Fixed-time Method Research Articles

Determination of Sulfide in Spring and Wastewater by a New Kinetic Spectrophotometric Method

AbstractA simple, rapid, and sensitive method has been developed for the determination of trace amounts of sulfide based on its reaction with thionine. The reaction is monitored spectrophotometrically by measuring the decreasing absorbance of the dyestuff at 600 nm by the fixed time method. After optimization of the measuring conditions the calibration curves were found linear up to 38.0 ppm (four regions), and the theoretical limit of detection was 0.076 ppm and the relative standard deviation for determination of 1.0 ppm sulfide (n = 10) was found to be 2.7%. The proposed method was applied successfully to the determination of sulfide in spring water and wastewater samples.

Kinetic Spectrophotometric Determination of Ranitidine

AbstractTwo spectrophotometric methods were developed for the determination of ranitidine. The first method was a kinetic spectrophotometric method based on the catalytic effect of ranitidine on the reaction between sodium azide and iodine in an aqueous solution. The calibration graph was linear from 4–24 μg/mL. The drug was determined by measuring the decrease in the absorbance of iodine at 348 nm using a fixed time method. The decrease in the absorbance after 1 minute from the initiation of the reaction was related to the concentration of drug. The detection limit of the procedure was 0.76 μg/mL. The proposed procedure was successfully utilized in the determination of the drug in pharmaceutical preparations with mean recovery in the range of 99.83 ‒ 101.16%.The second method is a colorimetric method, which depends on the measurement of absorbances of tris (o‐phenanthroline) iron(II) [method 2A] and tris (bipyridyl) iron(II) [method 2B] complexes at 512 nm. The complexes obeyed Beer's law over the concentration range of 2–16 μg/mL and 4–40 μg/mL for methods 2A and 2B, respectively. The developed method has been successfully applied for the determination of ranitidine in bulk drugs and pharmaceutical formulations. The common excipients and additives did not interfere in its determination.

Kinetic Spectrophotometric Determination of Josamycin in Formulations and Spiked Human Plasma Using 3-Methylbenzothiazolin-2-one Hydrazone/Fe+3 System

A simple kinetic spectrophotometric method was developed for the determination of josamycin in its dosage forms and spiked human plasma. The method is based on reaction of the drug with 3-methylbenzothiazolin-2-one hydrazone/ferric chloride system for a fixed time of 20 min at 70 degrees C and measuring the produced color at 665 nm. The absorbance-concentration plot is rectilinear over the range of 5.0-30.0 microg/mL with detection limit of 1.0 microg/mL (1.2 x 10(-6) M). The determination of josamycin by the fixed concentration and the rate-constant methods is also feasible with the calibration equations obtained, but the fixed-time method proved to be more applicable. The procedure was successfully applied to commercial tablets. The results obtained were favorably compared with those given by reference methods. The method was further extended to the in vitro determination of josamycin in spiked human plasma. The recovery (n = 8) was 100.76 +/- 3.43%. The stoichiometry of the reaction between the drug and the reagent was studied by adopting the limiting logarithmic method, and a proposal of the reaction pathway was presented.

Highly selective catalytic-spectrophotometric determination of vanadium(V) by using calmagite-bromate redox reaction

A highly selective and sensitive kinetic method for the determination of trace amounts of vanadium(v) is reported. The method is based on catalytic effect of bromate on the oxidation of calmagite in acidic solutions. The reaction is followed spectrophotometrically by measuring the change in absorbance of calmagite at λ = 523 nm using a fixed time method (5 min). Under optimum conditions vanadium can he determined in the range of 2-10 ng ml - 1 . The detection limit based on 3S b criterion was 0.27 ng ml - 1 , and relative standard deviation for ten replicate measurements of 5 ng ml - 1 of V v was 1.2%. Influence of 29 foreign ions were observed. The method was applied for the determination of vanadium in soil samples.

