Kinetic Fluorimetric Method Research Articles

Catalytic Fluorimetric Determination of Trace Cobalt in Vitamin B12

A new kinetic fluorimetric method is proposed for the determination of trace cobalt, based on the catalytic oxidation of reduced fluoresceine with hydrogen peroxide in the presence of triethanolamine as activator in a basic medium. The detection limit for cobalt is 0.016 ng/ml and the linear range of the determination is 0.08–1.40 ng/ml. The application of this method to the determination of trace cobalt in vitamin B12samples shows satisfactory results.

Kinetic behaviour of the malonaldehyde-thiobarbituric acid reaction. kinetic-fluorimetric determination of malonaldehyde in human serum

For the first time a fluorimetric-kinetic method for the determination of malonaldehyde (MLD) is proposed. The fluorescence emission of the thiobarbituric acid (TBA)-MLD reaction product has been monitored at 553 nm (excitation wavelength 515 nm), and the instrumental and experimental variables have been studied. A selective and fast kinetic-fluorimetric determination of malonaldehyde is proposed. The sensitivity of the method is very high, the detection limit is 0.30 ng ml −1, the application range is between 1.1 and 50 ng ml −1, and the determination time per sample is 500 s. The kinetic-fluorimetric method has been applied in the determination of two types of pathological human serum: rheumatic and hyperlipemic serum. In both cases, perchloric acid is used to precipitate the proteins.

Kinetic fluorimetric determination of Cu(II) and Zn(II) by their incorporation reactions into a water-soluble porphyrin

Kinetics of incorporation of Cu, Zn, Fe, Co, Ni and Mn divalent ions into coproporphyrin-I in imidazole buffer solution, pH 7.0, has been studied by monitoring the decrease in fluorescence intensity of the free base porphyrin. All reactions followed simple second-order rate law, the rate constants being decreased in the order Zn > Cu ⪢ Co > Fe ⪢ Mn, Ni. the kinetic fluorimetric method for the determination of Cu(II) and Zn(II) using their incorporation reactions into the porphyrin was developed. Initial rate and fixed-time methods were used to construct calibration graphs over the range 0–1.0 × 10 −5 M of both metals. The analytical characteristics of the method and effect of foreign ions were determined. In the presence of sodium thiosulphate as the masking reagent the determination of micromolar concentrations of Zn in the presence of a 10-fold excess of Cu is possible.

Kinetic fluorimetric determination of promethazine by a stopped-flow mixing technique

The oxidation of promethazine to its corresponding fluorescent sulphoxide was used to develop a novel kinetic fluorimetric method for the determination of this drug. The use of a stopped-flow mixing technique makes use of an oxidizing reagent unnecessary because the oxidation is rapidly carried out by dissolved oxygen. The method is simple and fast as it only requires a few seconds to obtain kinetic data which allows ready application to routine analyses. The calibration graph is linear over the range 0.5–80 μg ml −1 and the precision (%RSD) is close to 2%. The method was applied to the determination of promethazine hydrochloride in two pharmaceutical preparations.

Determination of Biacetyl by Sensitized Photochemical Kinetic Fluorimetry

Abstract A new in-situ photochemical kinetic fluorimetric method was proposed for the determination of biacetyl (BI). It is based on the sensitization of BI on the photochemical reaction of amaranth (AM). AM, a nonfluorescent compound was converted into an intensively fluorescent compound in a slightly alkaline medium by the sensitized photochemical reaction, and BI was indirectly determined by monitoring the change of the fluorescence intensity. The determination can be carried out by fixed-time method or tangent method. The kinetic behavior of the reaction and the effects of some experimental conditions were investigated and discussed. The calibration graph was rectilinear from 1.0 μg ml−1 to 10.0 μg ml−1 of BI (r = 0.999), the limit of detection was 1.0 ng ml−1, and the coefficient of variation was 0.44% for 0.90 μg ml−1 of BI (n = 6). The mechanism for the sensitization of BI was examined and the triplet-triplet energy transfer, in which BI acted as the energy donor and AM as the energy acceptor, was ...

Study on catalytic fluorimetric determination of trace manganese

A new kinetic fluorimetric method has been proposed for the determination of trace manganese. The method is based on the catalytic oxidation of rhodamine 6G with potassium periodate in the presence of nitrilo triacetic acid as activator, in near neutral media. The detection limit for manganese is 0.018 ng/ml. The linear range of the determination is 0.04–1.00 ng/ml. The proposed method suffers from few interferences in the presence of more than 30 foreign ions. The method has been used to determine trace manganese in hair, urine, fish and water samples. The results are satisfactory.

Kinetic Fluorimetric Method for the Determination of Tobramycin by Stopped-Flow Mixing Methodology

Abstract The reaction of tobramycin with o-phthaldialdehyde (OPA) in the presence of 2-mercaptoethanol was studied kinetically by using stopped-flow mixing methodology. New data on the kinetics of this reaction were exploited to develop a simple, fast method for tobramycin determination. The linear range (0.05–30.0 μg mL−1), detection limit (0.03 μg mL−1), precision (&RSD 1.92) and selectivity of the proposed kinetic method are quite acceptable. The method was satisfactorily applied to the analysis of pharmaceutical preparations with no pretreatment.

