Purnendu K. Dasgupta

Bio: Purnendu K. Dasgupta is an academic researcher from University of Texas at Arlington. The author has contributed to research in topics: Ion chromatography & Detection limit. The author has an hindex of 62, co-authored 506 publications receiving 16779 citations. Previous affiliations of Purnendu K. Dasgupta include Dow Chemical Company & Texas Tech University.

Polymethylmethacrylate open tubular ion exchange columns: nondestructive measurement of very small ion exchange capacities.

Abstract: We describe an approach to prepare an open tubular ion exchange (OTIE) column by coating a monolayer of anion exchange nanoparticle to a 16–20 μm bore polymethylmethacrylate (PMMA) capillary. The latex nanoparticle was electrostatically attached to carboxylate groups on the inner wall of capillary, pretreated with strong base for hydrolyzing the ester. Several approaches to nondestructively measure ion exchange capacities (IEC) of the columns were examined: (a) adsorption–desorption of an intensely fluorescent ion, e.g. fluorescein, and off-line fluorometry, (b) loading a weakly retained ion (e.g., IO3–), frontal displacement by a strongly bound ion (e.g., Cl–), and online optical or conductometric boundary detection, and (c) similar to the above except displacement being accompanied by reaction (e.g., acid–base titration). To our knowledge, this is the first time on-column titration has been used to measure capacities. By using different pH displacer solutions, we demonstrate for the first time the possi...

Measurement of acid dissociation constants of weak acids by cation exchange and conductometry

Abstract: A simple strategy is presented for the determination of acid dissociation constants based on the measurement of conductance of a known concentration of the acid and/or the conductance of a solution of its fully or partially neutralized alkali-metal salts. For an n-protic acid, 2n conductance measurements are minimally necessary. In the simplest case of a typical monoprotic acid, the conductance of its alkali salt solution is measured before and after passage through an H{sup +}-form exchanger. From these data both the pK{sub a} of the acid and the equivalent conductance of the anion can be computed. The underlying equations are rigorously solved for monoprotic acids and some diprotic acid systems. For other diprotic and multiprotic acid systems, initial estimates are obtained by making approximations; the complete data set is then subjected to multiparametric fitting. The method does not require pH measurements; conductance can generally be measured accurately at low enough ionic strengths to obviate the need for major activity correction. Several experimental measurements are presented and excellent agreement with literature pK{sub a} values is observed. The reliability of the equivalent conductance values computed in this fashion is limited, however.

Enhancement and quenching of fluorescence of metal chelates of 8-hydroxyquinoline-5-sulfonic acid

Abstract: Fluorescence enhancement of 8-hydroxyquinoline-5-sulfonic acid complexes of Mg, Ca, Sr, Ba, Al, Zn and Cd were studied in micellar and hydroorganic solvents Al is extraordinarily amenable to both types of fluorescence enhancement, an order of magnitude to two order of magnitude enhancement of fluorescence intensity has been observed with aqueous hexadecyltrimethylammonium chloride (HTAC) and certain mixed aqueous-organic solvents Fe(III) appears to be an unusually powerful fluorescence quencher in these systems — the effect is noticeable in low micromolar concentrations and is greatly amplified by cationic surfactants such as HTAC

Membrane based concentrators

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.

The origins and the future of microfluidics

Abstract: The manipulation of fluids in channels with dimensions of tens of micrometres--microfluidics--has emerged as a distinct new field. Microfluidics has the potential to influence subject areas from chemical synthesis and biological analysis to optics and information technology. But the field is still at an early stage of development. Even as the basic science and technological demonstrations develop, other problems must be addressed: choosing and focusing on initial applications, and developing strategies to complete the cycle of development, including commercialization. The solutions to these problems will require imagination and ingenuity.

Intrinsic peroxidase-like activity of ferromagnetic nanoparticles

Abstract: Nanoparticles containing magnetic materials, such as magnetite (Fe3O4), are particularly useful for imaging and separation techniques. As these nanoparticles are generally considered to be biologically and chemically inert, they are typically coated with metal catalysts, antibodies or enzymes to increase their functionality as separation agents. Here, we report that magnetite nanoparticles in fact possess an intrinsic enzyme mimetic activity similar to that found in natural peroxidases, which are widely used to oxidize organic substrates in the treatment of wastewater or as detection tools. Based on this finding, we have developed a novel immunoassay in which antibody-modified magnetite nanoparticles provide three functions: capture, separation and detection. The stability, ease of production and versatility of these nanoparticles makes them a powerful tool for a wide range of potential applications in medicine, biotechnology and environmental chemistry.

Hormones and endocrine-disrupting chemicals: Low-dose effects and nonmonotonic dose responses

Abstract: For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of “the dose makes the poison,” because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from...

2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum

Abstract: Background: Thyroid disease in pregnancy is a common clinical problem. Since the guidelines for the management of these disorders by the American Thyroid Association (ATA) were first published in 2...