Definitive diagnosis of mitochondrial neurogastrointestinal encephalomyopathy by biochemical assays.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by mutations in the gene encoding thymidine phosphorylase (TP). The clinical manifestations of MNGIE are recognizable and homogeneous, but in the early stages, the disease is often misdiagnosed. This study assesses the reliability of biochemical assays to diagnose MNGIE. We studied 180 patients with clinical features suggestive of MNGIE, 14 asymptomatic TP mutation carriers, and 20 controls. TP enzyme activity in the buffy coat was determined by a fixed-time method, and the plasma nucleosides thymidine (dThd) and deoxyuridine (dUrd) were assessed by a gradient-elution reversed phase HPLC method. TP was sequenced through standard procedures in patients who met the clinical criteria for MNGIE. Twenty-five of the 180 patients fulfilled the clinical criteria for MNGIE and had homozygous or compound heterozygous TP mutations. All had drastically decreased TP activity [mean (SD), 10 (15) nmol thymine formed. h(-1). (mg protein)(-1) vs 634 (217) nmol thymine formed. h(-1). (mg protein)(-1) for the controls]. Relative to the control mean, TP activities were reduced to 35% in mutation carriers and 65% in MNGIE-like patients. All 25 MNGIE patients had detectable plasma dThd [8.6 (3.4) micromol/L] and dUrd [14.2 (4.4) micromol/L]. Controls, carriers, and MNGIE-like patients showed no detectable plasma dThd and dUrd. We propose a diagnostic algorithm based on the determination of plasma dThd and dUrd, TP activity in buffy coat, or both to make a definitive diagnosis of MNGIE. Increased concentrations of dThd (>3 micromol/L) and dUrd (>5 micromol/L) in plasma or a decrease in buffy coat TP activity to </=8% relative to controls is sufficient to diagnose MNGIE.

Kinetic spectrophotometric method for the determination of norfloxacin in pharmaceutical formulations

A simple and sensitive kinetic spectrophotometric method is described, based on the oxidation of norfloxacin with alkaline potassium permanganate. The reaction is followed spectrophotometrically by measuring the rate of change of absorbance at 603 nm. The initial rate and fixed time (at 3 min) methods are utilized for constructing the calibration graphs to determine the concentration of the drug. The calibration graphs are linear in the concentration ranges 2.0–20 μg ml −1 and 1.0–20 μg ml −1 using the initial rate and fixed time methods, respectively. The results are validated statistically and through recovery studies. The method has been successfully applied to the determination of norfloxacin in commercial dosage forms. Statistical comparison of the results with the reference method shows excellent agreement and indicates no significant difference in accuracy and precision.

Use of pseudo-first order kinetics in flow injection for determination of trace inorganic iodine

This work utilizes pseudo-first order kinetics for the determination of iodine at the part per billion (ppb) levels. Flow injection (FI) system was developed and optimised for conditions in which the indicator reaction between Ce(IV) and As(III) gives first order kinetics. This oxidation–reduction reaction is catalysed by iodide ion and has been used for determination of trace levels of iodide for many years. Under pseudo-first order condition, analysis can be made in two ways, either a full kinetic or a fixed-time method. System development is presented as well as the characteristic evaluation of the kinetics. The system, with a simple and interferent-free in-line reduction step, has allowed successful quantitation of iodate, which has never been reported for this kinetic method. The system was used to determine total inorganic iodine in bottled drinking water that had been supplemented with iodate ion to the level of 100 μg I l −1.

Kinetic Spectrophotometric Determination of Trace Amounts of Sulfide

A method for the determination of trace amount of sulfide based on the addition reaction of sulfide with methyl green at pH 7.5 and <TEX>$25{\circ}C$</TEX> is described. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of the dyestuff at 637 nm by the initial rate and fixed time method. The calibration graph is linear in the range 30-1200 ppb. The theoretical limit of detection was 0.014 ppm. Seven replicate analysis of a sample solution containing 0.70 ppm sulfide gave a relative standard deviation of 1.5%. The interfering effects of various ions on sulfide determination have been reported and procedures for removal of interference have been described. The proposed method was applied successfully to the determination of sulfide in tap and wastewater samples.

Kinetic spectrophotometric determination of some sulfur containing compounds in pharmaceutical preparations and human serum

A kinetic spectrophotometric method was developed for the determination of carbocisteine, ethionamide, thioctic acid and penicillamine based on the catalytic effect on the reaction between sodium azide and iodine in aqueous solution. Ten to 100 μg ml −1 of carbocisteine and ethionamide, 0.1–1 μg ml −1 of thioctic acid and 0.01–0.1 μg ml −1 of penicillamine could be determined, respectively, by measuring the decrease in the absorbance of iodine at 348 nm by a fixed time method. The decrease in the absorbance in the first 5 min from the initiation of the reaction is related to the concentration of the drugs. The detection limits were 0.47, 0.71, 0.018 and 9.38×10 −4 μg ml −1 for the four drugs, respectively. The proposed procedure was successfully applied in the determination of these drugs in pharmaceutical preparations and human serum.

