Voltamperometric determination of kinetin with a carbon paste modified electrode

The electrochemical behaviour of kinetin (6-furfurylaminopurine) on a carbon paste modified with OV-17 silicone electrode, is studied. The determination of kinetin is possible working in square wave voltammetric techniques, reaching limits of determination of 38.7 ng ml⁻¹. The proposed method was successfully applied to determine the cytokinin in extracts of apples (previously spiked with kinetin) and the obtained results were in accordance with the results obtained with HPLC-UV.     

Evaluation of the factors affecting extraction of organic compounds based on the acid-induced phase cloud point approach

On the basis of a better analytical exploitation of acid-induced cloud point approach, a systematic study on the phase behaviour of acid aqueous solutions of anionic surfactants and factors affecting anionic surfactant-mediated extractions was performed. The anionic surfactants investigated were alkylsulphonates (ASS) with alkylchain lengths comprised between 8 and 16 carbon atoms. The critical hydrochloric acid concentration (minimal acid concentration required to separation in two liquid phases) was found to increase as alkylchain length of the anionic surfactant increased from 10 to 14. Non-acid-induced liquid-liquid phase separation was observed for sodium octanesulphonate (SOS) or sodium hexadecyl sulphonate (SHS) in the hydrochloric concentration range 0-10 M. Acid aqueous solutions of sodium decylsulphonate (SDeS) and sodium dodecylsulphonate (SDoS) separated into two liquid phases at temperatures ranging between 10 and 80 °C, while temperatures >35 °C were required for sodium tetradecylsulphonate. The influence on extraction efficiency and concentrating ability of experimental variables such as hydrophobicity and concentration of surfactant, nature and concentration of analyte, hydrochloric acid concentration, time and temperature of extraction and time of equilibration and centrifugation was examined. Advantages provided by anionic surfactant-mediated extractions over the use of non-ionic surfactants (cloud point extractions) are discussed.     

Simultaneous-fluorimetric methods for the determination of ammonia and urea by use of flow injection configurations with dual injection valves

Summary Two fluorimetric methods are proposed for the simultaneous determination of ammonia and urea based on the reaction of the former with o-phthalaldehyde/2-mercaptoethanol and on the use of a dual injection system in which the valves are coupled in series or in parallel. An enzymatic reactor converts urea into ammonia which is determined by the same reaction. These configurations provide very similar results with a linear determination range between 0.5 and 10.0 g ml^–1 and a sampling frequency of 60 h^–1. The proposed methods are very tolerant to foreign species commonly found in water, as shown by applying them to samples of different origins.     

Micellar-stabilized room-temperature phosphorimetric determination of the fungicide thiabendazole in canned pineapple samples

A method for the determination of the fungicide thiabendazole (TBZ) by micellar-stabilized room-temperature phosphorescence is described. It does not require any separation step and allows the direct determination of the fungicide in canned pineapple samples. The effect of various experimental conditions is discussed in detail. The analytical curve of thiabendazole gives a linear dynamic range of 23.8–500.0 ng mL^–1 and a detection limit of 23.8 ng mL^–1. Recoveries of 103.9 and 89.2% for syrup and canned pineapple pulp, respectively, were obtained for 250 ng mL^–1 thiabendazole.     

Fluorescence immunoassay for angiotensin I

A heterogeneous fluorescence immunoassay for angiotensin I is described. Fluorescein isothiocyanate (FITC) is used as fluorescent label; it is covalently linked to angiotensin I by reacting in pH 9.2 carbonate buffer at 18°C for 24 h. A Sephadex G-10 gel filtration column permits separation of conjugate from excess of FITC. The assay is applied to 4–40 ng ml^?1 angiotensin I, with a relative standard deviation of 5%.     

Synthesis of new functional derivatives of pyrazolidine from 1-acetyl-3-methyl-5-nitromethyl-2-phenylpyrazolidine

3-Nitromethylpyrazolidine reacts with derivatives of unsaturated acids and reducing agents with the formation of polyfunctional compounds of the pyrazolidine nucleus. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1365–1369, September, 2006.     

Multicommuted flow-through fluorescence optosensor for determination of furosemide and triamterene

Multicommutation implemented with flow-through optosensors is a very promising area of research. This recent approach benefits from the advantages of both methods and results in high sensitivity, selectivity, and speed, and little waste generation. This paper reports the simultaneous determination of furosemide and triamterene, two widely used diuretics, by measurement of their native fluorescence. The system has been proved to be useful for determination of both analytes in pharmaceutical preparations and for determination of triamterene in human urine and serum. A minicolumn filled with Sephadex SPC-25 microbeads was used to achieve separation of both analytes before detection in a flow-through cell filled with the same resin. The sensor is linear in the range 50–1200 and 0.4–8 ng mL⁻¹ with detection limits of 15 and 0.1 ng mL⁻¹ for furosemide and triamterene, respectively.     

