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.

Postcolumn Concentration in Liquid Chromatography. On-Line Eluent Evaporation and Analyte Postconcentration in Ion Chromatography

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...

Electrodialytic Reagent Introduction in Flow Systems

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.

Concurrent High-Sensitivity Conductometric Detection of Volatile Weak Acids in a Suppressed Anion Chromatography System

Abstract: A suppressed hydroxide eluent anion chromatograph effluent flows through the outside of a gas-permeable membrane tube while electrogenerated 100–200 μM LiOH flows through the lumen into a second conductivity detector. Undissociated volatile acid eluites (e.g., H2S, HCN, H2CO3, etc., represented as HA) transfer through the membrane and react as OH– + HA → A– + H2O; the conversion of high-mobility OH– to lower mobility A– results in a significant negative response for these analytes. With the chromatograph operated at a macroscale (0.3 mL/min) the LiOH flow can be 3–30-fold lower, resulting in corresponding enrichment of the transferred analyte prior to detection. Because there is no mixing of liquids, the detector noise is very low (<0.1 nS/cm), comparable to the principal chromatographic detector. Thus, despite a background of 25–45 μS/cm, limits of detection for sulfide and cyanide are in the submicromolar level, with a linear dynamic range up to 100 μM. Carbonate/bicarbonate can also be sensitively dete...

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...