Flow-Through Bulk Optode for the Spectrophotometric Determination of Perchlorate

A flow-through spectrophotometric bulk optode for the flow-injection determination of perchlorate is described. As active constituents, the optode incorporates the lipophilic pH indicator 5-octadecanoyloxy-2-(4-nitrophenylazo) phenol and methyltridodecyl ammonium chloride, dissolved in a plasticized poly(vinyl chloride) membrane which is entrapped in a cellulose support. The optode is applied in conjunction with the flow injection technique at pH 8.2 (TRIS buffer). The sensor is readily regenerated with a 10^–2M NaOH carrier solution. The analytical characteristics of this optode with respect to response time, dynamic measurement range, reproducibility and selectivity are discussed. The proposed FI method is applied to the determination of perchlorate in waters from different sources.Received December 16, 2002; accepted May 16, 2003 Published online August 8, 2003     

Capacitive chemical sensor for fenvalerate assay based on electropolymerized molecularly imprinted polymer as the sensitive layer

A capacitive chemical sensor for fenvalerate is reported. By using ac impedance measurements the sensor has been based on the decrease in capacitance caused by the analyte used as the template in the formulation of an electropolymerized molecularly imprinted polymer as receptor layer. Improvement of the insulating properties of the sensor was investigated in detail. The capacitive sensor was prepared by a deposition of a self-assembled monolayer of 2-mercaptobenzimidazole (2-MBI) before electropolymerization of 2-MBI and subsequent treatment with n-dodecanethiol to eliminate pinholes and defects in the polymerized 2-MBI film. From the calibration curve concentrations of fenvalerate up to 9 g mL^–1 could be detected with a linear determination range up to 5 g mL^–1 and a detection limit of 0.36 g mL^–1. No significant interference was observed from common pyrethroid insecticides.     

Piezoelectric enzyme sensor with improved temperature characteristics for determining urea in urine

Based on the conductivity change produced by the urea/urease reaction, a piezoelectric enzyme sensor is applied to the detection of urea in urine. The influence of the variation in solution temperature on frequency measurement is greatly reduced by using a buffer giving solution conditions with a near-zero frequency temperature coefficient for the sensor. The sum of the frequency shifts over the reaction time was used to increase the sensitivity of the determination. The linear range of the method is 1–30 g/ml for urea, with RSDs of 1–2.6%. The detection limit is 0.01 g/ml.     

Preparation of 103Pd seeds Part II. “Molecular Plating” of 103Pd onto copper rod

A method for ¹⁰³Pd molecular plating onto the surface of the copper rod is reported. The optimal composition of the plating bath was: palladium chloride 2 g/l, ammonium hydroxide (28%) 150 ml/l, sodium hypophosphite 12 g/l, and ammonium chloride 37 g/l. The whole procedure of ¹⁰³Pd molecular plating will last 50 minutes at 40 °C. This article provides valuable experience for the preparation of ¹⁰³Pd seeds.     

Solvent Extraction-spectrophotometric Determination of Trace Amounts of Total Ammonia-Ammonium Ion Content in Sewage, Soil and Shrimp by Dicyclohexyl-18-crown-6 and Orange II

A simple and sensitive extraction-spectrophotometric method for the determination of total dissolved ammonia and ammonium ion content is reported. The ternary complex DC18C6-ammonium-Orange II, (DC18C6–NH₄–OR II), was quantitatively extracted into dichloromethane and its absorbances is measured at 483 nm. Linear calibration graph is obtained over the concentration ranges of 0.05–3.00 g mL^–1 for ammonium. The relative standard deviations for 1.0 g mL^–1 of ammonium was 1.10%. The method was applied to real samples such as sewage, agricultural soil and Persian golf shrimp. The results showed high potential of the recommended method for the determination of total dissolved NH₃ and NH⁴⁺ content in different samples.     

