Diet, cellular, and systemic homeostasis control the cycling of potassium stable isotopes in endothermic vertebrates

The naturally occurring stable isotopes of potassium (41K/39K, expressed as δ41K) have the potential to make significant contributions to vertebrate and human biology. The utility of K stable isotopes is, however, conditioned by the understanding of the dietary and biological factors controlling natural variability of δ41K. This paper reports a systematic study of K isotopes in extant terrestrial endothermic vertebrates. δ41K has been measured in 158 samples of tissues, biofluids, and excreta from 40 individuals of four vertebrate species (rat, guinea pig, pig and quail) reared in two controlled feeding experiments. We show that biological processing of K by endothermic vertebrates produces remarkable intra-organism δ41K variations of ca. 1.6‰. Dietary δ41K is the primary control of interindividual variability and δ41K of bodily K is +0.5-0.6‰ higher than diet. Such a trophic isotope effect is expected to propagate throughout trophic chains, opening promising use for reconstructing dietary behaviors in vertebrate ecosystems. In individuals, cellular δ41K is related to the intensity of K cycling and effectors of K homeostasis, including plasma membrane permeability and electrical potential. Renal and intestinal transepithelial transports also control fractionation of K isotopes. Using a box-modeling approach, we establish a first model of K isotope homeostasis. We predict a strong sensitivity of δ41K to variations of intracellular and renal K cycling in normal and pathological contexts. Thus, K isotopes constitute a promising tool for the study of K dyshomeostasis.

Sampling, storage and laboratory approaches for dissolved organic matter characterisation in freshwaters: Moving from nutrient fraction to molecular-scale characterisation

Recent research has highlighted the importance of dissolved organic matter (DOM) for ecosystem function and because of this paradigm shift, it has become crucial to not only quantify its contribution to river nutrient loads but also to characterise its composition. There has been a significant research effort utilising optical methods, such as fluorescence and UV-Vis spectrophotometry, in order to start exploring DOM character. However, these methods still lack the granularity to understand the chemical composition at the molecular level, which is vital to properly understanding its functional role in freshwater ecosystems. As a direct result, there has been a shift towards including molecular-scale analyses to investigate the in-stream processing of the material. Alongside this, recent methodological advancements, particularly in mass spectrometry are opening new opportunities for probing one of the most complex environmental mixtures. However, in order to fully exploit these opportunities, it is key that the way that samples are collected, processed and stored is considered carefully such that sample integrity is maintained. There are additional challenges when collecting water samples for analysis at molecular scale, for example the ultra-low concentrations of individual compounds within DOM means that the samples are sensitive to contamination. This paper discusses current sample collection, processing and storage protocols for this C, N and P quantification and characterisation in freshwaters, and proposes a new standardised protocol suitable for both nutrient fraction quantification and molecular scale analyses, based on method development and testing undertaken in our UK Natural Environment Research Council large grant programme, characterising the nature, origins and ecological significance of Dissolved Organic Matter IN freshwater Ecosystems (DOMAINE).

The significance of petroleum bitumen in ancient Egyptian mummies

Mummification was practised in ancient Egypt for more than 3000 years, emerging from initial observations of buried bodies preserved by natural desiccation. The use of organic balms (and other funerary practices) was a later introduction necessitated by more humid burial environments, especially tombs. The dark colour of many mummies led to the assumption that petroleum bitumen (or natural asphalt) was ubiquitous in mummification; however, this has been questioned for more than 100 years. We test this by investigating 91 materials comprising balms, tissues and textiles from 39 mummies dating from ca 3200 BC to AD 395. Targeted petroleum bitumen biomarker (steranes and hopanes) analyses by gas chromatography-mass spectrometry selected ion monitoring (GC-MS SIM, m/z 217 and 191) showed no detectable bitumen use before the New Kingdom (ca 1550-1070 BC). However, bitumen was used in 50% of New Kingdom to Late Period mummies, rising to 87% of Ptolemaic/Roman Period mummies. Quantitative determinations using (14)C analyses reveal that even at peak use balms were never more than 45% w/w bitumen. Critically, the dark colour of balms can be simulated by heating/ageing mixtures of fats, resins and beeswax known to be used in balms. The application of black/dark brown balms to bodies was deliberate after the New Kingdom reflecting changing funerary beliefs and shifts in religious ideology.This article is part of the themed issue 'Quantitative mass spectrometry'.

