Showing papers by "Purnendu K. Dasgupta published in 2010"
TL;DR: The recent methods cover both established and emerging analytical disciplines and include naked eye visual detection, spectrophotometry/colorimetry, capillary electrophoresis with optical absorbance detection, fluorometry, chemiluminescence, near-infrared cavity ring down spectroscopy, atomic absorption spectrometry, electrochemical methods.
318 citations
TL;DR: In this paper, the authors measured ambient formaldehyde (HCHO) concentrations using a fluorometric instrument based on a diffusion scrubber and the Hantzsch reaction; hydrocarbons were simultaneously measured using gas chromatography-mass spectrometry (GC-MS).
77 citations
TL;DR: In this paper, the authors report on HCHO measurements in the Houston-Galveston Airshed (HGA) from summer 2006, showing that the HCHO/PAN ratios at the Moody Tower (MT) site close to downtown were dependent on the wind direction: southerly maritime winds brought in background levels (0.5-1 ppbv) while trajectories originating in the HSC resulted in high HCHO (up to 31.5 ppbV).
Abstract: . The Houston-Galveston Airshed (HGA) is one of the major metropolitan areas in the US that is classified as a nonattainment area of federal ozone standards. Formaldehyde (HCHO) is a key species in understanding ozone related air pollution; some of the highest HCHO concentrations in North America have been reported for the HGA. We report on HCHO measurements in the HGA from summer 2006. Among several sites, maximum HCHO mixing ratios were observed in the Houston Ship Channel (HSC), a region with a very high density of industrial/petrochemical operations. HCHO levels at the Moody Tower (MT) site close to downtown were dependent on the wind direction: southerly maritime winds brought in background levels (0.5–1 ppbv) while trajectories originating in the HSC resulted in high HCHO (up to 31.5 ppbv). Based on the best multiparametric linear regression model fit, the HCHO levels at the MT site can be accounted for as follows: 38.5±12.3% from primary vehicular emissions (using CO as an index of vehicular emission), 24.1±17.7% formed photochemically (using peroxyacetic nitric anhydride (PAN) as an index of photochemical activity) and 8.9±11.2% from industrial emissions (using SO2 as an index of industrial emissions). The balance 28.5±12.7% constituted the residual which cannot be easily ascribed to the above categories and/or which is transported into the HGA. The CO related HCHO fraction is dominant during the morning rush hour (06:00–09:00 h, all times are given in CDT); on a carbon basis, HCHO emissions are up to 0.7% of the CO emissions. The SO2 related HCHO fraction is significant between 09:00–12:00 h. After 12:00 h HCHO is largely formed through secondary processes. The HCHO/PAN ratios are dependent on the SO2 levels. The SO2 related HCHO fraction at the downtown site originates in the ship channel. Aside from traffic-related primary HCHO emissions, HCHO of industrial origin serves as an appreciable source for OH in the morning.
62 citations
TL;DR: It is reported here that a narrow capillary can be used to hydrodynamically separate a wide size range of DNA fragments in a single run without the need for gels, wall coatings, or an electric field.
Abstract: Gel electrophoresis is commonly used to separate DNA, but narrow capillaries or microchannels desired for high throughput efficient separations are difficult to fill with gels. We report here that a narrow capillary can be used to hydrodynamically separate a wide size range of DNA fragments in a single run without the need for gels, wall coatings, or an electric field. We also demonstrate that attractive separation is possible in a few minutes and that the separated DNA can be collected into individual fractions that remain viable for amplification via the polymerase chain reaction.
57 citations
TL;DR: A novel cyanide analyzer based on sensitive cobinamide chemistry relies on simultaneous reagent and sample injection and detection in a 50 cm liquid core waveguide (LCW) flow cell illuminated by a white light emitting diode, demonstrating applicability by analyzing the hydrolytic cyanide extract of apple and pear seeds with orange seeds as control and also measuring HCN in breath air samples.