Ammonium determination in wine by gas phase molecular absorption spectrometry

A procedure for the determination of ammonium is described, based on its transformation into ammonia gas and subsequent measurement by UV-visible molecular absorption spectrometry at 194 nm. Two different procedures for generating the ammonia are proposed, using NaOH solution and solid NaOH, respectively. After generation conditions for both procedures had been optimized, better sensitivity was observed with solid NaOH. In these conditions, the method showed two ranges of linear response: from 1 to 100 g and from 100 to 400 g of ammonium. Finally, we determined ammonium in wine samples. Preliminary studies indicated that the only observable interfering species was ethanol, which could be eliminated by subjecting the sample to vacuum evaporation until nearly dry. This process also increased the sensitivity of the method by as much as ten times. The values obtained from three different wine samples yielded results within the range of the concentration obtained by other authors. The recovery of ammonium added to the wine samples was around 95%.     

A Sensor for the Determination of Electropositive Elements

An electrochemical sensor, namely, a graphite thick-film electrode modified with Au(III) was proposed for the determination of Hg, As, Se, and Cu. The detection limits for mercury and arsenic using the new sensor are 0.005 and 0.1 g/L, respectively.     

Microtitration of various anions with quaternary ammonium halides using solid-state electrodes

Many solid-state electrodes were found to respond as endpoint detectors in the potentiometric titration of large inorganic and organic anions with quaternary ammonium halides. The best response was obtained with the iodide and cyanide electrodes although practically any electrode can function as endpoint sensor. The titrants were hexadecylpyridinium chloride and hexadecyltrimethylammonium chloride; hexadecyltrimethylammonium bromide and Hyamine 1622 may also be used. Some inorganic anions thus titratable are

perrhenate, persulfate, ferricyanide, hexafluorophosphate, and hexachloroplatinate. Examples of organic anions titratable are nitroform, tetraphenylborate, cyanotriphenylborate, picrate, long-chain sulfates and sulfonates, and some soaps. The reverse titration of quaternary ammonium halides vs dodecylsulfate is also feasible. Some titrations are feasible in a partially nonaqueous medium.     

Theoretical and Experimental Studies of the Nature of the Catalytic Activity of VO x /TiO2 Systems

The states of supported vanadium and the nature of activation of ammonia adsorbed on vanadium sites of V _x /Ti₂ catalysts are studied by ⁵¹V NMR spectroscopy and diffuse-reflectance IR Fourier-transform (DRIFT) spectroscopy using cluster quantum chemical calculations of N₃ adsorption. We employ the V _x /Ti₂ catalyst of two types: the monolayer catalyst in which vanadium is located on the surface of well-crystallized anatase and the catalyst in which vanadium embedded in the anatase lattice at a rather great depth. It is shown that ammonia is predominantly adsorbed on Lewis acid sites of the monolayer catalyst, whereas most of N₃ adsorbed on the catalyst containing bulk vanadium is in the form of ammonium ions. Analysis of experimental and calculated data suggests that, in the monolayer catalyst, N₃ molecules in the selective reduction of nitrogen oxides are activated on Lewis acid sites. Ammonia activation involves the dissociation of the N–H bond in a coordinated molecule, which results in the formation of the amide V–N₂ group and a water molecule coordinated by a V⁵⁺ ion. It is likely that, in the case of the catalyst containing bulk vanadium, this reaction occurs with the predominant participation of ammonium ions.     

A new detection method for purines in thin-layer chromatography

Summary The separation of some purines by thin-layer chromatography, utilizing precoated plates with Silicagel R as stationary phase and the following mobile phases: i-butanol: methylethylketone: ammonium hydroxide 25%: water (40252015) and n-propanol: ammonium hydroxide 25%: water (80155) is reported.Visualisation of the spots has been achieved by spraying with aqueous 1% uranyl acetate and irradiating with UV both at 254 and 366 nm. The visual detection of a spot was 0.01 g.     

