Wolfram Meier-Augenstein

Applied gas chromatography coupled to isotope ratio mass spectrometry

Compound-specific isotope analysis (CSIA) by isotope ratio mass spectrometry (IRMS) following on-line combustion (C) of compounds separated by gas chromatography (GC) is a relatively young analytical method. Due to its ability to measure isotope distribution at natural abundance level with great accuracy and high precision, GC-C-IRMS has increasingly become the method of choice in authenticity control of foodstuffs and determination of origin in archaeology, geochemistry, and environmental chemistry. In combination with stable isotope labelled compounds, GC-C-IRMS is also used more and more in biochemical and biomedical application as it offers a reliable and risk-free alternative to the use of radioactive tracers. The literature on these topics is reviewed from the advent of commercial GC-C-IRMS systems in 1990 up to the beginning of 1998. Demands on sample preparation and quality of GC separation for GC-C-IRMS are discussed also.

Physiology and pathophysiology of organic acids in cerebrospinal fluid.

SummaryConcentrations of organic acids in cerebrospinal fluid (CSF) appear to be directly dependent upon their rate of production in the brain. There is evidence that the net release of short-chain monocarboxylic acids from the brain is a major route for removing these products of cerebral metabolism. Concentrations of organic acids in blood and CSF are largely independent of each other. Quantitative reference values for the concentrations of organic acids in CSF and plasma as well as ratios of individual organic acids between CSF and plasma were determined in 35 pairs of samples from paediatric patients. Over 25 organic acids were quantifiable in all or in the majority of CSF and/or plasma specimens (limit of detection 1 µmol/L). There were substantial differences in the CSF/plasma ratios between subgroups of organic acids. Metabolites related to fatty-acid oxidation were present in CSF in substantially less amounts than in plasma. Organic acids related to carbohydrate and energy metabolism and to amino acid degradation were present in CSF in the same amounts as or slightly smaller amounts than in plasma. Finally, some organic acids were found in substantially higher amounts in CSF than in plasma, e.g. glycolate, glycerate, 2,4-dihydroxybutyrate, citrate and isocitrate.Studies of organic acids in CSF and plasma samples are presented from patients with ‘cerebral’ lactic acidosis, disorders of propionate and methylmalonate metabolism, glutaryl-CoA dehydrogenase deficiency andl-2-hydroxyglutaric acidura. It became apparent that derangements of organic acids in the CSF may occur independently of the systemic metabolism. Quantitative organic acid analysis in CSF will yield new information on the pathophysiology in the central nervous system (CNS) of these disorders and may prove necessary for successful monitoring of treatment of organoacidopathies, which present mainly with neurological disease. For example, in glutaryl-CoA dehydrogenase deficiency the urinary excretion of glutarate appears to be an inadequate parameter for monitoring the effect of dietary therapy, without plasma and CSF determinations. Inl-2-hydroxyglutaric aciduria the elevation ofl-2-hydroxyglutarate was found to be greater in CSF than in plasma. In addition, some other organic acids, glycolate, glycerate, 2,4-dihydroxybutyrate, citrate and isocitrate, were also elevated in the CSF of the patients out of proportion to normal levels in plasma and urine. High concentrations of an unknown compound, which was tentatively identified as 2,4-dihydroxyglutarate, were found in the CSF of patients withl-2-hydroxyglutaric aciduria. Quantitative determination of organic acids in CSF and plasma should aid the monitoring of treatment of patients with organic acid disorders, allow investigations of metabolites in known disorders, and detect neurometabolic diseases in which the diagnostic metabolites accumulate preferentially in CSF.

Stable isotope and DNA evidence for ritual sequences in Inca child sacrifice

Four recently discovered frozen child mummies from two of the highest peaks in the south central Andes now yield tantalizing evidence of the preparatory stages leading to Inca ritual killing as represented by the unique capacocha rite. Our interdisciplinary study examined hair from the mummies to obtain detailed genetic and diachronic isotopic information. This approach has allowed us to reconstruct aspects of individual identity and diet, make inferences concerning social background, and gain insight on the hitherto unknown processes by which victims were selected, elevated in social status, prepared for a high-altitude pilgrimage, and killed. Such direct information amplifies, yet also partly contrasts with, Spanish historical accounts.

Forensic isotope analysis leads to identification of a mutilated murder victim

The relationship between diet, geographic location and isotopic composition of human tissue has been successfully exploited in archaeological and palaeodietary studies, i.e. on ancient man, but cases in which this approach has been applied to present-day people e.g. to aid identification of mutilated or deteriorated bodies are far and few between. Stable isotope data are presented here from a case where for the first time stable isotope based intelligence aided victim identification by DNA analysis and subsequent apprehension of the perpetrators thus demonstrating that it is possible in principal for stable isotope data of present-day people to be useful for human provenancing, i.e. to yield valuable information about a persons life history and geographic origin.

