Abstract: A new fluorimetric sensor incorporated with flow injection (FI) technique has been developed for water vapor 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 vapor. The sensing system exhibited a relatively wide linear dynamic range from 0.252 to 2.52 kPa water vapor 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 vapors and NO, did not cause any interference. The addition of AOT to the organogel was shown to enhance the sensitivity for the detection of water vapor and also shortened the exposure and recovery times in which 1 cycle of Fl was completed within 1 min.

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: A mathematical response function derived from the Stern-Volmer equation was successfully applied to calibrate an optical oxygen (O2) sensor using tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(ii) ditetrakis(4-chlorophenyl)borate adsorbed on silica gel as the O2-sensitive material. The calibration of this optical sensor can be simply done by plotting the reciprocal of the luminescence intensity against the O2 concentration (1/I vs. [O2]). A single air sample injection method combined with an exponential dilution technique produces O2 standards at various concentrations. The modified Stern-Volmer plots demonstrate excellent agreement with the well known Stern-Volmer plot (I0/I vs. [O2]). The proposed method has the advantages of simple O2 standard preparation and no I0 data being needed for calibration. The response and recovery times of the optical O2 sensor are less than 0.2 and 1 s, respectively. The limit of detection is 2.6-3.6 ppm v/v. The photostability of the O2-sensitive material is good and there is no sign of photodegradation after 12 h of continuous use.