Showing papers by "Purnendu K. Dasgupta published in 2011"

Rapid point of care analyzer for the measurement of cyanide in blood.

Abstract: A simple, sensitive optical analyzer for the rapid determination of cyanide in blood in point of care applications is described. HCN is liberated by the addition of 20% H(3)PO(4) and is absorbed by a paper filter impregnated with borate-buffered (pH 9.0) hydroxoaquocobinamide (hereinafter called cobinamide). Cobinamide on the filter changes color from orange (λ(max) = 510 nm) to violet (λ(max) = 583 nm) upon reaction with cyanide. This color change is monitored in the transmission mode by a light emitting diode (LED) with a 583 nm emission maximum and a photodiode detector. The observed rate of color change increases 10 times when the cobinamide solution for filter impregnation is prepared in borate-buffer rather than in water. The use of a second LED emitting at 653 nm and alternate pulsing of the LEDs improves the limit of detection by 4 times to ~0.5 μM for a 1 mL blood sample. Blood cyanide levels of imminent concern (≥10 μM) can be accurately measured in ~2 min. The response is proportional to the mass of cyanide in the sample: smaller sample volumes can be successfully used with proportionate change in the concentration LODs. Bubbling air through the blood-acid mixture was found effective for mixing of the acid with the sample and the liberation of HCN. A small amount of ethanol added to the top of the blood was found to be the most effective means to prevent frothing during aeration. The relative standard deviation (RSD) for repetitive determination of blood samples containing 9 μM CN was 1.09% (n = 5). The technique was compared blind with a standard microdiffusion-spectrophotometric method used for the determination of cyanide in rabbit blood. The results showed good correlation (slope 1.05, r(2) 0.9257); independent calibration standards were used.

On-Line Electrodialytic Salt Removal in Electrospray Ionization Mass Spectrometry of Proteins

Abstract: Salts and buffers, commonly used in isolation and stabilization of biological analytes, have a deleterious effect on electrospray ionization mass spectrometry (ESI-MS). Excessive concentrations of salts lead to ion suppression and adduct formation, which mask or complicate ion signals. In this work, we describe a salt remover (SR), configured as a three-compartment flow-through system, where the central compartment is separated from the outer compartments by a cation-exchange membrane (CEM) and an anion-exchange membrane (AEM). One platinum electrode is placed in each of the outer compartments, where water or electrolyte is flowing. The CEM electrode is held at a negative potential relative to the AEM side; cations/anions migrate by electrophoresis to the CEM/AEM receiver liquids, respectively. Proteins have poorer electrophoretic mobility relative to the buffer components, permitting removal of the salt. The salt-free proteins proceed to the ESI source. The capillary scale SR (internal volume 2.5 μL) des...

Flow batteries for microfluidic networks: configuring an electroosmotic pump for nonterminal positions.

Abstract: A micropump provides flow and pressure for a lab-on-chip device, just as a battery supplies current and voltage for an electronic system. Numerous micropumps have been developed, but none is as versatile as a battery. One cannot easily insert a micropump into a nonterminal position of a fluidic line without affecting the rest of the fluidic system, and one cannot simply connect several micropumps in series to enhance the pressure output, etc. In this work we develop a flow battery (or pressure power supply) to address this issue. A flow battery consists of a +EOP (in which the liquid flows in the same direction as the field gradient) and a −EOP (in which the liquid flows opposite to the electric field gradient), and the outlet of the +EOP is directly connected to the inlet of the −EOP. An external high voltage is applied to this outlet−inlet joint via a short gel-filled capillary that allows ions but not bulk liquid flow, while the +EOP’s inlet and the −EOP’s outlet (the flow battery’s inlet and outlet) a...

