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At least 469 records · Page 26Linked to original sources
PubMed2006

Sulfonium and phosphonium, new ion-pairing agents with unique selectivity towards polarizable anions.

Ion-pair chromatography (IPC) almost universally relies upon ammonium-based ion-pairing agents (IPAs) for anion separations. This work compares tetrabutylammonium (TBA) with tetrabutylphosphonium (TBP) and tributylsulfonium (TBS). To best understand the retention behavior analytes used for characterization of the IPAs spanned the Hofmeister series; from kosmotropic monoanions (iodate, chloride, nitrite) and intermediate anions (nitrate, bromide) to chaotropic ions (perchlorate, thiocyanate, iodide). The studies demonstrate that tetrabutylphosphonium is the most chaotropic IPA, followed by tetrabutylammonium and finally tributylsulfonium is the least chaotropic. In the case of the chaotropic anions, the retention of perchlorate was least with tributylsulfonium, and greatest for tetrabutylphosphonium, with tetrabutylammonium being intermediate. The multivalent kosmotropic anions (sulfate, chromate, thiosulfate) demonstrated unique selectivity changes depending on the kosmotropic/chaotropic nature of the IPA. Demonstrating increases in retention with increasing IPA concentration only with tributylsulfonium, whereas the more chaotropic IPAs universally decreased the retention of the multivalent anions.

Anions↗
PubMed2006

Achieving rapid low-pressure ion chromatography separations on short silica-based monolithic columns.

Short silica-based monolithic columns (0.5-1 cm) are coated with the surfactant didodecyldimethylammonium bromide (DDAB) and used for fast ion exchange separations of small inorganic anions. Sources of extra-column band broadening are assessed and minimized to obtain separations of seven analytes (iodate, chloride, nitrate, bromide, nitrite, phosphate, sulphate) in two minutes at 2 mL/min. Eluents used are 6 and 9 mM 4-cyanophenol at pH 7.3-7.4 or 5 mM 4-hydroxybenzoic acid at pH 5.6. DDAB coating stability is improved by 15-fold by the addition of a DDAB coated pre-column before the injection valve. Separations are obtained using a low-pressure glass syringe.

Air Pressure↗
PubMed2006

Fast and high-resolution ion chromatography at high pH on short columns packed with 1.8 microm surfactant coated silica reverse-phase particles.

Rapid ion chromatographic separations of small inorganic anions are performed on columns packed with high-pH resistant Zorbax Extend-C18 1.8 microm silica particles. Seven anions (iodate, chloride, nitrite, bromide, nitrate, phosphate, sulphate) are separated with 1.3 and 2 cm long x 0.46 cm I.D. C18 columns coated with the surfactant didodecyldimethylammonium bromide (DDAB). A 40 s separation is achieved at 2 mL/min with a 2.5 mM 4-hydroxybenzoic acid eluent at pH 10. Finally, the DDAB removal procedure is improved to eliminate the pressure build-up caused by precipitation of the surfactant in the column upon uncoating.

Anions↗
PubMed2005

Redox reaction of iodine in paddy soil investigated by field observation and the I K-Edge XANES fingerprinting method.

In order to elucidate the cause for the leaching of iodine in a flooded paddy field, we investigated the transformation of an iodine species affected by the water management of the paddy field. The increased concentration of iodide (I(-)) in soil solution of a flooded paddy field suggested that I(-) was leached from the soil under anaerobic conditions. The post-edge feature of X-ray absorption near-edge structure (XANES) for iodate (IO(3)(-)) spiked to soil totally disappeared after anaerobic incubation of the soils, and I(-) was dissolved in the solution. On the other hand, I(-) in contact with the soil was not likely to be oxidized to IO(3)(-) under aerobic incubation. Iodine was leached out in soil solution as I(-) under anaerobic conditions, whereas part of the iodine species was retained by soil as I(2) or organoiodine both under anaerobic and aerobic conditions.

Iodine↗
PubMed2005

Exploiting genotypic variation in plant nutrient accumulation to alleviate micronutrient deficiency in populations.

