Flow injection analysis of water vapour based on a fluorosensor Original Research Article

A new fluorimetric sensor incorporated with flow injection (FI) technique has been developed for water vapour quantification. The sensor was fabricated by immobilising rhodamine 6G in an organogel deposited on an overhead transparency film. The organogel was prepared from a solution of gelatine, rhodamine 6G and sodium bis(2-ethylhexyl)sulphosuccinate (AOT) in water–isooctane. Isooctane was employed as the organic solvent and AOT as the surfactant, thus forming water-in-oil microemulsions with a high capacity for water solubilisation. The organogel-based optode membrane showed a strong fluorescence at 564 nm when it was excited at 540 nm. The fluorescence intensity of the optode membrane at 564 nm decreased upon exposure to water vapour. The sensing system exhibited a relatively wide linear dynamic range from 0.252 to 2.52 kPa water vapour pressure and also demonstrated a good linearity (correlation coefficient was 0.9912) at 20.0°C and 1 atm pressure. The sensor had good repeatability, photostability and long-term stability. Oxygen, carbon dioxide gases, acetone, toluene, ethanol, chloroform, acetic acid vapours and NOx did not cause any interference. The addition of AOT to the organogel was shown to enhance the sensitivity for the detection of water vapour and also shortened the exposure and recovery times in which 1 cycle of FI was completed within 1 min.