Stable isotope analysis of fatty acids by gas chromatography-isotope ratio mass spectrometry

Abstract Compound-specific isotope analysis (CSIA) of fatty acids is a relatively young analytical method. However, CSIA of fatty acids has increasingly become the method of choice in areas where accurate and precise knowledge of isotopic composition at natural abundance level is important. CSIA of fatty acids at natural abundance level provides information on biogenetic and geographic origin of lipids and oils that is invaluable for research into archaeology and the environment and almost indispensable these days for authenticity control and fraud detection in food analysis. In combination with naturally enriched or stable isotope labelled precursors, CSIA of fatty acids has also gained increasing importance in biochemical, -medical and -geochemical applications as it offers a reliable and risk-free alternative to the use of radioactive tracers.

Isotopic evidence for the provenance and turnover of organic carbon by soil microorganisms in the Antarctic dry valleys.

The extremely cold and arid Antarctic dry valleys are one of the most environmentally harsh terrestrial ecosystems supporting organisms in which the biogeochemical transformations of carbon are exclusively driven by microorganisms. The natural abundance of (13)C and (15)N in source organic materials and soils have been examined to obtain evidence for the provenance of the soil organic matter and the C loss as CO(2) during extended incubation (approximately 1200 days at 10 degrees C under moist conditions) has been used to determine the potential decay of soil organic C. The organic matter in soils remote from sources of liquid water or where lacustrine productivity was low had isotope signatures characteristic of endolithic (lichen) sources, whereas at more sheltered and productive sites, the organic matter in the soils that was a mixture mainly lacustrine detritus and moss-derived organic matter. Soil organic C declined by up to 42% during extended incubation under laboratory conditions (equivalent to 50-73 years in the field on a thermal time basis), indicating relatively fast turnover, consistent with previous studies indicating mean residence times for soil organic C in dry valley soils in the range 52-123 years and also with recent inputs of relatively labile source materials.

Use of gas chromatography-combustion-isotope ratio mass spectrometry in nutrition and metabolic research

Linking gas chromatography via an on-line combustion interface to isotope ratio mass spectrometry has opened the door to high-precision compound-specific isotope analysis. For this reason, gas chromatography-combustion-isotope ratio mass spectrometry is now increasingly employed in metabolic and nutritional research because it offers a reliable and risk-free alternative to the use of radioactive tracers.

Influence of gas chromatographic parameters on measurement of 13C/12C isotope ratios by gas-liquid chromatography-combustion isotope ratio mass spectrometry. I

A potential influence of gas chromatographic parameters on measured 13C/12C-isotope ratios of saturated fatty acid methyl esters in gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) has been studied. A dependence of measured isotope ratios on temperature gradients was observed and differences in measured δ13C-values for individual fatty acid methyl esters varied by 0.5 to 3‰. Possible reasons for this isotopic fractionation and its implications for 13C natural abundance work are discussed.

Inter-laboratory calibration of new silver orthophosphate comparison materials for the stable oxygen isotope analysis of phosphates

Stable oxygen isotope compositions (δ(18)O values) of two commercial and one synthesized silver orthophosphate reagents have been determined on the VSMOW scale. The analyses were carried out in three different laboratories: lab (1) applying off-line oxygen extraction in the form of CO(2) which was analyzed on a dual inlet and triple collector isotope ratio mass spectrometer, while labs (2) and (3) employed an isotope ratio mass spectrometer coupled to a high-temperature conversion/elemental analyzer (TC/EA) where Ag(3)PO(4) samples were analyzed as CO in continuous flow mode. The δ(18)O values for the proposed new comparison materials were linked to the generally accepted δ(18)O values for Vennemanns TU-1 and TU-2 standards as well as for Ag(3)PO(4) extracted from NBS120c. The weighted average δ(18)O(VSMOW) values for the new comparison materials UMCS-1, UMCS-2 and AGPO-SCRI were determined to be + 32.60 (± 0.12), + 19.40 (± 0.12) and + 14.58 (± 0.13)‰, respectively.

Emerging use of isotope ratio mass spectrometry as a tool for discrimination of 3,4-methylenedioxymethamphetamine by synthetic route

Drug profiling, or the ability to link batches of illicit drugs to a common source or synthetic route, has long been a goal of law enforcement agencies. Research in the past decade has explored drug profiling with isotope ratio mass spectrometry (IRMS). This type of research can be limited by the use of substances seized by police, of which the provenance is unknown. Fortunately, however, some studies in recent years have been carried out on drugs synthesized in-house and therefore of known history. In this study, 18 MDMA samples were synthesized in-house from aliquots of the same precursor by three common reductive amination routes and analyzed for 13C, 15N, and 2H isotope abundance using IRMS. For these three preparative methods, results indicate that 2H isotope abundance data is necessary for discrimination by synthetic route. Furthermore, hierarchical cluster analysis using 2H data on its own or combined with 13C and/or 15N provides a statistical means for accurate discrimination by synthetic route.