Rj Lynch

A 31P NMR and 35Cl NQR investigation of some hexachlorophosphates

Abstract The 31P NMR spectra in both solid state and solution, and the 35Cl NQR spectra in the solid, have been recorded for some hexachlorophosphates and for the compounds [C8H12N]2PCl7PCl7 and C14H14PCl7. The presence of the PCl6− ion as the only phosphorus-containing anion has been confirmed in all cases. Data are also reported for the chlorotriphenylphosphonium ion in Ph3PCl+PCl6−.

Evaluation of a complete HPLC solvent optimization system involving piece-wise quadratic modelling

SummaryInterpretive methods are accepted to give the best possible results for selectivity optimization in HPLC. However the methods are very complex, and most work so far has been detailed academic studies. This paper describes an evaluation of a complete integrated system incorporating peak labelling, modelling of retention behaviour and calculation of response surfaces, with particular emphasis on the retention modelling. The peak labelling section has been discussed previously.A piece-wise quadratic function is investigated for the modelling of retention times across an isoeluotropic plane to effect selectivity optimization in HPLC. This requires 10 data-points on the isoeluotropic plane. The predicted global optimum and local optima are evaluated by comparison of calculated and experimental retention data, for a nine component sample. Seven interstitial points, distributed across the whole plane between the data-points, are similarly evaluated for a related sample. The typical error (in retention time) is less than 2%, often 1%, and the maximum error is 4.2%. At the global optimum the error was found be less than 1.3% for all 9 peaks.

A study of the practical limitations of principal components analysis and the labelling of unresolved HPLC peaks

SummaryThe method of iterative target transformation factor analysis (ITTFA) used in conjunction with second derivative peak finding has shown to be a practical method for the peak deconvolution and reconstruction of HPLC chromatograms and spectra. The second derivative method of peak finding is acceptable for resolutions above 0.5 for peaks of similar heights. Above 0.5 resolution the labelling gives correct results where the spectra are substantially different and also when reasonably similar. Below this value the peak labelling was still accurate where the spectra were different. Solvent effects on the spectra of the compounds studied are small and do not hinder the peak labelling process. Thus small “local” libraries are feasible.

Optimization of chromatographic methods by a combination of optimization software and expert systems

Abstract Expert systems and other sophisticated computer programs can be of great benefit for the optimization of chromatographic separations. However, two factors have seriously hindered their proliferation. First, the area of method development for chromatography encompasses such a great variety and such a large amount of knowledge and expertise that it is not realistic to try and cover the entire area with a single program. Second, computer programs may be very complex to use, so that only experts can apply them. Steps towards the solution of both problems are described. Three different computer programs, two of which are expert systems, are used coherently for method optimization. Each system can assist the chromatographer in performing a certain well-defined task. The selectivity-optimization system (Diamond) is a package of conventional computer programs. Therefore, we refrain from calling it an expert system. One expert system is specifically applied to reduce the level of expertise required for applying this package. The most difficult decision that a Diamond user needs to make is the selection of the most appropriate optimization criterion. This decision can be made with the help of the expert system for CRIterion SElection (CRISE). The second expert system (System-Optimization System SOS) is used to transform the chromatogram with optimum selectivity that results from Diamond into the optimum overall method by establishing the best column dimensions, flow-rate, instrumentation, injected amount, etc . An example is presented to demonstrate that the coherent use of several sophisticated computer programs can make method development in chromatography both better and easier.

Use of high-performance liquid chromatographic peak deconvolution and peak labelling to identify antiparasitic components in plant extracts

Artemisia absynthium L. is a commonly used medicinal plant for parasitic diseases all over the world. By means of high-performance liquid chromatography with diode-array detection and the PU6100 solvent optimization system, two sesquiterpene lactones, alpha-santonin and ketopelenolid-A, were tentatively identified in methanolic extracts of this plant. alpha-Santonin is a well known antiparasitic compound and could be one of the active principles of this plant species. Reconstructed spectra are potentially useful in scanning a complex chromatogram for pharmacologically active compounds.