Stopped-flow fluorimetric determination of ampicillin in serum

A very simple and fast kinetic fluorimetric method for the determination of ampicillin is described. It is based on the stopped-flow technique and the addition of hydrogen peroxide to the reaction medium, and requires no prior heating to hydrolyse the β-lactam ring unlike most hitherto known determinations. Kinetic data can be obtained only a few seconds after the reactants have been mixed, which allows ready application of the method to routine analyses. The calibration graph is linear over the range 0.025–7.0 μg ml−1 ampicillin. The detection limit is 20 ng/ml and within-and between-assay precision is 2.6% resp. 2.7%. The method was satisfactorily applied to the analysis of serum samples by including a preliminary deproteination step using trichloroacetic acid. Mean recovery is 102.1%.

Kinetic-Fluorimetric Determination of Choline and Acetylcholine by Oxidation with Ce(IV)

Abstract A kinetic fluorimetric method for the determination of choline and acetylcholine based on the oxidation of these analytes by Ce(IV) in a sulfuric acid medium yielding fluorescent Ce(III) is proposed. The calibration graph of each analyte is linear over the range 1.7x10−5 − 1×10−3 M and the relative standard deviation is about 2% in both cases. The rate of appearance of Ce(III) fluorescence was found to be influenced by various processes in addition to the oxidation reaction and experiments were carried out in order to elucidate them.

Fluorimetric Determination of Thiamine and Cocarboxylase by a Differential Rate Method

Abstract A differential kinetic fluorimetric method is proposed for the simultaneous determination of thiamine (vitamin B) and its pyrophosphate ester (cocarboxylase). It is based on the oxidation of these analytes by mercury(II) in a basic medium to yield fluorescent thiochrome. The calibration graph of each analyte is linear in the range 4 × 10−8 −3 × 10−5 M. The logarithmic extrapolation method is used to resolve thiamine/cocarboxylase mixtures in ratios between 4:1 and 1:15. Results of precision and selectivity studies are reported. Thiamine and cocarboxylase are satisfactorily determined in synthetic multivitamin preparations by the proposed method. A method for the individual determination of cocarboxylase is also described and applied to the analysis of this analyte in commercial pharmaceutical preparations.

Kinetic-fluorimetric determination of flavonoids at the nanomole level.

A kinetic-fluorimetric method is proposed for the determination of flavonoids. The method is based on the activating effect of flavonoids on the aerobic oxidation of 2-hydroxynaphthaldehyde thiosemicarbazone in the presence of manganese(II), which acts as a catalyst. The reaction is monitored spectrofluorimetrically by measuring the initial rate at the excitation and emission wavelengths of the oxidation product. The concentration ranges for the determination of different flavonoids are some of the lowest achieved so far (e.g., a linear calibration graph is obtained for quercetin from 0.25 to 12.5 µM). The reactivities of 14 flavonoids have been studied, showing a relationship between the structure and reactivity of the flavonoids. This relationship is similar to that obtained in mutagenesis tests. The kinetic-fluorimetric method has also been applied to the determination of flavonoids in tea and red wine by using fecalase and hesperidinase.

Kinetic-fluorimetric study of the activator effect of zirconium(IV) on the air oxidation of morin catalysed by manganese(II)

A kinetic study of the activator effect of zirconium(IV) on the manganese(II)-catalysed air oxidation of morin has been made. The effect of ammonia, ethanol, morin, manganese(II) and zirconium(IV) concentrations and of temperature was examined in order to obtain the optimum conditions for the determination of zirconium(IV) and to establish the kinetic dependence of each of these variables for the catalysed and activated reactions. The reaction was followed by measuring the decrease in fluorescence at 548 nm, with an excitation wavelength of 417 nm. A kinetic-fluorimetric method for the determination of zirconium(IV) is proposed. The calibration graphs were obtained by applying the fixed time, fixed concentration, initial rate and rate constant methods. The method is linear up to 250 ng ml–1 of zirconium(IV). The precision was calculated for the different methods applied and was always smaller than 3%. The main interferences were due to BeII, CuII and MgII. Moreover, the zirconium(IV)'s activator effect has been used to improve the kinetic-fluorimetric determination of manganese(II). The method is linear up to 60 ng ml–1, with a detection limit of 0.26 ng ml–1 for manganese(II), and a sensitivity enhancement of about 50% is obtained in the presence of the activator.

Kinetic-fluorimetric determination of ascorbic acid at the nanomole level.

A kinetic-fluorimetric method is proposed for the determination of ascorbic acid. The method is based on the activating effect of ascorbic acid on the aerial oxidation of 2-hydroxynaphthaldehyde thiosemicarbazone in the presence of manganese(II), which acts as a catalyst. The reaction is monitored spectrofluorimetrically by measuring the initial rate at the excitation and emission wavelengths of the oxidation product. A linear calibration graph from 0.15 to 3 µM is obtained. The method has been applied to the determination of ascorbic acid in pharmaceuticals and fruit juices and of ascorbic acid and dehydroascorbic acid in urine.