Abstract: A novel cyanide analyzer based on sensitive cobinamide chemistry relies on simultaneous reagent and sample injection and detection in a 50 cm liquid core waveguide (LCW) flow cell illuminated by a white light emitting diode. The transmitted light is read by a fiber-optic charge coupled device (CCD) spectrometer. Alkaline cobinamide (orange, λmax = 510 nm) changes to violet (λmax = 583 nm) upon reaction with cyanide. Multiwavelength detection permits built-in correction for artifact responses intrinsic to a single-line flow injection system and corrects for drift. With optimum choice of the reaction medium, flow rate, and mixing coil length, the limit of detection (LOD, S/N = 3) is 30 nM and the linear dynamic range extends to 10 μM. The response base width for 1% carryover is <95 s, permitting a throughput of 38 samples/h. The relative standard deviations (rsd) for repetitive determinations at 0.15, 0.5, and 1 μM were 7.6% (n = 5), 3.2% (n = 7), and 1.7% (n = 6), respectively. Common ions at 250−80 000× c...
45 citations
TL;DR: In this paper, a matrix-isolated reaction chemistry based measurement of arsenic in water down to submicrograms per liter levels in a system that requires only air, water, electricity, and dilute sulfuric acid, the bulk of the latter being recycled.
Abstract: We describe matrix-isolated, reaction chemistry based measurement of arsenic in water down to submicrograms per liter levels in a system that requires only air, water, electricity, and dilute sulfuric acid, the bulk of the latter being recycled. Gas phase chemiluminescence (GPCL) measurement of arsenic is made in an automated batch system with arsenic in situ electroreduced to arsine that is reacted with ozone to emit light. The ozone is generated from oxygen that is simultaneously anodically produced. Of 22 different electrode materials studied, graphite was chosen as the cathode. As(V) is reduced much less efficiently to AsH3 than As(III). Prereducing all As to As(III) is difficult in the field and tedious. Oxidizing all As to As(V) is simple (e.g., with NaOCl) but greatly reduces subsequent conversion to AsH3 and hence sensitivity. The rate of the AsH3−O3 GPCL reaction and hence signal intensity increases with [O3]. Using oxygen to feed the ozonizer produces higher [O3] and substantial signal enhanceme...
36 citations
TL;DR: A novel system to analyze atmospheric nitrophenols (NPs) in both rain and air of Houston and Arlington, TX is reported and Illustrative air and rain data are presented.
Abstract: We report a novel system to analyze atmospheric nitrophenols (NPs). Rain or air sample extracts (1 mL) are preconcentrated on a narrow bore (2 mm) aliphatic anion exchanger. In the absence of strong retention of NPs exhibited by aromatic ion exchangers, retained NPs are eluted as a plug by injection of 100 microL of 0.1 M Na(2)SO(4) on to a short (2 x 50 mm) reverse phase C-18 column packed with 2.2 mum particles. The salt plug passes through the C-18 column unretained while the NPs are separated by an ammonium acetate buffered methanol-water eluent, compatible with mass spectrometry (MS). The eluted NPs are measured with a long path Teflon AF-based liquid core waveguide (0.15 x 1420 mm) illuminated by a 403 nm light emitting diode and detected by a monolithic photodiode-operational amplifier. The waveguide is rendered chemically active by suspending it over concentrated ammonia that permeates into the lumen. The NPs ionize to the yellow anion form (lambda(max) approximately 400 nm). The separation of 4-nitrophenol, 2,4-dinitrophenol, 2-methyl-4-nitrophenol, 3-methyl-4-nitrophenol, and 2-nitrophenol (these are the dominant NPs, typically in that order, in both rain and air of Houston and Arlington, TX, confirmed by tandem MS) takes just over 5 min with respective S/N = 3 limits of detection (LODs) of 60, 12, 30, 67, and 23 pg/mL compared to MS/MS LODs of 20, 49, 11, 20, and 210 pg/mL. Illustrative air and rain data are presented.