Palaeoenvironmental modelling of δ(13) C and δ(15) N values in the North Atlantic Islands: understanding past marine resource use

RATIONALE

Carbon (δ(13) C) and nitrogen (δ(15) N) analysis has been extensively used to investigate the importance of marine foods in the diet of archaeological populations in the North Atlantic Islands; however, few faunal studies exist to aid the interpretation of results. Palaeoenvironmental modelling of δ(13) C and δ(15) N values is crucial in determining whether changes in the stable isotope values are a result of dietary change, rather than temporal or geographical fluctuations in carbon and nitrogen. Investigating faunal dietary behaviour can provide an insight into past foddering and land management strategies.

METHODS

Detailed sampling of wild and domestic species for bulk collagen analysis was undertaken in order to characterise geographical variations in δ(13) C and δ(15) N values in the Outer Hebrides and Orkney. Samples from the Neolithic to the Norse period were analysed to assess temporal and geographical variations in δ(13) C and δ(15) N values, in addition to determining the contribution of marine foods to the diet of local fauna.

RESULTS

A δ(15) N shift of 1‰ was observed between the Outer Hebrides and Orkney in the Neolithic and Iron Age. A geographical variation in δ(13) C values was observed in the Norse period between Orkney and the Outer Hebrides. Temporal fluctuations in δ(13) C and δ(15) N values demonstrate variations in foddering practices of sheep in the Outer Hebrides. Pig specimens from the Outer Hebrides demonstrated evidence of marine food consumption in the Iron Age.

CONCLUSIONS

Faunal dietary behaviour can act as a vital indicator of the importance of marine resources in the past. Characterisation of faunal δ(13) C and δ(15) N values geographically and temporally is crucial in our interpretation of human dietary behaviour.

Physical and biological controls on the in situ kinetic isotope effect associated with oxidation of atmospheric CH4 in mineral soils

The amounts and delta(13)C values of CH4 at subambient concentrations in soil gas were determined along depth profiles in a U.K. grassland (Bronydd Mawr) and woodland (Leigh Woods). The data were used to determine in situ kinetic isotope effects (KIEs) associated with uptake of atmospheric CH4 by high-affinity methanotrophic bacteria that inha bit soil. Three independent calculation approaches yielded similar mean KIEs of 1.0211 +/- 0.0020 (n=18) for Bronydd Mawr and 1.0219 +/- 0.0010 (n=24) for Leigh Woods. Soil methanotrophy KIEs were largely invariant among oak, beech, and pine forest soils of different ages at Leigh Woods but exhibited a statistically significant relationship with methanotroph biomass in individual plots at Bronydd Mawr and Leigh Woods quantified previously by 13C stable isotope probing. This finding, albeit based upon a small data set suggests that 13C and 12C partitioning associated with the global soil sink for atmospheric CH4 may occur in part as a result of biological as well as physical processes. An accurate assessment of the relative importance of each process to the total KIE requires confirmation that significant partitioning of (13)CH4 and (12)CH4 occurs in pore spaces as a result of differences in diffusion rates.

Estimating high-affinity methanotrophic bacterial biomass, growth, and turnover in soil by phospholipid fatty acid 13C labeling

A time series phospholipid fatty acid (PLFA) 13C-labeling study was undertaken to determine methanotrophic taxon, calculate methanotrophic biomass, and assess carbon recycling in an upland brown earth soil from Bronydd Mawr (Wales, United Kingdom). Laboratory incubations of soils were performed at ambient CH4 concentrations using synthetic air containing 2 parts per million of volume of 13CH4. Flowthrough chambers maintained a stable CH4 concentration throughout the 11-week incubation. Soils were analyzed at weekly intervals by gas chromatography (GC), GC-mass spectrometry, and GC-combustion-isotope ratio mass spectrometry to identify and quantify individual PLFAs and trace the incorporation of 13C label into the microbial biomass. Incorporation of the 13C label was seen throughout the experiment, with the rate of incorporation decreasing after 9 weeks. The delta13C values of individual PLFAs showed that 13C label was incorporated into different components to various extents and at various rates, reflecting the diversity of PLFA sources. Quantitative assessments of 13C-labeled PLFAs showed that the methanotrophic population was of constant structure throughout the experiment. The dominant 13C-labeled PLFA was 18:1omega7c, with 16:1omega5 present at lower abundance, suggesting the presence of novel type II methanotrophs. The biomass of methane-oxidizing bacteria at optimum labeling was estimated to be about 7.2 x 10(6) cells g(-1) of soil (dry weight). While recycling of 13C label from the methanotrophic biomass must occur, it is a slower process than initial 13CH4 incorporation, with only about 5 to 10% of 13C-labeled PLFAs reflecting this process. Thus, 13C-labeled PLFA distributions determined at any time point during 13CH4 incubation can be used for chemotaxonomic assessments, although extended incubations are required to achieve optimum 13C labeling for methanotrophic biomass determinations.

