Isocratic networks in supercritical fluid chromatography II: Selectivities and effective plate numbers

The dependence of the selectivity α and the effective plate number, N, on temperature and pressure is shown in three-dimensional diagrams. The specific system studied was pentane as the mobile phase, unmodified silica as the stationary phase, and a set of four polycyclic hydrocarbons as the test mixture. Temperature and pressure ranges were from 25 to 300°C and from 30 to 75 bar, respectively. The plots for α and N are found to resemble those for capacity ratio, k′, and resolution, R, studied earlier with the same system [1]. A distinct maximum is observed for N in the supercritical region, as found earlier for k′ and R. This applies also to α for the homologous substrate pair naphthalene/anthracene, while the resemblance for α is less pronounced for the pair anthracene/pyrene.     

A local intercomparison study of ESR dosimetry using tooth enamel

Using electron spin resonance (ESR), tooth enamel is a possible dosimeter in case of a radiation accident. To check the present status of this technique, we conducted a local intercomparison study. We irradiated several samples of tooth enamel with a⁶⁰Co source. Three institutes in Belgium and The Netherlands recorded the ESR signal of the samples. The results of the measurements and the methods used are compared. It is concluded that ESR on tooth enamel can be a useful technique in accident dosimetry, provided further research is done.     

Theoretical study of hydrogen atom migration models in cyclic conformation of 1-pentene

Migration of hydrogen atoms in the cyclic conformation of 1-pentene is assumed. Four migration models are proposed and their relative stability studied by semiempirical methods. According to the results obtained by the MINDO/2 method all model structures assumed are more stable than the original cyclic conformation, whereas by CNDO/2 only one structure is relatively stable. From the results achieved the cyclic conformation of 1-pentene appears as a barrier structure behind which there are other relatively stable structures.     

Surface activation influencing the microstructure of Zn(Ca) phosphate coatings

Zinc and zinc calcium phosphate coatings on steel were formed by dipping in commercial baths. A surface activation with titanium phosphate influences not only the film morphology but also the composition of the conversion films. Qualitative phase analysis of the polycrystalline deposits reveals a typical phosphophyllite crystal growth apart from hopeite and scholzite respectively. The growth rate depends on the free surface of the steel; the contact area to the solution controls the rate of iron pickling.     

New approach for the clinical monitoring of 25‐hydroxyvitamin D3 and 25‐hydroxyvitamin D2 by ultra high performance liquid chromatography with MS/MS based on the standard reference material 972

Biomarkers, 25‐hydroxyvitamin D₃ and 25‐hydroxyvitamin D₂, are important indicators of the vitamin D general status and are monitored in several pathophysiological disorders, such as osteoporosis, diabetes, heart disease, etc. A novel ultra‐HPLC with MS/MS methodology for the analysis of 25‐hydroxyvitamin D derivatives coupled with a very simple and highly rapid sample preparation step was developed. Analytical parameters obtained showed linearity (R²) above 0.999 for both vitamins with accuracies between 95.8 and 102%. The LODs were as low as 0.22 and 0.67 nmol/L for 25‐hydroxyvitamin D₃ and 25‐hydroxyvitamin D₂, respectively. Intra‐assay precision (%RSD) was lower than 4.5%, and inter‐assay precision (%RSD) was lower than 6.5%. The feasibility of the developed methodology to be applied in clinical routine analysis has been proved by its application in blood samples from non‐agenarian patients, patients with familial hypercholesterolemia and patients suffering from age‐related macular degeneration.