Determination of Cr(VI) in plants by electrothermal atomic absorption spectrometry after leaching with sodium carbonate

The determination of chromium (VI) compounds in plants by electrothermal atomic absorption spectrometry (ET AAS) is proposed based on their leaching with 0.1 M Na₂CO₃. Due to the presence of relatively high amounts of Na₂CO₃ in the resulting samples, the temperature and time of pyrolysis and atomization stages must be optimized to minimize the influence of the matrix. A limit of detection (LOD) for determination of Cr(VI) in plants by ET AAS was found to be 0.024 μg g⁻¹.The concentration of Cr(VI) and total chromium in plants collected in different geographical areas (South Africa and Russia), grown on soils high in chromium was determined. The concentration of Cr(VI) and total Cr in stems and leaves of plants was in the range of 0.04–0.7 μg g⁻¹ and 0.5–10 μg g⁻¹, respectively. The limited uptake of Cr(III) by plants, in comparison to its concentration in soil, can be explained by the very low solubility of natural Cr(III) compounds.Results for the determination of Cr(VI) were confirmed by the analysis of BCR CRM 545 (Cr(VI) in welding dust) with good agreement between certified (39.5 ± 1.3 μg mg⁻¹) and found (38.8 ± 1.2 μg mg⁻¹) values. The total concentration of Cr in plants has also been determined by ET AAS after dry ashing of samples at 650 °C. Results were confirmed by the analysis of BCR CRM 281 (Trace elements in Rye Grass) with good agreement between the found (2.12 ± 0.16 μg g⁻¹) and certified value (2.14 ± 0.12 μg g⁻¹).     

Drying dissipative structure of sodium dextran sulfate in aqueous solution

Drying dissipative patterns were observed at room temperature on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of aqueous solution of sodium salts of dextran sulfate (NaDSS) having molecular weights of 5000, 36,000 ~ 50,000 and 500,000. These biopolyelectrolytes are one of the typical polysaccharides. The influences of the hexose units upon the macroscopic and microscopic drying patterns are studied. Formation of some ordered structure is observed for NaDSS in high polymer concentrations especially on a cover glass. Broad ring size decreased as polymer concentration decreased and/or its molecular weight increased. Drying patterns are clarified to be formed by the successive and cooperative pattern formation of convection, sedimentation, and solidification.     

Direct nitric oxide detection in aqueous solution by copper(II) fluorescein complexes

A series of FL(n) (n = 1-5) ligands, where FL(n) is a fluorescein modified with a functionalized 8-aminoquinoline group as a copper-binding moiety, were synthesized, and the chemical and photophysical properties of the free ligands and their copper complexes were investigated. UV-visible spectroscopy revealed a 1:1 binding stoichiometry for the Cu(II) complexes of FL(1), FL(3), and FL(5) in pH 7.0 buffered aqueous solutions. The reactions of FL(2) or FL(4) with CuCl(2), however, appear to produce a mixture of 1:1 and 1:2 complexes, as suggested by Job's plots. These binding modes were modeled by the synthesis and X-ray crystal structure determination of Cu(II) complexes of 2-[(quinolin-8-ylamino)methyl]phenol (modL), employed as a surrogate of the FL(n) ligand family. Two kinds of crystals, [Cu(modL)(2)](BF(4))(2) and [Cu(2)(modL')(2)(CH(3)OH)](BF(4))(2) (modL' = 2-[(quinolin-8-ylamino)methyl]phenolate), were obtained. The structures suggest that one oxygen and two nitrogen atoms of the FL(n) ligands most likely bind to Cu(II). Introduction of nitric oxide (NO) to pH 7.0 buffered aqueous solutions of Cu(FL(n)) (1 microM CuCl(2) and 1 microM FL(n)) at 37 degrees C induces an increase in fluorescence. The fluorescence response of Cu(FL(n)) to NO is direct and specific, which is a significant improvement over commercially available small molecule-based probes that are capable of detecting NO only indirectly. The NO-triggered fluorescence increase of Cu(FL(5)) occurs by reduction of Cu(II) to Cu(I) with concomitant dissociation of the N-nitrosated fluorophore ligand from copper. Spectroscopic and product analyses of the reaction of the FL(5) copper complex with NO indicated that the N-nitrosated fluorescein ligand (FL(5)-NO) is the species responsible for fluorescence turn-on. Density functional theory (DFT) calculations of FL(5) versus FL(5)-NO reveal how N-nitrosation of the fluorophore ligand brings about the fluorescence increase. The copper-based probes described in the present work form the basis for real-time detection of nitric oxide production in living cells.     

