Kinetic determination of alcohols and their binary mixtures with a stopped-flow spectrophotometric technique

The kinetic method described for the determination of a single alcohol (? 5 X 10^-4 M), or of a binary mixture of alcohols in aqueous solution is based on fast oxidation by silver(II), monitored spectrophotometrically by using a stopped-flow technique. Mixtures of alcohols having rate constants differing by a factor of ?3 can be resolved. The lower limit of determination is ca. 5 × 10^-4 M.     

Kinetic enzymatic determination of ethanol/methanol mixtures by the stopped-flow technique

The analytical use of the enzymatic oxidation of alcohols by alcohol oxidase was assessed applying the stopped-flow technique for mixing sample and reagents, and the DTNB (5,5'-dithiobis-(2-nitrobenzoic acid)/L-cysteine system as a new chromogenic reagent. The oxidation reaction was monitored by measuring the rate of absorbance decrease at 412 nm, the wavelength of maximum absorption of the reduced form of DTNB. The calibration graphs for the individual determination of the alcohols were linear over the range 1.0 x 10(-6)-1.0 x 10(-5)M, and the precision ranged between 2.1 and 4.8%. A differential rate principle was applied to the determination of ethanol/methanol mixtures involving mutual kinetic effects which allowed mixtures in molar ratios between 25:1.0 and 1.0:1.0 to be accurately resolved with good precision (r.s.d. less than 9 and 5%, respectively). Compared to the flow-injection analysis method, the proposed approach offers higher sensitivity and sample throughput, as well as the wider concentration ratio range for mixture resolution.     

Kinetic-photometric determination of spermine, spermidine and their mixtures by the stopped-flow technique

Summary Kinetic photometric stopped-flow methods are described for the individual and simultaneous determination of two biogenic amines: spermine and spermidine. They are based on the coloured reaction of these amines with sodium 1,2-naphthoquinone-4-sulfonate. The parameters used for the quantitative determinations are the initial rate and the increase in absorbance of the kinetic curves. Each amine can be rapidly determined in the range of 0.5–150 g ml^–1 with a precision (%RSD) of less than 1.8. The simultaneous determination of mixtures of spermine and spermidine is carried out by the proportional equations method. Spermine/spermidine mixtures in ratios between 120 and 201 are successfully resolved.

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Kinetisch-photometrische Bestimmung von Spermin, Spermidin und deren Gemischen mit dem Stopped-Flow-Verfahren

     

Kinetic spectrophotometric method for determination of perphenazine based on monitoring the oxidation intermediate by applying a stopped-flow technique

A novel and high-sensitive stopped-flow kinetic spectrophotometic method for the determination of perphenazine based on monitoring the variation of absorbance of the intermediate within a few seconds has been developed. The optimum conditions for various parameters on which the forming of the intermediate depends, were investigated. It was found that the initial reaction rate increased linearly with an increase in the perphenazine concentration in the range from 1.0 x 10(-5) to 1.6 x 10(-4)M. The detection limit was calculated to be 5.3 x 10(-6)M. The kinetics of the reaction was established by the aid of single-mixing or double-mixing stopped-flow techniques, a successive reaction model was proposed to analyze and simulate the reaction. The influence of both ascorbic acid and NADH on the time courses was also investigated.     

Chemiluminescence determination of citrate and pyruvate and their mixtures by the stopped-flow mixing technique

A novel kinetic chemiluminescent method using the stopped-flow mixing technique has been investigated for the rapid and sensitive determination of citrate and pyruvate. The method is based on a tris(2,2′-bipyridiyl)ruthenium(III) (Ru(bpy)₃³⁺) chemiluminescence (CL) reaction. Ru(bpy)₃³⁺ was generated in the mixing chamber by oxidising tris(2,2′-bipyridyl)ruthenium(II) with cerium(IV). After selecting the best operating parameters, calibration graphs were obtained over the concentration ranges 0.38-38 μg ml⁻¹ and 8.7-1300 ng ml⁻¹ for citrate and pyruvate, respectively. The limits of detection were 0.1 μg ml⁻¹ for citrate and 0.3 ng ml⁻¹ for pyruvate. Based on the differential rate of the chemiluminescent reaction corresponding to citrate and pyruvate, a very simple kinetic procedure was developed for the simultaneous determination of both compounds. Mixtures of citrate and pyruvate in ratios between 15:1 and 1.5:1 were satisfactorily resolved. The proposed method was successfully applied to the determination of citrate in pharmaceutical formulations, pyruvate in animal blood serum and both compounds in human urine.     

