Flow-injection spectrophotometric determination of ascorbic acid by reduction of vanadotungstophosphoric acid

Ascorbic acid may be determined spectrophotometrically at 360 nm based on reduction of vanadotungstophosphoric acid using flow-injection analysis. The carrier stream was distilled water and the reagent streams were buffer solution (pH 3.0), 1.735 × 10^?3 M dodecatungstophosphoric acid and 1.735 × 10^?3 M sodium vanadate. The injection rate was 80 h^?1. The calibration graph was linear up to 80 μg ml^?1 ascorbic acid and the relative standard deviation for the determination of 20 μg ml^?1 ascorbic acid was 1.5% (n=10). The detection limit was 1.0 μg ml^?1 ascorbic acid, based on an injection volume of 250 μl. The system was applied to the determination of ascorbic acid in vitamin C tablets.     

Spectrophotometric flow-injection determination of ascorbic acid by generation of triiodide

A method is proposed for the flow-injection determination of ascorbic acid (0.1–40 μg ml^?1). Iodine is generated in the flow system as triiodide ion or the triiodide/starch complex giving a steady spectrophotometric signal at 350 or 580 nm, respectively; inverse peaks caused by ascorbic acid samples are measured. The method is applied to the determination of ascorbic acid in a fruit juice, jam and vitamin C preparation.     

A new spectrophotometric method for the determination of nadolol

A new spectrophotometric method has been developed for the assay of nadolol in pure form and in tablets. The assay procedure is based on a derivatization methodology employing 4-carboxyl-2,6-dinitrobenzene diazonium ion (CDNBD) as a diazo coupling reagent. The azo dye formed between nadolol and CDNBD absorbed visible light at the wavelength maximum of 416 nm (λ_max) demonstrating a bathochromic shift from the absorption maximum of nadolol. Optimization studies established an optimal reaction time of 10 min at 60 °C. The assays were linear over 1.25–10 μg ml^?1 of nadolol, and the reaction occurred by a 3:1 reagent/drug stoichiometric ratio. The method is found to be selective and has a lower detection limit of 0.29 μg ml^?1. Recovery studies over three days gave mean recovery of 101.4% (RSD 3.0%). This new method has been successfully applied in the determination of nadolol and nadolol/bendroflumethiazide tablets with accuracy and precision similar to the official (USP) HPLC procedure (p > 0.05). The new procedure has the advantages of high sensitivity, lower limit of detection and could find application as an in-process quality control method for nadolol.     

Flow-injection spectrophotometric determination of cobalt by extraction as tetrathiocyanatocobaltate(II) with the ethylenebis(triphenylphosphoniu) cation

Cobalt (0–10 μg) may be determined spectrophotometrically at 625 nm after flow-injection extraction into chloroform of the ion associate ethylenebis(triphenylphosphonium) tetrathiocyanatocobaltate(II). The carrier stream contained 10% (w/v) ammonium fluoride and the reagent stream contained 0.5% (w/v) ethylenebis (triphenylphosphonium) bromide and 5% (w/v) ammonium thiocyanate. The injection rate was 20 h^?1. The calibration graph is linear up to 20 μg ml^?1 and detection limit is 0.23 μg ml^?1 cobalt, based on injection volumes of 500 μl. The system has been applied to the determination of cobalt in a range of tool steels.     

Flow-injection spectrophotometric determination of arylamines and sulphonamides by diazotization and coupling in a micellar medium

In a sodium dodecyl sulphate (SDS) micellar solution, the rate of coupling of a diazonium ion with N-(1- naphthyl)ethylenediamine (NED) increases greatly, the protonation of the resulting azo dyes takes place at higher pH values and the dyes are more soluble. These favourable features were applied to the development of a simple flow-injection spectrophotometric procedure for the determination of diazotizable substances of pharmaceutical interest. Limits of detection in the range 0.2–0.5 μg ml^?1 (signal-to-noise ratio=3), with relative standard deviation of 0.7–3% (n=3) for 5 μg ml^?1 standards, were obtained.     

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min^?1 providing a sample throughput of more than 15 samples h^?1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.     

