No abstract

Biosensors ®nd application in¯ow analysis due to their high selectivity and sensitivity. Decrease in the response during extended use, originated by degradation, inhibition or structural changes of the enzyme or leaching of active components by the¯ow, is the prevailing problem. As an alternative to additives and preparation techniques cited in the literature, it is proposed to use DNA as a matrix for improving preservation of the activity of a diphenol-sensor-based tyrosinase, Tyr, (EC 1.14.18.1). The Tyr±DNA mixture was incorporated into carbon paste, CP±DNA±Tyr, or applied on glassy carbon, GC±DNA± Tyr. The CP±DNA±Tyr, covered by a membrane-of Cuprophan, presented superior performance in amperometric operation under¯ow conditions (electroreduction of the products of the enzymatic oxidation of diphenols in the presence of O 2). In comparison with paste electrodes without DNA, CP±Tyr, a current increase of one order of magnitude was observed for catechol FIA peaks, with good repeatability during several hours of operation. The response decayed ca. 50% after every 3 to 4 days of use (with dry storage at 48C overnight). Original performance was recovered by simply substituting the used paste for a new portion of stock paste, stable for 2 months under refrigeration. Evaluation of 18 different substrates and potential interferents indicated that, at the adopted potential of À0,15 V vs. Ag/AgCl, only p-cresol gives a response comparable to catechol. Flow-injection determination of catechol samples was conducted at a frequency of 30 injections/h, with linear response from the detection limit of 1Â10 À6 up to 5Â10 À5 mol l À1 .

No abstract

The chemiluminescent reactions of bis(2,4,6-trichlorophenyl)oxalate (TCPO) and bis(2-nitrophenyl)oxalate (2-NPO) with hydrogen peroxide in acetonitrile/water micellar systems (anionic, cationic, and non-ionic) and γ-cyclodextrin were studied in the presence of fluoranthene or 9,10-diphenylanthracene, imidazole, and two buffer solutions, HTRIS+/TRIS and H2PO4–/HPO42–. The relative chemiluminenscence (CL) intensity is higher in the presence of the cationic (DDAB, CTAC, DODAC, and OTAC), anionic (SDS), and non-ionic (Tween 80) surfactants. In the presence of some non-ionic surfactants (Brij 35, Brij 76, and Tween 20), the CL intensity was partially quenched compared with the reaction with no surfactant. The sensitivity for hydrogen peroxide determination in the range 0.01 × 10−4to 1.0 × 10−4mol L–1, considering the slope of the calibration curves (maximum peak height of CL vs. concentration), improved with the introduction of DDAH, CTAB, and SDS in HTRIS+/TRIS buffer.