Generalized criterion of solvent polarity as a tool for control of chromatographic process

The generalized (reductive) criterion of solvent polarity was obtained by the method of multiparametric optimization of the Snyder index P", Hildebrand parameter _T , permittivity _r , and solvatochromism parameter E _T (30). Possibilities of employing this criterion for estimation of the elution power of normal and reversed mobile phases used in high-performance liquid chromatography were considered.     

Analysis of ecstasy with a monolithic reversed-phase column

Summary A new, rapid, and precise liquid chromatographic method has been developed for simultaneous identification and quantification of amphetamine,N-methyl-3,4-methylenedioxymetamphetamine,N-ethyl-3,4-methylenedioxymetamphetamine, andN-methyl-1-(3,4-methyl-enedioxyphenyl)-2-butanamine in the presence of other constituents. The compounds were separated on a monolithic column with a gradient prepared from acetonitrile and 20mm monobasic potassium buffer at a flow rate of 1.5 mL min⁻¹. Quantitation was performed with metoclopramide as internal standard. Use of different flow rates was investigated and enabled reduction of the separation time from 11 to 3.5 min for seven substances. The method was then applied to ten seized tablets to identify and quantify their active ingredients.     

Reversed Capillary Electrochromatography: Investigation of Peak Symmetry for Eluting Curves of Solutes

Summary A clean method without use of organic solvents has been developed for isolation and high-performance liquid chromatographic (HPLC) determination of oxytetracycline (OTC) and sulphadimidine (SDD) in cow's milk. Isolation is rapid and simple—homogenization with an inorganic acid solution by means of a handy ultrasonic homogenizer, which is easy-to-use and portable, followed by centrifugation. Reversed-phase HPLC was performed on a C₄ column, with 1.25 mmol L⁻¹ succinic acid solution as mobile phase, and identification was by means of a photodiode-array detector. Separation of the analytes was achieved in less than 8 min. Significant linearity was established over the concentration range of 0.1–1.0 μg mL⁻¹ for both target compounds (r>0.99,P<0.01). Average recoveries of OTC and SDD (each spiked at 0.1–1.0 μg mL⁻¹) were ≥88.8, and inter- and intra-assay variability was ≤2.8%. The total time required for analysis of one sample was <20 min. The limits of quantitation of the method (μg mL⁻¹ in milk) were 0.044 for OTC and 0.023 for SDD. No organic solvent was used at any stage of the analysis.     

Simultaneous Determination of Carbamate and Organophosphorus Pesticides in Honeybees by Liquid Chromatography-Mass Spectrometry

Summary The potential of liquid chromatography-mass spectrometry (LC-MS) has been studied for the simultaneous determination of sixteen carbamate and organophosphorus pesticides in honeybees using a traditional sample preparation protocol based on acetone extraction and dichloromethane partitioning. The performances of both atmospheric pressure chemical ionization (APCI) and electrospray (ES) interfaces were compared. APCI offered better sensitivity and specificity for a higher range of pesticides. Limits of quantification were from 0.01 to 0.17 mg kg^–1, at which recoveries obtained were between 64 and 93%, except for pirimicarb that was at 13%, with relative standard deviations ranging from 7 to 20%. Fenitrothion, fenoxycarb, methiocarb and phoxim were found in bees from Valencian Community beehives at concentrations between 0.03 and 3.75 mg kg^–1.     

Migration of Ethylene Terephthalate Oligomers from Roasting Bags into Olive Oil

Summary A high-performance liquid-chromatographic method with UV detection (HPLC–UV) has been developed for quantification of ethylene terephthalate oligomers in olive oil, from which they were extracted with acetonitrile. Oligomers, from monomers (M₁) to pentamers (M₅), were jointly and/or individually identified by liquid chromatography with mass spectrometry (electron-impact mass spectrometry (EIMS) low- and high-resolution) and were quantified by HPLC–UV using an acetonitrile solution of the major oligomer (the trimer M₃) as standard. For M₃ recovery was 98.9%, the detection limit was 60 g L^–2, and method precision was 2.03% (RSD). Migration of oligomers M₁–M₅ into 50 mL olive oil sealed in each of two brands of 10 cm × 10 cm poly(ethylene terephthalate) roasting bag was evaluated under two sets of conditions that approached but remained below the limit at which the bag material became physically deformed – heating for 7 min at 850 W in a microwave oven, or for 60 min at 200 °C in a conventional oven. Total migration was approximately 2.7 mg dm^–2 under the former conditions and 3.5–4.1 mg dm^–2 under the latter.Presented at the International Symposium on Separation and Characteristics of Natural and Synthetic Macromolecules, Amsterdam, The Netherlands, February 5–7, 2003     