Optimization of Culture Conditions for Enhanced Lysine Production Using Engineered Escherichia coli

In this study, culture conditions, including dissolved oxygen (DO) content, presence of osmoprotectants, residual glucose concentration, and ammonium sulfate-feeding strategies, were investigated for decreasing the inhibition effects of acetic acid, ammonium, and osmotic stress on l-lysine fermentation by Escherichia coli. The results revealed that higher DO content and lower residual glucose concentration could decrease acetic acid accumulation, betaine supplementation could enhance osmotic stress tolerance, and variable speed ammonium sulfate-feeding strategy could decrease ammonium inhibition. Thus, with 25 % DO content, 0–5.0 g/L of residual glucose concentration, and 1.5 g/L of betaine supplementation, 134.9 g/L of l-lysine was obtained after 72 h of culture, with l-lysine yield and productivity of 45.4 % and 1.9 g/(L?·?h), respectively.     

Trace analysis in highly concentrated salt solutions of sodium chloride and ammonium fluoride using flame atomic absorption spectrometry

Summary Aqueous solutions of high salt concentration are subjected to direct flame atomic absorption analysis. Blockage of nebulizer and burner is eliminated by employing the dosage scheme washing solution — sample — washing solution effected by means of a specially designed device. The microtrace content of bismuth, zinc and copper in sodium chloride and of copper, lead and iron in ammonium fluoride is determined by the standard addition method. Matrix effects are reduced in the analysis of sodium chloride by the addition of ethanol and in the analysis of ammonium fluoride by pre-heating of sample and washing solution. In order to improve the signal-to-noise ratio, ensemble summation is applied.The following trace element concentrations are determined: 0.5 mg/kg of Cu; 5 mg/kg of Bi and 0.25 mg/kg of Zn in sodium chloride and 0.47 mg/kg of Cu; 0.1 mg/kg of Pb and 3.7 mg/kg of Fe in ammonium fluoride.

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Bestimmung von Spurenelementen in hochkonzentrierten Salzlösungen (NaCl, NH₄F) mittels Flammen-Atom-Absorptions-Analyse

     

The enzymatic determination of mercury and copper using acid urease. The effects of buffers

We report on a quick and simple test based on enzyme inhibition for the detection of mercury and copper using free acid urease coupled to an optical sensor system. Lipophilized Nile Blue was incorporated in plasticized poly(vinyl chloride) (PVC) to produce an ammonium-sensitive layer with a thickness of around 4 m. The layer was fixed on one side of a disposable cuvette. A solution of buffer, enzyme and heavy metals was placed into the thermostated cell. Enzymatic hydrolysis was started upon addition of urea and the formation of ammonium was monitored. Mercury and copper were the strongest inhibitors; for this reason the inhibitory efficiency of these metals was examined in citrate, acetate and trismaleate buffers. The cuvette test was most sensitive and selective for mercury in a citrate buffer. The limit of detection for mercury(II) ions was as low as 1 g/L. Copper ions do not interfere because of complexation by citrate. The inhibitory effects of metal combinations on the activity of acid urease and the effects of optimum pH of the enzyme and the transducer on the dynamic range of the cuvette test are presented.     

Speciation of Cr(III) and Cr(VI) by reversed phase high-performance liquid chromatography using UV-detection

Summary A method for the simultaneous determination of Cr(III) and Cr(VI) in water samples is described. The different reaction products of Cr(III) and Cr(VI) species with ammonium pyrrolidinedithiocarbamate (APDC) are extracted with ethyl acetate and determined by reversed phase HPLC using UV-detection. The procedure is optimized and its detection limit accordingly improved as compared to literature data. The detection limits achieved are 2.4 g/l for Cr(III) and 2.1 g/l for Cr(VI) and the calibration curves are linear between 5 g/l and 5000 g/l. For the speciation of Cr, APDC was demonstrated to be more suitable as chelating agent than sodium diethyldithiocarbamate (NaDDC). The procedure was applied to the determination of both Cr species in galvanic waste waters and its accuracy was approved by comparing the results (at the 100 g/l level) with those of a photometric determination of Cr(VI) species.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Reaction of α-α'-dichloro-substituted 1,5-diketones with ammonia and ammonium acetate

Under the influence of ammonia or ammonium acetate, -'-dichloro-substituted 1,5-diketones undergo heterocyclization to give -chloropyridines or 2-benzoylpyrrole derivatives. The structure of the final product depends on the reagent and the character of the substituent in the 3 position of the starting dichloro diketones.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 352–354, March, 1985.     

