Simultaneous Kinetic Determination Research Articles

Simultaneous kinetic fluorimetric determination of amoxycillin and clavulanic acid by the stopped-flow mixing technique

Kinetic methodology was applied to the resolution of mixtures of amoxycillin and clavulanic acid. The method thereby developed is based on the formation of fluorescent derivatives in the presence of cerium(IV) in an acidic medium, and the simultaneous determination is made possible by the difference between the reaction rates of the two analytes. By using the stopped-flow mixing technique, kinetic data can be obtained within a few seconds of the reactants mixing, which allows the proposed method to be readily applied to routine analyses. The calibration graphs were linear over the range 0.06–15.0 µg ml–1 for amoxycillin and 0.10–17.5 µg ml–1 for clavulanic acid. The relative standard deviation was less than 3%. Mixtures of amoxycillin and clavulanic acid in ratios between 6:1 and 1:4 were satisfactorily resolved. The proposed simultaneous method was applied to the determination of these compounds in pharmaceutical preparations.

Evaluation of multicomponent kinetic analysis data by a partial least squares calibration method

A partial least squares (PLS) calibration method is suggested for the evaluation of multicomponent kinetic data. The advantage is that no kinetic model is assumed and only the information from the kinetic curves themselves is used. In the procedure proposed, a model is developed from samples of known composition, i.e., a calibration set, and is then used to predict unknowns, i.e., concentrations of the components in a test set. The use of the PLS method for multicomponent kinetic analysis is demonstrated on several simulated and experimental data. It was shown that it is possible to determine analytes in mixtures without any previous knowledge either of the rate constants, mechanism of the reactions or molar absorptivities of the components. The method has been validated on several two- and three-component simulated data and applied to the simultaneous kinetic determination of Co and V and the stopped-flow flow injection determination of Zn, Co and Fe.

New computational approach for the simultaneous photometric determination of catalysts and activators

A new method for the simultaneous kinetic determination of catalysts and activators was developed on the basis of a mathematical model. The parameters and variables are optimized from experimental data obtained by application of a multiple standard-addition method and use of the Gauss-Newton and Simplex method, both of which provide identical results. The proposed method was applied to the simultaneous photometric determination of Mn(II) and Pb(II) on the basis of their catalytic and activating effects, respectively, on the oxidation of Tiron by hydrogen peroxide. Data were both acquired and processed with the aid of software developed by the authors. The linear determination range achieved was 1.00–5.00 ng/ml Mn(II) and 200–800 ng/ml Pb(II). Experimental readings were made at 450 nm with a fibre optics detector. The most serious interference with the method was posed by Cr(III).

Simultaneous Kinetic Determination of Nickel(II) and Cobalt(II) with 5-Octyloxymethyl-8-quinolinol in the Nonionic Surfactant Micellar System

The formation rate of Ni(II) and Co(II) complexes with 5-octyloxymethyl-8-quinolinol was investigated in nonionic surfactant systems. The distribution of metal ions and of ligands between the aqueous and micellar phases affected the reaction rate. The slowest reaction was obtained for Triton X-100 and the reaction rate in the micellar phase was thirty times slower than the rate in the aqueous phase. The slow reaction in the micelle was applied to the determination of Ni(II) and Co(II). The formation of the Co(II) complex was forty-four times faster than Ni(II) at pH 7.O. The working curve for each metal was linear in the concentration range between (0.2–5.0)×10−5 mol dm-3.

Simultaneous kinetic determination of epinephrine and norepinephrine by the stopped-flow technique

A stopped-flow method for the simultaneous determination of epinephrine and norepinephrine, two catecholamines with a wide spectrum of biological activity, is proposed. The method is based on the oxidation of these compounds with 1,10-phenanthroline-iron(III) complex, which is monitored by measuring the initial rate of change of the absorbance of the ferroin formed at 510 nm. The difference in kinetic behaviour between the two species was exploited by applying a modified version of the proportional-equation method for the resolution of epinephrine-norepinephrine mixtures at the micrograms ml-1 level over the ratio range 1:10-10:1, with an error of less than 5% and an average precision of about 2.5%. The method was successfully applied to the determination of the two catecholamines in pharmaceuticals.

Simultaneous kinetic determination of secondary amines and their isomers by a spectrophotometric stopped-flow method based on the formation of dialkyldithiocarbamates

Secondary amines react with carbon disulphide to form stable dialkyldithiocarbamates at high pH in aqueous Triton X-100 solution. The formation rates of dimethyl-, diethyl-, di- n-propyl-, diisopropyl-, di- n-butyl- and diisobutyldithiocarbamates and pyrrolidinedithiocarbamate were measured by a stopped-flow spectrophotometric method. The reaction rates were a function of the pH of the solution and depended on the size and structure of the amines. The rate of isoalkylamines was far slower than that of the n-alkyl analogues. Individual concentrations of amines were determined in a mixture of di- n- and diisopropylamine and in a mixture of diiso- and di- n-butylamine.