Procyanidin size and composition by thiolysis with cysteamine hydrochloride and chromatography

Summary Cysteamine hydrochloride is shown to be an alternative thiol reagent to toluene-α-thiol for the estimation of structural parameters (mean size, galloylation) of plant polymeric procyanidins. Acid depolymerization in the presence of the thiol yields mixtures which may be directly analysed by RPHPLC. Alternatively, the terminal units of the polymer may be separated from the extension units by cation-exchange chromatography previous to RPHPLC. High reaction-recovery yields (ca. 90% thiolysis and RPHPLC, ca. 69% thiolysis, cation exchange and RPHPLC) are obtained and both procedures are precise.     

The Importance of Polarity/Polarizability Interaction on the Acidity Behavior of 9,10-Anthraquinone and 9-Anthrone Derivatives in Methanol-Water Mixed Solvents Using Target Factor Analysis and QSPR Approaches

The influence of solvent properties on acidity constants of some newly synthesized 9,10-anthraquinone and 9-anthrone derivatives was studied in methanol-water mixtures in a composition range of 0.57 to 1.0 methanol mole fraction. The model was established by using both multiple linear regression and target factor analysis. Both methods revealed that the solvent polarity/polarizability parameter ^* is a major factor in controlling the acidity behavior of the anthraquinones and anthrones studied in binary methanol-water mixed solvents. A QSPR study was conducted to drive the relationships between the ^* coefficient s and the polarity/polarizability of molecules. Both dipole moment and polarizability were found to have a linear relationship with s. The results confirm that, in the dipolar protic solvents used, the dipole-dipole interaction (for neutral molecules) and the ion-dipole interaction (for ionized molecules) are the major factors controlling the acidity behavior of these compounds.     

Analysis of the Association Process Between a Series of Phenol Derivatives with Two Novel Fluorinated Stationary Phase Using the Cl− Anion as Retention Marker

Summary Lithium chloride (LiCl) effect on the retention process of a phenol derivative series was investigated on two types of fluorinated stationary phase (i.e. a silica grafted with fluorinated linear alkyl chain (L-FSP) and a silica grafted with fluorinated aromatic ring stationary phase (A-FSP)). The results showed that the solute retention is enhanced when the A-FSP was used instead of the L-FSP due to additional – interactions. For the two fluorinated stationary phases (FSPs), the phenol-FSP association process can be divided into two LiCl concentration domains demonstrated that it was important to take into account the adsorbtion of Cl^– anion on the FSPs. As well, enthalpy-entropy compensation revealed that the solute retention mechanism was independent of the solute molecular structure and confirmed a change on the solute retention mechanism at a critical LiCl concentration value around 0.02M.     

Identification of Apigenin Metabolites in Rat Liver Perfusate by Column Switching High Performance Liquid Chromatography/Electrospray Ionization Mass Spectrometry

Summary.  A selective column switching high performance liquid chromatographic method has been used for the simultaneous determination of apigenin and metabolites in rat liver perfusate. This new method clearly separated apigenin and the metabolites with high resolution. The structures of metabolites were proposed based on selective ion recording and full scan analysis by electrospray ionization mass spectrometry. Corresponding author. E-mail: basly@pharma.unilim.fr Received May 15, 2002; accepted (revised) September 13, 2002     

A limit to alternate column recycle chromatography

Summary It was found experimentally that the potential for routine, rapid high-efficiency separations by alternate column, recycle, reversed-phase chromatography is limited by the increase of capacity factors with pressure.