Thiolated eggshell membranes sorb and speciate inorganic selenium

Abstract: Eggshell membranes (ESMs) provide a unique, disulfide bond-rich surface. Thioglycolate reduction was used to generate thiol (–SH) groups on the ESM surface by S–S bond cleavage. The thiol-bearing ESMs (TESMs) were characterized by scanning electron microscopy and Raman spectroscopy. The fibrous network structure of the ESM is retained in the TESMs. TESMs adsorb both Se(IV) and Se(VI) but by different mechanisms: Se(VI) is retained reversibly, possibly via ionic interactions, while Se(IV) is reduced to Se(0) and deposited. We thus demonstrate speciation of selenium species, by using samples (a) as such and after prior oxidation to Se(VI), (b) preconcentration on a TESM microcolumn, (c) elution by 0.5 M HNO3 that only elutes Se(VI) and (d) detection by graphite furnace atomic absorption spectrometry (GFAAS). The Se(IV) amount is determined by difference. For a 1.0 mL sample, the enrichment factor was 17.2, the S/N = 3 detection limit was 0.06 μg L−1 and the precision was 3.3% at 0.50 μg L−1. The linear range was 0.25–2.50 μg L−1. The procedure was validated by analyzing selenium in certified reference materials of human hair (GBW 09101) and rice (GBW 10010). We further demonstrate utility by speciation of inorganic selenium in a series of water samples.

Oxidation State-Differentiated Measurement of Aqueous Inorganic Arsenic by Continuous Flow Electrochemical Arsine Generation Coupled to Gas-Phase Chemiluminescence Detection

Abstract: The electrochemical reduction of inorganic As on a graphite cathode depends on the current density. We observed that while only inorganic As(III) is reduced to AsH3 at low current densities, at high current densities both forms of inorganic As are reduced. We describe a unique electrochemical reactor in which the cylindrical anode compartment is isolated from the outer concentric cathode compartment by a Nafion tube in which a hole is deliberately made and the entire anode compartment is inside the cylindrical cavity of a small volume (∼115 μL) cathode chamber. The evolved arsine is then quantitated by gas-phase chemiluminescence (GPCL) reaction with ozone; the latter is generated from oxygen formed during electrolysis. For the dimensions used, inorganic As(III) can be selectively determined at a current of 0.1 A while total inorganic As (both As(III) and As(V)) respond equally at an applied electrolysis current at 0.85 A, without any sample treatment. For a 1-mL sample, the system provides a limit of det...

Fenton digestion of milk for iodinalysis.

Abstract: Iodine is an essential micronutrient especially important in the neurodevelopment of infants. Spot samples of urinary iodine (UI) are used as an epidemiologic index of adult iodine nutrition. Individual infant iodine nutrition is of vital importance, but infant urine is difficult to collect, much less a 24 h sample. Monitoring the intake provides a pragmatic solution for determining infant iodine nutrition. Because of the high solids content of milk and the possible existence of iodine in an organically bound form, sample digestion is obligatory. The U.S. Food and Drug Administration, for example, uses wet ashing by HClO(4); special precautions and fume hoods are required. We present a method of Fenton digestion of human and bovine milk samples and infant formula. No specialized equipment or hazardous reagents are used; measurement is made by isotope dilution inductively coupled plasma mass spectrometry. In Fenton digestion, Fe(II) and H(2)O(2) oxidizes the sample. In an interlaboratory study, excellent agreement (r(2) = 0.9934) was observed with results obtained by HClO(4) digestion and Sandel-Kolthoff kinetic colorimetry. Average recoveries of iodide, triiodothyronine, and thyroxine ranged between 100% and 101%. Following digestion, iodine was found to exist entirely as iodide. Control of pH is imperative if loss cannot be corrected for by isotope dilution. Loss was below 20% for all samples when the pH was between 2.25 and 2.5.

