Vol 71, No 1 (2016)

The dependence of the intensity of X-ray fluorescence on the energy of photons exciting X-ray radiation is considered. For elements with small atomic numbers, the direct ionization of atoms, the major process for the majority of elements of the Periodic Table, is the main only at low energies of primary photons. With the growth of photon energy, the intensity of fluorescence due to photo and Auger electrons arising in the irradiated material increases. This component at certain energy becomes predominant. The further increase in the energy of primary photons leads to the suppression of the ionization of atoms by recoil electron arising in the incoherent (Compton) scattering of primary radiation. The effects of the energy of primary photons on the intensity of X-ray fluorescence for the studied processes differ significantly. The depth of these effects determines their contributions to the formation of the analytical signal. Study of the influence of excitation conditions allows the analyst to intelligently solve problems of the optimization of the X-ray fluorescence determination of elements with small atomic numbers.

Methods of the quality control of finished dosage forms by capillary zone electrophoresis and micellar electrokinetic chromatography have been proposed. The optimum conditions for the separation and determination of different classes of antibacterial substances, penicillins, fluoroquinolones, nitrofurans, sulfanilamides, metronidazole, and chloramphenicol have been selected. The analytical range for the active ingredients of drugs was 1–1000 mg/g for solid and 0.001–0.50% for liquid drugs. The relative standard deviation of the results of analysis did not exceed 4%.

Highly sensitive procedures are proposed for the chromatographic (high-performance liquid chromatography, HPLC) and luminescence determination of trace amounts of Rosuvastatin Calcium in washings after the cleanup of pharmaceutical equipment. The developed procedures are validated for the following parameters: specificity, linearity, accuracy, detection limit, and quantification limit. The calibration curves are presented in the concentration range 0.01–1.0 µg/mL (HPLC) and 0.1–10.0 µg/mL (luminescence); the detection limits are 0.005 and 0.032 µg/mL, respectively. The efficiency of the sampling method is over 90%. It is found that the difference in the results of analysis of samples by two procedures is statistically insignificant. The luminescence procedure compared to HPLC has several advantages, i.e., lesser labor intensity, rapidity, and lesser reagent consumption; but the HPLC procedure is an order of magnitude more sensitive.

A semi-automated microextraction by packed sorbent (MEPS) method was developed for the HPLC determination of ellagic acid (EA) in juice samples. The procedure includes enrichment of the analyte on a nanoporous silica sorbent by the MEPS method using a laboratory-made programmable apparatus. Three functionalized SBA-15 nanoporous sorbents were evaluated for this purpose and 3-[bis(2-hydroxyethyl)amino]propyl-triethoxysilane (HPTES)-SBA-15 showed superior efficiency. Only 2 mg of the adsorbent packed in a syringe’s hub was sufficient for a quantitative recovery of EA. Different factors influencing the performance of the MEPS method such as the nature of desorption solvent, elution volume, pH, number of extraction cycles (draw–eject) and sample volume were carefully studied and optimized. Under the optimized conditions, a detection limit of 0.8 mg/L and a linear calibration curve with an R² of 0.9995 were obtained for EA. The average recovery of the analyte for juice samples was 97.6% with a relative standard deviation of 4.4% for six replicates. The method was successfully applied to the HPLC determination of EA in pomegranate and grape juice samples.

A new simple colorimetric method for selective determination of arginine was developed using an azobenzothiazole-polyene dye. The benzothiazole moieties of the dye act as dipolar molecular receptors to arginine. Importantly, arginine could be recognized in solution with the naked eye due to the color change from orange to blue. Reproducibility of the assays was proven by calculating of the intraand inter-assay variations for the color responses and the variations were found to be 6.9 and 4.2%, respectively. Finally, the accurate measurements of arginine in real samples (commercial supplementary medicines) were achieved. In conclusion, validation of the developed method revealed excellent performance characteristics, including long life span, good arginine selectivity among a wide variety of other amino acids and long-term response stability.

Possibilities of the determination of Au, Ag, and Si in dispersions of nanoparticles and biological samples by inductively coupled plasma atomic absorption and atomic emission spectrometry are demonstrated. Conditions of complete sample mineralization and the quantitative transfer of gold and silver to solution are found. The parameters of analyte determination in flame, graphite furnace, and plasma are optimized. The completeness of the atomization of gold, silver, and silicon in plasma on the introduction of nanoparticles as colloidal solutions is estimated. The conducted research allowed the estimation of the degree of gold and silver reduction at different stages of synthesis of composite nanoparticles with the core/shell structure. Quantitative information on the dynamics of accumulation and the redistribution of composite nanoparticles with gold or silver shells in organs and tissues of mices after the intravenous administration of colloidal solutions of nanoparticles.

A low-cost and simply fabricated amperometric glucose biosensor based on glucose oxidase (GOx) and 1,10-phenanthroline-5,6-dione (PD) modified graphite rod electrode was developed. The electrode exhibited good electrocatalytic activity with a well-defined hyperbolic dependence of amperometric signal upon glucose concentration in the presence and in the absence of oxygen. The electrode showed a good reproducibility and repeatability with relative standard deviation of less than 3 and 5%, respectively. The interaction of GOx with PD mediator was confirmed by means of UV?Vis absorbance spectroscopy.

A reliable, cost effective and user-friendly method has been used for the determination of polybrominated diphenylethers (PBDE) in computer key board switches (CKBS). The presence of the commercially added BDE-209 which is decabromo diphenyl ether (Deca-BDE) congener has been identified, established and estimated using gas chromatography–mass spectrometry. For extracting the analyte quantitatively from the material, Soxhlet extraction using toluene followed by multi-layer silica column chromatography was used to obtain the desired unambiguous quantitative results as per standard method. The results were confirmed by repeating, reproducing using standard addition recovery and by calculating measurement uncertainty. The CKBS samples contain around 49.6 ± 0.5 mg/kg of BDE-209. The recovery of spiked standard was between 90–93% and the linearity of the standard curve had a correlation coefficient of R² = 0.9974.

The main representatives of narcotic substances of natural origin are considered. Methodological solutions used in their screening, identification, and quantitative determination in raw materials, dosage forms, and biological materials are discussed. Prospects of application of state-of-the art hybrid methods combining chromatographic separation with mass spectrometric determination are noted.