排序方式: 共有5条查询结果,搜索用时 156 毫秒
1
1.
Urmas Muinasmaa Clara R fols Elisabeth Bosch Martí Ros s 《Analytica chimica acta》1997,340(1-3):133-141
The dissociation constants of several acids (perchloric, hydrochloric, phosphoric, acetic and benzoic acids) and of some sodium salts (chloride, acetate and benzoate) have been conductometrically determined in tetrahydrofuran/water mixtures up to a 90% of tetrahydrofuran in volume. The results demonstrate that conductometry can be successfully applied to determine the dissociation constants of salts and moderately weak and strong acids in the studied mixtures. The dissociation constants of the acids and some bases taken from the literature have been fitted to solvent composition through a previously derived equation, which is based on a preferential solvation model. The fitting parameters obtained allow calculation of the dissociation constant for any solvent composition inside the applicability solvent composition range. From the pK value, the pH of any buffered solution, such as those used in liquid chromatography, can be calculated for the particular tetrahydrofuran/ water composition of interest. Appreciable ion-pairing for sodium salts and strong acids has been observed for tetrahydrofuran contents higher than 60% in volume. Therefore, the accurate calculation of the pH values of buffers in tetrahydrofuran-rich solutions must take into account the pK values of the acid and salt. 相似文献
2.
Urmas Muinasmaa Peeter Burk Jaan Pentchuk 《International journal of quantum chemistry》1997,62(6):653-658
The possibility to predict the stability constants of the complexes of magnesium, zinc, cadmium, and lead cations with anions of different carboxylic acids by PM3 calculations was investigated. Linear correlation between calculated complex-formation reaction enthalpies and experimentally measured stability constants were obtained for complexes of each metal, while the overall correlation was not satisfactory. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 653–658, 1997 相似文献
3.
Kati Helmja Maria Borissova Tatjana Knjazeva Martin Jaanus Urmas Muinasmaa Mihkel Kaljurand Merike Vaher 《Journal of chromatography. A》2009,1216(17):3666-3673
A procedure for collecting fractions during capillary electrophoresis for their analysis using various stand-alone instruments is described. The results of a systematic study of the optimization and application of capillary electrophoresis (CE) in conjunction with a reverse-phase high-performance liquid chromatography electrospray ionization quadrupole time of flight-tandem mass spectrometry (RP-HPLC-ESI-Q-TOF-MS/MS) and inductively-coupled mass spectrometry (ICP-MS) to the analysis of the seed extract of the Japanese Pagoda Tree (Sophora japonica) are presented. The off-line coupling of CE to the matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS) for the proteins mixture was applied. The cathode end of the capillary was placed inside a stainless steel needle using a coaxial liquid-sheath-flow configuration. The optimization of experimental parameters resulted in an efficient methodology for MS analysis of fractions. Several components contained in the extract of S. japonica were identified, some not previously known. It was demonstrated that low sensitivity, which is a real problem in off-line CE–MS analysis, could be tolerated because of a more flexible optimization of the CE separation conditions and the choice of independent stand-alone instruments for analysis of separated fractions. The estimated limit of detection for CE-RP-HPLC-ESI-Q-TOF-MS was 50 μM of polyphenols and for CE-ICP-MS, 1–100 μg/l. 相似文献
4.
5.
Urmas Nagel 《辐射效应与固体损伤》2013,168(1):405-410
Abstract Magnetic circular dichroism in the 4431 Å absorption line of the oxygen compensated CaF2:Dy3+ crystal has been used to measure transient phenomena in the Kramers doublet ground level 6H15/2 of the Dy3+ ion during magnetic field reversal. After inverting the field with a rate 10 T·s?1 <dB/dt < 400 T·s?1 a considerable spin inversion with the final electron spin polarization PF was achieved while PF=-0.86±0.03 relaxed to less than 0.05 when dB/dT < 10?2 T·s?1. 相似文献
1