Enhancement effect of lauric acid on the rectal absorption of propranolol from suppository in rats.

In a previous paper, we have demonstrated that medium chain fatty acids significantly enhance the in vitro rectal absorption of propranolol (PL) and that the enhancement may be partly due to the formation of a complex with a fatty acid at a 1:1 molar ratio. To confirm in vivo the enhancement effect of lauric acid on PL absorption, PL suppositories with lauric acid at various molar ratios were administered to rat rectum. PL absorption from Witepsol and macrogol suppositories with lauric acid at a 1:1 molar ratio was much larger than that after PL alone and the 1:2 or 1:3 molar ratio ones. The bioavailability (BA) after administration of the 1:1 molar ratio suppository (PL, 4 mg/kg) was 1.6- and 2.1-fold for the Witepsol and macrogol formulations respectively, compared with that after PL alone. A similar result was obtained with the PL solid dispersion suppository with lauric acid at a 1:1 molar ratio, showing a 1.7-fold higher BA compared with PL alone. The release of PL from the macrogol suppository was significantly faster at a 1:1 molar ratio than that of other preparations, but not so in the solid dispersion suppository. There was not good agreement between the release rates of PL from the suppositories and the plasma levels after dosing. These results supported the concept that a portion of PL, by forming a 1:1 complex with lauric acid, would penetrate across the rectal mucosa more easily than PL alone.     

Determination of trace metals in sodium by electro-thermal atomic absorption spectrometry

Graphite-furnace atomic absorption spectrometry is used to analyze sodium metal after conversion to sodium nitrate. Chromium, Ni, Co, Cd and Pb have detection limits in sodium of 0.18, 0.48, 0.11, 0.02 and 0.48 μg g^-1; these are similar to the concentrations in nuclear-grade sodium, except for lead, which is below the detection limit. The behaviour of sodium nitrate, chloride and sulphate as matrices is compared.     

The determination of sodium in pure limestones by atomic absorption spectrophotometry

The determination of sodium in pure limestones by atomic absorption spectrophotometry is described. The interferences of chloride and calcium ions are discussed; chloride affects the dissociation equilibrium, and calcium lowers the evaporation rate of sodium, thus lowering the concentration of free sodium atoms in the flame. The sensitivity achieved with a rather rough apparatus is 0.15 p.p.m. sodium.     

Determination of dextran sulfate sodium with crystal violet by triple-wavelength overlapping resonance Rayleigh scattering

A triple-wavelength overlapping resonance Rayleigh scattering (TWO-RRS) method was developed to detect dextran sulfate sodium (DSS) with crystal violet (CV). At pH 10.0 Britton Robinson buffer solution medium, the interaction of CV with DSS occurred which greatly enhanced the RRS intensity with the new RRS peaks appearing at 340, 501 and 671 nm and all these three peaks enhanced with the increase of DSS concentration in the range of 0.04-2.5 microg ml(-1) and the detection limit for the three single peaks was 0.024, 0.027, and 0.027 microg ml(-1), respectively, whereas that of the TWO-RRS method was 0.013 microg ml(-1). The TWO-RRS method was found to have much better flexibility and high sensitivity than the single-wavelength method. In this paper, the interaction conditions were optimized. The affecting factors and characteristics of RRS for the interaction of DSS with CV were investigated and a sensitive method for the determination of trace amounts of DSS using the TWO-RRS method was developed.     

Bromination by means of sodium monobromoisocyanurate (SMBI)

A variety of aromatic compounds with both activating and deactivating substituents were brominated with sodium monobromoisocyanurate (SMBI) 1, diethyl ether, diethyl ether-methanesulfonic acid, trifluoroacetic acid, or sulfuric acid were employed as solvents. Thus nitrobenzene was conveniently brominated in sulfuric acid, benzene was readily monobrominated in diethyl ether-methanesulfonic acid, and phenol was selectively brominated at the ortho position under mild conditions in refluxing diethyl ether. With substituents that are easily protonated, trifluoroacetic acid may be employed as solvent in the reaction with 1, in contrast NBS was ineffective in trifluoroacetic acid. This renders 1 a superior reagent relative to NBS. In addition to aromatics, alkenes, ketones and esters were also brominated with 1. Diethyl malonate was brominated with 1 and then subjected to a Bingel reaction with NaH to afford the desired methanofullerene in reasonable yield.     

