The experience of accreditation of an analytical laboratory at the Argentine Atomic Energy Commission

The implementation of a quality system based on the ISO/IEC 17025:1999 standard is a growing necessity for analytical laboratories to demonstrate their technical competence. In 2001, the Nuclear Analytical Techniques Group of the Argentine Atomic Energy Commission obtained the recognition of the International Atomic Energy Agency in the application of neutron activation analysis and the accreditation by the national accreditation body. The importance of the participation of the group in the Agency's Regional Programme for Latin America, ARCAL XXVI on Quality Assurance in Analytical laboratories is discussed, as well as the activities performed to attain these objectives. Some improvements worth mentioning resulted from the implementation of the quality system and, following the premise of continuous improvement, changes were introduced aiming at the laboratory re-accreditation.     

A segregated method for compressible flow computation. Part II: general divariant compressible flows

Typically, segregated methods have been used for the computation of incompressible flows whereas coupled solvers, for compressible flows. Compared to coupled solvers, segregated methods present the advantage of computational savings in RAM memory and CPU time, although at the cost of an inferior robustness. However, previously published segregated algorithms for general compressible flows are known to present pitfalls, like convergence to wrong solutions, lack of robustness in the presence of strong discontinuities, such as normal and oblique shocks, and complicated boundary condition imposition. Therefore, in this paper a segregated method for non‐isothermal compressible flows is proposed that preserves the thermodynamic coupling and overcomes the criticisms of existing methods. Copyright © 2005 John Wiley & Sons, Ltd.     

The chern classes of the eigenbundles of an automorphism of a curve

LetX be smooth complex projective curve. Leth be an automorphism ofX of orderp. We improve a formula to compute the characteristic classes of the normal bundles of certain components of the fixed point set ofh acting on the symmetric products ofX. The author was supported by the Emmy Noether Research Institute for Mathematics.     

Carrier thiols are targets of Photofrin II photosensitization of isolated rat liver mitochondria

To gain further insight into the ability of Photofrin II to photosensitize mitochondrial translocators, and to ascertain whether mitochondrial thiols are specific targets of Photofrin II, the activity of phosphate carrier was measured in isolated rat liver mitochondria irradiated with 365 nm light in the presence of Photofrin II. Photodynamic treatment decreased the maximum rate of phosphate uptake, without changing the phosphate affinity for its own carrier. The ability of the thiol reagent mersalyl (an inhibitor of phosphate, dicarboxylate and oxodicarboxylate carriers) to protect these carriers against Photofrin II photosensitization was also tested. Protection was observed, indicating the involvement of carrier thiols in mitochondrial photosensitization.     

Catalytic Enantioselective Synthesis of N,Cα,Cα‐Trisubstituted α‐Amino Acid Derivatives Using 1H‐Imidazol‐4(5H)‐ones as Key Templates

1H‐Imidazol‐4(5H)‐ones are introduced as novel nucleophilic α‐amino acid equivalents in asymmetric synthesis. These compounds not only allow highly efficient construction of tetrasubstituted stereogenic centers, but unlike hitherto known templates, provide direct access to N‐substituted (alkyl, allyl, aryl) α‐amino acid derivatives.     

Identification of Structure–Activity Relationships from Screening a Structurally Compact DNA‐Encoded Chemical Library

Methods for the rapid and inexpensive discovery of hit compounds are essential for pharmaceutical research and DNA‐encoded chemical libraries represent promising tools for this purpose. We here report on the design and synthesis of DAL‐100K, a DNA‐encoded chemical library containing 103 200 structurally compact compounds. Affinity screening experiments and DNA‐sequencing analysis provided ligands with nanomolar affinities to several proteins, including prostate‐specific membrane antigen and tankyrase 1. Correlations of sequence counts with binding affinities and potencies of enzyme inhibition were observed and enabled the identification of structural features critical for activity. These results indicate that libraries of this type represent a useful source of small‐molecule binders for target proteins of pharmaceutical interest and information on structural features important for binding.     

Application of thermal analysis for evaluating the digestion of microwave pre-treated sewage sludge

The effect of microwave pre-treatment (MwP) on anaerobic digestion of sewage sludge was studied by means of thermal analysis and evolved gas analysis. The effect of the pre-treatment at low energy input (<1000 kJ L^?1) on sludge solubilisation was studied with the aid of response surface methodology. The pre-treatment process was subsequently studied at energies of 488–2700 kJ L^?1 to evaluate the improvement in biogas production under mesophilic conditions. Organic matter modifications were studied using a Setaram TGA92 analyser at atmospheric pressure coupled to an MSC200 quadrupole mass spectrometer from Balzers. Particle size analysis was carried out using a Laser Diffraction Particle Size Analyser LS 13 320 Beckmann Coulter for evaluating the effect of MwP on sludge particles. Results showed an increase in organic matter solubilisation with the increase in the energy applied. Modifications in the specific surface area of the organic matter due to the MwP resulted in increments in methane yields. However, an accumulation of complex compounds was observed in thermal profiles at the maximum energy input (2700 kJ L^?1). Semi-continuous digestion experiments were evaluated using as substrate pre-treated sludge at the optimum energy value (975 kJ L^?1). Results showed a significant increase in methane yield (43 %) when evaluating the process at hydraulic retention times (HRTs) of 25–10 days.     

CZE separation of amitrol and triazine herbicides in environmental water samples with acid-assisted on-column preconcentration

A simple analytical scheme for the detection and quantification of amitrol and triazine herbicides (atrazine, ametryn and atraton) and degradation product (2‐hydroxyatrazine) in environmental water samples by CZE is reported. On‐column preconcentration of analytes from untreated water samples (mineral, spring, tap and river water) is accomplished by introducing an acid plug (200 mM citrate of pH 2.0) after the sample and then proceeding with the CZE separation, using 100 mM formiate buffer of pH 3.5 as running buffer and 25.0 KV as separation voltage. UV detection at 200 nm provides LODs from 50 to 300 nM in untreated samples and they were lowered tenfold by sample preconcentration by evaporation. Calculated recoveries were typically higher than 90%. Minimal detectable concentration of the electroactive amitrol could be decreased about 20‐fold when electrochemical detection was employed by monitoring the amperometric signal at +800 mV using a carbon paste electrode (LOD of 9.6 nM, 0.81 μg/L, versus 170 nM, 14.3 μg/L, using amperometric and UV detection, respectively) in untreated water samples.