28 citations
TL;DR: An automated atmospheric elemental mercury analyzer based on the dielectric barrier discharge (DBD) atomic emission technique was developed and applied to the determination of atmospheric mercury in two different locations.
27 citations
TL;DR: It is shown that power transforms also increase signal-to-noise ratio and make it easier to discern an event of detection, however, they may not improve the limit of detection.
Abstract: Power transformations are commonly used in image processing techniques to manipulate image contrast. Many analytical results, including chromatograms, are essentially presented as images, often to convey qualitative information. Power transformations have remarkable effects on the appearance of the image, in chromatography, for example, increasing apparent resolution between peaks by the factor √n and apparent column efficiency (plate counts) by a factor of n for an nth-power transform. The profile of a Gaussian peak is not qualitatively changed, but the peak becomes narrower, whereas for an exponentially tailing peak, asymmetry at the 10% peak height level changes markedly. Using several examples we show that power transforms also increase signal-to-noise ratio and make it easier to discern an event of detection. However, they may not improve the limit of detection. Power responses are intrinsic to some detection schemes, and in others they are imbedded in instrument firmware to increase apparent linear range that the casual user may not be aware of. The consequences are demonstrated and discussed.
25 citations
TL;DR: Henry's Law constant (K(H), M/atm) for the vapor-solution equilibrium of HCN was determined in 0.1 M sodium phosphate buffer from 287-311 K via air equilibration of aqueous cyanide partitioned by a microporous membrane.
Abstract: Primary data for the temperature dependent solubility of HCN in water do not presently exist for low concentrations of HCN at environmentally or physiologically relevant temperatures. Henry’s Law c...
23 citations
TL;DR: In the present charge detector (ChD), ions are actually removed, leading to further ionization and the detection of a proportionately greater analyte amount, resulting in identical calibration curves for all strong acid anions, obviating individual calibrations.
Abstract: We describe a flow-through ionic charge detector in the form of a three-compartmented system A central water channel is separated from two outer channels bearing water (or a dilute electrolyte) by a cation-exchange membrane (CEM) and an anion-exchange membrane (AEM) Independent fluid input/output ports address all channels One platinum electrode is put in each outer channel When the AEM-side electrode is positive with respect to the CEM-side electrode and voltage (∼1−10 V) is applied, the observed background current is from the transport of H+/OH− through the CEM/AEM to the negative/positive electrodes, respectively The H+ and OH− are generated by the ionization of water, in part aided by the electric field If an electrolyte (X+Y−) is injected in to the central channel, X+ and Y− migrate through the CEM and AEM to the negative and positive electrodes, respectively, and generate a current pulse The integrated area of the current signal (coulombs) elicited by this electrolyte injection is dependent o
TL;DR: In this work power functions applied to chromatographic data are discussed in the context of (a) complex separation problems, (b) 2D-HPLC separations, and (c) post-column reaction detectors.
TL;DR: An inexpensive sensitive gas-phase chemiluminescence (GPCL) based analyzer for arsenic is described and compared with results obtained by inductively coupled plasma-mass spectrometry (ICP-MS) as well as those from an automated GPCL analyzer.
TL;DR: This paper presents a simple to use "spreadsheet calculator" for concentric annular denuders of any dimension based on known solutions to analogous heat transfer problems and results from a commercial computational fluid dynamics package are compared.
TL;DR: An open channel scrubber is proposed as a miniature fieldable gas collector with superior collection efficiencies at relatively high sample air flow rates and is expected to lead development of an excellent micro-gas analysis system integrated with a detector for continuous measurements.
TL;DR: It is shown that incorporating α-cyclodextrin in an 890 nm thick Triton-X-100 film allows, in a single stage, a high degree of chirally selective transport (1.6:1) of α(+)-pinene over α(--pinene).
