Development of a radiochemical neutron activation analysis procedure for determination of rhenium in biological and environmental samples at ultratrace level

Summary Radiochemical neutron activation procedures using liquid-liquid extraction with tetraphenylarsonium chloride in chloroform from 1M HCl and solid extraction with ALIQUAT 336 incorporated in a polyacrylonitrile binding matrix from 0.1M HCl were developed for accurate determination of rhenium in biological and environmental samples at the sub-ng ^. g^-1 level. Concentrations of Re in the range of 0.1 to 2.4 ng ^. g^-1 were determined in several botanical reference materials (RM), while in a RM of road dust a value of ~10 ng ^. g^-1 was found. Significantly elevated values of Re, up to 90 ng ^. g^-1 were found in seaweed (brown algae). Results for Re in the brown algae Fucus vesiculosus in which elevated ⁹⁹Tc values had previously been determined suggested possible competition between Re and Tc in the accumulation process.     

Neutron and photon activation analyses in geochemical characterization of sediment profiles at the Jurassic–Cretaceous boundary

As a part of a project aimed at precise correlation of the Jurassic–Cretaceous (J/K) boundary interval in the Tethyan and Boreal realms, neutron and photon activation analyses were employed in geochemical characterization of limestone samples from the Brodno section, Slovakia, which offers a record of hemipelagic marine sediments around the J/K boundary in the Tethyan realm. Nickel and antimony anomalies exceeding almost twenty times the levels in neighboring beds were found near the beds assigned recently to the J/K boundary. Elucidation of their origin (volcanism, isochronous meteoritic impact, concentrating in, e.g., sulfides) requires further investigation.     

Radiobarites from the Cenozoic volcanic region of the Bohemian Massif: radiochemical study,history, and lead isotopic composition

A specific, radium bearing type of barites has been known from the Ohře (Eger) Rift, a region of Cenozoic volcanic activity in northwestern Bohemia, Czech Republic, since 1904. Barites from Karlovy Vary, Teplice and Děčín areas have been studied to elucidate geochemical history of these specific samples. Low background radiometric method using high-resolution gamma-ray spectrometry has shown that radioactivity of these barites (up to 8 Bq g⁻¹) is carried by ²²⁶Ra, which is not in equilibrium with the parent ²³⁸U. In all samples, uranium activity was below 0.005 Bq g⁻¹––the detection limit achieved by instrumental neutron activation analysis. The alpha track method on a crystal plate has shown that ²²⁶Ra is accumulated in surface layers or crystal cracks, therefore, the crystal rims must be relatively young, not older than 10–15 thousand years. In a lead fraction isolated from the barites, concentration and isotopic composition of lead were determined by photon activation analysis and ICP MS, respectively.     

Instrumental neutron and photon activation analyses of selected geochemical reference materials

Ten selected rock reference materials (USGS diabase W-1, basalt BCR-1, andesite AGV-1, granite G-2, granodiorite GSP-1, and CRPG basalt BE-N, granite GS-N, trachyte ISH-G, serpentine UB-N, glass standard VS-N) were analyzed by instrumental neutron and photon activation analyses. The results have been evaluated on average for the entire set of samples to detect possible systematic deviations of the determined values from the reference values. Out of 47 elements determined, 43 elements have been determined with reasonable agreement (deviation < 10% on average) with the reference values. Au could not be determined because of a high blank from packaging polyethylene foil. Systematically higher Dy and lower Ho and Tm (by about 20% on average) in the present results require further investigation. In several cases, reasons for greater differences between the determined and recommended values could not be traced in the procedures used within the study. The most suspect is the recommended value for W in the CRPG BE-N basalt, which is twenty-five times higher than the present value, probably due to inconsistent contamination from a W carbide mill used in production of this reference material.     

An Approach to Transfer Methods from HPLC to UHPLC Techniques in Some Carbapenems

Stability-indicating LC methods were developed and validated for the quantitative determination of doripenem, meropenem and tebipenem in the presence of their degradation products formed during forced degradation studies. Isocratic HPLC and UHPLC separations were performed with a core–shell Kinetex 1.7, 2.6 and 5 µm, all C18, 100A, 100 × 2.1 mm columns and the mobile phase composed of acetonitrile and 12 mmol L⁻¹ ammonium acetate in different ratios. The flow rates of the mobile phase were: 0.5 mL min⁻¹ for 1.7 µm column, and 1.0 mL min⁻¹ for 2.6 and 5 µm ones. Detection wavelength was 298 nm and temperature was set at 30 °C. All analysed drugs were exposed to stress conditions which caused their hydrolysis and thermal degradation. The methods were validated by evaluation of linearity, accuracy, precision, selectivity and robustness. Proposed methods were successfully applied for the determination of investigated antibiotics during kinetic studies in aqueous solutions and in the solid state. The advantages of chromatographic procedures which are based on the use of C18 stationary phases with different particle sizes in the analysis of selected carbapenems were discussed.

     

Isotope exchange study of the dissociation of metal —humic substance complexes

Isotope exchange was employed to study dissociation of metal cations from their complexes with humic substances (HS). Dissociation of cation from HS controls the rate of isotope exchange between two identical metal-HS solutions (but for the presence of a radiotracer) divided by a dialysis membrane. The rate of isotope exchange of Eu/¹⁵²Eu and Co/⁶⁰Co in the systems with various HS was monitored as a function of pH, ionic strength, and the degree of HS loading with metal. The apparent rate of Eu-HS dissociation was found to be enhanced by decreasing pH, increasing ionic strength, and increasing metal loading. Co-HS dissociation was too fast to be followed by the method. For interpretation of the experimental kinetic data, the multiple first order law has been applied. Based on the results, a concept of HS as a mixture of two types of binding sites is discussed.     

An Approach to Transfer Methods from HPLC to UHPLC Techniques in Some Carbapenems

Stability-indicating LC methods were developed and validated for the quantitative determination of doripenem, meropenem and tebipenem in the presence of their degradation products formed during forced degradation studies. Isocratic HPLC and UHPLC separations were performed with a core–shell Kinetex 1.7, 2.6 and 5 µm, all C18, 100A, 100 × 2.1 mm columns and the mobile phase composed of acetonitrile and 12 mmol L^?1 ammonium acetate in different ratios. The flow rates of the mobile phase were: 0.5 mL min^?1 for 1.7 µm column, and 1.0 mL min^?1 for 2.6 and 5 µm ones. Detection wavelength was 298 nm and temperature was set at 30 °C. All analysed drugs were exposed to stress conditions which caused their hydrolysis and thermal degradation. The methods were validated by evaluation of linearity, accuracy, precision, selectivity and robustness. Proposed methods were successfully applied for the determination of investigated antibiotics during kinetic studies in aqueous solutions and in the solid state. The advantages of chromatographic procedures which are based on the use of C18 stationary phases with different particle sizes in the analysis of selected carbapenems were discussed.