Kinetic spectrophotometric determination of indium/gallium mixtures

A kinetic method is presented for the determination of 0.5–5 μg ml^?1 gallium based on its activating effect on the copper(II)-catalyzed oxidation of 4,4′-dihydroxybenzophenone thiosemicarbazone by hydrogen peroxide. The reaction is monitored spectrophotometrically at 415 nm. Two sets of reaction conditions are established; one for the direct determination of gallium, and another, in which indium affects the gallium response, for determination of indium. Mixtures of these cations can be determined at μg ml^?1 levels and in gallium/indium ratios from 7.5:1 to 1:1.6, with an accuracy and precision of ca. 4.5%.     

顺序注射停留分光光度法测定磺胺乙酰钠

在HCl浓度为5.0×10-4mol/L时,磺胺乙酰钠-NaNO2-1-萘胺的重氮化偶合反应,生成不稳定的红色产物,利用顺序注射停留技术在473nm波长处检测该不稳定产物,建立了快速自动测定磺胺乙酰钠的新方法。该方法线性范围为5～2500μg/mL,检出限为0.018μg/mL,进样频率为62个/h。应用于药物中磺胺乙酰钠的测定,并与药典规定方法进行对照。     

Application of a stopped-flow time-difference technique to spectrophotometric determination of ultratrace levels of phosphate

Optimum conditions, interfering substances, and comparisons with other methods are described for a spectrophotometric method for phosphate, which is based on the stopped-flow technique and involves recording the progress curve for formation of the colored complex of 12-molybdophosphate with malachite green. Linear calibration plots were obtained for phosphate in the ranges 5–55 and 100–1000 μg 1⁻¹. The sensitivity and the running speed of the method crucially depend on the sulfuric acid concentration. The positive interferences of several anions, especially arsenate, thiosulfate, stannate, tungstate and iodide, are significantly less than in conventional methods. Results for total phosphorus in several foodstuffs agreed with results obtained by a molybdovanadophosphoric acid method.     

Kinetic determination of ascorbic acid by the 2,6-dichlorophenolindophenol reaction with a stopped-flow technique.

The reaction of ascorbic acid with 2.6-dichlorophenolindophenol is applied for the kinetic determination of ascorbic acid in 0.05M oxalic acid. Stopped-flow techniques are used; the concentrations of the reactants of the second-order reaction can be adjusted so that the transmittance signal remains nearly invariant for a wide range of voltage. Theoretical and experimental results are in very good agreement. Analytical working curves are presented for the determination of ascorbic acid in the ranges 5.0·10^-4–1.0·10^-2M and 5.0·10^-5–1.0-·10^-3M with errors of 1.0% and 2.2%. respectively. The method is simple, fast and sensitive.     

Kinetic fluorimetric determination of carbamazepine in serum by the stopped-flow technique

Summary A simple, fast method for the determination of carbamazepine in serum is reported for the first time. It is based on the fluorescent reaction of this drug with cerium(IV) in an acid medium. A stopped-flow mixing module coupled to a conventional spectrofluorimeter is used for this purpose. The linear range of the proposed method is 0.04–140 g ml^–1 of carbamazepine and the detection limit is 0.01 g ml^–1. The within- and between-assay precision data and selectivity results show the method to be adequate for the determination of carbamazepine in serum by including a preliminary extraction step with dichloromethane. Analytical recoveries from different serum samples are reported.     

Kinetic fluorimetric determination of histidine,histamine and their mixtures

Kinetic fluorimetric methods for the determination of histidine and histamine, both separately and in mixtures, are described; the methods are based on the accelerating effect of these compounds on the oxidation of 1,1,3-tricyano-2-amino-1-propene by hydrogen peroxide in the presence of copper. A differential rate method is used for resolution of mixtures of these compounds (10^?5 M level), in which synergic effects are taken into account. The relative standard deviations for histidine and histamine are 1.4% and 2.1%, respectively, for separate determinations but 4.0% and 3.4%, respectively, for determinations of mixtures. Histamine/histidine ratios between 1:1 and 16:1 are satisfactorily resolved.     

Kinetic spectrophotometric determination of Ga(III)-Al(III) mixtures by stopped-flow injection analysis using principal component regression

A multivariate calibration method based on principal component regression analysis is applied to the resolution of mixtures by kinetic methodology. Gallium(III) and Al(III) were determined in mixtures on the basis of their different rate of reaction with 4-(2-pyridylazo)resorcinol in a slightly basic medium by using a stopped-flow injection procedure. Mixtures containing 1-5 mg/l. Ga(III) and 20-100 mg/l. Al(III) were successfully resolved with errors less than 10%.     

