Discrimination of structural isomers of chlorinated phenols in waters using gas chromatography-mass spectrometry in the negative chemical ionization mode

The analysis and identification of structural isomers of mono-, di- and trichlorophenols is reported. The fragmentation of the phenols was examined by GC-MS in both electron impact (EI) and negative chemical ionization (NCI) modes, using methane as reagent gas. The ability of NCI to discriminate these isomeric compounds from differences in relative intensities for selected peaks is demonstrated. 3- and 4-chlorophenols have similar retention times; however, they can still be discriminated because their negative mass spectra and rather different. In dichlorophenols, the presence of one chlorine atom in the ortho position decreases their retention time and the relative intensity of the fragment ion at m/z 140. The NCI mass spectra for trichlorophenols are different from the rest, particularly for the m/z value corresponding to the chlorine atom. Tetra- and pentachlorophenols were also studied and sequential losses of Cl observed. An automatic solid-phase extraction system can optionally be used to preconcentrate chlorophenols in waters prior to determination at legally established toxic levels.     

Continuous flow spectrophotometric determination of paracetamol in pharmaceuticals following continuous microwave assisted alkaline hydrolysis

This paper reports a continuous flow-based spectrophotometric method for the determination of paracetamol in pharmaceuticals. Dilute samples containing paracetamol are continuously hydrolysed in an alkaline medium, using a household microwave oven, to p-aminophenol, which reacts with o-cresol in 3.5 M NaOH. The blue derivative thus formed exhibits an absorbance maximum at 620 nm. The detection limit of the method is 0.2 mug ml(-1) and the system obeys Beer's law from 0.6 to 20 mug ml(-1). Repeatability was checked by calculating the R.S.D. for 11 standard solutions containing a paracetamol concentration of 4 mug ml(-1) each and found to be 1.8%. The proposed method was validated by determining paracetamol in various pharmaceutical preparations with average R.S.D. of 2.4%.     

Electron correlation in the interacting quantum atoms partition via coupled‐cluster lagrangian densities

The electronic energy partition established by the Interacting Quantum Atoms (IQA) approach is an important method of wavefunction analyses which has yielded valuable insights about different phenomena in physical chemistry. Most of the IQA applications have relied upon approximations, which do not include either dynamical correlation (DC) such as Hartree‐Fock (HF) or external DC like CASSCF theory. Recently, DC was included in the IQA method by means of HF/Coupled‐Cluster (CC) transition densities (Chávez‐Calvillo et al., Comput. Theory Chem. 2015, 1053, 90). Despite the potential utility of this approach, it has a few drawbacks, for example, it is not consistent with the calculation of CC properties different from the total electronic energy. To improve this situation, we have implemented the IQA energy partition based on CC Lagrangian one‐ and two‐electron orbital density matrices. The development presented in this article is tested and illustrated with the H₂, LiH, H₂O, H₂S, N₂, and CO molecules for which the IQA results obtained under the consideration of (i) the CC Lagrangian, (ii) HF/CC transition densities, and (iii) HF are critically analyzed and compared. Additionally, the effect of the DC in the different components of the electronic energy in the formation of the T‐shaped (H₂)₂ van der Waals cluster and the bimolecular nucleophilic substitution between F^– and CH₃F is examined. We anticipate that the approach put forward in this article will provide new understandings on subjects in physical chemistry wherein DC plays a crucial role like molecular interactions along with chemical bonding and reactivity. © 2016 Wiley Periodicals, Inc.     

Aging markers from bottled red wine aged with chips, staves and barrels

This paper shows the results of the experiments carried on Spanish red wines aged through alternative as well as traditional oak barrel systems, i.e., chips stainless steel tanks and staves stainless steel tanks, at the same time and under the same conditions.Wine aging through wood pieces is not accepted as an enological practice by the European Union and, in fact, it is considered a fraud. It is, then, of a great interest to identify those parameters able to establish the aging technique that had been used in a wine ready to be consumed. With this idea in mind, the development of the same wine has been studied while aging for 3 years in three different systems.During the first six aging months wines stored with staves obtained characteristics that were halfway between wines treated with chips and those aged in barrels. However, as wood contact period length increased so did the differences between wines stored in traditional and alternative systems (either with staves or chips). These differences grew during the bottling period, so that after a 2-year bottling period wines from the three systems became different enough to tell them apart. Discriminant analysis of the variables studied made it possible to establish these differences. The most meaningful variables were yellow colour component, anthocyanins (cyanidin-3-glucoside, vitisin A and sum of pcoumaryl derivates), vanillin acid, protocachuic aldehyde and epicatechin.     

