Liquid chromatographic methods for chloral hydrate determination

Liquid chromatographic methods, based on reversed-phase (RP) and anion-exchange mechanisms, have been developed for chloral hydrate determination. Both methods are preceeded by derivatization of chloral hydrate. For RP separations, different reagents [namely dansylhydrazine and o-(4-nitrobenzyl)hydroxylamine] have been studied, but the best results have been achieved using 1,2-benzenedithiol with UV detection at 220 nm. The anion-exchange method is based on derivatization with NaOH to form sodium formate that is then analyzed by anion-exchange, with suppressed conductivity detection. Derivatization conditions were optimized in order to reach the best yield of reaction. The optimization of the procedure allowed to determine chloral hydrate with detection limits as low as 0.2 μg/l with good linearity and reproducibility. The anion-exchange method was also applied for chloral hydrate determination in a drinking water sample. A preconcentration procedure has also been studied.     

Thermodynamic Solution Properties of a Biodegradable Chelant (L-glutamic-N,N-diacetic Acid,L-GLDA) and Its Sequestering Ability toward Cd2+

The thermodynamics of the interaction of L-glutamic-N,N-diacetic acid (GLDA) with protons was studied potentiometrically at different temperatures, ionic strengths and ionic media. Four protonation constants and corresponding enthalpy changes occurred at infinite dilution together with temperature and ionic strength coefficients. The medium effect was also interpreted in terms of the formation of weak complexes between the ligand and the cations of supporting electrolytes, resulting in a greater tendency of GLDA to chemically interact with Na⁺ rather than K⁺ and, in turn, (CH₃)₄N⁺. Formation constants of GLDA with Cd²⁺ were determined in NaCl_(aq) at different ionic strength values. Five complex species were found, namely CdL²⁻, CdHL⁻, CdH₂L⁰_(aq), Cd₂L⁰_(aq), and Cd(OH)L³⁻, whose formation constant values at infinite dilution were log β = 12.68, 17.61, 20.76, 17.52, and 1.77, respectively. All the species results were relevant in the pH range of natural waters, although the Cd₂L⁰_(aq) was observed only for C_Cd ≥ C_GLDA and concentrations of >0.1 mmol dm⁻³. The sequestering ability of GLDA toward Cd²⁺, evaluated by means of pL_0.5, was maximum at pH~10, whereas the presence of a chloride containing a supporting electrolyte exerted a negative effect. Among new generation biodegradable ligands, GLDA was the most efficient in Cd²⁺ sequestration.     

The Effect of Metal Cations on the Aqueous Behavior of Dopamine. Thermodynamic Investigation of the Binary and Ternary Interactions with Cd2+, Cu2+ and UO22+ in NaCl at Different Ionic Strengths and Temperatures

The interactions of dopamine [2-(3,4-Dihydroxyphenyl)ethylamine, (Dop⁻)] with cadmium(II), copper(II) and uranyl(VI) were studied in NaCl(aq) at different ionic strengths (0 ≤ I/mol dm⁻³ ≤ 1.0) and temperatures (288.15 ≤ T/K ≤ 318.15). From the elaboration of the experimental data, it was found that the speciation models are featured by species of different stoichiometry and stability. In particular for cadmium, the formation of only MLH, ML and ML₂ (M = Cd²⁺; L = dopamine) species was obtained. For uranyl(VI) (UO₂²⁺), the speciation scheme is influenced by the use of UO₂(acetate)₂ salt as a chemical; in this case, the formation of ML₂, MLOH and the ternary MLAc (Ac = acetate) species in a wide pH range was observed. The most complex speciation model was obtained for the interaction of Cu²⁺ with dopamine; in this case we observed the formation of the following species: ML₂, M₂L, M₂L₂, M₂L₂(OH)₂, M₂LOH and ML₂OH. These speciation models were determined at each ionic strength and temperature investigated. As a further contribution to this kind of investigation, the ternary interactions of dopamine with UO₂²⁺/Cd²⁺ and UO₂²⁺/Cu²⁺ were investigated at I = 0.15 mol dm⁻³ and T = 298.15K. These systems have different speciation models, with the MM’L and M₂M’L₂OH [M = UO₂²⁺; M’ = Cd²⁺ or Cu²⁺, L = dopamine] common species; the species of the mixed Cd²⁺ containing system have a higher stability with respect the Cu²⁺ containing one. The dependence on the ionic strength of complex formation constants was modelled by using both an extended Debye–Hückel equation that included the Van’t Hoff term for the calculation of the formation enthalpy change values and the Specific Ion Interaction Theory (SIT). The results highlighted that, in general, the entropy is the driving force of the process. The quantification of the effective sequestering ability of dopamine towards the studied cations was evaluated by using a Boltzmann-type equation and the calculation of pL_0.5 parameter. The sequestering ability was quantified at different ionic strengths, temperatures and pHs, and this resulted, in general, that the pL_0.5 trend was always: UO₂²⁺ > Cu²⁺ > Cd²⁺.     

