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.     

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.     

Specific anion effects on glass electrode pH measurements of buffer solutions: bulk and surface phenomena

The effect of electrolytes on pH measurements via glass electrodes is explored with solutions buffered at pH 7 (phosphate and cacodylate). Salt and buffer concentrations are varied. Direct and reverse Hofmeister effects are observed. The phenomena are significant for salt concentrations above 0.1 M and for buffer concentrations below 20 mM. Changes in measured pH show up most strongly with anions. They can be related to the usual physicochemical parameters (anion molar volumes, molar refractivity, and surface tensions) that are characteristic of Hofmeister series. They correlate strongly with anionic excess polarizabilities; this suggests the involvement of non-electrostatic, or dispersion, forces acting on ions. These forces contribute to ionic adsorption at the glass electrode surface, and to the liquid junction potential.     

Novel formal synthesis of stereospecifically C-6 deuterated d-glucose employing configurationally stable alkoxymethyllithiums

The synthesis and testing of configurational stability of chirally monodeuterated PMB- and THP-substituted oxymethyllithiums are described. Macroscopically they are configurationally stable up to −35 °C, the limit of their chemical stability, and microscopically even up to 0 °C. Furthermore, THP-protected oxy-[D₁]methyllithium has been applied in the formal synthesis of (6R)-[6-D₁]-d-glucose (four steps, 40% yield), an example of its use as a homochiral hydroxymethyl synthon.     

Solution of the Dirichlet Problem for the Laplace equation

For open sets with a piecewise smooth boundary it is shown that a solution of the Dirichlet problem for the Laplace equation can be expressed in the form of the sum of the single layer potential and the double layer potential with the same density, where this density is given by a concrete series.