Showing papers by "Purnendu K. Dasgupta published in 1998"

High-Sensitivity Gas Sensors Based on Gas-Permeable Liquid Core Waveguides and Long-Path Absorbance Detection

Abstract: A new fluoropolymer is proposed as the basis of a novel class of sensors. The devices are based on selective chromogenic reactions and in situ long-path optical absorbance measurement. The polymer is transparent from 200 to 2000 nm and has the lowest known refractive index (RI) of any synthetic polymer. The RI is less than that of water. A tube of this material, filled with an aqueous solution (or virtually any other liquid), behaves as a liquid core optical fiber. As a result, long-path length optical cells are possible without significant loss of light. The material is highly permeable to a number of trace gases of environmental interest. Relative to common poly(tetrafluoroethylene) (PTFE)-type Teflon, the new amorphous fluoropolymer (Teflon AF 2400) is more than 3 orders of magnitude more permeable to many gases. If a Teflon AF tube is filled with a reagent that responds to a gaseous analyte by undergoing a change that is spectroscopically detectable, an unusually versatile, sensitive, and inexpensive ...

Chemical sensing techniques employing liquid-core optical fibers

Abstract: A gas or vapor permeable optical fiber waveguide with a liquid core is employed as a probe for the detection or measurement of a chemical specie of interest by filling the waveguide core region with a reagent liquid which undergoes a change in an optical characteristic thereof when exposed to the chemical specie and then inserting the filled waveguide into an environment in which the chemical specie may be present. The chemical specie, if present, will permeate through the waveguide wall and react with or be absorbed in the core liquid. Sensitivity is enhanced by controlling the pressure differential across the waveguide wall and/or by shaping the waveguide to enlarge the surface area. When the reaction generates light, the devices which detect that light will be shaped and disposed to maximize the collection thereof.

Measurement of Diffusive Flux of Ammonia from Water

Abstract: An instrument was developed for the measurement of gaseous ammonia concentration, NH(3(sw,eq)), in equilibrium with surface waters, notably ocean water. The instrument measures the ammonia flux from a flowing water surface under defined conditions and allows the calculation of NH(3(sw,eq)) from the principles of Fickian diffusion. The flux collector resembles a wetted parallel plate denuder previously developed for air sampling. The sample under study runs on one plate of the device; the ammonia released from the sample is collected by a slow flow of a receptor liquid on the other plate. The NH(3) + NH(4)(+) (hereinafter called N(T)) in the effluent receptor liquid is preconcentrated on a silica gel column and subsequently measured by a fluorometric flow injection analysis (FIA) system. With a 6-min cycle (4-min load, 2-min inject), the analytical system can measure down to 0.3 nM N(T) in the receptor liquid. Coupled with the flux collector, it is sufficiently sensitive to measure the ammonia flux from seawater. The instrument design is such that it is little affected by ambient ammonia. In both laboratory (N(T) 0.2-50 μM), and field investigations (N(T) 0.18-1.7 μM) good linearity between the ammonia flux and the N(T) concentration in seawater (spiked, synthetic, natural) was observed, although aged seawater, with depleted N(T) content, behaves in an unusual fashion upon N(T) addition, showing the existence of an "ammonia demand". NH(3(sw,eq)) levels from ocean water measured in the Coconut Island Laboratory, HI, ranged from 6.6 to 33 nmol/m(3) with an average of 17.4 ± 6.9 nmol/m(3), in comparison to 2.8-21 nmol/m(3) (average 10 ± 7 nmol/m(3)) NH(3(sw,eq)) values previously reported for the Central Pacific Ocean (Quinn, P. K.; et al. J. Geophys. Res. 1990, 95, 16405-16416).

Indoor Air Pollution and Sick Building Syndrome. Monitoring Aerosol Protein as a Measure of Bioaerosols

Abstract: Excess aerosol protein concentration is suggested to be a diagnostic marker for biological causes of impaired air quality of a building. A simple inexpensive instrument has been developed to measure aerosol protein concentration. Aerosol particles are collected by allowing injected steam to condense upon them, thus resulting in their growth, followed by cooling and impaction. The liquid stream, bearing dissolved and suspended aerosol constituents, is put through a silica preconcentration column that is eluted subsequently with dilute H3PO4. The eluite stream is reacted with acidic Coomassie blue G; the color of the protein-dye adduct is detected by optical absorbance at ∼600 nm. Optimization efforts have been carried out to choose the best stationary phase for protein preconcentration and reagent composition. In liquid-phase experiments, bovine serum albumin (BSA) displays a limit of detection (LOD) of 16 ng. In aerosol experiments, there is some increased noise and the LOD deteriorates by ∼2×. The system...

Chemical sensing method and apparatus employing liquid-core optical fibers

Abstract: of EP0909946A permeable optical fiber waveguide 10 with a liquid core 12 is employed as a probe for the detection or measurement of a chemical specie of interest by filling the waveguide core region with a light transmitting reagent liquid 12' which undergoes a change in an optical characteristic thereof when exposed to the chemical specie and then inserting the filled waveguide 10 into an environment in which the chemical specie may be present. The chemical specie, if present, will permeate through the waveguide wall and react with or be absorbed in the core liquid.