Showing papers by "Purnendu K. Dasgupta published in 2007"
TL;DR: Cow's milk samples from Japan show high levels of perchlorate, which are higher on average than those found in U.S. dairy milk samples reported by a 2004 Food and Drug Administration study.
Abstract: Perchlorate has been considered a potential threat to human health, especially to developing infants and children due to its ability to inhibit iodide uptake by the sodium iodide symporter (NIS) of the thyroid. Although the U.S. has been the prime focus of perchlorate contamination, at least some of the similar sources of perchlorate exist across the world, and it has been detected in many types of foods and beverages worldwide. We present here perchlorate data from cow's milk samples from Japan (mean 9.4 ± 2.7 μg/L, n = 54), which are higher on average than those found in U.S. dairy milk samples reported by a 2004 Food and Drug Administration (FDA) study (5.9 ± 1.8 μg/L, n = 104).
108 citations
TL;DR: A general and sensitive method of detecting singly charged anions by ESI-MS and LC-ESI-MS as positive ions is proposed, which provides the lowest reported detection limits for a variety of anions, especially PFOA, nitrate, monochloroacetic acid, dichloro-acetic acids, and bromochloraic acid, among others.
Abstract: Anion analysis continues to be of great importance to many scientific and technical fields. We propose here a general and sensitive method of detecting singly charged anions by ESI-MS and LC−ESI-MS as positive ions. This method utilizes a dicationic reagent to form a complex with the anion that retains an overall positive charge for analysis by MS. Nitrate, thiocyanate, perchlorate, perfluorooctanoic acid (PFOA), halogenated acetic acids, and various other inorganic and organic anions and are investigated. The use of tandem mass spectrometry to enhance the detection limits of some of the anions is demonstrated. Chaotropic anions provided the lowest detection limits, with PFOA detected at the hundreds of femtograms level. Indeed, this single approach provides the lowest reported detection limits for a variety of anions, especially PFOA, nitrate, monochloroacetic acid, dichloroacetic acid, and bromochloroacetic acid, among others. The integrated areas and signal-to-noise ratios for five ions during a chroma...
87 citations
TL;DR: In this paper, a month of semi-continuous and simultaneous measurements of particulate chloride and nitrate and gaseous HCl and HNO3 concentrations were made in the Tampa, Florida, as part of the Bay Region Atmospheric Chemistry Experiment (BRACE).
66 citations
TL;DR: In this article, a significant amount of particulate H 2 Ox/oxalate (Ox) occurred in the coarse particle fraction of a dichotomous sampler, the ratio of oxalate concentrations in the PM 10 to PM 2.5 fractions ranged from 1 to 2, with mean±sd being 1.4±0.2.
62 citations
TL;DR: This analyzer demonstrates the robustness of the CL detection system for arsenic and provides an affordable alternative to atomic spectrometry for use as a detector after chromatographic speciation.
Abstract: We present a newly developed gas-phase chemiluminescence (CL) detection method for the separation and quantification of inorganic and organic arsenic species. Arsenite, arsenate, dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) were separated by anion exchange using carbonate−bicarbonate and NaOH eluents with step-gradient elution. The separated species were passed through a UV photooxidation reactor which decomposed the organic species and converted them to inorganic As(V). Subsequent on-line hydride generation with acid and sodium borohydride produces AsH3 and H2, which are separated from the liquid in a gas−liquid separator. The produced AsH3, driven by H2, reacts with ozone in a small reflective cell located atop a photomultiplier tube, resulting in intense CL. In the present form, the limits of detection (LODs, signal-to-noise = 3), based on peak height, for arsenite, arsenate, MMA, and DMA are 0.4, 0.2, 0.5, and 0.3 μg/L, respectively, for a 100 μL injected sample. This analyzer demonstr...
33 citations
TL;DR: This work investigated the merits and pitfalls of isoprene measurement via its chemiluminescence (CL) reaction with ozone via its warm column preconcentration and passage through Ag+-form cation-exchange resin, which removes divalent sulfur gases.
Abstract: Isoprene, involved in the biosynthetic pathway to cholesterol, is the prevalent hydrocarbon in breath. Breath isoprene measurement is of great interest as a measure of basal cholesterol production ...
32 citations
TL;DR: The TLD technique should be an attractive approach for online analysis of volatile chemical species in 'dirty' samples, especially for volatile analytes of higher molecular mass.
27 citations
TL;DR: In this article, the authors present reactions and spectra of ozone-induced chemical luminance (CL) for various compounds and techniques for detecting such CL, and discuss real gas applications where real gas samples were successfully measured.
Abstract: Chemiluminescence (CL) is a powerful analytical tool for trace gas measurements. In this mini-review, we present reactions and spectra of ozone-induced CL for various compounds and techniques for detecting such CL. Next discussed are CL applications where real gas samples were successfully measured. Chemiluminescence monitoring has been used as universal nitrogen and sulfur detectors for gas chromatography and capillary electrophoresis. Chemiluminescence detection can be used as the basis of compact, affordable, and sensitive analyzers for real-sample analysis. Isoprene and sulfur compounds in breath and atmospheric samples have been successfully measured by coupling with a small collection system. Short-term (5 min) sorbent collection enhances the CL signal and considerably reduces interference. For sulfur gas analysis, methyl mercaptan and dimethyl sulfide can be separated on the same column that is used for collection. Waterborne arsenic is measured by automated arsine generation and CL reaction of ars...
26 citations
TL;DR: A light emitting diode (LED) based multi-reflection capillary scale absorbance detector based on both square and round capillaries and compare their performance with a conventional single-pass on-tube detector is described and can indeed be of value for sensitive detection in microflow systems.