Investigation of the hydrogen bonding in chlorocarboxylate anions using 35Cl quadrupole resonance spectroscopy

35 Cl quadrupole resonance frequencies have been measured in a wide range of normal and acid salts of chlorocarboxylic and chlorobenzoic acids. The multiplicity of 35Cl signals and the shifts of the 35Cl frequencies on deuteriation of the acid proton in salts containing the anion [RCO2‥ H ‥ CO2R]– have been used to establish the symmetry of the hydrogen bond. The observed deuteriation shifts can be as large as 0.9 % of the 35Cl frequency in asymmetric hydrogen bonds; they are negligibly small if the hydrogen bond is symmetric.

Temperature effects on liquid chromatographic absorbance stability at low wavelengths

SummaryThis paper is concerned with our investigation into the effects of temperature on the liquid chromatography absorbance baseline. Measurements were made to quantify the effects in terms of wavelength and solvents. Five solvents commonly used in HPLC were investigated, methanol, propanol, hexane, heptane and acetonitrile. The alcoholic solvents were found to have a high absorbance sensitivity to temperature at wavelengths around their ‘UV cut off’ points. Possible mechanisms for this effect are discussed and include solvent impurity, density changes and inter-molecular bonding.

Coordination complexes of bis(trichlorovinyl)mercury

Abstract The formation of complexes between bis(trichlorovinyl)mercury and a series of monodentate and bidentate nitrogen, phosphorus and sulphur bases has been studied. Adducts (Cl3C2)2HgL (L = phen dmp, tmp, bipy, diphos)** have been isolated in the solid state. These are the first reported bis(alkenyl)mercurial complexes and their thermal behaviour and spectral characteristics (infrared, 1H NMR, 35Cl NQR and mass spectra) have been examined. No complexes of the monodentate ligands selected could be isolated, but 1H NMR studies indicated the presence of weak ligand—mercury interaction in solution for triphenylphosphine, thiophene, pyridine as well as for the bidentate N,N,N′,N′,-tetramethylethane-1,2-diamine and 2,5-dithiahexane ligands. The acceptor properties of bis(trichlorovinyl)mercury appear to be intermediate between that of diphenylmercury and that of bis(pentafluorophenyl)mercury.

Effects of gasoline and diesel additives on kaolinite

Centrifuge tests were carried out to confirm and determine the effect of different pure alcohols, methyl t-butyl ether (MTBE) and mixtures of alcohols with gasoline and diesel on a thin disc of consolidated clay. The evolution of changes in the clay hydraulic conductivity with time was investigated and other structural changes due to chemical attack were monitored. The findings presented here demonstrate that the hydraulic conductivity of the clay appear to be generally related to the polarity of the chemicals and the dielectric constant. The cracking effect of butanol and MTBE on consolidated clay at low flow rate and low stress level was observed. The addition of ethanol or MTBE to diesel increased the clay permeability and the migration of organic chemical. The addition of ethanol to gasoline also caused an increase in the clay hydraulic conductivity. The effect of the association of alcohols with gasoline or diesel on the clay hydraulic conductivity is discussed, with a view to improving current pollution remediation techniques.

Pollution transport studies using an in-situ fibre optic photometric sensor

In order to study the migration of contaminants in soils, we are currently using an in situ fibre optic sensor to track the movement of a dye tracer. Details of the sensor is discussed and the results presented of one-dimensional transport experiments using a water soluble dye and a copper salt. Water was forced to percolate downwards in a bed of fine sand, with the hydraulic gradient kept constant during any given experiment. A pulse of contaminant was released on the soil surface, and its concentration was subsequently measured using sensors buried at two depths. This permitted the pollution plume to be tracked. It was found that the width was independent of hydraulic gradient, as predicted by the theory of mechanical dispersion for seepage flows with a high Peclet number.