Enantiomeric separation of gemfibrozil chiral analogues by capillary electrophoresis with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin as chiral selector

The enantiomeric separation of gemfibrozil chiral analogues was performed by capillary zone electrophoresis (CZE). Resolution of the enantiomers was achieved using heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD) as chiral selector dissolved into a buffer solution. In order to optimize the separation conditions, type, pH and concentration of running buffer and chiral selector concentration were varied. For each pH value, the optimum chiral selector concentration that produced the resolution of the isomers was found. The migration order of labile diastereoisomers formed was valued at the optimum experimental conditions by adding a pure optical isomer to the racemic mixture. Data from 1H NMR studies confirmed host-guest interaction between TM-beta-CD and 5-(2,5-dimethylphenoxy)-2-ethylpentanoic acid sodium salt. The hypothesized stoichiometry host:guest was 1:1. An apparent equilibrium constant (Ka) was estimated monitoring the chemical shift variation as a function of TM-beta-CD concentration. Salt effect on complexation equilibrium constant was also investigated.     

Twenty years of the Me.Tos. Project: an Italian national external quality assessment scheme for trace elements in biological fluids

The Me.Tos. Project, started in 1983 and still running, is an external quality assessment (EQA) scheme for laboratories performing specialized analyses in occupational and environmental laboratory medicine. Besides the organization of EQA exercises, initiatives for further education of the participants and the harmonization of EQA procedures at a European level are carried out. Participation in EQA schemes allows laboratories to comply with the international standards for the quality and competence of testing and clinical laboratories. The organization of the scheme includes the preparation of control materials, their distribution to the participants, according to strategies aimed to avoid identification of the samples, the statistical analysis of the results and the evaluation of laboratories' performance according to international guidelines and criteria set by the organizers. An overview of the scheme operation and the current performances of participants will be given.     

Estimates of uncertainty of measurement from proficiency testing data: a case study

The results obtained by a laboratory over a number of proficiency testing/external quality assessment schemes (PT/EQAS) rounds can give information on the uncertainty of its measurements for a given test, provided that conditions such as full coverage of the routine analytical range, traceability, and small uncertainty of the assigned values (compared to the spread of the results) are met and provided that systematic deviations and any other sources of uncertainty are considered. As organisers of the Italian EQAS (ITEQAS) in occupational and environmental laboratory medicine, we tested this hypothesis using as model data from well-performing laboratories taking part in ITEQAS for lead in blood over the last 2 years. We also investigated how different PT/EQAS features (frequency of trials and number of samples) would affect a laboratory estimate of its uncertainty. Such information can be helpful in improving PT/EQAS organisation and define, for a given test: (a) the state of the art of the uncertainty of current measurement procedures, (b) identify needs for improvement of analytical methodologies and (c) set targets for acceptable uncertainty values.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia.Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher.     

Release of rifampicin from chitosan, PLGA and chitosan-coated PLGA microparticles

Recently three groups of rifampicin (RIF)-loaded microparticles (MPs), consisting of chitosan (CHT), PLGA and PLGA/CHT mixtures, were assessed in terms of RIF-loading and retention during nebulisation. The CHT-coated PLGA MPs were found to exhibit high RIF-loading ability together with nebulisation ability, stability, and mucoadhesive properties. All MP types had comparable toxicity towards alveolar cells which was significantly lower than that of the free drug. Herein, we study the release of RIF from all MP-types, during incubation in buffer with pH values: 4.40 and 7.40. Results show that CHT particles exhibit a higher burst release compared to PLGA MPs; at pH 4.40, which is explained by the higher solubility of CHT in acidic media. At pH 7.40 burst release from CHT MP's is significantly lower when CHT is crosslinked with glutaraldehyde, which is consistent with their - previously observed - increased stability during nebulization. From PLGA MPs, RIF release was pH independent under the conditions applied, while the amount of PVA (stabilizer) considerably affected drug release. When PLGA MP's were coated with CHT, at pH 7.40 the retention of RIF increased further (compared to non-coated MPs), while at pH 4.40 the release was faster from the CHT-coated particles. Concluding, it is proven that when PLGA MPs are coated with CHT, in addition to increased particle mucoadhesive properties, the release kinetics of RIF are modified.     

Quantification of N-acetyl- and N-glycolylneuraminic acids by a stable isotope dilution assay using high-performance liquid chromatography-tandem mass spectrometry

The present report describes a method for the quantification of N-acetyl- and N-glycolylneuraminic acids without any derivatization, using their (13)C(3)-isotopologues as internal standards and a C(18) reversed-phase column modified by decylboronic acid which allows for the first time a complete chromatographic separation between the two analytes. The method is based on high-performance liquid chromatographic coupled with electrospray ion-trap mass spectrometry. The limit of quantification of the method is 0.1mg/L (2.0ng on column) for both analytes. The calibration curves are linear for both sialic acids over the range of 0.1-80mg/L (2.0-1600ng on column) with a correlation coefficient greater than 0.997. The proposed method was applied to the quantitative determination of sialic acids released from fetuin as a model of glycoproteins.     

