Ligand sensitized luminescence of uranyl by benzoic acid in acetonitrile medium: a new luminescent uranyl benzoate specie.
Benzoic acid (BA) is shown to sensitize and enhance the luminescence of uranyl ion in acetonitrile medium. Luminescence spectra and especially UV-Vis spectroscopy studies reveal the formation of tri benzoate complex of uranyl i.e. [UO2(C6H5COO)3](-) which is highly luminescent. In particular, three sharp bands at 431, 443, 461nm of absorption spectra provides evidence for tri benzoate specie of uranyl in acetonitrile medium. The luminescence lifetime of uranyl in this complex is 68μs which is much more compared to the lifetime of uncomplexed uranyl (20μs) in acetonitrile medium. In contrary to aqueous medium where uranyl benzoate forms 1:1 and 1:2 species, spectroscopic data reveal formation of 1:3 complex in acetonitrile medium. Addition of water to acetonitrile results in decrease of luminescence intensity of this specie and the luminescence features implode at 20% (v/v) of water content. For the first time, to the best of our knowledge, the existence of [UO2(C6H5COO)3](-) specie in acetonitrile is reported. Mechanism of luminescence enhancement is discussed.
Highly selective antenna effect in polystyrene membrane immobilized 2-pyridone sensitizer: Novel spectrofluorimetric method for assessment of nano scale terbium (III)
Abstract At room temperature, the contact of Tb 3+ ions dissolved in bidistilled water with a polystyrene film incorporating 2-pyridone (PS-Pyr) exhibits terbium-sensitized photoluminescence (PL) when excited at 295 nm. The Tb 3+ -sensitized emission is attributed to a complex formation as well as a highly efficient and selective energy transfer from 2-pyridone to Tb 3+ ions. This has been utilized as the basis for a selective spectrofluorimetric detection of Tb 3+ . The association constant and the lifetime of the formed complex were determined; also, the sensing mechanism of the optosensor was proposed. The linear response range covers a concentration range of Tb 3+ from 5.0 × 10 −9 to 1.0 × 10 −6  mol L −1 . The LOD and LOQ were 2.9 × 10 −9 and 9.7 × 10 −9  mol L −1 , respectively. The sensitizer exhibits a unique and a highly selective energy transfer towards Tb 3+ ions over a large number of interfering ions. Moreover, the proposed optosensor was easy to prepare, has a relatively fast response time ∼30 s and high stability for at least 42 days. The optosensor has been applied to the determination of terbium ion in synthetic samples with high sensitivity, good reproducibility and accuracy.
Novel method for the determination of the methoxyl content in lignin by headspace gas chromatography.
The paper reports on a headspace gas chromatographic (HS-GC) method for the determination of methoxyl in lignin. The method involves the quantitive cleavage of methoxyl with hydroiodic acid (HI) to form methyl iodide in a closed headspace sample vial at 130 °C for 30 min. After HI has been added, the sample is neutralized by injecting a sodium hydroxide solution; the methyl iodide in the vial was determined by HS-GC using a flame ionization detector. The results showed that the method has an excellent measurement precision (RSD < 0.69%) and accuracy (RSD < 3.5%) for the quantification of methoxyl content in lignin. The present method is simple and accurate and can be used for the efficient determination of methoxy1 content in lignin and related materials.