Abstract: An optical oxygen (O-2) sensor consisting tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ditetrakis(4-chlorophenyl) borate adsorbed on silica gel has been successfully fabricated and used to continuously monitor O-2 gas at low concentration. The luminescence material shows a very strong and stable pink emission when excited by blue light and it is efficiently quenched by O-2. The calibration of the optical sensor can be simply done by a single standard flow injection method. The results demonstrate excellent linear Stern-Volmer behavior when O-2 concentration is at low levels (0.0-0.05% v/v), but the Stern-Volmer plot has a slightly downward curvature at higher O-2 levels. The two-site quenching model correlates well with the calibrated O-2 concentration range (0.0-0.55%). The t(95) response times of the sensor are <0.2 s on going from 0.0% to 0.55% O-2 and <1 s on going from 0.55% to 0.0% O-2. The sensor has high photostability a long lifetime and no hysteresis in the response.

Abstract: he organic dye, Erythrosin B, exhibits strong room-temperature phosphorescence (RTP) when adsorbed on non-ionic resins or when encapsulated in silicone rubber films. In this paper, oxygen transducers based on the RTP intensity quenching of the immobilized dye (on Amberlite XAD-2 or embedded in silicone) have been optically and analytically characterized using continuous and gas-phase flow injection systems. The sensing phases proved to have good photochemical stability. Detection limits of 0.0005% of oxygen in dry argon were found and sr values of around 0.3%(at 0.02% oxygen level) were achieved. Typical response times were less than 2 s for full signal change and no hysteresis in the response was observed.

Abstract: The dye Erythrosine B (which gives room-temperature phosphorescence, RTP) has been covalently bound to a silica-based amino-functionalized exchanger. The resulting material turned out to be extremely useful as a luminescent probe for oxygen. The photochemical properties and the analytical performance of the RTP probe have been studied by use of a gas flow injection analysis system, which incorporates a convenient exponential dilution chamber for gas sample introduction. The possible origin of the non-linear Stern-Volmer quenching response observed is thoroughly discussed in terms of the quenching and lifetimes. The proposed sensing material is particularly suitable for measuring oxygen in gas mixtures at extremely low concentrations. The detection limit attained was 0.00006% (0.6 ppm) of oxygen in dry argon (making the system one of the more sensitive opto sensors for oxygen published so far). A typical precision of±0.2%, at the 0.025% oxygen level, was achieved. Response times were less than 2 s for full signal change and no hysteresis effects were noticed. A possible mechanism for the observed oxygen RTP quenching in the new sensing material is proposed. (17 References)

Abstract: A perfluorinated ion-exchange membrane-based sensor suitable for electroanal. measurements in electrolyte-free media is described, which was assembled following a novel design enabling an easier preparation procedure. It was fabricated by inserting the terminal portion of a working Pt wire electrode into a Nafion tubing of suitable diameter and welding the wire thus wrapped to the bottom of a cell body by an insulating epoxy resin. The remainder upper part of the working electrode was covered by a Teflon tubing to avoid the elec. contact with the internal electrolyte introduced into the cell body, which was equipped with a counter and a reference electrode. As a result of this configuration, the actual working-electrode surface is the wire circumference contacted by the polyelectrolyte material at the bottom of the assembly which is exposed to the sample. The performance of this sensor was tested by cyclic voltammetry, amperometric monitoring and flow injection analysis for the electroanal. of a series of prototype analytes either dissolved in electrolyte-free water (H2O2, hydroquinone, ferricyanide, I- and Br-) or present in N2 atmospheres (triethylamine and O2). Detection limits for these analytes were estimated (s = 3), together with the corresponding ranges within which the responses display a linear dependence on the analyte concentration. The novel assembly is suitable only for the anal. in electrolyte-free liquid samples, while for the anal. of gaseous atmospheres, especially for flowing gases, ion-exchange membrane sensors prepared by the more usual procedure based on the use of working electrode materials embedded into a moist polyelectrolyte membrane should be preferred.