Flow-injection spectrophotometric determination of silicate,phosphate and arsenate with on-line column separation

The simultaneous determination of silicate, phosphate and arsenate by using flow-injection analysis with on-line column separation is described. Determinations are based on measurement of the absorbance at 810 nm of the heteropoly blue formed with ascorbic acid as reducing reagent. Effects of flow rates, temperature of reaction coils and sample injection volumes are reported; optimum conditions are 0.25 ml min^?1 for the ascorbic acid stream, 95°C for the reaction coils and 300 μl for the injection volume. With the anion-exchange column (TSK-gel SAX), the optimal flow rate of the eluent is 0.75 ml min^?1. Relative retention times depend on the concentration of the KCl/NH₃/EDTA eluting solution; separation and simultaneous determination of the three ions are satisfactory at around 10^?4 mol l^?1 concentrations of the three ions.     

Spectrophotometric determination of aromatic primary amines and nitrite by flow injection analysis

Aromatic primary amines are determined by injection into dilute hydrochloric acid carrier which merges sequentially with 4-N-methylaminophenol and dichromate. The purple-red color formed by oxidative coupling of amines with 4-N-methylaminophenol is measured at 530 nm. In contrast to the manual procedure, the flow-injection procedure avoided errors arising from the instability of the coupling intermediate, oxidation of the amine, and too great an excess of the oxidant. The method improves the selectivity for certain amines in the presence of those which are sterically hindered or have an electron-deficient aromatic nucleus. Nitrite is determined by diazotization of sulfanilamide and quantifying the residual sulfanilamide by oxidative coupling. The sample thourghout for the assay of amines (0.05–20 μg ml^?1 NH₂-N) and nitrite (1–10 μg ml^?1 NO₂^--N) was 120 h^?1. A system for the consecutive determination of aromatic primary amines and nitrite is decribed.     

Solid phase extraction of zirconium as arsenazo(III) complex on agar and spectrophotometric determination

A new solid phase extraction method for the separation and determination of zirconium using agar as an adsorbent is described. The method is based on the adsorption of zirconium as arsenazo(III) complex on agar in a mini-column, elution with sulfuric acid-acetone mixture and determination by spectrophotometry. The effect of different parameters such as pH, concentration of the reagent, eluting reagent, and volume of the sample, amount of the adsorbent and interfering ions was investigated. The calibration graph was linear in the range of 5?C300 ng ml^?1 of zirconium under optimum conditions. The limit of detection based on 3S_b was 1.3 ng ml^?1 and the relative standard deviation (R.S.D) for ten replicate measurements of 15 and 200 ng ml^?1 of zirconium was 3.7 and 1.8%, respectively. The method was applied to the determination of zirconium in water and soil samples.     

The application of the ph-stat method to metal ion-catalyzed reactions

The pH-stat method, which is well known in organic chemistry and biochemistry, is used for the kinetic determination of metal ion catalysts. Indicator reactions that involve protons can be followed by controlled addition of standard base or acid. This is illustrated by the following examples: determination of copper(II) (0.03–0.3 μg ml^-1) with the indicator reaction ascorbic acid—peroxydisulphate; determination of molybdenum(VI) (0.2–2.5 μg ml^-1) with the indicator reaction thiosulphate—hydrogen peroxide; determination of zirconium(IV) (0.2–2 μg ml^-1) with the indicator reaction iodide—hydrogen peroxide; and determination of vanadium(V) (0.2–2 μg ml^-1) with the indicator reaction iodide—bromate. For one example, the copper—ascorbic acid—peroxydisulphate reaction, it is shown that the pH-stat method has distinct advantages over closed systems, giving considerably better sensitivity for the determination of copper (0.5–5 ng ml^-1 ).     

