Sequential and simultaneous determination of bromate and chlorite (DBPs) by flow techniques: kinetic differentiation.

3-3'-Dimethoxybenzidine (o-dianisidine, ODA) is oxidised by Br(2), among other oxidants, generating a compound that absorbs at 450 nm, while the non-oxidised reagent absorbs in the UV region. This reaction has been used previously as the basis of a continuous-flow method for the determination of bromate in ozonised water, with a detection limit lower than the maximum permitted for drinking water (10 microg L(-1)). The only interference observed in the method was that due to the chlorite ion (ClO(2)(-)), which generated the same ODA bromation product. Thus, in systems in which O(3) is employed as a disinfectant and disinfection is later enhanced with ClO(-) and ClO(2), there exists the possibility of finding BrO(3)(-) and ClO(2)(-), oxoanions generated as subproducts. The kinetic behaviour of the reaction between bromate and chlorite with bromine in acidic medium is different, allowing the proposal of a continuous-flow method for the simultaneous or sequential determination of both subproducts in water purification systems. None of the other subproducts interfered in the reaction. Kinetic differentiation was achieved by combining the temperature of the reaction and the length of the coils, after which it was possible to determine both analytes sequentially within a concentration range of 6-160 microg L(-1).

Consumer product in vitro digestion model: Bioaccessibility of contaminants and its application in risk assessment.

This paper describes the applicability of in vitro digestion models as a tool for consumer products in (ad hoc) risk assessment. In current risk assessment, oral bioavailability from a specific product is considered to be equal to bioavailability found in toxicity studies in which contaminants are usually ingested via liquids or food matrices. To become bioavailable, contaminants must first be released from the product during the digestion process (i.e. become bioaccessible). Contaminants in consumer products may be less bioaccessible than contaminants in liquid or food. Therefore, the actual risk after oral exposure could be overestimated. This paper describes the applicability of a simple, reliable, fast and relatively inexpensive in vitro method for determining the bioaccessibility of a contaminant from a consumer product. Different models, representing sucking and/or swallowing were developed. The experimental design of each model can be adjusted to the appropriate exposure scenarios as determined by the risk assessor. Several contaminated consumer products were tested in the various models. Although relevant in vivo data are scare, we succeeded to preliminary validate the model for one case. This case showed good correlation and never underestimated the bioavailability. However, validation check needs to be continued.

A new automated colorimetric method for measuring total oxidant status.

OBJECTIVES: To develop a new, colorimetric and automated method for measuring total oxidation status (TOS). DESIGN AND METHODS: The assay is based on the oxidation of ferrous ion to ferric ion in the presence of various oxidant species in acidic medium and the measurement of the ferric ion by xylenol orange. The oxidation reaction of the assay was enhanced and precipitation of proteins was prevented. In addition, autoxidation of ferrous ion present in the reagent was prevented during storage. The method was applied to an automated analyzer, which was calibrated with hydrogen peroxide and the analytical performance characteristics of the assay were determined. RESULTS: There were important correlations with hydrogen peroxide, tert-butyl hydroperoxide and cumene hydroperoxide solutions (r=0.99, P<0.001 for all). In addition, the new assay presented a typical sigmoidal reaction pattern in copper-induced lipoprotein autoxidation. The novel assay is linear up to 200 micromol H2O2 Equiv./L and its precision value is lower than 3%. The lower detection limit is 1.13 micromol H2O2 Equiv./L. The reagents are stable for at least 6 months on the automated analyzer. Serum TOS level was significantly higher in patients with osteoarthritis (21.23+/-3.11 micromol H2O2 Equiv./L) than in healthy subjects (14.19+/-3.16 micromol H2O2 Equiv./L, P<0.001) and the results showed a significant negative correlation with total antioxidant capacity (TAC) (r=-0.66 P<0.01). CONCLUSIONS: This easy, stable, reliable, sensitive, inexpensive and fully automated method that is described can be used to measure total oxidant status.

Precise method for the measurement of catalase activity in honey.

