Zoe Crossman

Regiospecific characterisation of the triacylglycerols in animal fats using high performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry

High performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry (HPLC-APCI MS) was applied to the characterisation of triacylglycerols (TAGs) in animal fats. The major TAGs in four fats (beef, chicken, lamb and pork) were identified and positional isomers assigned according to their APCI mass spectra. Beef and lamb fat TAGs were confirmed as containing higher proportions of saturated fatty acids compared with those of chicken and pork. HPLC-APCI MS was also shown to be of value in providing regiospecific information for the fatty acids in individual TAG species. For example, beef and lamb fat were shown to contain both cis- and trans-isomers of the 18:1 fatty acid, whilst chicken and pork contained only the cis-isomer. When the position of fatty acid substitution was determined from the APCI spectra, whilst the cis- 18:1 was predominantly found in the 2-position of the TAG, the trans-18:1 showed a preference for the 1/3-position. Similarly, it was confirmed that although the 2-position of beef, chicken and lamb fat TAGs was dominated by unsaturated fatty acids, in pork fat, a characteristically high proportion of palmitic acid was seen in this position. The TAGs identified compared well with those reported previously. The distributions of 2-position fatty acids seen in lamb and pork fat compared favourably with those obtained by the more traditional method of lipase degradation. Although the distributions for chicken and beef showed some discrepancies, these can be attributed to weaknesses in the quantification procedure or the specificity of the lipase. Overall, the technique of HPLC-APCI MS has been shown to be very powerful for the regiospecific analysis of animal fats.

A new method for identifying the origins of simple and complex hopanoids in sedimentary materials using stable isotope labelling with 13CH4 and compound specific stable isotope analyses

Forest soils were taken and incubated with 13C-labelled methane. The lipids from these soils were isolated using a Bligh Dyer extraction and fractionated. Simple hopanoids were present in the neutral fraction, while periodic acid/sodium borohydride treatment of the total lipid extract released primary alcohols from polyfunctionalised bacteriohopane derivatives. All hopanoids were analysed by GC, GC/MS and GC/C/IRMS. Specific hopanoids, namely: diploptene, 17β(H), 21β(H)-homohopanol and 17β(H), 21β(H)-bishomohopanol produced by methane oxidising bacteria were significantly enriched in 13C whilst others showed no enrichment.

A new stable isotope approach identifies the fate of ozone in plant-soil systems.

* We show that the stable isotope (18)O can be used to trace ozone into different components of the plant-soil system at environmentally relevant concentrations. * We exposed plants and soils to (18)O-labelled ozone and used isotopic enrichment in plant dry matter, leaf water and leaf apoplast, as well as in soil dry matter and soil water, to identify sites of ozone-derived (18)O accumulation. * It was shown that isotopic accumulation rates in plants can be used to infer the location of primary ozone-reaction sites, and that those in bare soils are dependent on water content. However, the isotopic accumulation rates measured in leaf tissue were much lower than the modelled stomatal flux of ozone. * Our new approach has considerable potential to elucidate the fate and reactions of ozone within both plants and soils, at scales ranging from plant communities to cellular defence mechanisms.

A new method for using O-18 to trace ozone deposition

Isotopically labelled ozone ((18)O(3)) is an ideal tool to study the deposition of O(3) to plants and soil, but no studies have made use of it due to the technical difficulties in producing isotopically enriched ozone. For (18)O(3) to be used in fumigation experiments, it has to be purified and stored safely prior to fumigations, to ensure that the label is present predominantly in the form of O(3), and to make efficient use of isotopically highly enriched oxygen. We present a simple apparatus that allows for the safe generation, purification, storage, and release of (18)O(3). Following the purification and release of O(3), about half (by volume) of the (18)O is present in the form of O(3). This means that for a given release of (18)O(3) into the fumigation system, a roughly identical volume of (18)O(2) is released. However, the small volume of this concurrent (18)O(2) release (100 nmol mol(-1) in our experiment) results in only a minor shift of the much larger atmospheric oxygen pool, with no detectable consequence for the isotopic enrichment of either soil or plant materials. We demonstrate here the feasibility of using (18)O as an isotopic tracer in O(3) fumigations by exposing dry soil to 100 nmol mol(-1) (18)O(3) for periods ranging from 1 to 11 h. The (18)O tracer accumulation in soil samples is measured using gas chromatography/isotope ratio mass spectrometry (GC/IRMS), and the results show a linear increase in (18)O/(16)O isotope ratio over time, with significant differences detectable after 1 h of exposure. The apparatus is adapted for use with fumigation chambers sustaining flow rates of 1 m(3) min(-1) for up to 12 h, but simple modifications now allow larger quantities of O(3) to be stored and continuously released (e.g. for use with open-top chambers or FACE facilities).

A new method for using 18O to trace ozone deposition

Isotopically labelled ozone ((18)O(3)) is an ideal tool to study the deposition of O(3) to plants and soil, but no studies have made use of it due to the technical difficulties in producing isotopically enriched ozone. For (18)O(3) to be used in fumigation experiments, it has to be purified and stored safely prior to fumigations, to ensure that the label is present predominantly in the form of O(3), and to make efficient use of isotopically highly enriched oxygen. We present a simple apparatus that allows for the safe generation, purification, storage, and release of (18)O(3). Following the purification and release of O(3), about half (by volume) of the (18)O is present in the form of O(3). This means that for a given release of (18)O(3) into the fumigation system, a roughly identical volume of (18)O(2) is released. However, the small volume of this concurrent (18)O(2) release (100 nmol mol(-1) in our experiment) results in only a minor shift of the much larger atmospheric oxygen pool, with no detectable consequence for the isotopic enrichment of either soil or plant materials. We demonstrate here the feasibility of using (18)O as an isotopic tracer in O(3) fumigations by exposing dry soil to 100 nmol mol(-1) (18)O(3) for periods ranging from 1 to 11 h. The (18)O tracer accumulation in soil samples is measured using gas chromatography/isotope ratio mass spectrometry (GC/IRMS), and the results show a linear increase in (18)O/(16)O isotope ratio over time, with significant differences detectable after 1 h of exposure. The apparatus is adapted for use with fumigation chambers sustaining flow rates of 1 m(3) min(-1) for up to 12 h, but simple modifications now allow larger quantities of O(3) to be stored and continuously released (e.g. for use with open-top chambers or FACE facilities).