Showing papers by "Purnendu K. Dasgupta published in 2015"
TL;DR: A new electrodialytic separation concept that permits simultaneous matrix isolation, preconcentration, and chromium speciation is presented and it is shown that effects of salinity can be eliminated with proper membrane functionalization and receptor optimization.
Abstract: Large amounts of chromium (Cr) compounds are used for manufacturing of various products and various chemical processes. Some inevitably find their way into the environment. Environmental Cr is dominantly inorganic and is either in the cationic +3 oxidation state or in the anionic oxochromium +6 oxidation state. The two differ dramatically in their implications; Cr(III) is essential to human nutrition and even sold as a supplement, while Cr(VI) is a potent carcinogen. Drinking water standards for chromium may be based on total Cr or Cr(VI) only. Thus, Cr speciation analysis is very important. Despite their high sensitivity, atomic spectrometric techniques or induction coupled plasma-mass spectrometry (ICP-MS) cannot directly differentiate the oxidation states. We present here a new electrodialytic separation concept. Sample analyte ions are quantitatively transferred via appropriately ionically functionalized dialysis membranes into individual receptors that are introduced into the ICP-MS. There was no significant conversion of Cr(VI) to Cr(III) or vice versa during the very short (6 s) separation process. Effects of salinity (up to ∼20 mM NaCl) can be eliminated with proper membrane functionalization and receptor optimization. With the ICP-MS detector we used, the limits of detection for either form of Cr was 0.1 μg/L without preconcentration. Up to 10-fold preconcentration was readily possible by increasing the donor solution flow rate relative to the acceptor solution flow rates. The proposed approach permits simultaneous matrix isolation, preconcentration, and chromium speciation.
35 citations
TL;DR: The device was applied to the determination of Fe, Cu and Zn in equine and bovine serum; the reproducibility was better than conventional digestion method and could be ameliorated by transient instead of continuous sample introduction.
13 citations
TL;DR: Based on its mixing efficiency and small dispersion, the BT design was found to be the best for practicing postcolumn reaction and was then used to introduce electrogenerated LiOH in a suppressed ion chromatography system to perform sensitive detection of weak acids in a second dimension.
Abstract: Three mixer designs, a back-flow tee mixer (BT), an end-blocked membrane tee mixer (EMT), and a tubular membrane mixer (TM), were fabricated and compared to three commercially available mixers, Visco-Jet Micro mixer (VJM) and HS binary tee mixer with 2 and 10 μL volume (HS-2 and HS-10) mixing cartridges. Internal volumes ranged from 8.3 to 20.3 μL. Performance characteristics were evaluated by the Villermaux–Dushman reaction, noise in baseline conductance upon mixing an electrolyte solution with water, and dispersion/relative dispersion of an injected solute. No single characteristic would uniquely qualify a particular device. In typical postcolumn use when a small reagent flow is added to a principal flow stream using a low-pulsation high-end chromatographic pump, with the worst of these mixers, imperfect mixing accounted for 99.6% of the observed noise. EMT, BT, and TM with asymmetric inlets provided better mixing performances relative to VJM, HS-2, and HS-10 with symmetric inlet ports, especially when ...
12 citations
TL;DR: Limits of detection for sulfide and cyanide are in the submicromolar level, with a linear dynamic range up to 100 μM, and Carbonate/bicarbonate can also be sensitively detected.
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...
11 citations
TL;DR: These highly phosphorylated InsPs have a much greater affinity for alkali metals than quaternary ammonium ions, and this difference in cation affinity was exploited to improve separation through the use of a tetramethylammonium hydroxides-sodium hydroxide gradient.
Abstract: The separation of myo-inositol mono-, di-, tri-, tetra-, pentakis-, and hexakisphosphate (InsP1, InsP2, InsP3, InsP4, InsP5, InsP6) was carried out using hydroxide eluent ion chromatography. Acid hydrolysis of InsP6 (phytate) was used to prepare a distribution of InsPs, ranging from InsP1 to InsP5’s and including unhydrolyzed InsP6. Counting all possible positional isomers (many of which have stereoisomers that will not be separable by conventional ion exchange), 40 chromatographically separable peaks are possible; up to 22 were separated and identified by mass spectrometry. InsPs show unusual ion-exchange behavior in two respects: (a) the retention order is not monotonically related with the charge on the ion and (b) at the same hydroxide eluent concentration, retention is greatly dependent on the eluent metal cation. The retention of InsP3–InsP6 was determined to be controlled by steric factors while elution was influenced by eluent cation complexation. These highly phosphorylated InsPs have a much grea...
9 citations
TL;DR: The MIE device is expected to be useful for clinical studies that require several/many temporally spaced blood samples by keeping the invasive nature of blood collection as minimal as possible.