26 citations
TL;DR: In this paper, three semi-continuous methods for detecting nitric acid (HNO3) were tested against the annular denuder + filter pack (ADS) integrated collection technique at the Tampa Bay Regional Atmospheric Chemistry Experiment (BRACE) Sydney research station ∼ 20 km downwind of the Tampa, Florida, urban core.
21 citations
TL;DR: Limits of detection (LODs) are better than those previously observed with custom-synthesized dicationic agents and are readily attainable with a single-quadrupole mass spectrometer.
Abstract: Perchlorate and other hydrophobic ions can be measured with high sensitivity and selectivity by forming a positively charged ion pair with a dicationic agent. A commercially available reagent, 1,6-bis(trimethylammonium)hexane dibromide (Br(N(CH3)3)(CH2)6(N(CH3)3)Br) allows for the determination of perchlorate by electrospray ionization mass spectrometry as the [(N(CH3)3)(CH2)6(N(CH3)3)ClO4]+ ion. Limits of detection (LODs) are better than those previously observed with custom-synthesized dicationic agents. An LOD of 20 ng/L is readily attainable with a single-quadrupole mass spectrometer.
Patent•
12 Jun 2007TL;DR: In this paper, a sample concentrator for concentrating analytes in a solvent-containing liquid sample stream, including concentrator housing having a sample stream flow channel and a gas stream flow channels having an inlet and an outlet, a heater for gas in the gas stream conduit, and a hydrophilic ion exchange or non-ionic membrane barrier separating said stream flow and sample stream stream flow, is described.
Abstract: A sample concentrator for concentrating analytes in a solvent-containing liquid sample stream, including concentrator housing having a sample stream flow channel and a gas stream flow channel having an inlet and an outlet, a heater for gas in the gas stream conduit, and a hydrophilic ion exchange or non-ionic membrane barrier separating said gas stream flow channel and said sample stream flow channel. Solvent is evaporated from the liquid sample stream in said sample stream flow channel in or at the interface with said membrane, when the gas stream is at an elevated temperature. A regeneration step is used to regenerate the ion exchange membrane barrier.
TL;DR: It is shown that this selectivity order is easily achieved on recently described methracrylate-based monolithic capillary cation exchange columns (Ueki, Y.; Umemura, T.; Li, J. X.; Odake, T; Tsunoda, K.); and under such conditions, Li+ (and other alkali cations) elutes after NMe4+.
Abstract: Although ion exchange is often depicted as a process driven by electrostatic forces, ionic solvation or hydrophobic forces contribute greatly to ion exchange selectivity and is often the dominant factor. On a variety of commercial anion exchange columns, monovalent ClO4- elutes after doubly charged SO42- and even triply charged PO43-. For identically charged alkali metal ions, electrostatic charge densities based on crystal radii would suggest Li+ to be the most strongly retained on a cation exchanger. In practice, it is typically the least strongly held cation on most cation exchangers, because of its very high hydration energy and with most eluents its capacity factor approaches zero. Even when the ion is very poorly solvated, as with tetraalkylammonium (NR4+) cations, there has never been a report on a polymeric ion exchanger of an ideal electrostatic selectivity order where NR4+ cations elute in their increasing charge density order: R = n-butyl first, followed by n-propyl, ethyl, and last, methyl. W...
TL;DR: The platform and equipment used to make airborne measurements as part of the Bay Regional Atmospheric Chemistry Experiment (BRACE) were described in detail in this article, where a De Havilland DHC-6 Twin Otter was used to measure chemical and meteorological parameters during the BRACE field intensive in May, 2002.
TL;DR: The present system involves active mass transport radially outward through the walls of a tube, in which many of the traditional paradigms of flow through a tubular conduit no longer hold true.
Abstract: On-line sample concentration by evaporation through a narrow-bore membrane tube is described. The device can be deployed just prior to the detector or the sample may be concentrated prior to injection. As solution flows through a solvent-permeable membrane tube, (heated) drying gas (nitrogen/air) flows outside it to remove the solvent. The removal rate increases with increasing sample residence time, drying gas flow rate, and temperature. Various membranes and three concentrator designs (a rectangular maze, a serpentine and a filament-filled helix, the last performing the best) were fabricated and tested for post- and preseparation applications in suppressed anion chromatography. An order of magnitude concentration factors are readily obtained. The present system involves active mass transport radially outward through the walls of a tube. This is a system in which many of the traditional paradigms of flow through a tubular conduit no longer hold true. Because the flow rate continuously varies along the tu...
TL;DR: A DeHavilland DHC-6 Twin Otter was deployed in Tampa, FL to measure aerosols and primary and secondary trace gases in support of the Bay Regional Atmospheric Chemistry Experiment (BRACE) as discussed by the authors.
01 Jan 2007
TL;DR: In this paper, the authors report fully automated self-calibrating formaldehyde analyzers relying on a hybrid flow format and include operational scheme and design details, including syringe pumps.
Abstract: We report fully automated self-calibrating formaldehyde analyzers relying on a hybrid flow format and include operational scheme and design details. Long-term operation is made possible with the use of syringe pumps. Four identical analyzers were built and showed low LODs of 120 pptv or better (S/N =3) and good linearity over 0-50 ppbv HCHO concentration range (r 2 > 0.9960). The analyzer can resume normal operation after short-term power failure with at most two cycles of data loss following restart. Good agreement between analyzers was observed for either indoor or outdoor measurements. The use of an integrated HCHO calibration source and full control by the host computer via a graphical user interface program enables the instrument to switch between zero, calibration and sampling modes in a programmed automated manner. Detailed field data from deployment in three urban Texas locations from the summer of 2006 are presented and some features of the data are briefly discussed.