Showing papers by "Purnendu K. Dasgupta published in 2004"
TL;DR: The liquid-core waveguides have proved to be an important innovation that has led to improvements in detection limits when incorporated into many types of optical analysis systems, especially UV-Vis absorbance, fluorescence and Raman measurements.
Abstract: Optical chemical analysis systems are the most important tools to analytical chemists in need of sensitive measurement techniques. Liquid-core waveguides (Fig. 1) have proved to be an important innovation that has led to improvements in detection limits when incorporated into many types of optical analysis systems, especially UV–Vis absorbance, fluorescence and Raman measurements.
107 citations
TL;DR: A membrane-based collection/analysis system that differentially monitors H2S and CH3SH, and to which a conductometric SO2 analyzer using the same collector was coupled, which compared well with a standard procedure involving Tedlar bag collection, preconcentration and thermal desorption from a Tenax trap, and measurement by gas chromatography/flame photometric detection.
Abstract: We describe a membrane-based collection/analysis system that differentially monitors H2S and CH3SH, and to which a conductometric SO2 analyzer using the same collector was coupled. A diffusion scrubber (DS) comprised of a Nafion tube collects H2S selectively while a porous polytetrafluoroethylene (pPTFE) DS collects both H2S and CH3SH. Both gases are measured via their ability to react with fluorescein mercuric acetate (FMA) which results in decreased fluorescence. The limited dynamic range of a negative signal procedure was overcome by using dual DS units comprised of short and long scrubbers, placed serially in the liquid flow line. Different DS designs and membrane materials were investigated. H2S, CH3SH, and SO2 from a biogenic point source were continuously measured, and the H2S/CH3SH data compared well with a standard procedure involving Tedlar bag collection, preconcentration and thermal desorption from a Tenax trap, and measurement by gas chromatography/flame photometric detection. Walkaround portability of the instrument and very large dynamic range measurement of H2S and SO2 were demonstrated around the Mt. Aso volcano.
52 citations
TL;DR: Theoretical aspects and practical limitations of packed and open tubular capillary columns are considered in this paper, where applications of ICs are described and emerging technologies such as chip-scale IC and the use of monolithic columns are discussed.
Abstract: This review summarizes progress in capillary ion chromatography. Theoretical aspects and practical limitations of packed and open tubular capillary columns are considered. Applications of packed and open tubular capillary IC are described. Emerging technologies such chip-scale IC and the use of monolithic columns are discussed.
46 citations
TL;DR: A durable microfabricated humidity sensor made of interdigitated rhodium electrodes on a silicon substrate covered with a sensing film of Nafion perfluorosulfonate ionomer is described, able to attain crack-free Rh deposits by adaptation of pulsed electroplating techniques.
Abstract: We describe a durable microfabricated humidity sensor made of interdigitated rhodium electrodes on a silicon substrate covered with a sensing film of Nafion perfluorosulfonate ionomer. Rhodium electrodes are much less prone to oxidative degradation compared to previously described gold electrode-based sensors. Even with dc excitation, Rh electrode sensors exhibit excellent long-term response stability. It has been found that low-amplitude (+/-1 V) square wave excitation can prolong the usability of gold electrode-based sensors to at least several months; however, this mode of interrogation cannot provide subsecond response times. Rhodium deposition on the microsensors is much more difficult than that of gold. We were able to attain crack-free Rh deposits by adaptation of pulsed electroplating techniques. At excitation voltages of >2 V dc, the Rh sensors respond to moisture with 10 90% rise and fall times of 30-50 ms. These are the fastest microfabricated water vapor sensors reported to date. We demonstrate applications as a breath monitor. Such sensors should also be of utility in atmospheric eddy measurements. Short-term repeatability is better than 0.6% RSD (n = 7).
43 citations
TL;DR: A continuously wetted cellulose acetate membrane-based parallel plate diffusion denuder that has a small enough internal liquid holdup volume to permit reasonably rapid response time and quantitative removal of common soluble atmospheric trace gases at flow rates up to 1.7 L/min is described.
Abstract: A continuously wetted cellulose acetate membrane-based parallel plate diffusion denuder is described. This is the first membrane-based denuder that has a small enough internal liquid holdup volume to permit reasonably rapid response time (10 --> 90% rise time of approximately 1.2 min for a transient event at a liquid flow rate of 500 microL/min) while permitting quantitative removal of common soluble atmospheric trace gases at flow rates up to 1.7 L/min. The latter attribute permits the use of the device as the first element in a particle sampling and analysis system for the quantitative removal of potentially interfering soluble trace gases. Particle losses in the denuder range from 0.9 to 2.9% over an aerodynamic diameter range of 0.38-3.48 microm, averaging 1.8%. However, only approximately 0.5% of the particles actually appears in the denuder effluent liquid. The relatively compact (300 mm H x 57 mm W x 26 mm D) wet denuder should be attractive in a number of applications. We show excellent agreement for HONO measurements with a conventional larger parallel plate wetted denuder in field measurements.
29 citations
TL;DR: The application of hollow and filament-filled single asymmetric membrane fibers, consisting of a thin silicone layer on a tubular microporous support, for removing CO(2) in suppressed ion chromatography effluents is described, permitting better quantitation of poorly retained anions that elute close to the dip, allows practical gradient chromatography, and improves noise levels and attainable detection limits.