High-performance liquid chromatographic investigations on the cleavage kinetics of side-chain-protected arginine derivatives with a sophisticated post-column reaction detector

In the field of peptide synthesis, only a few exact data on the behaviour of side-chain-protecting groups and their specific cleavage methods are available. A method is described for the separation and highly specific detection of guanidino-protected and -free arginine residues. The simultaneous determination of the cleavage kinetics of α- and side-chain-protecting groups of arginine becomes feasible. A high-performance liquid chromatographic system with a highly specific post-column reaction detector for the (released) guanidino group in arginine derivatives was developed. The cleavage kinetics of the most important protecting groups for the guanidino residue in arginine derivatives were established.

Simultaneous kinetic determination of zineb and maneb by the continuous addition of reagent technique

The continuous addition of reagent technique was applied to the simultaneous kinetic determination of zinc ethylenebis(dithiocarbamate)(zineb) and manganese ethylenebis(dithiocarbamate)(maneb) in mixtures. The method developed for this purpose is based on the continuous addition of zincon to a solution containing zinc(II) and manganese(II) released in the acid decomposition of the pesticides. The sequential formation of the zinc and manganese complexes with the reagent is monitored spectrophotometrically. Two consecutive kinetic curves are obtained, the slope of the straight portion of which is related to the concentration of each pesticide. The method allows the resolution of zineb-maneb mixtures at the µg ml–1 level over the ratio range 1:12–10:1, with an average relative standard deviation of 1.3%, and was applied satisfactorily to the determination of both pesticides in commercial formulations.

Characteristics of methods for the simultaneous determination of catalysts by first-order inhibition kinetics.

Factors that affect the simultaneous kinetic determination of catalysts based on differences in rates of inhibition by a common inhibitor are investigated by computer simulation. Both derivative and integral models for the kinetic responses are studied. Nonlinear regression is used to fit data with a fixed level of noise for the combined responses due to the first-order inhibition of two catalysts. Effects of rate constants, ratios of rate constants, fitting ranges, data density, and number of replicate determinations on reliability, useful activity range, sensitivity, scatter, limits of detection, and measurement/data-processing times are considered. It is found that values for rate constants, ratios of rate constants, and fitting ranges which provide results with desired reliability are restricted. Small ratios of rate constants and short fitting ranges were observed to produce the largest useful activity ranges and shortest measurement times but also gave the worst accuracy and most dependence on initial estimates of fitting parameters. Values of the coefficients of correlation between the individual first-order responses can aid in the selection of the smallest ratio of rate constants and fitting range which will yield suitable results.

Simultaneous kinetic determination of copper, cobalt and nickel by means of -group interchange reactions

The kinetic determination of copper, cobalt and nickel in binary and ternary mixtures without prior separation is described. The methods are based on the difference in the reaction rate of interchange of ▪- groups between thiosemicarbazide and 6-methylpicolinaldehyde azine in the presence of these ions at pH 4.5. Through these reactions the corresponding metal thiosemicarbazone complexes are formed. Various ratios of these ions at the 10 −5 M level can be determined photometrically by either the logarithmic extrapolation method or a combined initial-rate and fixed-time method proposed here for the first time.

Simultaneous kinetic determination of zinc, magnesium, copper and nickel by a ligand substitution reaction

The rate of the ligand substitution reaction between calmagite [3-hydroxy-4-(2-hydroxy-5-methylphenylazo)-naphthalene-1-sulphonic acid] complexes of Zn(II), Mg(II), Cu(II) and Ni(II) and EDTA was studied at 25.0 °C and pH 9.5 by a stopped-flow spectrophotometric technique. The reactions were first order in calmagite complexes and in incoming ligand for Zn, Cu and Ni, while a zero-order dependence on EDTA was observed for Mg. The change of absorbance at 500 nm, accompanying the substitution reaction, was used for the determination of the metal ion. For multi-component mixtures such as Zn, Mg and Cu or Ni, the absorbance change during the reaction was separated kinetically for each component, in the reactivity order Zn > Mg > Cu ≈ Ni, so that metal ions at concentrations down to 10–6M could be determined simultaneously. The method was applied to the analysis of standard mixtures and samples of river water, tap water and mineral waters.

Simultaneous kinetic determination of iron and chromium at the nanogram level

The oxidation of pyridoxal 2-pyridylhydrazone by hydrogen peroxide is induced by Fe(II). The reaction is monitored fluorimetrically and is preceded by an induction period, the length of which is inversely proportional to the Fe(II) concentration. This effect allows the quantitative determination of this ion. The traditional kinetic methods (tangent, fixed time, and variable time) have also been applied and between 5 and 60 ng/mL of Fe(II) can be determined. The transient inhibitory effect of Cr(VI) on the first stage of this oxidation is reported. A noncatalytic cycle appears to be associated with them. The conversion of the rate-modifying ion to an inactive form by a redox reaction seems to account for the lack of a catalytic cycle. A judicious choice of reaction conditions permits the determination of 50-1000 ng/mL of Cr(VI). The determination of the Fe(II)-Cr(VI) mixture (10-70 ng/mL Fe(II) and 50-350 ng/mL Cr(VI)) is reported on the basis of this transient inhibitory effect through initial rate and length of induction period measurements. 22 references, 3 figures, 3 tables.