An improved method is reported for the determination of catalase activity in honey. We tested different dialysis membranes, dialysis fluid compositions and amounts, dialysis temperatures, sample amounts, and dialysis times. The best results were obtained by dialysis of 7.50 g sample in a cellulose dialysis sack, using two 3 L portions of 0.015 M sodium phosphate buffer (pH 7.0) as the dialysis fluid at 4 degrees C for 22 h. As in previous methods, catalase activity was determined on the basis of the rate of disappearance of the substrate, H202, with the H202 determined spectrophotometrically at 400 nm in an assay system containing o-dianisidine and peroxidase. Trials indicated that the best solvent for the o-dianisidine was 0.2 M sodium phosphate buffer, pH 6.1; the best starting H202 concentration was 3 mM; the best HCl concentration for stopping the reaction was 6 N; and the best sample volume for catalase measurement was 7.0 mL. Precision values (relative standard deviations for analyses of 10 subsamples of each of 3 samples) were high, ranging from 0.48% for samples with high catalase activity to 1.98% for samples with low catalase activity.

DNA sensor for o-dianisidine.

o-Dianisidine (3,3'-dimethoxybenzidine) is applied in the production of some dyes and also used in analytical tests. However, this compound is anticipated to be a human carcinogen. An analytical strategy utilizing square wave voltammetry for the determination of o-dianisidine is presented. An electrochemical system was consisted of three electrodes: carbon paste working electrode, platinum wire counter electrode and silver-silver chloride (Ag/AgCl) reference electrode. However, square wave voltammograms of direct measurements of o-dianisidine were found to be hardly reproducible, exhibiting few peaks due to some labile short-lived intermediates with the only exception of a quite stable peak at +0.7 V vs. Ag/AgCl. Quantitative determination of o-dianisidine gave satisfactory results only when the carbon paste working electrode was replaced by deoxyribonucleic acids (DNA) electrode obtained by immobilization of double-stranded (ds) DNA on carbon electrode. Square wave voltammogram of DNA showed two peaks attributed to adenine and guanine and the latter was used as analytical signal. After interaction with o-dianisidine, guanine oxidation peak was reduced to the extent related to the concentration of the analyte. Initial reduction of guanine peak took place already at the concentration of o-dianisidine equal to 0.4 microM; high concentrations (above 100 microM) of the analyte quenched completely a guanine response. The presented electrochemical system enables a specific detection of o-dianisidine by the presence of an oxidation peak at +0.7 V and its quantitative determination by measuring a reduction of guanine peak by means of a DNA sensor.

Detection system for membrane immunoassay based on the trapping of a highly colored intermediate of the peroxidase reaction.

The oxidation of ortho-dianisidine by membrane bound horseradish peroxidase in the presence of sodium dextran sulfate affords a dark-green insoluble product, identified as an unstable meriquinone intermediate previously reported in literature. Cationic and unsubstituted dextrans do not stabilize the intermediate. The highest yield of the intermediate is observed at pH 4.0-5.0 and concentration of dextran sulfate ca. 0.5%. New highly sensitive detection system for peroxidase has been developed on the basis of ortho-dianisidine oxidation to the meriquinone intermediate in the presence of sodium dextran sulfate. Under certain conditions, with lowered sodium dextran sulfate concentrations, a progressive further oxidation of the green intermediate to the yellow-brown final product is observed on passing to higher enzyme concentrations. This finding opens a possibility to develop a detection system in which the color of the mixture of reaction products serves as a measure of the enzyme concentration.

An ultrasensitive colorimetric assay for manganese.

An ultrasensitive colorimetric assay for manganese is described. It is based upon the catalysis, by Mn(II), of the photochemical oxidation of o-dianisidine, sensitized by riboflavin. Catalase increases the Mn(II)-catalyzed rate of photosensitized oxidation of dianisidine to the bisazobiphenyl, while superoxide dismutase inhibits the rate. The mechanism appears to involve oxidation of Mn(II) by O2-, followed by oxidation of dianisidine by MnO2+ in equilibrium Mn(III). Cu(II) interferes, but Zn(II), Fe(II), Fe(III), Co(II), and Ni(II) do not. Chelating agents and thiol reductants also interfere. Interference by Cu(II) can be overcome by the addition of cyanide, while interference by organic compounds can be surmounted by wet ashing. This assay provides a linear response to Mn(II) over the range 10-2500 nM. The limit of detection was 5 nM Mn(II).