A kinetic spectrophotometric method for the determination of nitrite by stopped-flow technique.

A novel and highly sensitive stopped-flow kinetic spectrophotometric method for the determination of nitrite, based on monitoring the variation in the absorbance of the intermediate within a very short period, has been developed. The optimum conditions for various parameters on which the reaction of nitrite with perphenazine depends, were investigated. It was found that the initial reaction rate increased linearly with increasing nitrite concentration in the range from 1.0 x 10(-8) to 6.0 x 10(-6) M. The detection limit was calculated to be 4.8 x 10(-9) M. This method was used for the determination of nitrite in natural and drinking-water with satisfactory results. The influence of cationic, non-ionic and anion surfactants was also studied in this work.     

Kinetic determination of methotrimeprazine, thioridazine and their mixture by use of a modular stopped-flow/diode-array detection system

The oxidation reactions of methotrimeprazine and thioridazine by iron(III) were used to develop kinetic methods based on measurements of the formation rate of the corresponding coloured phenothiazinyl free radicals. The calibration graphs were linear over the range 0.8-60 microg/ml for methotrimeprazine and 1.1-60 microg/ml for thioridazine. The relative standard deviation was 1.1-3.4%. The method was used to determine the analytes in commercially available pharmaceutical preparations. The different absorption maxima of the oxidation products formed and also the different, high initial rates of the reactions for both analytes allow their simultaneous determination by using a stopped-flow module coupled to a diode-array spectrophotometric detector. Reaction rate and absorbance increment measurements of the kinetic curves obtained were used to resolve mixtures of both phenothiazines by using the proportional-equation method and establishing three different equation systems that allowed the results obtained in each case to be compared. Mixtures of methotrimeprazine and thioridazine in ratios between 8:1 and 1:8 were satisfactorily resolved.     

Kinetic spectrophotometric determination of hydrazine

A sensitive kinetic method for determining low levels of hydrazine has been described. The method is based on the measurement of the rate of the reaction between hydrazine and Mo(VI) in the presence of hydrochloric acid. The redox reaction was monitored spectrophotometrically at 710 nm. The variable-time and fixed-time methods were used. The calibration graph was linear for hydrazine concentrations of 1.0 × 10⁻⁴-1.4 × 10⁻² M, using the fixed-time method of analysis. The method is simple, rapid, precise, sensitive and widely applicable.     

Kinetic spectrophotometric determination of hydrazine

A kinetic spectrophotometric method for hydrazine determination in the range of 9.36×10⁻⁷ to 4.37×10⁻⁵ mol dm⁻³, based on the inhibitory effect of hydrazine on the oxidation of Victoria Blue 4- R by KBrO₃, was developed and validated. Kinetic parameters are reported for both the indicating and the inhibiting reaction. The detection limit was established as 9.98×10⁻⁸ mol dm⁻³. The selectivity of the proposed method was tested considering the influence of different ions that may be present in real samples. The method was successfully applied for hydrazine determination in various samples (very pure water from the water-steam system of a power plant and Isoniazid tablets, a pharmaceutical product).      

Kinetic spectrophotometric assay of sulfonamides by use of the griess reactionand a stopped-flow procedure

The time interval between two preset levels of the output signal is used as a measure of the sulfonamide concentration. Nitrite and N-(1-naphthyl)ethylenediamine, are used as reagents, and 0.5–5 × 10^?5 M of a sulphonamide can be determined. The method is applied to urine.     

Kinetic spectrophotometric determination of amodiaquine and chloroquine

Abstract  

Two simple, sensitive, and selective spectrophotometric methods were developed for determining amodiaquine (AQ) and chloroquine (CQ) based on their oxidation with potassium iodate and potassium bromate, respectively. The initial rates of oxidation of AQ and CQ were monitored at 342 and 343 nm, the wavelengths of maximum absorptions of the two drugs. The various experimental parameters affecting oxidation reactions were thoroughly studied and optimized. Beer’s law was obeyed for 0.2–4.0 and 0.5–5.0 μg cm⁻³, with correlation coefficients of 0.9999 and 0.9998 (n = 6) and a detection limit (based on the 3S _b -criterion) of 0.04 and 0.06 μg cm⁻³ for AQ and CQ. The proposed methods were conveniently applied to determining AQ and CQ in pure and dosage forms.