Biomedical subjects

Kean Li

Publications and source records attributed to Kean Li.

5 recordsLinked to original sources

PubMed2006

Application of molecularly imprinted polymers to solid-phase extraction of analytes from real samples.

A review is presented of recent developments in the use of molecularly imprinted polymers (MIPs) as selective materials for solid-phase extraction. Compared with traditional sorbents, MIPs can not only concentrate but also selectively separate the target analytes from real samples, which is crucial for the quantitatively determination of analytes in complex samples. Consequently, as one of the most effective sorbents, MIPs have been successfully applied to the pretreatment of analytes in foods, drugs, and biological and environmental samples in the past five years.

Biocompatible Materials↗

PubMed2005

Copper ion-selective fluorescent sensor based on the inner filter effect using a spiropyran derivative.

A highly selective copper(II) ion fluorescent sensor has been designed based on the UV-visible absorption of a spiropyran derivative coupled with the use of a metal porphyrin operative on the fluorescence inner filter effect. Spiropyrans, which combine the characteristics of metal binding and signal transduction, have been widely utilized in cationic ion recognition by UV-visible spectroscopy. In the present work, the viability of converting the absorption signal of the spiropyran molecule into a fluorescence signal was explored. On account of overlap of the absorption band of the spiropyran (lambda(abs) = 547 nm) in the presence of copper ion with the Q-band of an added fluorophore, zinc meso-tetraphenylporphyrin (lambda(abs) = 556 nm), the effective light absorbed by the porphyrin and concomitantly the emitted light intensity vary as a result of varying absorption of the spiropyran via fluorescence inner filter effect. The metal binding characteristic of the spiropyran presents an excellent selectivity for copper ion in comparison with several other heavy or transition metal ions. Since the changes in the absorbance of the absorber translate into exponential changes in fluorescence of the fluorophore, the novelty of the present device is that the analytical signal is more sensitive over that of the absorptiometry or that of the fluorometry using one single dye. To realize a practical fluorescent sensor, both the absorber and fluorophore were immobilized in a plasticized poly(vinyl chloride) membrane, and the sensing characteristics of the membrane for copper ion were investigated. The sensor is useful for measuring Cu2+ at concentrations ranging from 7.5 x 10(-7) to 3.6 x 10(-5) M with a detection limit of 1.5 x 10(-7) M. The sensor is chemically reversible, the fluorescence was switched off by immersing the membrane in copper ion solution and switched on by washing it with EDTA solution.

Benzopyrans↗

PubMed2005

Ionic liquid-based aqueous two-phase system, a sample pretreatment procedure prior to high-performance liquid chromatography of opium alkaloids.

An ionic liquid, 1-butyl-3-methylimidazolium chloride ([C4 mim]Cl)/salt aqueous two-phase systems (ATPS) was presented as a simple, rapid and effective sample pretreatment technique coupled with high-performance liquid chromatography (HPLC) for analysis of the major opium alkaloids in Pericarpium papaveris. To find optimal conditions, the partition behaviors of codeine and papaverine in ionic liquid/salt aqueous two-phase systems were investigated. Various factors were considered systematically, and the results indicated that both the pH value and the salting-out ability of salt had great influence on phase separation. The recoveries of codeine and papaverine were 90.0-100.2% and 99.3-102.0%, respectively, from aqueous samples of P. papaveris by the proposed method.

Chemical Fractionation↗

PubMed2005

Extraction of testosterone and epitestosterone in human urine using aqueous two-phase systems of ionic liquid and salt.

Based on aqueous two-phase systems (ATPS) consisting of 1-butyl-3-methylimidazolium chloride, a hydrophilic ionic liquid (IL), and K2HPO4, a new and simple extraction technique, coupled with a reversed-phase high performance liquid chromatography (RP-HPLC), was developed for the simultaneous concentration and analysis of testosterone (T) and epitestosterone (ET) in human urine. Under the optimal conditions, the extraction efficiencies for both analytes were 80-90% in a one-step extraction. The method required only 3.0 mL of urine and a single hydrolysis/deproteinization/extraction step followed by direct injection of the IL-rich upper phase into HPLC system for analysis. The method has been satisfactorily applied to the analysis of T and ET in human urine with detection limits of 1 ng/mL and linear ranges of 10-500 ng/mL for both compounds. Compared with conventional liquid-liquid extraction or solid phase extraction, this new method is much "greener" due to no use of volatile organic solvent and low consumption of IL. The proposed extraction technique opens up new possibilities in the separation of other drugs.

Chemical Fractionation↗

PubMed2005

Molecular modeling of the intercalation of porphyrins into alpha-zirconium phosphate.

In this work, n-alkylamines (number of carbon atoms ranging from 3 to 10) were investigated in detail by molecular modeling as spacers for intercalating porphyrins into alpha-zirconium phosphate (alpha-ZrP). Pre-intercalated n-alkylamines can form either a flat monolayer or a canted bilayer in the gallery of alpha-ZrP. Based on the interlayer state and intercalative potential of the two modes in alpha-ZrP, it is suggested that the flat monolayer is a better spacer than the bilayer and that n-propylamine (PA) and n-butylamine (BA) in mobile monolayers are the best spacers among the n-alkylamines studied, as is also found experimentally. The intercalation behavior of TMPyP [5,10,15,20-tetrakis (1-methylpyridinium-4-yl) porphyrin] and several other porphyrins was investigated by calculating the intercalative potential. The calculated results showed that the porphyrins were densely packed in a canted monolayer model, and an increase of polarity of the substituent would facilitate the intercalation of the porphyrins.

Alkylation↗