Kinetic studies on the oxidation of ascorbic acid by technetium(VII)

The pertechnetate ion oxidizes ascorbic acid in strong acid medium to form red species. A reaction mechanism has been developed which correctly predicts all the experimental facts. The results obtained support the postulate according to which the red species corresponds to a complex formed between Tc(V) and dehydroascorbic acid. The rate constants and Arrhenius parameters have been investigated.     

Effect of surfactants on the fluorescence intensity of organic reagents

The effect of 45 surfactants on the fluorescence intensity of 12 organic reagents has been studied and discussed. It has been found that there is a marked enhancement in the fluorescence intensity of organic reagents with nonrigid structures and with phenyl groups closely located.     

A potentiometric technique for kinetic determination of citrate, based on inhibition of crystalline growth of lead carbonate seed crystals

The growth of lead carbonate seed crystals is strongly inhibited by the presence of citric acid. The kinetics of crystal growth were followed potentiometrically with a lead ion-selective electrode. The study of different variables on such a process was carried out with the aim of developing kinetic procedures to determine citrate (0.5–2.0 μg/ml). The selectivity and sensitivity of these processes allow the application of his crystallization reaction to direct determination of citrate in drinks and in a pharmaceutical product.     

Determination of 2-ethylhexyl 4-(dimethylamino) benzoate using membrane-assisted liquid–liquid extraction and gas chromatography-mass spectrometric detection

A flow-cell for micro-porous membrane liquid–liquid extraction with a sheet membrane was used to extract 2-ethylhexyl 4-(dimethylamino) benzoate (EDB) from urine of solar-cream users and spiked wine samples. The cell enabled the target analyte to be extracted from 7.9 mL of donor solution into 200 μL of acceptor solution (decane). After extraction, the acceptor solution was transferred to a micro-vial for GC-MS analysis without derivation. In this work, variables affecting the enrichment factor were also studied, such as organic solvent, extraction time, recirculation flow of the donor solution through the donor chamber, presence of potassium chloride and ethanol in the donor solution and pH. The method has been evaluated in terms of linearity, sensitivity, precision, limits of detection and quantification and extraction efficiency. Limits of quantification were 1 and 3 μg L⁻¹ EDB for urine and wine, respectively. Quantitative analysis has been carried out by applying the method of standard additions. Within- and between-day relative standard deviations were lower than 12% and 20%, respectively. EDB was found in the urine of users of cream containing EDB in the concentration interval 1.2–7.2 μg L⁻¹. Therefore, this provides evidence of EDB dermal absorption and subsequent excretion through the urinary tract. EDB was not found in the analysed wine samples.     

Kinetic fluorimetric determination of cerium with 1,5-diphenyl-3-(2-stiryl)-Δ2-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.     

Kinetic-fluorimetric determination of cerium with 1-amino-4-hydroxyanthraquinone

A simple, sensitive, and selective method for the kinetic—fluorimetric determination of cerium (0.1–0.9 ppm), based on the oxidative reaction between cerium(IV) and 1-amino-4-hydroxyanthraquinone, has been developed. The reaction is followed by the measurement of the rate of appearance of yellow fluorescence (λ_ex = 480 nm, λ_em = 575 nm). About 20 cations and anions show negligible interference effects, even when present in large amounts. Only V(V) interferes at similar concentrations to those of Ce(IV) to be determined.     

Catalytic and inhibitory effects of technetium on reduction processes

Interactions between technetium and some anthraquinones and tartrazin in the presence of tin(II) are described. It was found that whereas the reductive process between Sn(II) and 1-amino-4-hydroxyanthraquinone is catalyzed by technetium, the reduction of tartrazin is inhibited by this element. Study of such processes seems to indicate that the catalytic effect of technetium on the reduction processes is due to Tc(V) action whereas the inhibitory effect is due to the Tc(IV) species.     

Kinetics and mechanism of the oxidation of thioglycolic acid and glutathione by technetium(VII)

The oxidation of glutathione and thioglycolic acid by pertechnetate ion has been studied. In each case a reaction mechanism is proposed which is in agreement with the experimental kinetic orders, and which satisfactorily accounts for all other experimental findings. Rate constants and Arrhenius parameters are reported.     

Interaction of some steroids with inorganic species in the presence of concentrated sulfuric acid: Kinetic-fluorometric study

The influence of 30 ionic species added previously to the addition of concentrated sulfuric acid on three steroids was studied. It has been proven that in the presence of some ionic species (Mg(II), Cr(III), Ce(IV), …) formation of fluorescent products occurs to a higher extent, permitting the establishment of methods for their determination. This process was investigated and the experimental variables and interference in each determination were reported.