Improving the quality of potentiometric pH measurements

Like all experimentally determined physical and chemical properties, pH measurements are affected by the limited precision and accuracy of the measurement procedures. Fundamental studies of pH standards, based on measurement of the potential of an electrochemical cell without transference, known as the Harned cell, containing a platinum–hydrogen electrode and a silver–silver chloride reference electrode, indicate that vapour condensation phenomena on potentiometric cell walls not immersed in the thermostatic bath are a major source of error in assessment of pH values. In this work a study was conducted on phthalate buffer, 0.05 mol kg⁻¹ KHPhth, and results are reported for the effect of this phenomenon on the assignment of pH values and on their corresponding uncertainties. Identification and quantification of this effect constitute an original contribution to improvement of the primary method of pH measurement and, therefore, more rigorous pH (PS) values.     

Distinguished People and Places Important in the History of Portuguese Analytical Chemistry

The people and places of importance in the history of chemistry in Portugal have been reviewed with particular reference to analytical chemistry.     

Central configurations of the N-body problem via equivariant Morse theory

In this paper we use the equivariant Morse theory to give an estimate of the minimal number of central configurations in the N-body problem in ³. In the case of equal masses we prove that the planar central configurations are saddle points for the potential energy. From this we deduce the presence of non-planar central configurations, for every N 4.The principal difficulty in applying Morse theory is that the potential function is defined on a manifold on which the group O(3) does not act freely. To avoid this problem the equivariant cohomology functor is applied in order to obtain the Morse inequalities.     

Chemical Characterization and Antibiofilm Activities of Bulbs and Leaves of Two Aglione (Allium ampeloprasum var. holmense Asch. et Graebn.) Landraces Grown in Southern Italy

The present study was carried out to determine some biochemical characteristics, in particular the total polyphenol content and the free radical scavenging activity, of the extracts recovered from bulbs and aerial parts (these last often considered as by-products) of two landraces of A. ampeloprasum var. holmense cultivated in Southern Italy. For the first time, the capacity of the extracts of these landraces to inhibit the formation of biofilm of different Gram-negative and Gram-positive bacteria and to affect the metabolism of the cells present within the bacterial biofilm was evaluated. All extracts exhibited an amount of total polyphenols not lower than 2.86 mg/g of dried product and revealed a noteworthy antioxidant activity, with EC₅₀ values not exceeding 4.95 mg. In both cases, the aerial parts extracts were more effective than the bulb extracts, which also showed a minor amount of total polyphenols. The extracts inhibited mainly the adhesive capability of Pseudomonas aeruginosa and Staphylococcus aureus, by 95.78% and 85.01%, respectively. The extracts demonstrated to inhibit also the metabolism of the bacterial cells reaching levels up to 90%. Finally, as assessed by the assays performed on the 24-h preformed biofilms, all the extracts were also capable to cause a reduction in bacterial biomass and to affect their metabolism.     

Controlled Production of Exopolysaccharides from Enterobacter A47 as a Function of Carbon Source with Demonstration of Their Film and Emulsifying Abilities

The bacterium Enterobacter A47 has demonstrated the ability to synthesise distinct exopolysaccharides (EPS) as a function of the substrate used. The culture's performance was evaluated in experiments using either glucose or xylose, as single carbon sources, and compared with the substrate (glycerol) used in previous studies. The highest EPS production (13.23 g L^?1) was obtained in the glucose fed assay, with a volumetric productivity of 3.38 g L^?1 day^?1. The use of xylose resulted in lower productivity (1.39 g L^?1 day^?1). The synthesised polymers have the same main sugar monomers (fucose, glucose, galactose and glucuronic acid), but their relative proportion varied with the substrate used. The acyl groups' content and composition were also affected by the substrate used. The polymers produced from glycerol (EPS-s) and glucose (EPS-g) had identical shear-thinning behaviour and good emulsion-stabilising capacity and their films had similar mechanical and water vapour properties. However, the emulsions stabilised with EPS-g were less stable and destabilised within short periods of time or when subjected to heat and freezing/thawing procedures. On the other hand, the polymer produced from xylose had little emulsion-stabilising capacity and lower apparent viscosity than EPS-s and EPS-g, but its films were considerably more elastic.     

Molecular formula analysis of fragment ions by isotope‐selective collision‐induced dissociation tandem mass spectrometry of pharmacologically active compounds

The purpose of this work is to explore the mass fragment characterization of commonly used drugs through a novel approach, which involves isotope‐selective tandem mass spectrometry (MS/MS). Collision‐induced dissociation (CID) was performed with a low‐resolution linear ion trap mass spectrometer in positive electrospray ionization. Three pharmacologically active ingredients, i.e. omeprazole, meloxicam and brinzolamide, selected as model compounds in their own formulation, were investigated as a sodiated adduct [C₁₇H₁₉N₃O₃S + Na]⁺ (omeprazole) and as protonated adducts, [C₁₄H₁₃N₃O₄S₂ + H]⁺ and [C₁₂H₂₁N₃O₅S₃ + H]⁺, meloxicam and brinzolamide, respectively. Selecting a narrow window of ±0.5 m/z units, precursor ion fragmentation by CID‐MS/MS of isotopologues A + 0, A + 1 and A + 2 was found very useful to confirm the chemical formula of product ions, thus aiding the establishment of characteristic fragmentation pathways of all three examined compounds. The correctness of putative molecular formula of product ions was easily demonstrated by exploiting the isotope peak abundance ratios (i.e. I_F+0/I_F+1 and I_F+0/I_F+2) as simple constraints in low‐resolution MS instrumentations. Copyright © 2014 John Wiley & Sons, Ltd.     

Uniqueness and nondegeneracy for some nonlinear elliptic problems in a ball

In this paper we study the uniqueness and nondegeneracy of positive solutions of nonlinear problems of the type Δ_pu+f(r,u)=0 in the unit ball B, u=0 on ∂B. Here Δ_p denotes the p Laplace operator Δ_p=div(|∇u|^p−2∇u), p>1. The main ideas rely on the Maximum Principle and an implicit function theorem that we derive in a suitable weighted space. This space is essential to deal with the case p≠2.     

Effect of condensation phenomena on potentiometric measurements

Results of potentiometric analysis, namely those of pH measurements, depend on temperature control of the experimental setup, as it is expressed in the analytical law, the Nernst equation, starting from the primary level, where reference values are conventionally assigned to standard solutions, through the whole traceability chain, down to the service laboratory.Fundamental studies of pH standards, based on the measurement of the potential of an electrochemical cell without transference, known as Harned cell, containing a platinum-hydrogen electrode and a silver-silver chloride reference electrode, refer condensation phenomena on the portions of the cell walls which are not immersed in the thermostatic bath, as one of the major sources of error in the assessment of both the silver-silver chloride electrode standard potential and on pH values. In this work such effect, which is bound to happen due to significant temperature differences between the ambient air temperature and the water bath, has been quantified, presenting an original contribution to the improvement of the quality of potentiometric analysis results. This was possible due to the availability of a climatic cabin “WALKIN” with a temperature control of ±0.01 °C, which permitted that temperature gradients were built between the thermostat water bath (controlled to ±0.005 °C) where cells filled to about 2/3 full were immersed up to 90% of their height, and the surrounding environment.