A Spectrophotometric Determination of Ascorbic Acid

A new, simple and sensitive method for the spectrophotometric indirect determination of ascorbic acid in fruits, beverages, and pharmaceuticals is described. In this method, the ascorbic acid reduces Cu²⁺ to Cu⁺ and reacts with 2,9‐dimethyl‐1,10‐phenanothroline (neucoproine) to form Cu (neucoproine)⁺ complex, and it was extracted with N‐phenylbenzimidoylthiourea (PBITU) in chloroform. The apparent value of molar absorptivity of the complex in terms of ascorbic acid is (3.52) × 10⁴ L mole^?1 cm^?1 at λ_max, 460. The detection limit of ascorbic acid is 40 μg L^?1 and the method obeys Beer's law over the concentration range of 0.1–4.0 μg mL^?1. The proposed method was successfully applied for the determination of ascorbic acid in various samples. The validity of the present method was checked by the flow injection analysis (FIA) method.     

Spectrophotometric determination of nitrite in polluted waters using 3-nitroaniline

Nitrite reacts with 3-nitroaniline in the presence of hydrochloric acid to form a diazonium cation, which is subsequently coupled with N-(1-naphtyl)ethylenediammonium chloride to form a stable purple azo dye. The method is suitable for the determination of 0.01–0.80 μg ml^?1 nitrite. The reactions are very fast and require no control of temperature. The observed molar absorptivity and Sandell's sensitivity of the azo dye are 4.9 × 10⁴ l mol^?1 cm^?1 and 9.4 × 10^?4 μg cm^?2, respectively. The method is free from most interferences. The method has been applied successfully to polluted river water.     

Indirect Flow-Injection Analysis of Ascorbic Acid by Photochemical Reduction of Methylene Blue

Abstract

Ascorbic acid was determined indirectly by spectrophotometry at 666 nm based on the photochemical reduction of methylene blue using flow-injection analysis. The carrier stream was 12.7 μgml^?1 methylene blue in phthalate-HCl buffer solution at pH 3.2. The reactor was irradiated with a 500-Watt halogen lamp to facilitate the development of the photochemical reaction. The system allows determination of ascorbic acid in the range 0.18–6.12 μgml^?1 with relative standard deviations of 2.09 and 0.31% for 1.97 and 4.92 μgml^?1 samples, respectively, and a sampling frequency of 50–55 h^?1. The proposed method was applied successfully to the determination of ascorbic acid in vitamin C tablets.     

Flow Injection Analysis Determination of Ascorbic Acid with Spectrofluorimetric Detection

Abstract

A flow injection system for the fluorescence determination of low level of ascorbic acid is proposed. The method is based on the rapid oxidation of ascorbic acid by thallium(I). The fluorescence signal at 419 nm is proportional to the amount of ascorbic acid in the range of (1.4–28.0) × 10^?7 mole. The relative standard deviations for ten replicate measurements of 1.4 × 10^?6 mole of ascorbic acid was 1.3%. The sample rate of 45 ± 5 sample per hour was achieved. The usefulness of the method was tested in the determination of ascorbic acid in fruit juices and vitamin C tablets.     

Indirect flow-injection determination of ascorbic acid by flame atomic absorption spectrometry

A continuous-flow procedure is proposed for the indirect determination of ascorbic acid, based on its reducing properties because of the oxidation of its 1,2-enediol group. Iron(III) was injected into a 1,10-phenanthroline stream, which was mixed with a sample carrier and then with a sodium picrate solution stream. In these conditions the iron(III) was reduced to iron(II) by the ascorbic acid. Thus, the iron(II) formed reacts with 1,10-phenanthroline to form a charged red complex, which with picrate ion forms a stable red-orange uncharged ion-association complex that is adsorbed on-line on a non-ionic polymeric adsorbent (Amberlite XAD-4), proportionally to the ascorbic acid in the sample. The unadsorbed iron was determined by flame atomic absorption spectrometry. The proposed method allows the determination of ascorbic acid in the range 0.5–25 g ml^–1 with a relative standard deviation of 2.9% at a rate of ca. 90 samples h^–1. This method has been applied to the determination of ascorbic acid in pharmaceutical preparations, fruit juices and sweets. The results obtained in the analysis are compared with those provided by the 2,6-dichloroindophenol method.     

