Critical evaluation of the determination of pharmaceuticals, personal care products, phenolic endocrine disrupters and faecal steroids by GC/MS and PTV-GC/MS in environmental waters

An analytical method is described for the determination of a broad range of emerging and priority pollutants, together with sewage molecular markers in environmental waters. The step-by-step study of the GC/MS analyses focuses on the effects of experimental variables using a large volume injection (LVI) technique [a programmed temperature-vaporising (PTV) inlet], the evaluation of a clean-up step using classical and newer sorbents (i.e. Al-N, Fl, NH₂, PSA, Si, CN and DIOL), and the revision of how organic matter [i.e. humic acids (HA) content] affects method performance. Reproducibility and recoveries from spiked coastal water samples at different analyte concentrations (100, 250 and 500 ng L⁻¹) as well as with different levels of spiked humic acids (2, 10 and 20 mg L⁻¹) are reported indicating a good performance of the extraction procedure with low levels of HA (<10 mg L⁻¹). The presence of HA is a critical parameter during the solid-phase extraction (SPE) procedures. Of the clean-up sorbents tested, CN and DIOL proved most efficient in cleaning-up the extracts with recoveries in the range of 66-77% and 100-114%, respectively for the selected analytes. Both GC/MS and PTV-GC/MS instrumental configurations were tested using final sewage effluents, riverine, estuarine and coastal water samples. However, limited applicability of the PTV inlet is reported for environmental applications, affording only a modest improvement in chromatographic signal-to-noise ratios.     

Erratum to: Determination of metal ion content of beverages and estimation of target hazard quotients: a comparative study

This is a correction to the following paper: Hague T, Petroczi A, Andrews PR, Barker J, Naughton DP: Determination of metal ion content of beverages and estimation of target hazard quotients: a comparative study. Chem Central J 2008, 2:13.     

Using conformationally locked nucleosides to calibrate the anomeric effect: Implications for glycosyl bond stability

Steric and electronic parameters, such as the anomeric effect (AE) and gauche effect play significant roles in steering the North&lrarr;South equilibrium of nucleosides in solution.Two isomeric oxa-bicyclo[3.1.0]hexane nucleosides that are conformationally locked in either the North or the South conformation of the pseudorotational cycle were designed to study the consequences of having the AE operational or not, independent of other parameters. The rigidity of the system allowed the orientation of the orbitals involved to be set in ‘fixed’ relationships, either antiperiplanar where the AE is permanently ‘on’, or gauche where the AE is impaired. The consequences of these two alternatives were subjected to high-level calculations and measured experimentally by X-ray crystallography, hydrolytic stability of the glycosyl bond, and pK_a values.     

Doubly diastereoselective conjugate addition of enantiopure lithium amides to enantiopure N-enoyl oxazolidin-2-ones: a mechanistic probe

The doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a range of enantiopure N-enoyl oxazolidin-2-ones has been used as a mechanistic probe to determine that the reactive conformation is the anti-s-cis form. The β-amino carbonyl products resulting from these conjugate addition reactions are useful templates for further elaboration into an α,β,α-pseudotripeptide.     

Preparation and evaluation of amphiphilic silica‐based monolithic column having surface‐bound octanoyl‐aminopropyl moieties for capillary electrochromatography

A novel amphiphilic silica‐based monolithic column having surface‐bound octanoyl‐aminopropyl moieties was successfully prepared by a one‐step in situ derivatization process. As expected, the amphiphilic monolithic column exhibited RP chromatographic behavior toward non‐polar solutes (e.g., alkyl benzenes) with high column performance. As the pH of the buffer inside the column increases, the EOF changed from −2.65×10⁻⁸m² V⁻¹s⁻¹ at pH 3.0 to 1.20×10⁻⁸ m² V⁻¹s⁻¹ at pH 8.0 with the reversion of EOF at about pH 6.4. Using acidic mobile phase, five aromatic acids can be efficiently separated in less than 6 min under co‐EOF conditions. For basic compounds, symmetrical peaks were obtained due to the existence of hydrophilic acyl amide group, which can effectively minimize the adsorption of the positively charged basic analyte to the silica‐based surface of the capillary column.     

