Position of starting spot in TLC: Influence on average plate height

Summary The influence of the distance between the solvent entry and the starting zone positions, Z₀, on the average plate height was studied. This factor was found to be of major importance and could be optimized. The Guiochon and Siouffi model greatly underestimates the plate height for low values of Z₀.     

A study of the mechanisms involved in the separation of metal ions with a mixed-bed stationary phase

Summary The optimization of chromatographic methods for the determination of metal species require an understanding of the mechanisms involved. In this work, the separation of Cd, Co, Cu, Fe(II/III), Mn, Pb and Zn using a mixed bed column (IonPac CS5A) and a cation-exchange column (IonPac CS2) is studied as a function of mobile phase composition. The type and concentration of complexing agent and of ionic strength modificators were evaluated. The charge of analytes were calculated using the classical ion exchange approach to highlight the effect of eluent composition on retention. The comparative study enabled us to identify an optimal eluent composition for the separation of the nine metal species.     

Determination of benzene, toluene, ethylbenzene and xylenes in air by solid phase micro-extraction/gas chromatography/mass spectrometry

The aim of the study was to analyse BTEX compounds (benzene, toluene, ethylbenzene, xylenes) in air by solid phase micro-extraction/gas chromatography/mass spectrometry (SPME/GC/MS), and this article presents the features of the calibration method proposed. Examples of real-world air analysis are given. Standard gaseous mixtures of BTEX in air were generated by dynamic dilution. SPME sampling was carried out under non-equilibrium conditions using a Carboxen/PDMS fibre exposed for 30 min to standard gas mixtures or to ambient air. The behaviour of the analytical response was studied from 0 to 65 g/m³ by adding increasing amounts of BTEX to the air matrix. Detection limits range from 0.05 to 0.1 g/m³ for benzene, depending on the fibre. Inter-fibre relative standard deviations (reproducibility) are larger than 18%, although the repeatability for an individual fibre is better than 10%. Therefore, each fibre should be considered to be a particular sampling device, and characterised individually depending on the required accuracy. Sampling indoor and outdoor air by SPME appears to be a suitable short-delay diagnostic method for volatile organic compounds, taking advantage of short sampling time and simplicity.     

Dinuclear Cu(II) complexes of isomeric bis-(3-acetylacetonate)benzene ligands: synthesis, structure, and magnetic properties

Highly versatile coordinating ligands are designed and synthesized with two β-diketonate groups linked at the carbon 3 through a phenyl ring. The rigid aromatic spacer is introduced in the molecules to orient the two acetylacetone units along different angles and coordination vectors. The resulting para, meta, and ortho bis-(3-acetylacetonate)benzene ligands show efficient chelating properties toward Cu(II) ions. In the presence of 2,2'-bipyridine, they promptly react and yield three dimers, 1, 2, and 3, with the bis-acetylacetonate unit in bridging position between two metal centers. X-ray single crystal diffraction shows that the compounds form supramolecular chains in the solid state because of intermolecular interactions. Each of the dinuclear complexes shows a magnetic behavior which is determined by the combination of structural parameters and spin polarization effects. Notably, the para derivative (1) displays a moderate antiferromagnetic coupling (J = -3.3 cm(-1)) along a remarkably long Cu···Cu distance (12.30 ?).     

Deformable liposomes containing alkylcarbonates of γ-cyclodextrins for dermal applications

Liposomes made with hydrogenated soya lecithin (HPC) mixed with dodecylcarbonate γ-cyclodextrin (C12CD) at 20:1, 10:1 and 5:1 w/w ratios were prepared by the solvent evaporation method. C12CD had emulsifying properties and the possibility of producing deformable liposomes, as topical delivery system of progesterone (PG), was evaluated. Liposome size, deformability and drug entrapment were determined and the interaction between C12CD and HPC was investigated using differential scanning calorimetry (DSC). The size and the amount of PG loaded in the liposomes depended on the lipid:C12CD ratio: the smallest liposomes were obtained using 20:1 ratio and the maximum drug entrapment at 5:1 ratio. DSC analysis suggested that C12CD interacted with liposomes disrupting and fluidizing the lipid bilayer. PG transepidermal permeation through intact pig skin and PG skin uptake from deformable liposomes were assessed and compared to the values obtained from aqueous suspension and conventional liposomes. The PG permeations were negligible for all systems, while skin uptake increased for liposomes containing C12CD. This was attributed to the deformability and to the increase in the drug entrapment efficiency of these liposomes. The use of C12CD in liposome formulations can improve PG topical therapy.     

Inclusion of cinnamaldehyde in modified γ-cyclodextrins

This work deals with the formation of inclusion complexes between cinnamaldehyde and two synthetic alkylcarbonates of γ-cyclodextrin, namely ethylcarbonate-γ-CD and octylcarbonate-γ-CD. Complexation was monitored by phase-solubility studies, by FT-IR spectroscopy and by DSC and TG analysis. The diffusion of cinnamaldehyde through a cellulose membrane was investigated in the absence and in the presence of each of the two γ-CD alkylcarbonates. Studies on photostability and stability over time were carried out on different cosmetic formulations containing pure cinnamaldehyde or an equivalent amount of cinnamaldehyde complexed with the two alkylcarbonates. Phase-solubility diagrams, DSC, FTIR and TGA analysis suggested the formation of inclusion complexes. The diffusion of cinnamaldehyde through the cellulose membrane decreased in the presence of the two alkylcarbonates confirming the interaction of this molecule with the inclusion agents. Moreover the stability of cinnamaldehyde to light and heat resulted increased by complexing this fragrance material with the two alkylcarbonates.