Simultaneous kinetic determination of ppb levels of manganese and zinc with signal accumulation of stopped-flow spectrophotometry

This method of simultaneous determination of traces of Mn and Zn, based on the difference of the rate of ligand substitution reaction between 1-(2-thiazolylazo)-2-naphthol (TAN) chelates and EDTA, is simple and free of interferences from other metal ions and anions. The procedure is as follows; place a sample solution containing (0.042.5)μg of Mn and Zn in a 50 cm3 volumetric flask, add 20 mg of N-(dithio-carboxy)-glycine to mask Cd, Cu and Hg and 2 cm3 of 2.0×10-3 mol dm-3 TAN solution (10 % Triton X-100), adjust the pH to 8.9 with 5 cm3 of Kolthoff's buffer solution and then dilute to the mark with water. The reaction is initiated by mixing this solution with 2.0×10-3 mol dm-3 EDTA solution (0.4 % Triton X-100, pH 8.9) at 25 °C using a stopped-flow apparatus. The reaction is run ten times and the signals of these runs are accumulated to improve the S/N. From the resultant curve Mn and Zn are determined graphically. The method can be applied to the determination of Mn and Zn in tap water.

Simultaneous kinetic determination of metal ion mixtures based on a ligand substitution reaction

The rates of the ligand substitution reactions between 2-(4-sulfophenylazo)-l,8-dihydroxy-3, 6-naphthalenedisulfonic acid (SPADNS) complexes of Co 2+, Ni 2+, Pb 2+ and Cu 2+ and EDTA (or CDTA) have been studied at 25.0°C, pH 8.0–9.3, by stopped-flow spectrophotometry. The reactions are first order in SPADNS complex and in incoming ligand. The absorbance change during the reaction progress can be kinetically separated for each component of a mixture, so that metal ions down to 10 -6 M can be determined. Components of very high reactivity, such as Cd 2+, Mn 2+ or Zn 2+, can also be determined as part of a multicomponent mixture.

Simultaneous kinetic determination of phosphate and silicate based on heteropoly blue formation

Small amounts of phosphate (0.08–1.16 μg ml -1) and larger amounts of silicate (12–60 μg ml -1) can be determined simultaneously by a kinetic method based on the difference in the rates of the heteropoly blue formation with molybdenum (V)—molybdenum (VI) mixtures in 0.28 M perchloric acid. The interference of large amounts of iron(III) on the determination of phosphate can be eliminated by masking with sodium hydrogen sulfite; this method is applicable to reagent-grade iron(III) chloride.

Simultaneous kinetic determination of uric acid ascorbic acid mixtures

A kinetic stopped-flow method is described for the simultaneous determination of uric acid and ascorbic acid with tris (2,2'-bipyridine)iron(III). For the least favourable ratios of uric to ascorbic acid, in a total concentration of 10 -5 M, the error in the determination of uric acid is estimated at ±10%.

Simultaneous kinetic determination of mixtures of ions by digital analysis of amperometric or potentiometric data

Electroanalytical techniques allow the kinetic determination of concentrations of ions in their mixtures when the reactions used proceed at sufficiently slow velocity. Amperometry and potentiometry with digital data acquisition and treatment have been used for determinations of calcium and magnesium ions based on the exchange reactions between lead(II) and alkaline earth metal complexes of (trans-1,2-cyclohexylenedinitrilo)tetraacetic acid. Over a concentration range of 10–4–5 × 10–7M precision and accuracy are about 5–10% in amperometry and 5% in potentiometry.

Tribo-Ellipsometry: A New Technique to Study the Relationship of Repassivation Kinetics to Stress Corrosion

Abstract Since the susceptibility of a material to stress corrosion cracking (SCC) may be related to the rupture of a protective film and the repassivation rate of the material thus exposed, a technique, tribo-ellipsometry, has been developed which simulates film rupture by abrading off the surface oxide. During the subsequent repassivation of the exposed surface, this technique allows simultaneous determination of film growth kinetics by ellipsometry and current transients during that time interval following removal of the oxide film. The major advantage of the technique is that the ellipsometric transient allows one to determine which part of the current transient is responsible for repassivation and which part is involved in metal dissolution. The utility of the technique is demonstrated by comparing repassivation rates for a low carbon steel in a sodium nitrate solution in which the metal is susceptible to SCC to those in a sodium nitrite solution, in which it is not. Results obtained using this metho...

Simultaneous kinetic determination of mixtures by on-line regression analysis

Simultaneous kinetic determination of mixtures by on-line regression analysis

Organic Peroxides. III. The Behavior of Cyclohexaneformyl Peroxide in the Presence of Excess Stable Radicals. The Simultaneous Determination of Kinetics and Free Radical Efficiencies in the Thermal Decompositions of Free Radical Initiators

Organic Peroxides. III. The Behavior of Cyclohexaneformyl Peroxide in the Presence of Excess Stable Radicals. The Simultaneous Determination of Kinetics and Free Radical Efficiencies in the Thermal Decompositions of Free Radical Initiators