Conformation dependence of DNA electrophoretic mobility in a converging channel

The electrophoresis of λ‐DNA is observed in a microscale converging channel where the center‐of‐masses trajectories of DNA molecules are tracked to measure instantaneous electrophoretic (EP) mobilities of DNA molecules of various stretch lengths and conformations. Contrary to the usual assumption that DNA mobility is a constant, independent of field and DNA length in free solution, we find DNA EP mobility varies along the axis in the contracting geometry. We correlate this mobility variation with the local stretch and conformational changes of the DNA, which are induced by the electric field gradient produced by the contraction. A “shish‐kebab” model of a rigid polymer segment is developed, which consists of aligned spheres acting as charge and drag centers. The EP mobility of the shish‐kebab is obtained by determining the electrohydrodynamic interactions of aligned spheres driven by the electric field. Multiple shish‐kebabs are then connected end‐to‐end to form a freely jointed chain model for a flexible DNA chain. DNA EP mobility is finally obtained as an ensemble average over the shish‐kebab orientations that are biased to match the overall stretch of the DNA chain. Using physically reasonable parameters, the model agrees well with experimental results for the dependence of EP mobility on stretch and conformation. We find that the magnitude of the EP mobility increases with DNA stretch, and that this increase is more pronounced for folded conformations.     

Uptake and biological responses to nano-Fe versus soluble FeCl3 in excised mussel gills

Nano-Fe particle uptake was experimentally examined in vitro using excised gills and blood cells of the edible blue mussel Mytilus sp. Whole gills were exposed to both Fe₂O₃ nanoparticles and a solution of the hydrated FeCl₃ salt, for up to 12 h, and blood cells for 30 min. Equimolar Fe⁺³ in the nano- and the soluble form was estimated under the assumption of dense spherical particles accommodating the same number of Fe⁺³ as in the dissolved salt solution, namely: 1,000 μg L⁻¹ Fe₂O₃ equivalent to 100 μg L⁻¹ FeCl₃·6H₂O. Putative toxic impact of nano-Fe in gill epithelia and blood cells was assessed by an array of techniques including light- and electron microscopy, biomarkers for oxidative stress (lipid peroxidation levels), neurotoxic effects (acetylcholinesterase activity) and cytotoxicity (neutral red retention). Total and filtered fractions (20 and 200 nm, respectively) of Fe were analysed by ICP-OES. Our results provide evidence for the following: (1) much of both the soluble (95%) and the nano-Fe (90%) were removed from the water column within 12 h; (2) dissolved- and nano-Fe seemed to follow different routes of uptake within the gill epithelium; (3) both nano-Fe and soluble FeCl₃ caused similar impairment of lysosomal stability in circulating blood cells; (4) lipid peroxidation in gills exposed to the two distinct forms of Fe was increased, while acetylcholinesterase activity was unaffected. In these short-term in vitro studies, there appears to be little difference in toxic response between exposure to the Fe salt and the nano-Fe indicating that, in this case, the nanoparticles do not invoke special properties affecting biological function in gills. However, with the use of nano-Fe as a food additive, clearly longer-term in vivo studies are warranted.     

Rheology of interfacial layers

The response of interfacial layers to deformations in size and shape depends on their composition. The corresponding main mechanical quantities are elasticity and viscosity of dilation and shear, respectively. Hence, the interfacial rheology represents a kind of two-dimensional equivalent to the traditional bulk rheology. Due to growing interest in the quantitative understanding of foams and emulsions, more works are dedicated to studies on interfacial rheology. This overview presents the theoretical basis for traditional and recently developed experimental tools and discusses their application to different interfacial systems. While dilational rheology provides information on the composition of mixed interfacial layers, the shear rheology gives answers essentially on structures formed at an interface. The most frequently used methods at present are the oscillating drop and bubble tensiometry methods for dilational deformations and oscillating ring/bicone rheometers for shear deformations.