Synthesis of 4-Benzylsulfonyl-5-polyfluoroalkyl-ν-triazoles from 1,1-Dihydropolyfluoroalkyl Benzyl Sulfones

The reaction of 1,1-dihydropolyfluoroalkyl benzyl sulfones with sodium azide or trimethylsilyl azide in the presence of tertiary amines gives ammonium salts of 4-benzylsulfonyl-5-polyfluoroalkyl--triazoles. The proposed reaction scheme includes the participation of catalytic amounts of azide ion in the cyclization of the formed intermediate vinyl azides to triazoles. X-ray analysis of 1,4-diazabicyclo[2.2.2]octane salt of 4-benzylsulfonyl-5-(-H-hexafluoropropyl)--triazole has been carried out.     

Cyclodextrin-based optosensor for determination of tryptophan

A flow-through optosensor for tryptophan is described. The sensor is developed in conjunction with a flow-injection analysis system and uses immobilized -cyclodextrin as the sensing agent. The detection limit for tryptophan was 4ng ml^–1. The RSD for determination of 1 g ml^–1 of tryptophan was 2.8%.     

Development of a method for recovery of 233U from thorium oxalate cake in reconversion step of reprocessing of irradiated thorium rods

A method is developed for the selective leaching of ²³³U from a thorium oxalate cake. The leaching capacity of ammonium carbonate and nitric acid have been investigated, showing that (NH₄)₂CO₃ leads to higher recovery. The maximum leaching efficiency is obtained using 0.5% ammonium carbonate, with a minimal thorium pick-up. A uranium recovery of 94% is obtained after three consecutive contact experiments in carbonate media, with minimal thorium uptake in the leachate. This process was applied to an actual plant stream, allowing the reduction of the ²³³U -activity from 5.64 to 0.3 Ci/g of thorium oxalate cake.     

Die Thiocyanatextraktion und Dithizonbestimmung von Zink in Eisen(III)-oxid

Zusammenfassung Eine Methode zur Zinkbestimmung in Eisen(III)-oxid wird vorgeschlagen. Sie beruht auf der Extraktion des Zinkthiocyanatkomplexes aus schwach saurer Lösung mit Isoamylalkohol. Eisen wird mit Ammoniumfluorid, Kupfer mit Natriumthiosulfat maskiert. Kobalt und Nickel stören nicht, wenn der Extrakt mit einer Waschlösung, die Nitroso-R-Salz enthält, gewaschen wird. Zink wird mit einer Pufferlösung (pH 9) re-extrahiert und mit Dithizon colorimetrisch bestimmt. Bei der Extraktion wird Zink gleichzeitig von gröeren Mengen Cd, Pb und Bi, die die colorimetrische Bestimmung in ammoniakalischer Lösung stören, abgetrennt.

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Thiocyanate extraction and dithizone determination of zinc in iron(III) oxide

A Separation of microgram amounts of zinc from large amounts of iron (100 mg) and from 100 g of Co, Cd, Ni, Cu and 200 g of Bi, Pb has been worked out. Zinc is extracted by isoamyl alcohol from a solution containing ammonium thiocyanate, ammonium fluoride (for masking iron) and sodium thiosulphate (for masking copper). Cobalt and nickel are removed from the extract by shaking with a washing solution containing nitroso-R-salt. Zinc is in this way also separated from Cd, Pb and Bi interfering with the colorimetric determination with dithizone. The method was applied to the determination of zinc in ferric oxide.