The stability of ethanol in stored blood. II. The mechanism of ethanol oxidation

A new method for the i.r. analysis of zinc-dialkyldithiocarbamate mixtures has been developed. The identification and detection limits were improved, compared to the standard method, by the use of microtechniques (identification limit 2 μg, detection limit 30–80 μg). Binary and ternary mixtures can be analysed without preliminary separation, because the other components of the mixtures have very little influence on the measured absorption band. Beer's law was obeyed for the binary and two ternary mixtures. The relative standard deviations and the coefficients of correlation were calculated for the macro- and micromethods. A comparison of statistical data shows that i.r. spectroscopy is suitable for quantitative analysis even in the region of 80–10 μg of substance.     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

The characterization of closely related polymeric materials by thermogravimetry—mass spectrometry

The potential of a new technique in forensic science, thermogravimetry—mass spectrometry, is illustrated by its application to the examination of acrylic fibres and white alkyd gloss paints, small samples of which are difficult to differentiate even by a combination of current techniques. A simple interface allowing the coupling of a magnetic sector mass spectrometer to a thermobalance is described. This combination allows up to five experimental parameters to be determined simultaneously either for classification of the material under investigation or for the detailed direct comparison of samples. The thermobalance allows the temperatures at which weight losses occur and their relative proportions to be determined; the basic parameter obtained from the mass spectrometer is the total ion current trace. From this, single qualitative mass spectra may be chosen for examination and ions, whose presence or absence may be diagnostic or which vary characteristically throughout the analysis, can be selected. The variations of these ions may then be examined by computer-generated mass thermograms (analagous to mass chromatograms in g.c.—m.s.) or, if computer facilities are not available, by multiple ion detection. The residue from the analysis can be used for trace element analysis, e.g. by energy-dispersive x-ray fluorescence spectrometry.     

The stability of ethanol in stored blood. I. Important variables and interpretation of results

The effects of the factors time, sodium fluoride concentration, ethanol concentration, temperature of storage and type of container on the ethanol losses from stored human blood have been investigated by means of a 2⁵ factorial experiment. The important factors were found to be temperature, fluoride concentration and time of storage. A detailed study of the important factors enabled three distinct mechanisms of ethanol loss to be identified. These were a highly temperature-dependent ethanol oxidation reaction which was independent of the ethanol concentration over a wide range; destruction of ethanol by the action of micro-organisms in the absence of a preservative, which could be inhibited by 0.5% (w/v) sodium fluoride, and diffusion which was found to occur from 5.6% of the polypropylene containers used in Britain for the purposes of the Road Traffic Act 1972.     

A splitless Curie point pyrolysis capillary inlet system for use with the adsorption wire technique of vapour analysis

Summary A splitless Curie point pyrolysis inlet system for capillary columns has been built using conventional packed column apparatus. This has enabled the adsorption wire analysis system, for the rapid collection and direct GC analysis of vapours, to be used with capillary columns. Use of the technique for detecting traces of hydrocarbon fuels in arson investigation is described, as are problems occurring in its use.