Kinetic fluorimetric determination of organic peroxides and lipohydroperoxides at the nanomole level

A new kinetic fluorimetric method for determination of cumene hydroperoxide, tert-butyl hydroperoxide and lipohydroperoxides is reported. It is based on the manganese(II)-catalysed oxidation of 2-hydroxynaphthaldehyde thiosemicarbazone (HNTS) by a hydroperoxide. Measurements are made by the initial-rate method, which allows determination of as little as 0.1 nmole of peroxide and also permits establishment of the differences in reactivity between the hydroperoxides assayed. The method has been applied to the determination of lipohydroperoxides in six commercial oil samples (grape, corn, sunflower seed, cod-liver and linseed). The results obtained can be expressed as meq of peroxide per kg of oil, and are in close agreement with those obtained by the classical iodometric method.

Kinetic spectrofluorimetric determination of silver, based on its catalytic effect on the oxidation of pyrocatechol-1-aldehyde 2-pyridylhydrazone by peroxodisulphate in the presence of 1,10-phenanthroline as activator

A kinetic fluorimetric method for the determination of silver is described, based on its catalytic effect on the oxidation of pyrocatechol-1-aldehyde 2-pyridylhydrazone by peroxodisulphate. In aqueous solution silver concentrations of 0.2–0.8 μg ml can be determined, and 10–80 ng ml in the presence of 1,10-phenanthroline as activator. The fluorescent species obtained (λ ex 357 nm, λ em 445 nm) results from oxidation of the reagent. The kinetic parameters and the interferences are reported, and the method is applied to the determination of silver in developed panchromatic plates.

Selective kinetic fluorimetric determination of copper at the [formula omitted] level

A kinetic fluorimetric method for copper, based on a previously described system with 1,1,3-tricyano-2-amino-1-propene as reagent, has been developed. It has been shown that the determination is based on copper-catalysed oxidation of the reagent rather than on complex formation with it, although complex-formation with imidazole seems needed to stabilize the copper(I) that is thought to be the catalyst. The application of several kinetic methods (tangent, fixed-time and variable-time) allows determination of very low concentrations of copper (1–35 ng ml ) with a sensitivity about 100 times that of an earlier method. Of 47 ions tested, only EDTA interfered when present at the same concentration as copper. The method has been applied to the determination of copper in blood serum samples.

Kinetic-fluorimetric study of the catalytic effect of manganese(II) on the air oxidation of morin

A kinetic study of the air oxidation of morin catalysed by trace amounts of manganese(II) has been made. The effect of ammonia, ethanol, morin and manganese(II) concentrations was examined, and the partial orders with respect to these reagents and the kinetic constants were obtained. The catalysed reaction is of zero order with respect to morin (for the range 1.48 × 10–5–2.07 × 10–5M), 0.75 order with respect to ammonia (between 0.40 and 6.68 M) and first order with respect to manganese(II). The effect of temperature was also studied. The activation energy was calculated by applying the Arrhenius equation (linear between 20 and 40 °C). The reaction was followed by measuring the decrease in fluorescence at 548 nm, with an excitation wavelength of 415 nm. A kinetic-fluorimetric method for the determination of trace amounts of manganese(II) is proposed. Calibration graphs were obtained by applying the fixed time, fixed concentration, initial rate and rate constant methods. The method is linear up to 70 ng ml–1 of manganese(II); the detection and quantitation limits were found to be 0.54 and 1.81 ng ml–1, respectively. The precision was calculated for the different methods applied, and varies between 1.9%(initial rate) and 4.5%(fixed time at 5 min). BeII, CuII and ZrIV increase the catalysed reaction rate, and MgII, CrIII and FeIII decrease the reaction rate.

Kinetic-fl uorimetric Determination of Selenium in the Environment with Use of Methylene Blue

Abstract A kinetic-fluorimetric method for determination of traces of selenium (0.01–0.4 ppm) is described. It is based on the fact that the reducing power of alkali sulfides can be considerably enhanced by the addition of elemental selenium. The experimental variables and interferences have been studied. The selenium quantities are estimated in diverse environmental samples.

Kinetic fluorimetric determination of cerium with 1,5-diphenyl-3-(2-stiryl)-Δ 2-pyrazoline

A kinetic fluorimetric method for the determination of cerium(IV) (0.04–0.2 ppm) is described. The fluorescent species obtained results from oxidative transformation of the reagent. The reaction are described and the experimental variables and interferences in the determination are reported.

Selective determination of trace amounts of iron by a kinetic fluorimetric method

The coupled catalysis of iron(III) and vanadium(V) in the autoxidation of sodium 4,8-diamino-1,5-dihydroxyanthraquinone-2,6-disulphonate (DADHADS) is discussed. The reaction is followed by measuring the rate of appearance of the intensely fluorescent oxidation product, and the initial rate method is applied to determine trace amounts of iron(III). The sensitivity and selectivity of the method have been studied. Iron contents between 0.06 and 1.0 µg ml–1 have been determined with a relative standard deviation of 5.8% and a detection limit of 18 ng ml–1.