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.     

Fluorimetric determination of total ascorbic acid by a stopped-flow mixing technique

A simple, rapid and automatic fluorimetric method for the determination of total ascorbic acid is described. The method makes use of the stopped-flow mixing technique in order to achieve the rapid oxidation of ascorbic acid by dissolved oxygen to dehydroascorbic acid, which then reacts with o-phenylenediamine to form a fluorescent quinoxaline. The initial rate and fluorescence signal of this system are directly proportional to the ascorbic acid concentration. The calibration graph was linear over the range 0.1-30 microg ml(-1) (kinetic method) and 0.25-34 microg ml(-1) (equilibrium method). The precision (% RSD) was close to 0.5%. The method has been used for the determination of ascorbic acid in pharmaceutical formulations, fruit juices, soft drinks and blood serum.     

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.     

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.     

Flow-injection catalytic kinetic determination of manganese using stopped-flow and gradient calibration

Based on the principle of Mn(II) catalysis of the Tiron-hydrogen peroxide reaction, a catalytic kinetic spectrophotometric determination of traces of manganese (ca. 10^?7 M) by flow injection was established. In combination with a microcomputer, by using gradient dilution and the stopped-flow method, onlya single standard solution was needed for calibration. The method has a high selectivity and a sampling rate of 40 h^?1. Traces of manganese in natural water were determined with a maximum relative standard deviation of 5.5% (n = 6).     

Sensitive determination of captopril by time-resolved chemiluminescence using the stopped-flow analysis based on potassium permanganate oxidation

The chemiluminescent behaviour of captopril when reacted with a common oxidant, potassium permanganate in different acidic media is described, using the stopped-flow technique in a continuous-flow system. A 22 bit analogue-to-digital converter that acquires analogue signals at −10 and +10 V and allows the power supply to the peristaltic pump to be interrupted is used in the time-resolved chemiluminescence manifold to ensure rapid, efficient mixing of chemiluminescent reagent and sample immediately before reaching the detector; this results in high precision and detectability, particularly with fast, short-lived emissions.The optimum chemical conditions for the chemiluminescence emission were investigated. It was found that a weak CL emission was emitted during the oxidation of this drug with potassium permanganate in acidic solution. The effect of common emission enhancers such as formic acid, formaldehyde, glutaraldehyde, acetaldehyde, quinine, fluorescein, rhodamine B and rhodamine 6G was studied. The parameters selected were 4.0 mol L⁻¹ sulphuric acid, 0.25 mmol L⁻¹ permanganate and 0.75 mol L⁻¹ formaldehyde.Four quantitative parameters adjustable via software settings, two of them typically kinetic parameters, such as rate of the light-development reaction and rate of the light-decay reaction, and the other conventional parameters, such as maximum emission intensity and total emission area, were used to obtain linear calibration graphs with each measurement parameter. The detection limits ranged from 0.011 to 0.026 μg mL⁻¹ and R.S.D. values (n = 10) of 1.21-3.93 at a 0.50 μg mL⁻¹ and 2.01-3.41 at a 1.60 μg mL⁻¹ concentration levels were obtained. The method was satisfactorily applied to the determination of captopril in pharmaceutical preparations.     

Determination of proteins in serum by fluorescence quenching of rose bengal using the stopped-flow mixing technique

The stopped-flow mixing technique was used to develop a very fast, sensitive and accurate method for determining total proteins. The method is based on the lower fluorescence of Rose Bengal caused by binding of the dye to the proteins. The decrease in the fluorescence intensity, measured at 572 nm with excitation 555 nm, was linearly related to protein concentration from 1.3 to 24.5 micrograms ml-1. The detection limit was 0.3 microgram ml-1. The method was satisfactorily applied to the determination of total proteins in different serum samples.     

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。     

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.     