Abstract: A micro ion extractor (MIE) was developed for trace anion determination by ion chromatography–mass spectrometry from a single drop (25 μL) of whole blood without pretreatment. Target analytes were iodide and thiocyanate, which play key roles in thyroid hormone production. Whole blood (25 μL) was pipetted from an earlobe or finger prick and placed in the 16 μL cavity of the device. A reproducible fraction of iodide and thiocyanate was transferred through a membrane to an acceptor solution layer by electromigration for 60 s. An isolator solution layer and a cation exchange membrane is provided between the acceptor and the anode to prevent gas formation or redox processes in the acceptor. The acceptor contents are transferred online to the ion chromatograph. Isolator solution composition and applied voltage were optimized. Recoveries from samples from 16 different volunteers of both sexes and differing ages were the same within ±10% relative standard deviation. Dietary effects on blood iodide and thiocyanate...
9 citations
TL;DR: An absorption spectrometric method using a polytetrafluoroethylene (PTFE) cell as a diffuse reflector, intended for real-time monitoring of ultrapure water, improves both the limit of detection (LOD) and the dynamic range.
Abstract: We present an absorption spectrometric method using a polytetrafluoroethylene (PTFE) cell as a diffuse reflector. The system was used for monitoring ultrapure water. All compounds absorb to some degree at low UV wavelengths, and the absorption at 214 nm from a zinc lamp source was monitored using a charge-coupled device (CCD) spectrometer. The absorption was interpreted in terms of total organic carbon present. The cell acts as a nonlinear absorbance amplifier, improving both the limit of detection (LOD) and the dynamic range. Potassium hydrogen phthalate (KHP) and glucose were used to evaluate the system and provided respective LODs of 46.5 ng/L and 4.5 mg/L as carbon. Although the physical path length was 25 cm, a maximum effective path length of 280 cm was observed at the lowest tested KHP concentrations. The system is intended for real-time monitoring of ultrapure water.
8 citations
Patent•
09 Jan 2015Abstract: A sensor platform for analyzing an analyte with a predetermined reagent is presented. The sensor platform has a housing defining an interior chamber configured to hold the analyte. A tube defining an inner lumen extends through the chamber. At least a portion of the tube is porous and configured to absorb the analyte at a predetermined rate. A sensor is coupled to an end of the tube and is configured to sense changes in the material positioned in the inner lumen of the tube as the reagent reacts with the absorbed analyte.
3 citations
Patent•
26 Mar 2015TL;DR: In this article, a system for increasing light throughput in cavity enhanced spectrometry, and a model for cavity enhanced absorption measurements are presented, where an input aperture is defined in the entrance mirror to allow light from a source to enter the cavity.
Abstract: A system for increasing light throughput in cavity enhanced spectrometry, and a model for cavity enhanced absorption measurements are presented. The cavity has an entrance mirror, an opposed exit mirror and a detector positioned adjacent the exit mirror. An input aperture is defined in the entrance mirror to allow light from a source to enter the cavity. The input aperture improves light throughput without significant departure from the theoretically predicted amplification of absorbance. This results in improvement of detection limits, even with mirrors of modest reflectivity and inexpensive detectors.
Patent•
06 Nov 2015TL;DR: In this article, a cavity-enhanced absorption spectroscopy system is presented, where a liquid sample can be provided for purposes of evaluation, the absorbance cell having diffusely reflective inner surfaces, a light source configured to emit light into the liquid sample, and a light detector configured to capture the light after it has passed through the sample.
Abstract: In one embodiment, a cavity-enhanced absorption spectroscopy system includes a cavity-enhanced absorbance cell in which a liquid sample can be provided for purposes of evaluation, the absorbance cell having diffusely reflective inner surfaces, a light source configured to emit light into the liquid sample within the absorbance cell, and a light detector configured to capture the light after it has passed through the liquid sample.
TL;DR: This work believes that direct addition of a related compound to blood samples and isolating the colored measurand on a solid phase extraction cartridge is not a practically usable procedure regardless of the exact chromogenic reagent used.
Abstract: Cyanide poisoning from Inhaled HCN is all too common in victims of smoke inhalation in fires. While the toxic effects arise primarily from its inhibitory effects on cytochrome c oxidase, the majority of the cyanide binds to methemoglobin (metHb) in the blood. It can be considered as the detoxification mechanism: one of the antidotes used earlier was nitrite which primarily works by converting hemoglobin to metHb (normally present to the extent of ~1% of the total hemoglobin). Vitamin B12 (hydroxocobalamin) and related analogs have long been known to have high affinity for cyanide and has been used as antidotes - the binding of cyanide to many compounds in this general family also results in a significant change in color that can be used for analytical purposes. Mannel Croise and Zelder (Anal. Methods, 2012, 4, 2632) have advocated direct addition of a related compound to blood samples and isolating the colored measurand on a solid phase extraction cartridge. While they demonstrated attractive rapid measurement of cyanide in spiked blood samples, we believe that this is not a practically usable procedure regardless of the exact chromogenic reagent used. Cyanide bound to metHb dissociates too slowly for a 1 min reaction to work as suggested - we believe for reasons unknown (eg., metHb levels in their blood samples unusually low), cyanide added to their blood samples did not (have time to) bind to metHb and these samples may not resemble real situations where significant amount of the cyanide will be bound to metHb.