Determination of Thallium in Antarctic Snow by Means of Laser Induced Atomic Fluorescence and High Resolution Inductively Coupled Plasma Mass Spectrometry

Abstract

Measurements of thallium levels in Antarctic snow samples collected in an area surrounding the Italian Station at Terra Nova Bay in different campaigns have been performed without preconcentration by means of Laser Induced Atomic Fluorescence Spectroscopy (LIAF) as well as by High Resolution Inductively Coupled Plasma Mass Spectrometry (HR ICP-MS).

The data obtained by both methods compare favourably and are of the order of tenths of pg/g. The data is discussed taking into account the effect of the marine aerosol and the crustal contribution to the thallium content in samples.     

Asymmetric local displacements in the Bi2Sr2CaCu2O8+β superconductor

Instantaneous in-plane Cu-O bond distribution in the Bi₂Sr₂CaCu₂O_8+β (Bi2212) superconductor has been investigated by high k-resolution Cu K-edge extended X-ray absorption fine structure (EXAFS) measured with polarized vector parallel to the two orthogonal Cu-O-Cu bonds of the CuO₂ square plane. The results show an anisotropic Cu-O distribution in the two directions and provide further information on the local atomic displacements in the lattice-charge stripes. Received 5 June 2000     

Thermally and optically induced effects on sub-band gap absorption in nanocrystalline CdSe (nc-CdSe) thin films

Nanocrystalline cadmium selenide (nc-CdSe) thin films have been prepared by thermal evaporation using the inert gas condensation (IGC) technique. Transmission electron microscopy (TEM) studies show that the CdSe nanocrystals (NCs) are spherical in shape. Constant photocurrent method (CPM) is used to determine the value of absorption coefficient in low absorption region of as-deposited, annealed and light soaked nc-CdSe thin films. Values of optical band gap (E_g) have been determined by using Tauc's relation for as-deposited, annealed and light soaked nc-CdSe thin films from the α values evaluated from reflection and transmission measurements. We have used a derivative procedure to sub-gap absorption spectra in order to get information on the energetic distribution of the occupied density of states below Fermi level. Constants such as optical gap E_g, Urbach edge E_u have been obtained from CPM spectra in as-deposited, annealed and light soaked nc-CdSe thin films. Concentration of defect states has also been calculated in as-deposited, annealed and light soaked nc-CdSe thin films.     

The low frequency behaviour in high frequency capacitance–voltage characteristics due to contribution of band-to-band tunnelling and generation–recombination in Hg0.75Cd0.25Te MIS capacitors

Hg_1−xCd_xTe Metal–Insulator–Semiconductor (MIS) capacitors were studied both experimentally and theoretically to investigate the capacitance contributions due to band-to-band (btb) tunnelling and generation–recombination (gr) of carriers to inversion layer capacitance. A good fit to the data has been obtained by including the btb contributions rather than gr contributions.     

Soft biometrics in conjunction with optics based biohashing

Biometric systems are gaining importance because of increased reliability for authentication and identification. A biometric recognition technique has been proposed earlier, in which biohashing code has been generated by using a joint transform correlator. The main drawback of the base biohashing method is the low performance of the technique when an “impostor” steals the pseudo-random numbers of the genuine and tries to authenticate as genuine. In the proposed technique, soft biometrics of the same person has been used to improve the discrimination between the genuine and the impostor populations. The soft biometrics are those characteristics that provide some information about the individual, but lack the distinctiveness and permanence to sufficiently differentiate between any two individuals. In the enrolment process, biohash code of the target face images has been integrated with the different soft biometrics of the same person. The obtained code has been stored for verification. In the verification process, biohash code of the face image to be verified is again diffused with the soft biometric of the person. The obtained code is matched with the stored code of the target. The receiving operating characteristic (ROC) curve and the equal error rate (EER) have been used to evaluate the performance of the technique. A detailed study has been carried out to find out the optimum values of the weighting factor for the diffusion process.     

