RESUMO
A novel LC-based method for the determination of enantiomeric excess (ee) in a sample mixture has been developed by employing on-line 2D LC. The orthogonal separation system is composed of an NH2 column as the first dimension to elute the target chiral compound from the crude mixture and a chiral column as the second dimension to determine the ee of the target chiral product. A series of crude mixtures from asymmetric reactions have been directly analyzed without prepurification. Good reproducibility (intra- and interday precisions were all under 1.33%) and good accuracy (deviations from ee values determined by 1D HPLC were all <1.03%) have been obtained. Compared with the traditional method for the determination of ee, on-line 2D HPLC can be used in real time and holds great potential in the time-saving determination of ee in asymmetric synthesis.
Assuntos
Cromatografia Líquida de Alta Pressão/métodos , Flavanonas/análise , Sistemas On-Line , Quinolonas/análise , Flavanonas/síntese química , Quinolonas/síntese químicaRESUMO
The use of PZT films in sliver-mode high-frequency ultrasonic transducers applications requires thick, dense, and crack-free films with excellent piezoelectric and dielectric properties. In this work, PZT composite solutions were used to deposit PZT films >10 µm in thickness. It was found that the functional properties depend strongly on the mass ratio of PZT sol-gel solution to PZT powder in the composite solution. Both the remanent polarization, P(r), and transverse piezoelectric coefficient, e(31,) (f), increase with increasing proportion of the sol-gel solution in the precursor. Films prepared using a solution-to-powder mass ratio of 0.5 have a remanent polarization of 8 µC/cm(2), a dielectric constant of 450 (at 1 kHz), and e(31,) (f) = -2.8 C/m(2). Increasing the solution-to-powder mass ratio to 6, the films were found to have remanent polarizations as large as 37 µC/cm(2), a dielectric constant of 1250 (at 1 kHz) and e(31,) (f) = -5.8 C/m(2).