Kinetic Spectrophotometric Determination of Ascorbic Acid in Pharmaceutical Samples by Oxidation of Ponceau 4R by Hydrogen Peroxide

A new sensitive and simple kinetic method is developed for determination of traces of ascorbic acid based on its activated effect on oxidation of trisodium‐2‐hydroxy‐1‐(4‐sulphonato‐1‐naphthylazo)naphthalene‐6,8‐disulphonato (red artificial color Ponceau 4R) by hydrogen peroxide, in the presence of Cu(II) as catalyst, in borate buffer. The reaction is followed spectrophotometrically by tracing the oxidation product at 478.4 nm within 1 min after addition of H₂O₂. The optimum reaction conditions are: borate buffer (pH = 11.00), Ponceau 4R (9.6·10^?6 mol/L), H₂O₂ (2·10^?2 mol/L), Cu(II) (8·10^?7 mol/L) at 22 °C. Following this procedure, ascorbic acid can be determined with a linear calibration graph up to 1.76 ng/mL and a detection limit of 0.28, based on 3S criterion. The relative error ranges between 6.77‐1.66% for the concentration interval of ascorbic acid 1.76‐17.61 ng/mL. The effects of certain foreign ions upon the reaction rate were determined for an assessment of the selectivity of the method. The method was applied for determination of ascorbic acid in pharmaceutical samples, and spectrophotometric method was used like an comparative method.     

Determination of uranium in process stream solutions from uranium extraction plant employing energy dispersive X-ray fluorescence spectrometry

Energy dispersive X-Ray fluorescence (EDXRFS) method is developed and standardized for the determination of uranium on routine basis in various process stream solutions, covering a vide range of concentrations from 0.1 to 400?g?L^?1, from an Uranium Extraction Plant at Nuclear Fuel Complex. The method has been applied to aqueous stream samples. Except for dilution, no much sample preparation was involved in the analysis and accordingly the experimental parameters were optimized. The calibration curve in the range of 0.1?C10?g?L^?1 of U was drawn manually using synthetic standard solutions prepared from U₃O₈ powder and L?? (13.61?keV) line of uranium was used for the measurements. The results from EDXRFS method are compared with other methods and are found to be in good agreement. The EDXRFS measurements carried over a range of 0.1?C350?g?L^?1 of uranium have shown a RSD of ±1?C5%. Also, the limitations of reported methods in literature and the advantages of present method are highlighted in the paper.     

Flow-injection extraction spectrophotometric determination of dichromate with the tetramethylenebis(triphenylphosphonium)cation

Chromium(VI) (0–5 μg) can be determined spectrophotometrically at 365 nm after flow-injection extraction into chloroform of the ion-associate, tetramethylenebis(triphenylphosphonium) dichromate. The carrier stream is distilled water and the reagent stream contains 1 M sulphuric acid and 0.5% (w/v) tetramethylenebis(triphenylphosphonium) bromide. The sampling rate is 24 h^?1. The calibration graph is linear up to 20 μg ml^?1 and the detection limit is 0.44 μg ml?1 chromium, based on injection volumes of 250 μl. The system has been applied to the determination of chromium in a range of steels.     

Kinetic Spectrophotometric Determination of Vanadium (V) Based on its Inhibitory Effect on the Thionine – Ascorbic Acid Reaction

ABSTRACT

A simple and sensitive kinetic method for the determination of vanadium(V) based on its inhibitory effect on the reduction of thionine by ascorbic acid at pH=5 is described. The reaction rate is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 598 nm after a fixed time (10 min). The calibration graph is linear in the range of 10 ? 120 ng ml^?1 of vanadium(V) and the detection limit is 6 ng ml^?1. The relative standard deviation (RSD) for 80 ng ml^?1 of V(V) was 0.96% (n=10). The method was successfully applied to the determination of vanadium in a certified reference sample.     

Flow-Injection Biamperometry of Phenol

ABSTRACT

A simple and rapid method determination of phenol is described, using a bromination reaction and biamperometric detection. The method is based on measurements of the intensity of current passing through two identical inert electrodes giving the concentration of phenol in samples. The sample is injected into a stream of carrier and merged with a stream of acidic bromine solution which brominates phenol in the reaction coil. A linear relationship between peak height and phenol concentration is observed in the range of 0.05 to 8 μg ml^?1 of phenol. The relative standard deviation was 2.8% for analysis of 5μg ml^?1 phenol and the sampling rate was 70 h^?1