Determination of inorganic anions in environmental waters with a hydroxide-selective column

US Environmental Protection Agency Method 300.0 specifies the use of an IonPac AS4A anion-exchange column with a carbonate-hydrogencarbonate eluent and suppressed conductivity detection for the determination of inorganic anions in environmental waters by ion chromatography. Hydroxide eluents have not typically been used for the routine analysis of common inorganic anions due to the lack of an appropriate hydroxide selective column and the difficulty in preparing contaminant free hydroxide eluents. The use of ion chromatography with a hydroxide-selective IonPac AS17 column, automated eluent generation and potassium hydroxide gradient represents a new approach to the routine determination of inorganic anions in environmental waters. This new approach, which is a modification of Method 300.0, allows equivalent method performance with improved linearity, precision, and method detection limits. The AS17 column provides superior retention of fluoride from the column void volume and improved resolution from small organic acids, such as formate and acetate, compared to the AS4A column. Quantitative recoveries were obtained for all the common inorganic anions spiked into typical environmental waters using this new approach, and the Performance Based Measurement System Tier 1 method validation quality control acceptance criteria are well within the acceptable ranges defined by Method 300.0. In addition, the EG40 eluent generator eliminates the need to manually prepare eluents, increasing the level of automation and ease-of-use of the ion chromatography system.     

On the decay of the ozonide radical in aqueous alkaline solutions

In flash photolysis of an oxygenated aqueous potassium persulphate solution at pH 12.5 the decay of the ozonide radical has been found to follow $\text{3}\text{2}$ order kinetics which has been explained by reactions O^?₃ + O^? ? 2 O^?₂ and O^?₃ + HO₂ → 2 O₂ + OH^?     

Simple and rapid synthesis of ternary polyaniline/titanium oxide/graphene by simultaneous TiO<Subscript>2</Subscript> generation and aniline oxidation as hybrid materials for supercapacitor applications

This paper reports a simple methodology for the synthesis of a polyaniline/titanium oxide/graphene hybrid (Pani/TiO₂/GN) using a simple methodology, and their application as a supercapacitor electrode material for energy storage. The Pani/TiO₂/GN hybrid was prepared by a simple approach by simultaneous generation of Pani and TiO₂ in situ from aniline and titanium iso-propoxide, respectively, in the presence of GN under ice bath conditions. The incorporation of GN improved the electrical conductivity of Pani and helped to decrease the charge transfer resistance, whereas TiO₂ generation by an in situ method increased the surface area considerably and enhanced the capacitance of the Pani/TiO₂/GN hybrid. TEM showed that Pani and TiO₂ were well incorporated and coated on the GN successfully. The shift of the peaks in the FTIR spectrum and XRD pattern of the Pani/TiO₂/GN hybrid compared to their pure counterparts suggested that TiO₂ and Pani had been perfectly coated on the GN, and there was a strong interaction among Pani, GN, and TiO₂ particles. The electrochemical performance of the as-prepared Pani/TiO₂/GN hybrid electrode showed a high specific capacitance of 403.2 F g^?1 at a current density of 2 A g^?1 and excellent cycling stability for up to 1000 cycles. This suggested that the effective incorporation of GN and TiO₂ into Pani and the high surface area could simultaneously increase the electrochemical capacitance and cyclic stability of the Pani/TiO₂/GN hybrid, leading to superior electrochemical performance.

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Graphical abstract The electrochemical performance of as-prepared Pani/TiO₂/GN hybrid electrode showed a high specific capacitance of 403.2 F g^?-1 at a current density of 2 A g^?-1 and excellent cycling stability for up to 1000 cycles. This suggested that the effective incorporation of GN and TiO₂ into Pani and the high surface area could simultaneously increase the electrochemical capacitance and cycle stability of the Pani/TiO₂/GN hybrid, leading to superior electrochemical performance.

     

The formation of highly fluorescent zinc phosphate in the presence of uranium and its application to the direct fluorimetry of uranium in aqueous media

The formation and composition of highly fluorescent zinc phosphates in the presence of traces of uranium were investigated and a direct fluorimetric determination of uranium in aqueous media was developed, based on the formation of finely dispersed and stabilized fluorescent precipitates. The standard deviation for 20 μg of uranium, in 25 ml is 5% ; with the fluorimeter described, 10^-2 μg of uranium per ml can be determined with an error of 50%. The method is very selective and can be employed for analysis of uranium in ores; it is less sensitive than conventional fluorimetry of fused alkali fluorides but is much simpler and faster. Interferences can often be eliminated by suitable masking reactions.