Two-dimensional molecular magnets based on [Pt(mnt)2]− ions: Structures and magnetic properties

Two compounds of composition [FBzPy][Pt(mnt)₂] (1) and [FBzPy][Pt(mnt)₂] · 0.25-MeCN (2) ([FBzPy]⁺ = 1-(4′-fluorobenzyl)pyridinium and mnt²⁻ = maleonitriledithiolate) were prepared and their crystal structures were determined. The solvent molecule, MeCN, incorporated into lattice leads the anionic stacking pattern to be distinct between 1 and 2. The regular anionic stacking columns are connected by the anionic dimers to construct into 2D anionic networks in 1, while the anionic fourfold subunit develop into anionic layers though lateral S⋯S interactions in 2. As for two compounds, the magnetic susceptibilities in 2–350 K were measured, and the magnetic exchange schemes were built based on the analyses both crystal structures and extended Hückel molecular orbital calculations. The magnetic coupling model of an alternating AFM Heisenberg chain with an isolated AFM coupling dimer was dealt with 1, while a spin dimer with s = 1/2 with 2, and the magnetic coupling parameters were further gained via simulating the temperature dependent magnetic susceptibility data of two compounds.     

The mechanism of formation of volatile hydrides by tetrahydroborate(III) derivatization: A mass spectrometric study performed with deuterium labeled reagents

In order to clarify the mechanism of hydride formation, the isotopic composition of arsine, stibine, bismuthine, germane, stannane and hydrogen selenide formed by derivatization with either NaBD₄ (TDB) or NaBH₄ (THB) with inorganic As(III), Sb(III), Bi(III), Ge(IV), Sn(IV) and Se(IV) in aqueous reaction media and under various reaction conditions was determined. Batch hydride generation and gas chromatography–mass spectrometry (GC–MS) were employed. The analyte, present in 0.5–5 ml of acid solution (0.1–10 M in HCl or HNO₃ or HClO₄) was derivatized with 1 ml of 0.25–0.5 M TDB / THB in 0.1 M NaOH solution. For TDB derivatization in H₂O reaction media, almost pure BiD₃ and SbD₃ were always obtained for Bi(III) and Sb(III). Nearly pure AsD₃ could be obtained only under some reaction conditions. In general, for As(III), the isotopic composition of the arsines depends strongly on reaction conditions and included all possible AsH_nD_3−n from almost pure AsD₃ to almost pure AsH₃. For Ge(IV) and Sn(IV), the isotopic composition of generated GeH_nD_4−n and SnH_nD_4−n depends on reaction conditions, but pure GeD₄ and SnD₄ could never be obtained. Pure H₂Se was obtained in all cases, independent of reaction conditions. The occurrence of side reactions involving D–H exchange in TBD during its hydrolysis and before the derivatization step, as well as on recently formed hydrides following derivatization was investigated. D–H exchange in TDB during acid hydrolysis appears to occur to a limited extent. Amongst the hydrides, H₂Se undergoes H–D exchange whereas germane and stannane do not exchange at all. Arsine undergoes D–H exchange at elevated acidities (pH < 0) whereas stibine and bismuthine do not exchange significantly during the generation and stripping steps.A reaction model for hydride generation is proposed accounting for primary reactions giving rise to hydride formation through reaction intermediates, as well as side reactions involving D–H exchange and decomposition of reactive hydroboron species, reaction intermediates and final products. Hydrides are formed by direct hydrogen transfer from boron to the analyte atom, most likely through concerted mechanisms taking place via reaction intermediates.     

Phlogophites intercalated with Al2O3 pillars and modified with transition metals as catalysts of the DeNOx process

Natural phlogophite, pre-treated with acids and intercalated with alumina pillars, was used as catalytic support. Transition metals (Fe, Cu) were deposited on the surface of the modified clay materials by an ion-exchange method. The obtained samples were characterized with respect to structure (XRD), texture (BET), composition (EPMA) and chemical nature of the deposited transition metals species (UV-vis-DRS). The phlogophite based materials have been found to be active and selective catalysts of the DeNOx process. The Fe-containing samples were catalytically active at lower temperatures than the clays modified with copper. A competitive ammonia oxidation by oxygen decreased the effectiveness of the DeNOx process in the high temperature range.