More than 2 billion people consume diets that are less diverse than 30 years ago, leading to deficiencies in micronutrients, especially iron (Fe), zinc (Zn), selenium (Se), iodine (I), and also vitamin A. A strategy that exploits genetic variability to breed staple crops with enhanced ability to fortify themselves with micronutrients (genetic biofortification) offers a sustainable, cost-effective alternative to conventional supplementation and fortification programs. This is more likely to reach those most in need, has the added advantages of requiring no change in current consumer behaviour to be effective, and is transportable to a range of countries. Research by our group, along with studies elsewhere, has demonstrated conclusively that substantial genotypic variation exists in nutrient (e.g. Fe, Zn) and nutrient promotor (e.g. inulin) concentrations in wheat and other staple foods. A rapid screening technique has been developed for lutein content of wheat and triticale, and also for pro-vitamin A carotenoids in bread wheat. This will allow cost-effective screening of a wider range of genotypes that may reveal greater genotypic variation in these traits. Moreover, deeper understanding of genetic control mechanisms and development of molecular markers will facilitate breeding programs. We suggest that a combined strategy utilising plant breeding for higher micronutrient density; maximising the effects of nutritional promoters (e.g. inulin, vitamin C) by promoting favourable dietary combinations, as well as by plant breeding; and agronomic biofortification (e.g. adding iodide or iodate as fertiliser; applying selenate to cereal crops by spraying or adding to fertiliser) is likely to be the most effective way to improve the nutrition of populations. Furthermore, the importance of detecting and exploiting beneficial interactions is illustrated by our discovery that in Fe-deficient chickens, circulating Fe concentrations can be restored to normal levels by lutein supplementation. Further bioavailability/bioefficacy trials with animals and humans are needed, using varying dietary concentrations of Fe, Zn, carotenoids, inulin, Se and I to elucidate other important interactions in order to optimise delivery in biofortification programs.

Carotenoids↗
PubMed2006

Indirect spectrophotometric determination of arbutin, whitening agent through oxidation by periodate and complexation with ferric chloride.

A simple and accurate spectrophotometric method for the determination of arbutin (glycosylated hydroquinone) is described. It is based on the oxidation of arbutin by periodate in presence of iodate. Excess periodate causes liberation of iodine at pH 8.0. The unreacted periodate is determined by measurement of the liberated iodine spectrophotometrically in the wavelength range (300-500 nm). A calibration curve was constructed for more accurate results and the correlation coefficient of linear regression analysis was -0.9778. The precision of this method was better than 6.17% R.S.D. (n=3). Regression analysis of Bear-Lambert plot shows good correlation in the concentration range 25-125 ug/ml. The identification limit was determined to be 25 ug/ml a detailed study of the reaction conditions was carried out, including effect of changing pH, time, temperature and volume of periodate. Analyzing pure and authentic samples containing arbutin tested the validity of the proposed method which has an average percent recovery of 100.86%. An alternative method is also proposed which involves a complexation reaction between arbutin and ferric chloride solution. The produced complex which is yellowish-green in color was determined spectophotometrically.

Arbutin↗
PubMed2005

Enhancement of sonochemical degradation of phenol using hydrogen atom scavengers.

Sonochemical degradation of phenol was found to be enhanced in the presence of the volatile hydrogen atom scavengers CCl4 and perfluorohexane. The non-volatile hydrogen atom scavenger iodate did not enhance phenol degradation. The first order rate constant for aqueous phenol degradation in separate experiments using different sonochemical probes increased in the presence of 150 microM CCl4 from 0.014 to 0.031 min(-1) (probe 1) and from 0.022 to 0.061 min(-1) (probe 2). In the presence of <1.5 microM C6H14, the first order rate constant increased from 0.014 to 0.032 min(-1) (probe 1). Hydroquinone was the major observed reaction intermediate both in the presence and absence of hydrogen atom scavengers. Hydroquinone yields were substantially higher in the presence of hydrogen atom scavengers, suggesting that hydroxyl radical pathways for phenol degradation were enhanced by the hydrogen atom scavengers. These additives may be useful in improving pollutant degradation efficiency or improving synthetic processes that rely on hydroxyl radical as a key intermediate.

