sensor has been developed and validated. [ABSTRACT FROM AUTHOR]

A study for the validation of orthophosphate determination using an FI-manifold/spectrophotometric detection set-up is made. Under optimized conditions, the method with the largest valid range (0–50 mg L–1), with the possibility of extending it even higher) is the molybdate/ascorbic acid method; its reproducibility and interferences are similar to other tested methods. A study among the conventional digestion methods is then made to test the adaptability of the method to FI systems. The persulfate digestion method was found to be more suitable for use with flow systems. The persulfate digester was connected in-line with the FI-manifold; under optimized conditions, the sensitivity of the method is decreased, especially when used with organic phosphorus compounds, but it is still reasonable for use. The sensitivity is also dependent on the nature of the phosphate species attached to the organic residue. In addition, it was found that colloid precipitate phase in the sample decreases the sensitivity. Finally, real wastewater samples were tested using the UV radiation-assisted, persulfate digester-implemented FI-system method, and using the batch method. It was found from the correlation of the two methods that the fraction of P-recovery in the FIA system was 2/3 of the total phosphate, suggesting that the rest was due to the polyphosphate content. [ABSTRACT FROM AUTHOR]

A study for the validation of orthophosphate determination using an FI-manifold/spectrophotometric detection set-up is made. Under optimized conditions, the method with the largest valid range (0–50 mg L–1), with the possibility of extending it even higher) is the molybdate/ascorbic acid method; its reproducibility and interferences are similar to other tested methods. A study among the conventional digestion methods is then made to test the adaptability of the method to FI systems. The persulfate digestion method was found to be more suitable for use with flow systems. The persulfate digester was connected in-line with the FI-manifold; under optimized conditions, the sensitivity of the method is decreased, especially when used with organic phosphorus compounds, but it is still reasonable for use. The sensitivity is also dependent on the nature of the phosphate species attached to the organic residue. In addition, it was found that colloid precipitate phase in the sample decreases the sensitivity. Finally, real wastewater samples were tested using the UV radiation-assisted, persulfate digester-implemented FI-system method, and using the batch method. It was found from the correlation of the two methods that the fraction of P-recovery in the FIA system was 2/3 of the total phosphate, suggesting that the rest was due to the polyphosphate content. [ABSTRACT FROM AUTHOR]

In this study, a simple spectrophotometric method based on the reaction between ascorbic acid and the copper(II)–ammonia complex is presented for the determination of the vitamin C content of pharmaceutical preparations. During this reaction, ascorbic acid is oxidized and the copper(II)–ammonia complex is reduced to the copper(I)–ammonia complex, and the absorbance decrease at 600 nm (λmax for the copper(II)–NH3 complex) is measured. Stirring the final solution in the presence of air leads to the primary absorbance again being obtained, which indicates that the copper(I)–NH3 complex is quantitatively oxidized to the copper(II)–NH3 complex by O2. The linear dynamic range of the calibration curve is 0.8–6 mmol with a detection limit of 0.26 mmol. The relative standard deviation for eight repeated experiments is 2.4%, which shows that the proposed method has a good repeatability. Finally, this method was used in the analysis of the vitamin C content of different pharmaceutical preparations, such as multivitamin tablets and syrups, vitamin-C tablets and powders, and effervescent tablets. The obtained results are in good agreement with iodimetric data. [ABSTRACT FROM AUTHOR]

Caffeine and vitamins C, PP, and B6 have been determined in energy drinks by capillary electrophoresis. Its advantages and disadvantages over high-performance liquid chromatography have been considered and the influence of analysis conditions on the error of analysis and error sources in capillary electrophoresis have been estimated. [ABSTRACT FROM AUTHOR]

A procedure was developed for the rapid analysis of a new multicomponent anticatarrhal medication Maksikold by high-performance liquid chromatography (HPLC). The possibility of the simultaneous determination of all active substances in the preparation, including ascorbic acid, is an advantage of the proposed procedure. For the efficient resolution of the peaks of analytes and interfering additives, a mobile phase with the pH varied in the course of an experimental run was used. The procedure was used to analyze pilot samples of the preparation. The results obtained exhibit a high precision. [ABSTRACT FROM AUTHOR]