Pretreatment device for dissolved ions analysis and dissolved ion analysis system

Abstract: Provided is a pretreatment device for analysis of dissolved ions, which enables the separation of dissolved ions to be analyzed from a sample solution in a short period of time and which is applicable to both a case in which the dissolved ions to be measured is a cation and a case in which the dissolved ions to be measured is an anion. A pretreatment device 10 for analysis of dissolved ions, which comprises: a sample solution flow channel 11 through which a sample solution containing dissolved ions to be measured flows; an acceptor solution flow channel 13 which is arranged adjacent to the sample solution flow channel 11 so as to intercalate a dialysis membrane 12 between the acceptor solution flow channel 13 and the sample solution flow channel 11; a pair of electrodes 14 a, 14 b which are so arranged as to intercalate the sample solution flow channel 11 and the acceptor solution flow channel 13 therebetween; and a direct current power source 5 which enables the generation of a predetermined potential difference between the electrodes 14 a, 14 b. When the pretreatment device 10 is used, it becomes possible to separate dissolved ions to be analyzed from a sample solution in a short period of time, and the device 10 is effective for a pretreatment in the analysis of an ion, such as the ion chromatography method, the ICP emission spectrometry method, the atomic absorption spectrometry method, and the mass spectrometry method.

Systems and methods for electrochemical analysis of arsenic

Abstract: Embodiments of methods for electrochemical analysis of arsenic are described. In one embodiment, a method includes detecting arsenic (III) by, at least in part, applying electrolytic current to an arsenic compound that has not been reduced with a reducing agent. In another embodiment, a method for electrochemical analysis of arsenic includes detecting arsenic (V) by, at least in part, applying electrolytic current to an arsenic compound that has not been reduced with a reducing agent.

Pretreatment device for analysis of dissolved ion, dissolved ion analysis system, and pretreatment method for analysis of dissolved ion

Abstract: Provided is a pretreatment device for use in the analysis of a dissolved ion, which enables the separation of a dissolved ion to be analyzed from a sample solution within a short time and which is applicable to both a case in which the dissolved ion to be measured is a cation and a case in which the dissolved ion to be measured is an anion. A pretreatment device (10) for use in the analysis of a dissolved ion, which comprises: a sample solution flow path (11) through which a sample solution containing the dissolved ion to be measured flows; an extracted solution flow path (13) which is arranged adjacent to the sample solution flow path (11) so as to intercalate a dialysis membrane (12) between the extracted solution flow path (13) and the sample solution flow path (11); a pair of electrodes (14a, 14b) which are so arranged as to intercalate the sample solution flow path (11) and the extracted solution flow path (13) therebetween; and a direct current power source (5) which enables the generation of a predetermined potential difference between the electrodes (14a, 14b). When the pretreatment device (10) is used, it becomes possible to separate a dissolved ion to be analyzed from a sample solution within a short time, and the device (10) is effective for a pretreatment in the analysis of an ion, such as an ion chromatography method, an ICP emission spectrometry method, an atomic absorption spectrometry method and a mass spectrometry method.

Rapid nondestructive spectrometric measurement of temperature-dependent gas-liquid solubility equilibria.

Abstract: Gas-liquid solubility equilibria (Henry's Law behavior) are of basic interest to many different areas. Temperature-dependent aqueous solubilities of various organic compounds are of fundamental importance in many branches of environmental science. In a number of situations, the gas/dissolved solute of interest has characteristic spectroscopic absorption that is distinct from that of the solvent. For such cases, we report facile nondestructive rapid measurement of the temperature-dependent Henry's law constant (K(H)) in a static sealed spectrometric cell. Combined with a special cell design, multiwavelength measurement permits a large range of K(H) to be spanned. It is possible to derive the K(H) values from the absorbance measured in the gas phase only, the liquid phase only (preferred), and both phases. Underlying principles are developed, and all three approaches are illustrated for a solute like acetone in water. A thermostatic spectrophotometer cell compartment, widely used and available, facilitates rapid temperature changes and allows rapid temperature-dependent equilibrium measurements. Applicability is shown for both acetone and methyl isobutyl ketone. Very little sample is required for the measurement; the K(H) for 4-hydroxynonenal, a marker for oxidative stress, is measured to be 56.9 ± 2.6 M/atm (n = 3) at 37.4 °C with 1 mg of the material available.