LC Evaluation of Intestinal Transport of Praziquantel

Praziquantel (PZQ) is a highly lipophilic drug with low aqueous solubility. Despite this, it is well absorbed from the gastrointestinal tract. In this study, a simple LC method was developed and validated, in order to monitor the concentration of PZQ in TC-199 buffer in vitro, in the rat everted gut sac absorption model. PZQ was analyzed by a reversed-phase LC method with an isocratic mobile phase containing acetonitrile and water in the proportions 45:55. The flow-rate was 1 mL min⁻¹ and PZQ was determined by measuring absorbance at 215 nm, at 25 °C. The method was found to be specific, as none of the components of TC-199 or intestinal sac artefacts interfered with the drug peak. Recovery was within acceptable statistical limits. The limit of detection was 0.54 μg mL⁻¹ and the limit of quantitation was 1.63 μg mL⁻¹. The calibration curve was found to be linear in the concentration range of 10–90 μg mL⁻¹ PZQ. The proposed method was found to be rapid and selective and hence can be applied in the monitoring of the absorption of PZQ in in vitro everted gut sac absorption studies.

     

Cocrystals of Praziquantel with Phenolic Acids: Discovery,Characterization, and Evaluation

Solvent-assisted grinding (SAG) and solution slow evaporation (SSE) methods are generally used for the preparation of cocrystals. However, even by using the same solvent, active pharmaceutical ingredient (API), and cocrystal coformer (CCF), the cocrystals prepared using the two methods above are sometimes inconsistent. In the present study, in the cocrystal synthesis of praziquantel (PRA) with polyhydroxy phenolic acid, including protocatechuic acid (PA), gallic acid (GA), and ferulic acid (FA), five different cocrystals were prepared using SAG and SSE. Three of the cocrystals prepared using the SAG method have the structural characteristics of carboxylic acid dimer, and two cocrystals prepared using the SSE method formed cocrystal solvates with the structural characteristics of carboxylic acid monomer. For phenolic acids containing only one phenolic hydroxyl group (ferulic acid), when preparing cocrystals with PRA by using SAG and SSE, the same product was obtained. In addition, the weak molecular interactions that were observed in the cocrystal are explained at the molecular level by using theoretical calculation methods. Finally, the in vitro solubility of cocrystals without crystal solvents and in vivo bioavailability of PRA-FA were evaluated to further understand the influence on the physicochemical properties of API for the introduction of CCF.     

Evaluation of Pentaproline-Based Chiral Stationary Phase by LC

A pentaproline-based chiral stationary phase was prepared and the selectivity of the column was evaluated with 194 racemic compounds in three mobile phase modes: normal-phase mode, polar organic mode and reversed-phase mode. 94 racemates out of 194 were separated and the normal-phase mode proved to be the separation mode of broadest applicability. The column is stable in all common organic solvents and no degradation in column performance was observed in any mode even after more than 1,000 injections. A brief sample loading test was performed on the 250 mm × 4.6 mm column and 13.2 mg of α-methyl-9-anthracenemethanol was baseline separated. Retention behavior in the normal-phase mode and the effect of analyte structure on retention and enantioselectivity are discussed.

     

LC Determination of the Intestinal Absorption of Etoposide in Vitro and in Rat Plasma

Etoposide (VP16), an anti-neoplastic agent, exhibits low and variable bioavailability. We have developed and validated a rapid, sensitive, and accurate LC–UV method for the determination of VP16 in vitro and in rat plasma after oral administration. The method was then used to investigate the absorption characteristics of VP16 with an in vitro diffusion chamber system across isolated rat intestinal membranes as a model. Borneol and eugenol were used to enhance the intestinal absorption of VP16. We also examined the effect of borneol and eugenol on the intestinal absorption of VP16 in vivo. The results showed that the plasma concentration of VP16 was significantly increased; relative bioavailability was 2.2-fold and 2.9-fold enhancement in the presence of borneol and eugenol, respectively, compared to VP16 administered alone.     

LC Determination of the Intestinal Absorption of Etoposide in Vitro and in Rat Plasma

Etoposide (VP16), an anti-neoplastic agent, exhibits low and variable bioavailability. We have developed and validated a rapid, sensitive, and accurate LC–UV method for the determination of VP16 in vitro and in rat plasma after oral administration. The method was then used to investigate the absorption characteristics of VP16 with an in vitro diffusion chamber system across isolated rat intestinal membranes as a model. Borneol and eugenol were used to enhance the intestinal absorption of VP16. We also examined the effect of borneol and eugenol on the intestinal absorption of VP16 in vivo. The results showed that the plasma concentration of VP16 was significantly increased; relative bioavailability was 2.2-fold and 2.9-fold enhancement in the presence of borneol and eugenol, respectively, compared to VP16 administered alone.

