RESUMEN
Peroxidase was extracted from a natural source (turnip) and irradiated with 60Co (0.1 kGy). It was then used in the construction of biosensors for hydrogen peroxide determination, in order to study the effect of the gamma irradiation on the performance of the biosensors. The biosensors were constructed using two immobilization procedures: cross-linking with glutaraldehyde and covalent binding through carbodiimide. The biosensor prepared using covalent binding through carbodiimide showed a higher sensitivity for H2O2. A good enhancement in stability and sensitivity was obtained for the biosensors from irradiated material, when compared to biosensors prepared with non-irradiated enzyme. However, the initial linear response range (1.0 to 10.0 mmol dm-3) and response time (0.5 s) were equal with or without irradiation.
RESUMEN
An automated system to perform titration and standard addition in monosegemented flow analysis by employing the simultaneous multiple injection is described. The system was controlled by aPC-AT-386 microcomputer through a home-made parallel interface, employing a diode array spectrophotometer as detector. Software was written in QuickBasic 4.5 to control the system and for data acquisition. A three-way solenoid valve was used in conjunction with a proportional injector to add the titrant solution or the standard solution to the sample, to carry out titration or standard addition, respectively. Only one standard solution was used in each procedure and different quantities of titrant or standard were added to the sample by controlling the time interval in which the solenoid valve was switched on. Titration and standard addition curves similar to those of the manual methods were obtained in both cases, since the sample dispersion was very low due to the air bubbles of the monosegment. The titration system was evaluated through the determination of Fe(II) with a KMnO4 standard solution in pharmaceutical preparations. The standard addition process was assessed by determining Cr(VI) in natural waters and domestic wastewater using the diphenylcarbazide method. The results obtained in both methodologies did not differ significantly from the reference methods at a 95% confidence level.
RESUMEN
An automated system to perform liquid-liquid extraction in monosegmented flow analysis is described. The system is controlled by a microcomputer that can track the localization of the aqueous monosegmented sample in the manifold. Optical switches are employed to sense the gas-liquid interface of the air bubbles that define the monosegment. The logical level changes, generated by the switches, are flagged by the computer through a home-made interface that also contains the analogue-to-digital converter for signal acquisition. The sequence of operations, necessary for a single extraction or for concentration of the analyte in the organic phase, is triggered by these logical transitions. The system was evaluated for extraction of Cd(II), Cu(II) and Zn(II) and concentration of Cd(II) from aqueous solutions at pH 9.9 (NH(3)/NH(4)Cl buffer) into chloroform containing PAN (1-(2-pyridylazo)-2-naphthol) . The results show a mean repeatability of 3% (rsd) for a 2.0 mg l(-1) Cd(II) solution and a linear increase of the concentration factor for a 0.5mg l(-1) Cd(II) solution observed for up to nine extraction cycles.