Micelle formation in sodium hexadecyl sulfate surfactant solutions studied by small-angle neutron scattering

Micelle formation in aqueous sodium hexadecyl sulfate solutions is studied by small-angle neutron scattering. Measurements are carried out at different concentrations (1.1, 2.2, 3.2, 5.4, 10.9 and 32.8 mM/dm³) and at different temperatures (40°, 50°, and 60°C). The monotonous evolution of interparticle correlation can be observed on the measured scattering patterns. At high concentrations (10.9 and 32.8 mM/dm³) scattering patterns are described by interacting ellipsoids, but at low concentrations by non-interacting ellipsoids. Computation of the distance distribution function proved the ellipsoidal shape at 10.9 and 32.8 mM/dm³, but showed an unexpectedly large particle dimension and elongation of the micelles at lower concentrations.     

Emission Mössbauer study of the interface between a cobalt substrate and a polyimide coating

The emission Mössbauer technique is used to study the chemical structure of the interphase formed between a cobalt substrate and a polyimide coating. The results are interpreted to indicate that the coating is bonded to the cobalt substrate by means of carboxylate bonds with Co²⁺ ions in the oxide film at the interface.     

Preliminary study to prepare a reference material of toluene metabolite – o-cresol and benzene metabolite-phenol – in human urine

The candidate reference material (RM) was prepared by freeze-drying pooled urine samples obtained from healthy persons occupationally exposed to toluene. Homogeneity testing yielded no significant differences of urinary concentrations of o-cresol and phenol in 15 randomly selected units of RM. Stability testing showed no significant changes of concentrations of the above analytes over a period of 6 months. Property (pre-certified) values of phenol and o-cresol concentrations and their uncertainties (9.06±0.47 mg l⁻¹ and 1.03±0.06 mg l⁻¹, respectively) were estimated from results of a small-scale interlaboratory comparison in which two laboratories participated using four different analytical methods.     

High resolution applications of laser-induced breakdown spectroscopy for environmental and forensic applications

Laser-induced breakdown spectroscopy (LIBS) has been used in the elemental analysis for a variety of environmental samples and as a proof of concept for a host of forensic applications. In the first application, LIBS was used for the rapid detection of carbon from a number of different soil types. In this application, a major breakthrough was achieved by using a multivariate analytical approach that has brought us closer towards a “universal calibration curve”. In a second application, it has been demonstrated that LIBS in combination with multivariate analysis can be employed to analyze the chemical composition of annual tree growth rings and correlate them to external parameters such as changes in climate, forest fires, and disturbances involving human activity. The objectives of using this technology in fire scar determinations are: 1) To determine the characteristic spectra of wood exposed to forest fires and 2) To examine the viability of this technique for detecting fire occurrences in stems that did not develop fire scars. These examples demonstrate that LIBS-based techniques are inherently well suited for diverse environmental applications. LIBS was also applied to a variety of proof of concept forensic applications such as the analysis of cremains (human cremation remains) and elemental composition analysis of prosthetic implants.     

New type of bonding formed from an overlap between pi aromatic and pi C=O molecular orbitals stabilizes the coexistence in one molecule of the ionic and neutral meso-ionic forms of imidazopyridine

New bis(imidazo)pyridine dye has been synthesized and tested as a potential photoinitaitor for free-radical polymerization induced with the visible emission of an argon ion laser. The X-ray analysis based on data collected at 170 and 130 K, as well as density functional theory (DFT) calculations, revealed the presence of two different forms of imidazopyridine rings within the same molecule. These two forms of the same moiety had not only different geometries but different electronic structures as well. One of the imidazopyridine rings was in the ionic form, while the other was in the meso-ionic form. DFT calculations provided an explanation for such an observed phenomena. The averaging of ionic and meso-ionic forms of imidazopyridine rings within the same molecule is hindered because of an attractive interaction between them. Analysis of electronic density revealed that, indeed, a new type of bonding is formed as the result of an overlap between pi aromatic and pi C=O molecular orbitals. This bonding, like the hydrogen bond, is primarily of electrostatic character, and its energy was estimated at 3.5 kcal/mol.     

Creatinine determination in urine from the point of view of reference values

In this paper, the creation of a certified reference material for urinary creatinine is described. We used the Jaffe method and HPLC method for establishment of the certified value. Homogeneity tests are also described. We obtained material with sufficient homogeneity, stability, and with certified value (expanded uncertainty, k=2 for CI 95%) (7.77±0.27) mmol·L⁻¹. This material was consequently used for the interlaboratory comparison (EQA Czech Republic for clinical chemistry). Twenty-nine percent of the participants obtained measurement results within the interval of the certified value ± expanded uncertainty, while 85% of the participants obtained values inside the interval of the certified value ± target measurement uncertainty. Direct use of the certified reference materials for method evaluation in EQA programs means a significant advance for monitoring and documentation traceability of results in routine measurements.