Journal Article↗
PubMed1986

Effects of some chemical reagents on sodium current inactivation in myelinated nerve fibers of the frog.

The effect of several chemical reagents on the sodium current was studied in voltage-clamped single nerve fibers of the frog. The oxidants halazone and hypochlorous acid drastically inhibited inactivation. Their effect was similar to that of chloramine T (Wang, 1984a). The curve relating the steady-state inactivation parameter h infinity to the conditioning potential E became nonmonotonic after treatment with the oxidants, i.e., dh infinity/dE greater than 0 for E greater than -20 mV. By contrast, the oxidants periodate, iodate, and hydrogen peroxide (applied for the same time, but at higher concentrations) merely produced a parallel shift of the h infinity(E) curve to more negative values of membrane potential. Diethylpyrocarbonate, a reagent that preferentially modifies histidine groups, had one marked effect: a strong shift of the h infinity(E) curve to more negative values of membrane potential. Almost no effect was observed after application of the tyrosine-reactive reagent N-acetylimidazole. Similarly, the arginine-reactive reagent glyoxal had only minor effects on the Na permeability. The results suggest that methionine is not critically involved in the kinetics of Na current inactivation. Similarly, an essential tyrosine or arginine residue seems to be unavailable to chemical reagents from outside on the frog node of Ranvier. Deduced from the reactivities of (some of) the reagents used, modification of membrane lipids is a tentative explanation for the effects observed on inactivation kinetics.

Animals↗
PubMed1990

CT scanning as an adjunct to screening for medullary carcinoma of the thyroid.

CT scanning of the thyroid following oral administration of potassium iodate was performed on two sisters in whom raised calcitonin levels had been found at a pentagastrin stimulation test undertaken to screen for medullary carcinoma of the thyroid. Three histologically proven, clinically occult C-cell carcinomas measuring 2 mm or less were detected by CT scanning. This technique may be useful prior to surgery in patients in whom medullary carcinoma of the thyroid is suspected but not proven.

Adolescent↗
PubMed1982

Studies on experimentally induced retinal degeneration. 1. Effect of lipid peroxides on electroretinographic activity in the albino rabbit.

Lipid hydroperoxides (LHP) have been synthesized and purified from linoleic, linolenic, arachidonic and docosahexaenoic acids, using soybean lipoxygenase and oxygen. Intravitreal injections into the eyes of mature, albino rabbits produced an early and then progressive decrease in the amplitude of a-, b- and c-waves of the ERG. Depending upon the amount and activity of the LHP preparation, ERG's were markedly decreased in amplitude (greater than 50%) within 4 days following the injection and by 12 days, the activity from peroxide treated eyes was essentially nonrecordable. In preliminary studies, these effects were less pronounced in adult pigmented rabbits of similar age, however, a younger pigmented rabbit was only slightly less susceptible to damage than the albino animals. In other experiments, peroxidized native phospholipids, malonaldehyde, hydrogen peroxide and sodium iodate were also shown to be cytotoxic, but not all were as toxic as the LHP. In contrast, retinol, vitamin A acetate and retinoic acid had no effect upon ERG activity, nor did the parent fatty-acid compounds or the borate buffer in which they were injected. These studies confirm previous reports where indirect production of lipid peroxides caused retinal degeneration. The present report extends these observations to demonstrate that when the retina and RPE are exposed to a sample of purified LHP, retinal function is altered in an irreversible way. We also demonstrate that a metabolic by-product (malonaldehyde) is likewise cytotoxic. However, the mechanisms by which the parent LHP and/or metabolites might act could be quite different. This new animal model should prove useful in evaluating further the ultrastructural changes which are observed during peroxidative damage of the retina in vivo, as well as in evaluating the therapeutic approaches to these problems of retinal degeneration.

Animals↗
PubMed2001

Titrimetric micro-determination of therapeutically active phenothiazines using periodate.