     

LC Evaluation of In Vitro Release of AZT from Microemulsions

A reversed phase LC method was developed and validated to analyze the in vitro release of AZT from microemulsions. A mobile phase of acetonitrile:water (15:85) was used. The method validation showed good selectivity and linearity (r = 0.9993) for sample concentrations ranging from 0.6 to 100.0 μg mL⁻¹. The RSD values (0.7–4.3%) and percentage recovery (88.1–109.8%) were within acceptable limits. The limit of detection (LOD) and limit of quantitation (LOQ) were found to be 0.012 and 0.041 μg mL⁻¹. Quantitative analysis of the values obtained in the drug release assay indicates that the microemulsions used promote sustained release of AZT, which follows a Fickian diffusion mechanism.

     

Evaluation ofo-phthalaldehyde as bifunctional fluorogenic post-column reagent for glutathione in LC

Summary A method for the assay of various forms of glutathione in human plasma has been developed. The reduced form was measured after direct injection of deproteinized plasma with perchloric acid. The unbound oxidized forms were assayed in deproteinized plasma after reduction with dithiothreitol. The total amount of glutathione was determined by reduction before protein precipitation. Separation of reduced glutathione from other endogenous thiols was by ion-pair, reversed-phase, high-performance liquid chromatography. Post-column derivatization withortho-phthalaldehyde made the assay more selective than when using pyrenemaleimide as thiol fluorogenic reagent. The linear range was 0.02 to 2.0 g mL^–1 with good repeatability (relative standard deviation less than 5% for the lowest concentration measured).     

Intestinal Transport and Biotransformation of Resibufogenin and Cinobufagin in Chan Su via HPLC/APCI-MS~n

In vitro models of human colon carcinoma cell line(Caco-2 cell monolayer) and human intestinal bacteria were used to investigate the intestinal transport and biotransformation of resibufogenin and cinobufagin in Chan Su by HPLC/APCI-MSn. The experimental results of Caco-2 cell monolayer demonstrate that the apparent permeability coefficients(Papp) of resibufogenin and cinobufagin are higher than 10-6 cm/s, which indicates that both resibufogenin and cinobufagin have a good absorption in the small intestine....     

Evaluation of the Enantiomeric Separation of Dipeptides Using a Chiral Crown Ether LC Column

Abstract

The direct optical resolution of six dipeptides into four stereoisomers each was achieved on an enantioselective crown ether column. An inclusion complex is formed between the stationary phase and the solute when using an acidic mobile phase. The acidic mobile phase serves to protonate the requisite primary amine of the dipeptide thereby allowing an attractive interaction between the ammonium functional group and the oxygens of the crown ether. Due to the differences in stability of the complexes formed, the four optical isomers elute at different times allowing the stereoisomeric separation. One of the factors affecting enantioselectivity is the distance between the primary amine functional group and the stereogenic center of the chiral moiety. Dipeptides are particularly useful molecules for the studying this “distance effect” since the bonding order of the two amino acids can be reversed. In addition to the enantiomeric separations of dipeptides possessing two stereogenic centers, the behavior of dipeptide separations possessing only one chiral center (i.e., with achiral glycine as one of the residues) is examined to gain additional insight into the mechanism and the effect of the proximity of the primary amine group to the chiral center.     

Quality Evaluation of Petasites tricholobus through Simultaneous Determination of Four Bioactive Bakkenolides by LC

A liquid chromatographic method was developed to evaluate the quality of Petasites tricholobus through a simultaneous determination of four major active bakkenolides. The wavelengths at 265 and 235 nm were chosen to determine four bakkenolides: bakkenolide-B, bakkenolide-D, bakkenolide-IIIa and bakkenolide-IVa. The recovery of the method was in the range of 98.6 to 103.1%, and all the bakkenolides showed good linearity (r ² > 0.999) within test ranges. The developed method was applied to the determination of four bakkenolides in the collected herb samples. The results showed that the content of bakkenolides in rhizome was higher than in other parts of the plant and the older the rhizome, the higher was the bakkenolide content. This simple, rapid, low-cost and reliable LC-VWD method is suitable for routine quantitative analysis and quality control of petasites species plants.     

流动注射-化学发光法测定猪饲料中的吡喹酮

基于吡喹酮对Luminol-NaIO_4化学发光体系有较强的抑制作用,并结合流动注射分析技术,建立了测定吡喹酮的流动注射-化学发光(FI-CL)新方法。在最佳实验条件下,吡喹酮在4.0×10~(-8)～1.0×10~(-6) mol/L浓度范围内与相对化学发光强度呈良好的线性关系,该方法对测定吡喹酮显示出较高的灵敏度,检出限(LOD,3σ)为9.9×10~(-9) mol/L。对2.0×10~(-7) mol/L的吡喹酮平行测定11次,其相对标准偏差(RSD)为1.4%。采用该方法对猪饲料样品进行加标实验,回收率为98.5%～100%。该方法已经成功用于猪饲料样品中吡喹酮的测定。     

Evaluation of relative LC/MS response of metabolites to parent drug in LC/nanospray ionization mass spectrometry: potential implications in MIST assessment

There is an increasing demand for quantitative data on metabolite exposure triggered by regulatory guidances. This contribution describes the accuracy of nanoelectrospray ionization mass spectrometry response of drug compounds and their metabolites from biological matrices compared with radiometric quantification. This is a comprehensive investigation of a set of real-life pharmaceutical compounds in relevant matrices such as urine, bile, feces and plasma. The data suggest that nanoelectrospray mass spectrometry can be used for semi-quantitation of metabolites in the absence of reference standards. Therefore, this approach is suitable to screen out non-relevant metabolites early in development as long as an adequate analytical error margin is applied thus balancing risks and resources.     

