A pH optode based on thymol blue: application to determination of CO2 using flow injection analysis system

Abstract

An optode based on thymol blue (TB), an acid-based indicator, has been constructed and evaluated as a detector in FIA system for CO 2 determination. The dye was chemically immobilised on the surface of a bifurcated glass optical fibre bundle, using silanisation in organic media. In FIA system, hydrogen carbonate or carbonate samples are injected in a buffer carrier solution, and then are mixed with phosphoric acid solution to generate CO 2 , which diffuses through a PTFE membrane, in order to be collected in an acceptor carrier fluid, pumped towards to detection cell, in which the optode was adapted. The proposed system presents two linear response ranges, from 1.0 x 10 -3 to 1.0 x 10 -2 mol l -1 , and from 2.0 x 10 -2 to 0.10 mol l -1 . The sampling frequency was 11 sample h -1 , with good repeatability (R.S.D < 4 %, n = 10). In flow conditions the optode lifetime was 170 h. The system was applied in the analysis of commercial mineral water and the results obtained in the hydrogen carbonate determination did not differ significantly from those obtained by potentiometry, at a confidence level of 95 %.

Use of In‐Situ Methods

“…emission of fluorescent light) and this forms the basis of operation these sensors. These devices are frequently used to measure oxygen (Prien, 2007), but they can also be used for pH and pCO 2 (Zhu et al ., 2005;Schroeder et al ., 2007;Sotomayor et al ., 2010).…”