Abstract: The application of hollow and filament-filled single asymmetric membrane fibers, consisting of a thin silicone layer on a tubular microporous support, for removing CO2 in suppressed ion chromatography effluents is described. With appropriate choice of the removal device and operating conditions, the CO2 can be essentially quantitatively (99+%) removed. For carbonate-based eluents, the use of such devices greatly reduces or eliminates the water dip, permitting better quantitation of poorly retained anions that elute close to the dip, allows practical gradient chromatography, and improves noise levels and attainable detection limits. In hydroxide eluent chromatography, the device largely removes the response from CO2 present in the samples; this greatly aids atmospheric trace gas analysis by IC. Device dimensions are such that the dispersion introduced by the device is small.
24 citations
TL;DR: A novel AlGaN light-emitting diode (LED) fabricated on a sapphire substrate that has peak emission at 291 nm is used, demonstrating that a compact detector based on this LED and an off-the-shelf gated photodetection module can provide an LOD of 0.4 nM, thus providing a basis for convenient early warning detectors.
Abstract: Dipicolinic acid (DPA, 2,6-pyridinedicarboxylic acid) is a substance uniquely present in bacterial spores such as that from anthrax (B. anthracis). It is known that DPA can be detected by the long-lived fluorescence of its terbium chelate; the best limit of detection (LOD) reported thus far using a large benchtop gated fluorescence instrument using a pulsed Xe lamp is 2 nM. We use a novel AlGaN light-emitting diode (LED) fabricated on a sapphire substrate that has peak emission at 291 nm. Although the overlap of the emission band of this LED with the absorption band of Tb-DPA (λmax doublet: 273, 279 nm) is not ideal, we demonstrate that a compact detector based on this LED and an off-the-shelf gated photodetection module can provide an LOD of 0.4 nM, thus providing a basis for convenient early warning detectors.
24 citations
TL;DR: In this article, a flow-through PTFE tube was fabricated for the rapid decomposition of hydrogen peroxide (H 2 O 2 ) at concentrations up to 1 m. This was achieved at a mean reactor temperature of 108°C from a neutral aqueous solution with a mean residence time of ∼270 s.
23 citations
Patent•
19 Aug 2004TL;DR: In this article, a denuder assembly is adapted for the collection and removal of a gaseous analyte from a sample gas, where the denuder includes a housing including an internal cavity, a gas inlet fluidly coupled with the sample gas source, denuder liquid inlet and denuder source, and a barrier sheet extending across the internal cavity.
Abstract: A denuder assembly is adapted for the collection and removal of a gaseous analyte from a sample gas. The denuder includes a housing including an internal cavity, a sample gas inlet fluidly coupled with a sample gas source, a denuder liquid inlet fluidly coupled with a denuder liquid source, a barrier sheet extending across the internal cavity and separating the internal cavity into a liquid reservoir and a gas flow-through channel fluidly coupled with and downstream of the sample gas inlet, the barrier sheet having a liquid-reservoir surface and a gas-channel surface and being porous to gas and liquid; and a denuder liquid disposed in the liquid reservoir and permeating the barrier sheet to coat the gas-channel surface of the barrier sheet thereby allowing the denuder liquid on the gas-channel surface to contact the sample gas flowing within the gas flow-through channel and allowing the analyte to diffuse through the barrier sheet into the liquid reservoir. A method of using the denuder assembly for collection and removal of soluble atmospheric gases is also disclosed.
14 citations
TL;DR: Studies on the dependence of the pK(a) on the ionic strength or dielectric constant of the solution were conducted in an automated fashion by delivering NaCl solution or acetonitrile through an additional channel with good throughput and precision.
9 citations
20 Oct 2004
TL;DR: In this paper, an AlGaN light-emitting diode (LED) emitting with a peak wavelength at 291 nm and a radiant power of 0.5 mW @ 100 mA was fabricated on a sapphire substrate.
Abstract: An AlGaN Light-emitting diode (LED) emitting with a peak wavelength at 291 nm and a radiant power of 0.5 mW @ 100 mA was fabricated on a sapphire substrate. A compact gated fluorescence detection system was built using this LED as the excitation light source. We demonstrate that it provides sufficient power using Terbium enhanced fluorescence to detect subnanomolar concentrations of dipicolinic acid (DPA, 2, 6-pyridinedicarboxylic acid), a substance uniquely present in bacterial spores such as that from B. anthracis, providing a basis for convenient early warning detectors. We also describe initial results from a novel approach for biological aerosol detection using long lived fluorescence from a Europium tagged dye that binds to proteins.
Patent•
18 May 2004
TL;DR: In this article, a self-monitoring flow-through heater has been proposed, where the wire has a high specific resistivity and a high temperature coefficient of resistance, so that monitoring the voltage across and current flowing through the wire measures the mean temperature of the wire and of the fluid in the tube.
Abstract: A self-monitoring flow-through heater. The heater has a wire inside a tube, and the wire heats and monitors the temperature of a fluid flowing through the tube. The wire has a high specific resistivity and a high temperature coefficient of resistance, so that monitoring the voltage across and/or the current flowing through the wire measures the mean temperature of the wire and of the fluid in the tube.