Determination of Henry’s constant using a photoacoustic sensor

We present a simple method for measuring Henry's constant k(H) of ethanol using photoacoustic spectroscopy. At T = 298.1 K the measured value for k(H) is (0.877 +/- 0.039) kPa (.) ka (.) mol(-1). Our data show that Henry's law is valid at ethanol Molalities between 0.1 mol (.) kg(-1) and 1.4 mol (.) kg(-1). The temperature dependence of Henry's constant was carefully examined by measuring the ethanol vapour pressure of six different aqueous solutions between T = 273.1 K and T = 298.1 K. By analysing the gas phase concentration and applying Henry's law, an ethanol molality of 0.864 mol (.) kg(-1) in the liquid phase can be measured with an error of +/-0.038 mol (.) kg(-1). The detection limit of the photoacoustic sensor is a gaseous-ethanol pressure of 10(-3) kPa. Ethanol molality changes as low as 1.10(-3) mol (.) kg(-1) can be measured

Coupling Fiber Optics to a Permeation Liquid Membrane for Heavy Metal Sensor Development

We present the first sensing system for metal ions based on the combination of separation/preconcentration by a permeation liquid membrane (PLM) and fluorescence detection with an optical fiber. As a model, a system for the detection of Cu(II) ions was developed. The wall of a polypropylene hollow fiber serves as support for the permeable liquid membrane. The lumen of the fiber contains the strip solution in which Cu(II) is accumulated. Calcein, a fluorochromic dye, acts as stripping agent and at the same time as metal indicator. The quenching of the calcein fluorescence upon metal accumulation in the strip phase is detected with a multimode optical fiber, which is incorporated into the lumen. Fluorescence is excited with a blue LED and detected with a photon counter. Taking advantage of the high selectivity and sensitivity of PLM preconcentration, a detection limit for Cu(II) of approximately 50 nM was achieved. Among five tested heavy metal ions, Pb(II) was the only major interfering species. The incorporation of small silica optical fibers into the polypropylene capillary allows for real-time monitoring of the Cu(II) accumulation process