方波伏安法评估聚苯胺膜修饰电极的电荷传输速度

研究导电聚合物的电荷传输机制与速度对于其在应用方面的研究极为重要［‘］．例如在电池的研究中，充放电的速度决定于导电聚合物的电荷传输速度；在电致变色器件的研究中，响应时间也是决定于导电聚合物在氧化还原态间的变化速度，即电荷传输速度．显然较低的电荷传输速度不利于器件的实用化，因此人们必须找到一种能够迅速准确评价电荷传输速度的方法，由于导电聚合物是一个特殊的体系，用一般的电化学方法对其电荷传输速度进行测定时常常遇到这样或那样的问题［‘j．一般说来，导电聚合物的氧化还原过程中均伴随着抗衡离子的运动．体系…     

Morphological studies of a hydrogen-bonded LC polymer obtained by photopolymerization in LC solvents

Anisotropic morphologies and the phase behaviour of a hydrogen-bonded LC polymer obtained by photopolymerization in two kinds of LC solvent are discussed. The hydrogen-bonded LC monomer, 4-(6-acryloyloxyhexyloxy) benzoic acid (A6OBA), was photopolymerized in 4-cyano-4'-hexyloxybiphenyl (6OCB) and in 4-cyano-4'-undecyloxybiphenyl (11OCB), which show a nematic phase and a smectic A phase, respectively. After photo-polymerization, the LC media were removed by extraction and the pure polymer was observed by scanning electron microscopy. SEM images showed that the polymer possessed fibrous morphology with a fibre diameter of a few micrometers, based on polymerization-induced phase separation. The overall geometries reflected typical LC characteristics such as schlieren and focal-conic fan textures. It was found that the hydrogen bond between benzoic acid groups in the monomer was rigid enough to fix the anisotropic phase-separated structure forming during the early stage of phase separation; however, it could not permanently maintain the fibre structure due to dissociation at elevated temperature. X-ray measurements revealed that a well developed layer structure of the hydrogen-bonded mesogen existed in the polymer obtained from the smectic phase of 11OCB, whereas a polymer layer structure could develop only partially from the nematic phase of 6OCB.     

Nanoflow LC/IMS-MS and LC/IMS-CID/MS of protein mixtures

A simple ion trap/ion mobility/time-of-flight (TOF) mass spectrometer has been coupled with nanoflow liquid chromatography to examine the feasibility of analyzing mixtures of intact proteins. In this approach proteins are separated using reversed-phase chromatography. As components elute from the column, they are electrosprayed into the gas phase and separated again in a drift tube prior to being dispersed and analyzed in a TOF mass spectrometer. The mobilities of ions through a buffer gas depend upon their collision cross sections and charge states; separation based on these gas-phase parameters provides a new means of simplifying mass spectra and characterizing mixtures. Additionally it is possible to induce dissociation at the exit of the drift tube and examine the fragmentation patterns of specific protein ion charge states and conformations. The approach is demonstrated by examining a simple three-component mixture containing ubiquitin, cytochrome c, and myoglobin and several larger prepared protein mixtures. The potential of this approach for use in proteomic applications is considered.     

RP—HPLC法测定吡喹酮及其脂质体在小鼠体内的分布

应用RP-HPLC法测定吡喹酮及其脂质体在小鼠体内的分布。用外标定量法测定各组织中的含量,其回收率在96.46～103.13%之间,变异系数小于2.95%。实验结果表明,吡喹酮脂质体较游离吡喹酮在小鼠肝、脾组织内药物总含量明显增高,半衰期延长。     

Performance Evaluation of Charged Aerosol and Evaporative Light Scattering Detection for the Determination of Ginsenosides by LC

A sensitive LC-CAD method was developed for simultaneous determination of seven major triterpenoid saponins, namely ginsenosides Rg₁, Re, Rb₁, Rc, Rb₂, Rb₃ and Rd in Panax ginseng C. A. Meyer, a commonly used traditional Chinese medicine. This CAD method was evaluated in sensitivity, linearity and reproducibility compared to ELSD and UV. It was found the developed method has improved sensitivity, linearity and reproducibility compared to ELSD. This method was successfully applied to analyze the ginsenosides in ten samples of Panax ginseng. The validation results indicated that the improved method can be utilized as another approach for quality control of P. ginseng.     

LC Determination of Coumarin-3-Acyl Derivatives for Evaluation of the Stability and Monoamine Oxidase Inhibition Mechanism

A simple and rapid LC method has been developed for the determination of coumarin 3-acyl derivatives synthesized and assayed for their inhibitory activity against monoamine oxidases (MAOs). The proposed liquid chromatography method can be used satisfactorily for the purity control of the synthesized compounds and can also be used to study the stability of these potentially reactive compounds. Moreover using this method it has been possible to elucidate the mechanism of MAO inhibition by direct determination of the biochemical reaction mixture.