Li-Ren Chen

Determination of serum thyroxine enantiomers in patients by liquid chromatography with a chiral mobile phase

A chromatographic method for the separation and determination of D- and L-thyroxine enantiomers (D-, and L-T4) in human serum with a chiral ligand ion-exchange system using a chiral mobile phase additive and a silica column was established. An aqueous eluent containing L-proline (L-pro) sufficiently complexed copper II ions and triethylamine (TEA) was used. It was monitored with a UV detector. The separation was completed in 12 min. The method has acceptable sensitivity, precision and accuracy for analysis. The limit of detection and the limit of quantitation for both D- and L-T4 were 0.1 microg/ml and 0.8 microg/ml, respectively. Calibration curves were linear within 1-100 microg/ml; the mean correlation coefficients were r(D-T4)=0.9986 for D-T4 and r(L-T4)=0.9978 for L-T4. T4 enantiomers were separated on baseline under the optimum condition. L-T4 eluted before D-T4. The concentration of D-T4 and L-T4 in 45 thyroid patients serum (hyperthyroid, hypothyroid, thyroidectomy, goitre or thyroiditis) using HPLC was determined, those results showed that D,L-T4 concentration varied in different thyroid patient. Attention should be paid to this result in treating thyroid disease in the clinic.

Effect of different sample pretreatment methods on the concentrations of excitatory amino acids in cerebrospinal fluid determined by high-performance liquid chromatography

Using high-performance liquid chromatography (HPLC), the effect of different sample pretreatment methods on the concentrations of excitatory amino acids (EAAs, glutamate and aspartate) measured in cerebrospinal fluid (CSF) was investigated. The results showed that the measured values of glutamate and aspartate were constant when the samples were stored at -80 degrees C and then methanol was used for CSF deproteinization before assay; the values of glutamate (Glu) increased when 0.3 M perchloric acid was used for CSF deproteinization with the CSF subsequently being stored at -20 degrees C; the values of Glu changed when the samples were stored at -20 degrees C over 8 weeks with methanol subsequently being used for CSF deproteinization before assay. This reference data suggested that the CSF sample would be better stored at -80 degrees C. If the sample is stored at -20 degrees C over 8 weeks, the Glu values change with the storage time. If strong acidic reagents are used for precipitation of protein in the CSF sample and then stored at -20 degrees C, Glu values are abnormally increased. From this study, an accurate and sensitive reversed-phase high-performance liquid chromatographic method has been developed for anti-excitotoxicity therapy and thorough study of EAAs in a clinical setting.

Polysiloxane-encapsulated stationary phase for reversed-phase high-performance liquid chromatography

SummarySilica beads of 6-μm average diameter were silanized with methylvinyldiethoxysilane and then subjected to encapsulation with poly(methylvinylsiloxane). The resulting product is a new stationary phase for reversed-phase high performance liquid chromatography (RP-HPLC) which has superior ability for the separation of polar, non-polar and basic compounds. The chromatographic peaks are symmetric. Its stability has been studied; after continuous use for three months the carbon content and chromatographic behaviour of the phase were unchanged. on to the silica surface to given an uniform organic film. Material prepared in this way has both good chromatographic behaviour and superior selectivity. Because contact of the silica matrix with the mobile phase is avoided, the alkali-resisting ability of the stationary phase is increased. The non-specific adsorption of alkaline solutes on to the silica surface is also avoided because of the complete coverage of surface silanol groups. Reports of stationary phases encapsulated with polystyrene [6], polybutadiene [I] and octadecylsiloxane polymers have recently appeared in the literature [3].In this paper we report the encapsulation of poly-(methylvinylsiloxane) (analogous to the phase SE-31 often used in GC) on to a silica matrix previously modified with methylvinyldiethoxysilane. The resulting phase has superior performance in reversed-phase HPLC.

The separation of the new chiral metal cluster (μ3-Se)RuCoW (CO)8-C5H4C(O)CH3 on an amylopectin tris-(phenylcarbamate) chiral column by HPLC

The preparation of amylopectin tris(phenylcarbamate) (ATP) chiral stationary phases(CSPs) coated on a small-particle (5μm, 120A) spherical silica support, according to a process that is reported, is presented. A new chiral tetrahedral cluster (μ 3 -Se)RuCoW(CO) 8 C 5 H 4 C(O)CH3 2 which was synthesized by the thermal reaction of the precursor (μ 3 -Se)RuCo 2 (CO) 9 1 with the functionally substituted cyclopentadienyl tricarbonyl metal complex anions [W(CO) 3 C 5 H 4 C(O)CH 3 ] is resolved on the amylopectin tris (phenylcarbamate) chiral stationary phases.

Phenylvinylmethylpolysiloxane Encapsulated Stationary Phase for Reversed-Phase Liquid Chromatography

Silica beads of 6μm average diameter were silanized with methylvinyldiethoxysilane and then coated with phenyl-vinylmethylpolysiloxane. The chromatography (RP-HPLC) with the prepared material has superior ability for the separation of polar, non-polar and basic compounds. The chromatographic peaks are symmetric. Its stability has been studied. After continuous use for four months, the carbon content and chromatographic behavior of the phase were unchanged.

System peaks in single column ion chromatography (SCIC) with indirect spectrophotometric detection

SummaryThe most popular eluents for SCIC are organic acids and their salts with one or more kinds of ion taking part in the elution process. These ions compete for ion-exchange equilibria. After an injection, the equilibria are disturbed and a re-equilibration process occurs resulting in extraneous peaks (system peak). A mechanism based on these aspects is proposed which is used successfully in the interpretation of the effects of sample properties and eluent parameters on system peaks. Experiments in the analysis of both cations and anions have been carried out to support this mechanism with eluents comprising two kinds of eluent ions. An equation for capacity factors in such systems is also derived.