Development of biosensors based on hexacyanoferrates.

Ferric and copper hexacyanoferrates (PB and CuHCF, respectively) were electrodeposited on glassy carbon electrodes providing a suitable catalytic surface for the amperometric detection of hydrogen peroxide. Additionally glucose oxidase was immobilized on top of these electrodes to form glucose biosensors. The biosensors were made by casting glucose oxidase-Nafion layers onto the surface of the modified electrodes. The operational stability of the films and the biosensors were evaluated by injecting a standard solution (5 muM H(2)O(2) for PB, 5 mM H(2)O(2) for CuHCF and 2.5 mM glucose for both) over 5-10 h in a flow-injection system with the electrodes polarized at -50 (PB) and -200 mV (CuHCF) versus Ag/AgCl, respectively. The glucose biosensors demonstrated suitability for glucose determination: 0.0-2.5 mM (R(2)=0.9977) for PB and 0.0-10 mM (R(2)=0.9927) for CuHCF, respectively. The visualization of the redox catalyst modifiers (PB and CuHCF films) was presented by scanning electron micrographs.

Pervaporation: an integrated evaporation/gas-diffusion approach to analytical continuous separation techniques.

A flexible pervaporation module was developed and characterized. The spacers it uses allows the volume of the donor and/or acceptor to be altered as required. The performance of the module was tested as regards both dynamic behaviour and continuous pervaporation in terms of flow-rates, temperature, type of membrane, flow mode, etc. A method for the determination of ethanol in different types of wine was developed and applied to various samples in order to validate the proposed continuous separation approach.

Development of a tubular periodate electrode for flow-injection determination of glycerol.

Periodate electrodes without inner reference solution based on tetraoctylammonium periodate plus solvent mediator (dibutyl phthalate or 2-nitrophenyl octylether) were constructed. Linear dynamic range, practical detection limit, slope, stability, selectivity coefficients, pH dependence, response time and lifetime were evaluated. A tubular version was further developed and coupled to a flow-injection system for glycerol determination in samples relevant to the industrial production of soaps, detergents and similar. The method involves glycerol oxidation by periodate with potentiometric evaluation of its consumption. The influence of oxidizing agent concentration (10(-5)-10(-2)M NalO(4)), ionic strength (0.0-1.0M Na(2)SO(4)) and mean resident time were investigated and the feasibility of using a single-fine manifold was discussed. The proposed system handles about 40 samples/hr, is very stable and suitable to industrial control. Results within the 1000 and 5000 mg/l range glycerol are precise (r.s.d. <0.005) and in fair agreement with conventional procedures. Baseline drift or noise is not observed and a thermostat water bath is not required. A noteworthy feature is the almost linear relationship between glycerol concentration and recorded peak height which is a consequence of combined effects of reaction kinetics and electrode Nernstian response.