A Study of the Near-Ultraviolet Spectrum of Vega

UV, optical, and near-IR spectra of Vega have been combined to test our understanding of stellar atmospheric opacities, and to examine the possibility of constraining chemical abundances from low-resolution UV fluxes. We have carried out a detailed analysis assuming Local Thermodynamic Equilibrium (LTE) to identify the most important contributors to the UV continuous opacity: H, H$^{-}$, C I, and Si II. Our analysis also assumes that Vega is spherically symmetric and its atmosphere is well described with the plane parallel approximation. Comparing observations and computed fluxes we have been able to discriminate between two different flux scales that have been proposed, the IUE-INES and the HST scales, favoring the latter. The effective temperature and angular diameter derived from the analysis of observed optical and near-UV spectra are in very good agreement with previous determinations based on different techniques. The silicon abundance is poorly constrained by the UV observations of the continuum and strong lines, but the situation is more favorable for carbon and the abundances inferred from the UV continuum and optical absorption lines are in good agreement. Some spectral intervals in the UV spectrum of Vega that the calculations do not reproduce well are likely affected by deviations from LTE, but we conclude that our understanding of UV atmospheric opacities is fairly complete for early A-type stars.Comment: 13 pages, 9 figures, to be published in Ap

Determination of icariin in urine by high performance liquid chromatography with tandem mass-spectrometric detection

C использованием метода высокоэффективной жидкостной хроматографии-тандемной масс-спектрометрии разработан способ селективного определения икариина в пробах мочи. Для анализа биологических проб использовали обращенно-фазовый вариант высокоэффективной хроматографии на сорбентах с привитыми C18 группами. Определение осуществляли методом тандемной масс-спектрометрии с ионизацией электрораспылением в режиме регистрации выбранных ионных переходов для положительных ионов (энергия соударений - 40 %, ионный переход - с m/z = 677.2433 → 313.0703 (100 %), 369.1330 (35 %)). Выбрана процедура пробоподготовки, включающая в себя твёрдофазную экстракцию на картриджах SUPELCO HLB, концентрирование органического экстракта в токе азота и перерастворение сухого остатка. Предел детектирования составил 1 нг∙мл⁻¹. При валидации методики оценивали степень извлечения икариина из биологической жидкости (97 %), селективность и специфичность определения целевого соединения, а также влияние матрицы на ионизацию (4 %).Using the liquid chromatography tandem mass spectrometry, the approach for the selective detection of icariin in urine samples was developed. Biological samples analysis was performed by the reversed-phase chromatography using the C18 sorbent. The method of tandem mass spectrometry with the multiple reaction monitoring (MRM) mode using the electrospray ionization technique in positive ion mode was used (the collision energy - 40 %, m/z = 677.2433 → 313.0703 (100 %), 369.1330 (35 %)). The sample preparation procedure comprising of the solid-phase extraction based on SUPELCO HLB cartridges, the evaporation of the organic extract in a stream of nitrogen and the reconstitution of residue was selected. The detection limit was 1 ng ml⁻¹. During the method validation, the extraction of icariin from a biological fluid (97%), the selectivity and the specificity of the target compound as well as the matrix effects of ionization (4 %) were studied