Abstract: Soap films can not only be made with sub-μm thickness, they can have intrinsic permeabilities comparable to many commercial membranes, permitting very high transmembrane flux. Soap films readily incorporate a wide range of modifiers to allow highly tailored selectivity: We show that incorporating α-cyclodextrin in an 890 nm thick Triton-X-100 film allows, in a single stage, a high degree of chirally selective transport (1.6:1) of α(+)-pinene over α(-)-pinene.
TL;DR: It is shown that the electrodialytic introduction of aromatic dye anions is readily possible through both unmodified cellulose dialysis membranes and through cellulose membranes modified with methacrylate skeleton anion exchangers.
Abstract: We report on electrodialytic introduction of ionizable molecules of significant size (e.g., 4-(2-pyridyl(azo) resorcinol, PAR)) in capillary scale flow systems. Such reagent introduction can be conducted without volumetric dilution, easily programmed through current control and with excellent mixing characteristics. Electrodialytic transport of large hydrophobic aromatic ions through conventional aromatic ion exchangers is inefficient. Such ions are strongly retained by hydrophobic and pi-pi interactions. An external electric field cannot modulate this retention. We show that the electrodialytic introduction of aromatic dye anions is readily possible through both unmodified cellulose dialysis membranes and through cellulose membranes modified with methacrylate skeleton anion exchangers. The applied electrodialysis current conveniently controls the reagent flux. Although the applied voltage is sufficient to cause electrolytic production of hydrogen and oxygen; the gases are generated outside the flowstream of interest. The present device was constructed with a sub-microliter internal volume. We show capillary scale trace analysis of transition metals. A limit of detection of 0.5 fmol Zn (S/N = 3) is demonstrated with a capillary scale flow injection system with a simple light emitting diode based detector.
TL;DR: A fully automated measurement system for ambient aerosol organic carbon, capable of unattended operation over extended periods, is described and provides information on the ease of oxidation of thecarbonaceous aerosol and hence the nature of the carbon contained therein.
Abstract: A fully automated measurement system for ambient aerosol organic carbon, capable of unattended operation over extended periods, is described. Particles are collected in a cyclone with water as the collection medium. The collected sample is periodically aspirated by a syringe pump into a holding loop and then delivered to a wet oxidation reactor (WOR). Acid is added, and the WOR is purged to measure dissolved CO2 or inorganic carbonates (IC) as evolved CO2. The IC background can often be small and sufficiently constant to be corrected for, without separate measurement, by a blank subtraction. The organic material is now oxidized stepwise or in one step to CO2. The one-step oxidation involves UV-persulfate treatment in the presence of ozone. This treatment converts organic carbon (OC) to CO2, but elemental carbon is not oxidized. The CO2 is continuously purged from solution and collected by two sequential miniature diffusion scrubbers (DSs), a short DS preceding a longer one. Each DS consists of a LiOH-fill...
01 Nov 2010
TL;DR: In this paper, a simple and robust sensing platform for detection of biological materials is reported, which combines the combined use of dye-doped nanoparticle tags and nanoporous high surface area (∼1,400 m2/g) films to achieve high intrinsic signal amplification.
Abstract: In this paper, a simple and robust sensing assay platform for detection of biological materials is reported. The fluorescence based sensing platform benefits from the combined use of our novel dye-doped nanoparticle tags and nanoporous high surface area (∼1,400 m2/g) films to achieve high intrinsic signal amplification. The dye-doped nanoparticles are synthesized from poly-methylsilsesquioxane (PMSSQ) encapsulating fluorescent dye molecules that can be conjugated to antibodies and proteins. We have achieved conjugation of up to 64 dye molecules per single antibody, which represents more than an order of magnitude increase in conjugation efficiency compared to conjugation of free dye molecules. Capture of the dye-doped nanoparticle labeled antibodies by nanoporous organosilicate (NPO) films has yielded 540 fold increase in fluorescence response compared to immobilization of dye labeled antibodies on (flat) glass substrates. This assay demonstrates a general way for detection of analytes in very low concentration.