Degradation of methyl tert-butyl ether in water: effects of the combined use of sonolysis and photocatalysis

The degradation of methyl tert-butyl ether (MTBE) in water was kinetically investigated in a O(2)/Ar 80:20 atmosphere employing either sonolysis at 20 kHz, or photocatalysis on TiO(2) (with 315 nm< lambda(irr) <400 nm), or simultaneous sonolysis and photocatalysis (i.e. sonophotocatalysis), as degradation techniques. In all investigated conditions, MTBE concentration decreased according to a first order rate law; under ultrasound the degradation rate was stirring-dependent. The time profile of the reaction intermediates gave information on the reaction paths prevailing under the different experimental conditions. The energy consumption of the employed degradation techniques was also evaluated, which might be decisive for their practical application.     

Lichen-based biosensor for the determination of benzene and 2-chlorophenol: microcalorimetric and amperometric investigations

Preliminary microcalorimetric studies have been performed to analyse the response of a whole epiphytic lichen tissue (Evernia prunastri) to 2-chlorophenol (2Cl-), a pollutant of oil mill waste-water, in order to evaluate whether the tissue might be used to assess the toxic characteristics of polluted waters. The obtained results (lichen viability expressed in hours, enthalpy variations for the 2Cl-/lichen interactions) were used to create a lichen-based biosensor that uses an amperometric oxygen electrode (a Clark electrode) as a transducer. The lichen catalyses aromatic ring cleavage (via pyrocatechase enzymes present in the lichen), and transforms aromatic substances like 2Cl- into muconic acid (C₆H₆O₄). Following a full electroanalytical characterisation, the performance of the proposed lichen biosensor was compared to that of a biosensor based on Pseudomonas putida cells, which was originally constructed to monitor benzene in different matrices (water, air, petrol and oil) and was tested in our laboratory previously.     

Physical characterization of poly(ω‐pentadecalactone) synthesized by lipase‐catalyzed ring‐opening polymerization

The Candida antarctica lipase B (Novozyme‐435)‐catalyzed ring‐opening polymerization of ω‐pentadecalactone in toluene was performed. Poly(ω‐pentadecalactone) [poly(PDL)] was obtained in a 93% isolated yield in 4 h with a number‐average molecular weight of 64.5 × 10³ g/mol and a polydispersity index of 2.0. The solid‐state properties of poly(PDL) were investigated by thermogravimetric analysis (TGA) coupled with mass spectrometry, differential scanning calorimetry (DSC), stress–strain measurements, wide‐angle X‐ray diffraction, and dynamic mechanical and dielectric spectroscopies. Poly(PDL) is a crystalline polymer that melts around 100 °C. The polyester shows good thermal stability, with a main TGA weight loss centered at 425 °C. Because of the high degree of poly(PDL) crystallinity, the glass transition (?27 °C) is revealed by relaxation techniques such as dynamic mechanical and dielectric spectroscopies, rather than by DSC. In addition to the glass transition, the viscoelastic spectrum of poly(PDL) also shows two low‐temperature secondary relaxations centered at ?130 (γ) and ?90 °C (β). They are attributed to local motions of the long methylene sequence (γ) and complex units involving water associated with the ester groups (β). The mechanical properties of poly(PDL) are typical of a hard, tough material, with an elastic modulus and yield parameters comparable to those of low‐density polyethylene. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1721–1729, 2001     

Mechanical characterization of polymeric thin films by atomic force microscopy based techniques

Polymeric thin films have been awakening continuous and growing interest for application in nanotechnology. For such applications, the assessment of their (nano)mechanical properties is a key issue, since they may dramatically vary between the bulk and the thin film state, even for the same polymer. Therefore, techniques are required for the in situ characterization of mechanical properties of thin films that must be nondestructive or only minimally destructive. Also, they must also be able to probe nanometer-thick ultrathin films and layers and capable of imaging the mechanical properties of the sample with nanometer lateral resolution, since, for instance, at these scales blends or copolymers are not uniform, their phases being separated. Atomic force microscopy (AFM) has been proposed as a tool for the development of a number of techniques that match such requirements. In this review, we describe the state of the art of the main AFM-based methods for qualitative and quantitative single-point measurements and imaging of mechanical properties of polymeric thin films, illustrating their specific merits and limitations.