Simultaneous liquid-liquid microextraction/methylation for the determination of haloacetic acids in drinking waters by headspace gas chromatography

A novel analytical method that combines simultaneous liquid-liquid microextraction/methylation and headspace gas chromatography-mass spectrometry for the determination of nine haloacetic acids (HAAs) in water was reported. A mechanistic model on the basis of mass transfer with chemical reaction in which methylation of HAAs was accomplished in n-pentane-water (150 microl-10 ml) two-phase system with a tetrabutylammonium salt as phase transfer catalyst was proposed. Derivatisation with dimethylsulphate was completed in 3 min by shaking at room temperature. The methyl ester derivatives and the organic phase were completely volatilised by static headspace technique, being the gaseous phase analysed. Parameters related to the extraction/methylation and headspace generation of HAAs were studied and the results were compared with methyl haloacetate standards to establish the yield of each step. The thermal instability of HAAs, by degradation to their respective halogenated hydrocarbon by decarboxylation, and the possible hydrolysation of the methyl esters were rigorously controlled in the whole process to obtain a reliable and robust method. The proposed method yielded detection limits very low which ranges from 0.02 to 0.4 microg l(-1) and a relative standard deviation of ca. 7.5%. Finally, the method was validated with the US Environmental Protection Agency (EPA) method 552.2 for the analysis of HAAs in drinking and swimming pool water samples containing concentrations of HAAs that must be higher than 10 microg l(-1) due to the fact that this method is less sensitive than the proposed one.     

Sample screening systems in analytical chemistry

The state of the art and the potential of sample screening systems (SSS) for the expeditious, reliable selection of samples to meet the requirements of customers and legislation is presented and discussed. The underlying procedures use simple equipment and operations and provide a yes/no binary response that occasionally requires confirmation. After a brief discussion of the distinction between ‘screening' and ‘analysis' and the principal features of analytical screening systems, the main aims and features of SSS are presented. Several classifications of these allow one to offer a general view of the topic. Representative examples are classified according to the complexity of the sample pretreatment required, and are used to demonstrate the impact SSS may have on analytical chemistry in the next century.     

MOIRA: A decision support system for decision making on aquatic ecosystems contaminated by radioactive fallout

Interventions to restore radionuclide contaminated aquatic ecosystems may reduce individual and collective radiation doses, but may also result in detrimental ecological, social and economic effects. Decision makers must carefully evaluate possible impacts before choosing a countermeasure, hence decision analysis methods constitute an important aid to rank intervention strategies after the contamination of an aquatic ecosystem. We describe MOIRA, a decision support system for the identification of optimal remedial strategies to restore water systems after accidental introduction of radioactive substances. MOIRA includes an evaluation module based on a multi-attribute value model to rank alternatives and a module to perform multiparametric sensitivity analyses, both with respect to weights and values, to allow us to gain insights into the problem. The problem is under certainty since the validation of models used to quantify countermeasure impacts suggests little uncertainty in policy effects.The system is implemented in a PC based decision support system which allows the inclusion of all relevant information.     

Period stabilization in the Busse–Heikes model of the Küppers–Lortz instability

The Busse–Heikes dynamical model is described in terms of relaxational and non-relaxational dynamics. Within this dynamical picture a diverging alternating period is calculated in a reduced dynamics given by a time-dependent Hamiltonian with decreasing energy. A mean period is calculated which results from noise stabilization of a mean energy. The consideration of spatial-dependent amplitudes leads to vertex formation. The competition of front motion around the vertices and the Küppers–Lortz instability in determining an alternating period is discussed.