停流流动注射-诱导动力学光度法同时测定微量铁和锑

依据诱导反应的基本原理, 提出了一种同时测定多元素的方法; 研究了Fe(II)、Sb(III)诱导的Cr(VI)-I^-氧化还原反应体系, 并据此建立了停流-诱导动力学光度法同时测定微量铁和锑的工作条件。线性范围分别为0~1.2μg.mL^-1Fe(II)和0~2.0μg.mL^-1Sb(III); 检测限为0.012μg/mL^-1Fe(II)和0.014μg.mL^-1Sb(III)。除Ti(III)、V(IV)及As(III)外, 其余共存离子不影响测定。用本法测定了锌标准物及模拟样品中的铁和锑含量, 结果满意。     

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.     

顺序注射停流分光光度法测定痕量碘

食物中碘的含量一直是人们关注的问题,研究食物中微量碘的分析方法具有重要的现实意义.目前测定碘的方法主要有色谱法[1,2]、荧光法[3,4]、分光光度法[5,6]等.     

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.     

A kinetic study of the permanganate—oxalate reaction and kinetic determination of manganese(II) and oxalic acid by the stopped-flow technique

The reduction of permanganate by oxalate in the presence of manganese(II) ion in acidic media is described. All reactions were run at 525 nm and constant ionic strength 1.0 M. The reaction was found to obey the rate expression —$\text{d[MnO}{}_4{}^{\mathrm{-}}\text{]}\text{d}\text{t}$ = k [Mn²⁺] [C₂O₄^2-]² [MnO₄^-] [H⁺]^-2 = k' [MnC₂O₄] [MnO₄^-]. The values of k and k' were shown to be 5.4 × 10⁴ M^-1 s^-1 and 8.2 × 10⁴ M^-1 s^-1, respectively. Reaction rate methods for the determination of manganese(II) and oxalic acid are reported. The rate of disappearance of permanganate was monitored automatically and related directly to manganese-(II) and oxalic acid concentrations. Manganese(II) in the ranges 1–10 × 10^-4 M and 1–10 × 10^-3 M and oxalic acid in the range 0–20 μg ml^-1 can be determined very rapidly with a precision of 1–2%.     

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.     

Enzymatic determination of N-methylcarbamate pesticides at the nanomolar level by the stopped-flow technique

A sensitive and selective kinetic enzymatic method for the determination of N-methylcarbamate pesticides is presented. It is based on their inhibitory effect on electric eel acetylcholinesterase and the use of 5,5'-dithiobis(2-nitrobenzoic) acid (DTNB) as chromogenic reagent for the thiocholine released from the acetylthiocholine iodide substrate. The fast DTNB-thiocholine reaction is monitored photometrically by the stopped-flow technique. Carbaryl, propoxur and carbofuran can be determined at concentrations in the ranges 6.5-120, 2-15 and 0.1-5.0 ng/ml, respectively, by the proposed method. An interference study was also reported.     

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-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.

---

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

     

Determination of trace amounts of bromide by flow injection/stopped-flow detection technique using kinetic-spectrophotometric method

A simple, sensitive and selective method for the determination of bromide in seawater by using a flow injection/stopped-flow detection technique was examined. The detection system was developed for a new kinetic-spectrophotometric determination of bromide in the presence of chloride matrix without any extraction and/or separation. The detection was based on the kinetic effect of bromide on the oxidation of methylene blue (MB) with hydrogen peroxide in a strongly acidic solution. Large amounts of chloride could enhance the sensitivity of the method as an activator. The decolorisation of the blue color of MB was used for the spectrophotometric determination of bromide at 746 nm. A stopped-flow approach was used to improve the sensitivity of the measurement and provide good linearity of the calibration over the range of 0-3.2 μg ml⁻¹ of bromide. The relative standard deviation was 0.74% for the determination of 2.4 μg ml⁻¹ bromide (n = 5). The detection limit (3σ) was 0.1 μg ml⁻¹ with a sampling frequency of 12 h⁻¹. The influence of potential interfering ions was studied. The proposed method was applied to the determination of bromide in seawater samples and provided satisfactory results.