The Role of the trans-Planar Mesophase in the Polymorphic Behavior of Syndiotactic Polypropylene

The transformations of the trans-planar mesophase of syndiotactic polypropylene (sPP) subjected to thermal, mechanical and solvent treatments, were investigated. The unoriented trans-planar mesophase, obtained by quenching the melt at 0°C, was annealed at 80°C and the thermal transformation was investigated by X-rays, infrared and dynamic-mechanical analysis. The presence of the helical form II was recognized in the annealed sample. The oriented trans-planar mesophase, obtained by drawing at room temperature and releasing the tension, was immersed in liquid dichloromethane for 24 hours. After drying the sample showed the presence of the oriented form II, although it was not possible to exclude a partial transition into form IV. On the basis of the present and literature results we suggested a scheme of the polymorphic transitions of sPP, in which the central role of the trans-planar mesophase is enlightened.     

Elastic Behaviour of Oriented Syndiotactic Poly(propylene)

Due to a typing error, the name of the second co‐author, Liberata Guadagno, was spelled incorrectly. We would like to apologize for any inconvenience this mistake may have caused!     

Adaptive Modelling of Mutated FMO3 Enzyme Could Unveil Unexplored Scenarios Linking Variant Haplotypes to TMAU Phenotypes

Background: Trimethylaminuria (TMAU) is a rare genetic disease characterized by the accumulation of trimethylamine (TMA) and its subsequent excretion trough main body fluids, determining the characteristic fish odour in affected patients. We realized an experimental study to investigate the role of several coding variants in the causative gene FMO3, that were only considered as polymorphic or benign, even if the available literature on them did not functionally explain their ineffectiveness on the encoded enzyme. Methods: Mutational analysis of 26 TMAU patients was realized by Sanger sequencing. Detected variants were, subsequently, deeply statistically and in silico characterized to determine their possible effects on the enzyme activity. To achieve this goal, a docking prediction for TMA/FMO3 and an unbinding pathway study were performed. Finally, a TMAO/TMA urine quantification by 1H-NMR spectroscopy was performed to support modelling results. Results: The FMO3 screening of all patients highlighted the presence of 17 variants distributed in 26 different haplotypes. Both non-sense and missense considered variants might impair the enzymatic kinetics of FMO3, probably reducing the interaction time between the protein catalytic site and TMA, or losing the wild-type binding site. Conclusions: Even if further functional assays will confirm our predictive results, considering the possible role of FMO3 variants with still uncertain effects, might be a relevant step towards the detection of novel scenarios in TMAU etiopathogenesis.     

Critical Reappraisal of Methods for Measuring Urine Saturation with Calcium Salts

Background: Metabolic and physicochemical evaluation is recommended to manage the condition of patients with nephrolithiasis. The estimation of the saturation state (β values) is often included in the diagnostic work-up, and it is preferably performed through calculations. The free concentrations of constituent ions are estimated by considering the main ionic soluble complexes. It is contended that this approach is liable to an overestimation of β values because some complexes may be overlooked. A recent report found that β values could be significantly lowered upon the addition of new and so far neglected complexes, [Ca(PO₄)Cit]⁴⁻ and [Ca₂H₂(PO₄)₂]. The aim of this work was to assess whether these complexes can be relevant to explaining the chemistry of urine. Methods: The Ca–phosphate–citrate aqueous system was investigated by potentiometric titrations. The stability constants of the parent binary complexes [Cacit]⁻ and [CaPO₄]⁻, and the coordination tendency of PO₄³⁻ toward [Ca(cit)]⁻ to form the ternary complex, were estimated. β_CaOx and β_CaHPO4 were then calculated on 5 natural urines by chemical models, including or not including the [CaPO₄]⁻ and [Ca(PO₄)cit]⁴⁻ species. Results: Species distribution diagrams show that the [Ca(PO₄)cit]⁴⁻ species was only noticeable at pH > 8.5 and below 10% of the total calcium. β values estimated on natural urine were slightly lowered by the formation of [CaPO₄]⁻ species, whereas [Ca(PO₄)cit]⁴⁻ results were irrelevant. Conclusions: While [CaPO₄]⁻ species have an impact on saturation levels at higher pHs, the existence of ternary complex and of the dimer is rejected.     

GC Methods for the Determination of Methanol and Ethanol in Insulating Mineral Oils as Markers of Cellulose Degradation in Power Transformers

Methanol and ethanol in transformer oils have been recently proposed as new markers of thermal and mechanical degradation of cellulose (the solid insulation in power transformers). In this work, we optimized and compared the performance of two headspace gas chromatographic methods based on flame ionization (HS–GC–FID) and mass spectrometry detection (HS–GC–MS) to determine methanol and ethanol in insulating mineral oil. For methanol and ethanol, the detection limits were 12 and 27 μg kg^?1 (HS–GC–FID) and 1.3 and 3.1 μg kg^?1 (HS–GC–MS). Repeatability was evaluated in transformer oils for both the methods at different concentration levels of analytes and RSD values were found to lie between 1.8 and 16 %. The accuracy of the methods was assessed under a proficiency test (Cigré JWG A2/D1.46). The methods were compared by a F-test and a one-sided paired t test performed on 21 transformer oils in service. Correlations of methanol and ethanol content in sampled oils against their actual time of service are provided. For each sample, the content of traditional markers (furan-2-carbaldehyde and CO₂) was also measured, finding a correlation between light alcohols and CO₂ content. This indicates that methanol and ethanol determination may be helpful in providing further information on the thermal degradation conditions of transformers’ solid insulation. The method developed is currently routinely applied by the laboratories of Sea Marconi Technologies for the assessment of transformers’ conditions.