Kinetic spectrophotometric determination of trace amounts of selenium based on the catalytic reduction of maxilon blue-SG by sulfide

A simple and sensitive catalytic spectrophotometric method was developed for the determination of trace amounts of selenium. The method is based on the catalytic effect of selenium in form Se(IV) on the reduction of Maxilon Blue-SG by sodium sulfide. Indicator reaction is followed spectrophotometrically by measuring the absorbance change at λ max=654 nm and constant temperature (30.0±0.1 °C) by fixed time method. Selenium could quantitatively be determined in the range 0.004–0.200 μg ml −1 Se(IV) with a detection limit of 0.205 ng ml −1 Se(IV). All of the variables that affected the reaction rate were investigated and established optimum conditions to give maximum sensitivity. The R.S.D.s of the method ( N=12) for the Se(IV) concentrations of 0.004, 0.016, 0.040 and 0.160 μg ml −1 are between 2.27 and 0.32%, respectively, and depended on Se(IV) concentration. The interference effect of various anion and cations on the Se(IV) determination was also fully studied. The selectivity of catalytic reaction was greatly improved with the use of the strong cation exchange resin. The developed kinetic–catalytic reaction was applied to the determination of selenium in real samples as Antioxidant-S, Selsun (which is a healthcare product for the treatment of dandruff) and analytical grade sodium metabisulfite, and in spring water samples without any pre-concentration. The acceptable recoveries were obtained by the method for appropriate standard Se(IV) additions. The method is simple, practical and suitable for using in small laboratories owing to its precision, sensitivity and relative selectivity.

Kinetic spectrophotometric determination of famotidine in commercial dosage forms.

A simple kinetic spectrophotometric method is described for the determination of famotidine. The method is based on the oxidation of the drug with alkaline potassium permanganate. The reaction is followed spectrometrically by measuring the rate of change of the absorbance at 610 nm. The initial-rate and fixed-time (at 12 min) methods are adopted for determining the drug concentration. The calibration graphs are linear in the ranges of 2-10 microg mL(-1) and 1-8 microg mL(-1) using the initial-rate and fixed-time methods, respectively. The method has been applied to the determination of famotidine in tablet formulations. The obtained results are compared statistically with those given by a reference spectrophotometric method.

Kinetic Spectrophotometric Determination of the Macrolide Antibiotic Josamycin in Formulations

A simple kinetic spectrophotometric method was developed for the determination of josamycin in its dosage forms. The method is based on oxidation of the drug with alkaline potassium permanganate at room temperature for a fixed time of 20 min and measuring the produced green color at 611 nm. The absorbance-concentration plot is rectilinear over the range of 2-10 microg/mL (2.4 x 10(6)-1.2 x 10(-5)M) with minimum detectability of 1.0 microg/mL (1.2 x 10(-6)M). The determination of josamycin by fixed concentration and the rate-constant methods is also feasible with the calibration equations obtained, but the fixed-time method proved to be more applicable. The procedure was applied successfully to commercial tablets, and statistical analysis showed that the results compared favorably with those obtained by reference methods. The effect of sensitizers and surfactants on the performance of the proposed method was also studied. A proposal of the reaction pathway was presented.

Determination of manganese (II) in some medicinal plants and their decoctions by a kinetic spectrophotometric method.

The catalytic effect of manganese (II) on the oxidation of the azo dye tropaeolin 00 with potassium periodate in the presence of 1,10-phenanthroline was investigated. The reaction was followed spectrophotometrically by measuring the decrease in the absorbance of the azo dye at 445 nm. Under the optimum analytical conditions, manganese (II) in the range 0.05-2.5 ng/mL could be determined by the fixed-time method with a detection limit of 0.02 ng/mL. The developed method is highly sensitive, selective and simple, and was applied successfully to analyse decoctions of some medicinal plants for trace amounts of total manganese (II) and free manganese (II) ions without separation.

Kinetic-catalytic determination of vanadium(IV) using methyl orange-bromate redox reaction.

Determination of V(IV) based on its catalytic effect on the reaction between Methyl Orange and bromate in thepresence of citric acid was studied. The calibration curve obtained by fixed-time method was linear in the range of 2.5-300 ng ml(-1). By use of slope method, a calibration curve containing two linear portions were obtained. Using fixed-time and slope methods, we obtained detection limits of 0.8 and 1.5 ng ml(-1), respectively. Fe2+, As(III), V(V) and Hg2+ interfered. The method was successful for analysis of water samples.

Kinetic Spectrophotometric Determination of Sulfite Using a Full Curve (PLS) and a Fixed Time Method

The univariate and multivariate calibration method was applied for the determination of sulfite based on the addition reaction of sulfite with new fuchsin at pH = 7.5 and 25°C. The decrease in absorbance of new fuchsin at 540 nm over a fixed time is proportional to the concentration of sulfite over the range of 0.15–2.0 µg mL−1. The detection limit and RSD% are 0.08 µg mL−1 and 1.1% respectively. The experimental calibration matrix for PLS calibration method was designed with 20 samples. The cross-validation method was used for selection of the optimal number of factors. The RMSEP was 0.0043 at optimum value of factors. The effects of various cations and anions on sulfite determination were investigated.

