No abstract

Hypericin, extracted from H. perforatum, can induce the generation of reactive oxygen species by visible light irradiation, which may consequently induce the conformational change of hemoglobin. We have not only employed UV-vis spectroscopy to observe the changes of UV-vis spectra of the protein, which reveals the conformational changes of the protein, but also employed electrochemical method to obtain its enhanced peroxidase activity. The photodynamic effect of hypericin on the conformation and catalytic activity of the protein has also been proven to be strongly dependent on the irradiation time, the hypericin concentration and the presence of oxygen. This work is beneficial not only to the fabrication of more sensitive hydrogen peroxide biosensor, but also to the guidance of the usage of this medicinal herb molecule, since the conformational change of the protein and the enhanced peroxidase can be easily obtained only by visible light irradiation on hypericin, the process of which is so common to happen.

No abstract

A simple and efficient method based on a novel solid phase extraction (SPE) cartridge and ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/ MS) was developed for the determination of clenbuterol residue in pork. The minced pork sample was ultrasonically extracted by 5% (v/v) perchloric acid and centrifuged at 10 000 r/min for 15 min, then the supernatant was purified by an SMCX cartridge, which is a novel SPE column based on homemade silica matrix with two mixed modes of reversed-phase and strong cation exchange, for the selective enrichment and purification of the analyte. The linear range of the method was 0.25 - 50 microg/kg with a correlation coefficient of 0.998 2. The average recoveries ranged from 62.2% to 72.0% at the three spiked levels of 1.25, 12.5 and 50 microg/kg with the relative standard deviations (RSDs) between 4.2% and 6.1%. The limit of detection (S/N = 3) was 0.05 microg/kg. The method is simple, fast and can be extended to enrich and determine beta-agonist drugs.