The absorption and structure of fluorescein and its ethyl derivatives in various solutions

Ethyl fluorescein and diethyl fluorescein were synthesized. Their absorption spectra in different pH solutions and in organic solvents with different polarity were measured. These were systematically compared with those of fluorescein, and the forms of these dyes in various media were reasonably assigned.     

Preparation of sodium dimolybdate by the pyrolysis of sodium oxomolybdenum (VI) oxalate

Thermal studies on various oxalato complexes have been of immense interest as they yield finely divided, highly reactive oxides which are usually obtained at a much lower temperature than that required in the conventional method of preparation, i.e., heating a mixture of two or more constituents [1]. A survey of the literature reveals that the compounds having the general formula A₂[Mo₂O₅(C₂O₄)₂(H₂O)₂], where A = K⁺, NH⁺₄[2] and A = Cs⁺ [3], have been prepared and their thermal decomposition is studied, but no such information is available regarding the preparation and characterisation of Na₂[Mo₂O₅(C₂O₄)₂(H₂O)₂] (SMO), which forms the subject of study of this paper. Sodium dimolybdate (Na₂Mo₂O₇), the decomposition product of SMO, is obtained at 280°C, a temperature much lower than that required in the conventional method of preparation of heating a mixture of Na₂MoO₄ and MoO₃ [4].     

Spectrophotometric procedure for indirect determination of ranitidine in pharmaceutical formulation using fluorescein sodium

A simple and sensitive spectrophotometric method for the determination of ranitidine hydrochloride (R·HCl) in pharmaceutical formulation is proposed. The procedure is based on the oxidation of R·HCl by bromine, generated in situ by the action of bromate?Cbromide mixture in acid medium, followed by estimation of surplus oxidant by its reaction with fluorescein sodium salt (FL). The decrease in concentration of FL is estimated by measuring its absorbance at ?? _max?=?436?nm. All variables affecting the reaction conditions, such as concentration of NaBrO₃, HCl, NaBr and FL, and reaction time were carefully studied and optimized. The analytical curve was linear in the R·HCl concentration range from 0.3 to 8???g?mL^?1 with a detection limit of 0.13???g?mL^?1. The reliability of the proposed spectrophotometric method was established by parallel determination of pure and dosage forms containing R·HCl, by the reference method and by recovery studies.     

Enhancement effect of sodium dodecyl benzene sulfonate (SDBS) and its application into voltammetric determination of telmisartan

A sensitive and rapid electrochemical method was developed for the determination of telmisartan based on the enhancement effect of sodium dodecyl benzene sulfonate (SDBS). In 0.1 mol L⁻¹ HClO₄ and in the presence of 7.5 × 10⁻⁵ mol L⁻¹ SDBS, a well-defined and sensitive oxidation peak was observed for telmisartan at the acetylene black (AB) paste electrode. However, the oxidation peak is poor-shaped and the peak current is very low in the absence of SDBS, suggesting that SDBS shows obvious enhancement effect for the determination of telmisartan. After all the experimental parameters were optimized, a sensitive and simple electrochemical method was developed for determining telmisartan. The oxidation peak current is proportional to the concentration of telmisartan over the range from 2.5 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹. The detection limit is 7.5 × 10⁻⁸ mol L⁻¹ after 2 min of accumulation. This new voltammetric method was successfully used to detect telmisartan in drugs.     

Diffusion of dextran within poly(methacrylic acid) hydrogels

We describe an investigation of fluorescence correlation spectroscopy into the diffusion of fluorescein‐tagged dextran (FDEX) in a poly(methacrylic acid) (PMAA) hydrogel. The temperature dependence of FDEX diffusion is shown to follow Zimm behavior in pure water, and the decrease in the diffusion coefficient when in the PMAA hydrogel has been modeled. The addition of acid and alkali (HCl and NaOH, respectively) not only control the swelling and collapse of the hydrogel but also reveal a strong pH dependence of the dextran diffusion coefficient, which shows a (nonmonatonic) increase with pH. The addition of NaCl and CaCl₂ salts similarly showed evidence of network swelling, most notably at low salt concentration, but also that the diffusion coefficient within the gel at these low concentrations is larger than that in the equivalent solution without the hydrogel, indicating that the combination of hydrogel and salt works to increase the diffusion coefficient above that in pure water. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012