Kinetic–Spectrophotometric Determination of Trace Silver(I) Using Its Catalytic Effect on the Oxidation Reaction of Fuchsin by Peroxodisulfate in the Presence of 1,10-Phenanthroline As an Activator

A kinetic spectrophotometric method for the determination of trace amounts of Ag(I) in the range of 2–20 ng mL–1 is reported. The method is based on the catalytic effect of Ag(I) on the oxidation reaction of fuschin by potassium peroxodisulfate in the presence of 1,10-phenanthroline as an activator at pH = 5. The reaction is followed spectrophotometrically by measuring the change in absorbance (ΔA) at 544 nm using a fixed time method (6 min). The reaction variables were optimized in order to achieve the highest sensitivity. The 3s criterion detection limit was 0.7 ng mL–1, and the relative standard deviation for ten replicate measurements of 16 ng mL–1 of Ag(I) was 0.95% (n = 10). The method was successfully applied to the determination of silver in expired black and white photographic films and results showed good agreements with those obtained by atomic absorption spectrometry.

Kinetic spectrophotometric method for the determination of rhodium by its catalytic effect on the oxidation of O-toluidine blue by periodate in micellar media

A simple kinetic spectrophotometric method was developed for the determination of ultra trace amounts of Rh(III). The method is based on the catalytic effect of rhodium(III) on the oxidation of o-Toluidine blue by periodate in micellar media. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of o-Toluidine blue at 628 nm with a fixed-time method. The decrease in the absorbance of o-Toluidine blue is proportional to the concentration of Rh(III) in the concentration range 1.0–400.0 ng/mL, with a fixed time of 0.5–4.5 min from initiation of the reaction. The limit of detection is 0.2 ng/mL Rh(III). The relative standard deviation for the determination of 0.020 and 0.100 μg/mL Rh(III) was 2.2 and 1.5%, respectively. The method was applied to the determination of rhodium in water.

Determination of some catecholamines based on their reaction with periodate

An indirect kinetic-spectrophotometric method is proposed for the determination of trace amounts of levodopa, methyldopa, dopamine, and adrenaline based on their reaction with periodate in acidic media. The excess periodate that is related to the amount of catecholamines is determined by its reaction with iodide in the presence of methylene blue. The reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of the solution at 665 nm with a fixed time method of 3.0 min. The relative standard deviation for seven replicate determinations of 0.5 μgmL–1 of L-dopa, methyldopa, dopamine and adrenaline was 1.80, 1.20, 0.92 and 1.35%, respectively. The method was successfully applied to the determination of catecholamines in pure form and in pharmaceutical preparations.

Application of generalized artificial neural networks coupled with an orthogonal design to optimization of a system for the kinetic spectrophotometric determination of Hg(II)

Abstract A simple and sensitive kinetic method for the determination of traces of mercury (70–760 ng ml −1 ) based on its inhibitory effect on the addition reaction between methyl green and sulfite ion is proposed. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of methyl green at 596 nm between 2 and 4 min using a fixed time method. Artificial neural networks with back propagation algorithm coupled with an orthogonal array design were applied to the modeling of the proposed kinetic system and optimization of experimental conditions. An orthogonal design was utilized to design the experimental protocol, in which pH, concentration of sulfite, temperature, and concentration of methyl green were varied simultaneously. Optimum experimental conditions in term of sensitivity were generated by using ANNs. The rate of decrease in absorbance is inversely proportional to the concentration of Hg(II) over entire concentration range tested (100–550 ng ml −1 ) with a detection limit of 45 ng ml −1 and a relative standard deviation at 200–400 ng ml −1 Hg(II) of 3.2% ( n =5). A simple preconcentration step improved the limit of detection and linear dynamic range of the method to about 8 and 12–760 ng ml −1 , respectively, by about 10 times enrichment of mercury between 12 and 75 ng ml −1 . The method was based on enrichment of Hg(II) from dilute samples on an anionic ion exchanger fixed on a plastic strip and was applied to the determination of Hg(II) in environmental samples with satisfactory results.

Kinetic Spectrophotometric Determination of Atenolol in Dosage Forms

A simple kinetic procedure is described for the determination of atenolol in its dosage forms. The procedure is based on coupling the drug with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole in pH 8 borate buffer at the boiling temperature for a fixed time of 30 min, and then measuring the absorbance of the reaction product at 460 nm. The absorbance-concentration plot is rectilinear over the range 5-50 microg/mL with a minimum detection limit of 1.3 microg (4.9 x 10(-6) M). The determination of atenolol by the fixed-concentration and rate-constant methods is also feasible with the calibration equations obtained, but the fixed-time method proved to be more applicable. The procedure was applied successfully to commercial tablets, and statistical analysis showed that the results compared favorably with those obtained by the official methods. The interference likely to be introduced from some coformulated drugs and the effect of sensitizers and surfactants on the performance of the proposed method were also studied. A proposed reaction pathway is presented.