Two new simple, accurate and precise titrimetric micro-procedures are described for the analysis of phenothiazines in pure sample, tablets, injections and syrup using periodate as the oxidant. The first method is based on the oxidation of phenothiazines with periodate in acid medium and the iodate formed in the reaction is determined by reacting it with iodide and titrating the liberated iodine with thiosulfate after masking the excess of periodate with molybdate. In the second procedure, the unreacted (excess) periodate is determined iodometrically under basic conditions. The reaction conditions have been optimised and the stoichiometry of the reaction has been evaluated. A linear relationship exists between the amount of the drug and the titration end-point as shown by the values of correlation coefficient, r (0.9991-0.9999). The slope of the linear relationship has been calculated and found to be in the range, 0.1457-0.3120. The methods were applied to the analysis of dosage forms with results comparable to those given by the official methods. Both the methods are indirect visual titration methods, and are simpler than, and superior to, many existing methods for the assay of phenothiazines.

Chemistry, Pharmaceutical↗
PubMed2001

Effect of temperature on retention and selectivity in ion chromatography of anions.

The temperature dependence of retention of a wide range of inorganic anions is studied on two commercially available ion exchangers (Dionex AS11 and AS14 columns). Anion retention exhibited both exothermic and endothermic behavior, such that varying the temperature from ambient to 60 degrees C produced selectivity changes. The anions displayed three groupings of temperature dependence: weakly retained singly charged anions (e.g., iodate, bromate, nitrite, bromide and nitrate); multiply charged anions (sulfate, oxalate, phosphate and thiosulfate); and strongly retained singly charged anions (iodide, thiocyanate and perchlorate). Temperature was ineffective at changing the selectivity of retention between anions of the same grouping. However, significant selectivity changes, including elution order reversal, could be achieved between anions from different groupings.

Anions↗
PubMed2001

Fast separation of UV absorbing anions using ion-interaction chromatography.

Ion-interaction chromatography on a short (30 x 4.6 mm) 3 microm ODS column has been investigated with the aim of developing fast chromatographic separations of selected inorganic anions. Tetrabutylammonium chloride (TBA-Cl) was used as the ion-interaction reagent in mobile phases that also contained up to 20% methanol. Separations of simple test mixtures of up to eight UV absorbing anions illustrated how excellent efficiencies (>50,000 plates/m) could be obtained under optimized conditions. The use of an optimised mobile phase containing 20 mM TBA-Cl and 20% methanol resulted in the baseline separation of five important anions (iodate, bromate, nitrite, bromide and nitrate) in a separation window of just 28 s, with a shortest total analysis time of 50 s. The method was briefly applied to the rapid analysis of nitrite and nitrate in both a drinking water and a river water sample with a view to future on-line monitoring.

Anions↗
PubMed2002

Determination of trace level bromate and perchlorate in drinking water by ion chromatography with an evaporative preconcentration technique.

A simple sample preconcentration technique employing microwave-based evaporation for the determination of trace level bromate and perchlorate in drinking water with ion chromatography is presented. With a hydrophilic anion-exchange column and a sodium hydroxide eluent in linear gradient, bromate and perchlorate can be determined in one injection within 35 min. Prior to ion chromatographic analysis, the drinking water sample was treated with an OnGuard-Ag cartridge to remove the superfluous chloride and concentrated 20-fold using a PTFE beaker in a domestic microwave oven for 15 min. The recoveries of the anions ranged from 94.6% for NO2- to 105.2% for F-. The detection limits for bromate, perchlorate, iodate and chlorate were 0.1, 0.2, 0.1 and 0.2 microg/l, respectively. The developed method is applicable for the quantitation of bromate and perchlorate in drinking water samples.

Bromates↗
PubMed2002

Rapid and direct determination of iodide in seawater by electrostatic ion chromatography.

