Spectroscopic and photochemical properties of the lichen compound lobaric acid

Lichens synthesize and accumulate photoprotective compounds against possible damage induced by UV radiation in the photobiont. A biological model has been recently formulated that allows the use of lichens to evaluate changes at different UV radiation levels. The thermodynamics, photophysical and photochemical properties of lobaric acid were studied in acetonitrile, ethanol and Brij 35(3%) micelles at different pH values. Also the sun protector factor (SPF) was determined by in vitro methods. Lobaric acid was extracted from Stereoculon alpinum Laur. and characterized by means of standard procedures. Solutions were irradiated in oxygen and under nitrogen conditions with a UV medium pressure lamp. Lobaric acid absorbs at 287, 303 nm, and no fluorescence emission was observed. The maximum value of the molar extinction coefficient (5479.6 M(-1) cm(-1)) was obtained in Brij 35 at pH 12. Solubility is pH dependant and is highest in Brij 35 at pH 12 (4.45 x 10(-4) M). Photoconsumption quantum yields ranged between 10(-4) and 10(-5) in aerobic and anaerobic experimental conditions. Lobaric acid SPF was very low (0.5) compared with homosalate (4.0), (reference solar filter). Two pKa values, 5.05 (carboxylic acid group deprotonation) and 9.75 (phenolic OH deprotonation), were determined.     

Two-proton multiplets in theN=82 nucleus 62 144 Sm82 from in-beamγ-measurements

In a high sensitivity (,2n) in-beam study of ₆₂ ¹⁴⁴ Sm₈₂, with the Kölner Würfel OSIRIS -detector array including a Compton polarimeter, we have identified the complete two-proton multiplets d ₅ ^2/–2 , d ₅ ^2/–1 g ₇ ^2/–1 , g ₇ ^2/–2 , h_11/2d ₅ ^2/–1 and the 9^– to 4^– members of the h_11·/2g ₇ ^2/–1 multiplet.Work partially supported by CICYT (Spain).     

Germanium speciation by LC-HG-ICP/OES

Liquid chromatography-hydride generation-inductively coupled plasma optical emission spectroscopy (LC-HG-ICP/OES) has been used to determine inorganic and organometallic species of germanium. In recent studies these coupled systems has been applied successfully to the speciation of arsenic. To establish separation conditions for germanium two reversed stationary phases and different solvent mixtures for elution, in isocratic or gradient mode have been tested. The reduction of germanium species to the corresponding volatile hydride is a critical step, especially for acidity control, thus the conditions for reduction using different concentrations of acid have been studied systematically. For the conditions established quality parameters as limit of detection (at the g l^–1 level), precision and recovery have been determined for the germanium species considered in a saline matrix.     

Fluorimetric determination of sulphate by ternary complex formation with zirconium and biacetylmonoxime nicotinylhydrazone

A fluorimetric procedure for the determination of sulphate (0.5-6 mug ml ) based on the formation of a ternary complex with biacetylmonoxime nicotinylhydrazone and zirconium(IV) is described. The excitation and fluorescence maxima are at 415 and 505 nm, respectively. The method is rapid and the procedure reproducible. The precision is +/- 2% near to the middle range of the calibration curves. There is no interference from most common ions. Phosphate and fluoride are tolerated at 100-fold molar ratio to sulphate. The method has been applied to the determination of sulphate in a variety of water samples.     

Extraction method for arsenic speciation in marine organisms

Three extraction systems have been assayed to extract arsenic species from biological marine sample, using methanol, methanol-chloroform (1:1) and methanol-water (1:1) as solvents. From a comparative study methanol-water 1:1 was chosen. A clean-up of the raw extract using C₁₈ cartridges is proposed. The results obtained from flounder (Pleuronectes platessa), sole (Solea solea), mussel (Mytilus edulis) and cockle (Cardium edule) are reported.     

Assessment of Four Inter-Comparison Exercises in Organic Elemental Analysis

 Four inter-comparison exercises on organic elemental analysis were carried out between 1997 and 2001 by the Department of Analytical Chemistry of the University of Barcelona, together with the Microanalysis Service and the Institute of the Marine Sciences, which both belong to the CSIC in Barcelona, and the University of A Coru?a. More than sixty laboratories participated in these exercises. Here we describe the design and characteristics of the trials, the samples and the homogeneity tests applied. We report the results obtained for the analysis of carbon, hydrogen, nitrogen, sulphur and oxygen, their statistical analysis, and the most relevant aspects of the technical discussion meetings. Received December 20, 2001; accepted March 18, 2002; published online July 22, 2002