An electrostatic ion chromatographic (IC) method for rapid and direct determination of iodide in seawater is reported. Separation was achieved using a reversed-phase ODS packed column (250x4.6 mm I.D.) modified by coating with Zwittergent-3-14 micelles, with an eluent comprising an aqueous solution containing 0.2 mM NaClO4 and 0.3 mM Zwittergent-3-14 and using UV detection at 210 nm. Samples prepared by dissolving NaIO3, NaNO2, NaBr, NaBrO3, NaNO3, NaI, and NaSCN in artificial or real seawaters were analyzed using this IC system. Nitrite, iodate, bromide, bromate, and nitrate showed very little or no retention, while iodide and thiocyanate were well separated, being eluted within 6 and 16 min, respectively. The detection limit for iodide obtained by injecting 400 microL of sample was 0.011 microM (S/N = 3), and the precision values obtained by analyzing samples containing 0.1 or 0.3 microM iodide in real seawater samples were 2.3% RSD and 1.2% RSD, respectively. Direct determination of iodide in real seawater samples was possible using this proposed IC system.

Chromatography, Liquid↗
PubMed1998

Analysis of oxyhalides in water by ion chromatography-ionspray mass spectrometry.

A sensitive method for analyzing chlorite, chlorate, bromate and iodate in water by ion chromatography (IC) coupled with ionspray tandem mass spectrometry (IS-MS-MS) has been developed. Prior to analysis, samples were subjected to off-line sample clean-up with Ba, Ag and H-form resins to remove sulfate, chloride and hydrogencarbonate, respectively. Oxyhalides in the purified samples were concentrated and separated on a short, high-performance anion-exchange column. An eluent consisting of ammonium nitrate in methanol-water (9:1, v/v) was found to be suitable for separating the analytes, while providing enhanced detector sensitivity. The coupling of IC with IS-MS-MS allows for the identification of the four oxyhalides mentioned above in a single run with very high specificity and sensitivity.

Drinking↗
PubMed1999

Combination of suppressed and non-suppressed ion chromatography with atmospheric pressure ionization mass spectrometry for the determination of anions.

Non-suppressed and suppressed ion chromatography in combination with atmospheric pressure ionization mass spectrometry are compared with special respect to sensitivity for the analysis of low-molecular-mass anions. Iodate, bromate, bromide, sulfate, thiosulfate and bromide could be separated by non-suppressed ion chromatography using a low-capacity anion-exchange column and ammonium citrate as mobile phase. Absolute detection limits between 0.4 and 0.7 ng could be achieved; employing a column requiring a flow-rate of 1 ml/min for optimum performance, splitting was necessary so that only 120 microliters/min entered the interface of the mass spectrometer resulting in detection limits between 0.03 and 0.06 mg/l. The same stationary phase (packed into a narrow-bore column which allowed operation without splitting) was suitable for the separation of oxyhalides in the suppressed mode with detection limits of 0.5 microgram/l (50 pg) with sodium carbonate as eluent. The method was applied to the analysis of drinking water for oxyhalides. The sample pretreatment for the removal of matrix anions (sulfate, chloride and hydrogencarbonate) is described.

Anions↗
PubMed1999

Analysis of low-molecular-mass inorganic and organic anions by ion chromatography-atmospheric pressure ionization mass spectrometry.

Different nonvolatile mobile phases have been tested for the combination of ion-exchange chromatography combined with mass spectrometric detection of anions and organic acids. Buffer systems based on carbonate, sulfate, oxalate and citrate as the eluting species have been used. Among these, citrate proved to be the most versatile eluent allowing the separation of anions with absolute detection limits between 0.4 and 0.7 ng and of organic acids with detection limits between 0.4 and 4 ng in the non-suppressed mode. In the suppressed eluent mode iodate, bromate and chlorate could be separated using sodium carbonate as the mobile phase resulting in detection limits of 50 pg. The method was applied to the analysis of water samples containing oxyhalides originating from ozonization. Additionally, organic acids were separated by chromatographic separation techniques like reversed-phase, ion-pair or ion-exclusion chromatography and the compatibility with mass spectrometry was investigated with special respect to sensitivity of this detection mode.

Anions↗