Adverse physicochemical properties of tripalmitin in beta cells lead to morphological changes and lipotoxicity in vitro

AIMS/HYPOTHESIS

Long-term exposure of beta cells to lipids, particularly saturated fatty acids in vitro, results in cellular dysfunction and apoptosis (lipotoxicity); this could contribute to obesity-related diabetes. Our aims were to relate cell death to intracellular triglyceride concentration, composition and localisation following incubation of INS1 cells in saturated and unsaturated NEFA in high and low glucose concentrations.

MATERIALS AND METHODS

Insulin-producing INS1 cells were cultured (24 h; 3 and 20 mmol/l glucose) with palmitic, oleic or linoleic acids and the resulting intracellular lipids were analysed by gas chromatography and microscopy. Cell death was determined by quantitative microscopy and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and glucose-stimulated insulin secretion by ELISA.

RESULTS

All NEFA (0.5 mmol/l, 0.5% albumin) inhibited glucose-stimulated (20 mmol/l) insulin secretion. Cytotoxicity was evident only with palmitic acid (p<0.05), in which case intracellular triglyceride consisted largely of tripalmitin in angular-shaped dilated endoplasmic reticulum. Cytotoxicity and morphological disruption were reduced by addition of unsaturated NEFA. Triglyceride content (control cells; 14.5 ng/mug protein) increased up to 10-fold following incubation in NEFA (oleic acid 153.2 ng/mug protein; p<0.05) and triglyceride and phospholipid fractions were both enriched with the specific fatty acid added to the medium (p<0.05).

CONCLUSIONS/INTERPRETATION

In INS1 cells, palmitic acid is converted in the endoplasmic reticulum to solid tripalmitin (melting point >65 degrees C), which could induce endoplasmic reticulum stress proteins and signal apoptosis; lipid-induced apoptosis would therefore be a consequence of the physicochemical properties of these triglycerides. Since cellular triglycerides composed of single species of fatty acid are not likely to occur in vivo, destruction of beta cells by saturated fatty acids could be predominantly an in vitro scenario.

Gas chromatographic, mass spectrometric and stable carbon isotopic investigations of organic residues of plant oils and animal fats employed as illuminants in archaeological lamps from Egypt

Man's use of illuminants in lamps or as torches to extend the working day and range of environments accessible to him would have been a major technological advance in human civilisation. The most obvious evidence for this in the archaeological record comes from pottery and stone vessels showing sooting due to the use of a wick in conjunction with a lipid-based fuel or illuminant. A wide range of potential fuels would have been exploited depending upon availability and burning requirements. Reported herein are the results of chemical investigations of a number of lamps recovered from excavations of the site of Qasr Ibrim, Egypt. Gas chromatographic, mass spectrometric and stable carbon isotopic analyses of both free (solvent extractable) and 'bound'(released from solvent extracted pottery by base treatment) lipids have revealed a wide range of saturated fatty acids, hydroxy fatty acids and alpha, omega-dicarboxylic acids. Examination of the distributions of compounds and comparisons with the fatty acid compositions of modern plant oils have allowed a range of fats and oils to be recognised. Specific illuminants identified include Brassicaceae (Cruciferae) seed oil (most likely radish oil, Raphanus sativus), castor oil (from Ricinus communis), animal fat, with less diagnostic distributions and delta(13)C values being consistent with low stearic acid plant oils, such as linseed (Linum usitatissimum) or sesame (Sesamum indicum) oils. The identifications of the various oils and fats are supported by parallel investigations of illuminant residues produced by burning various oils in replica pottery lamps. The findings are entirely consistent with the classical writers including Strabo, Pliny and Theophrastrus.

Quantification of dung carbon incorporation in a temperate grassland soil following spring application using bulk stable carbon isotope determinations

Herbivore dung constitutes a substantial input of C to temperate grassland soils, and its fate must be determined in order to fully understand nutrient cycling in this ecosystem. This experiment used changes in bulk delta13C values of the 0-1 cm and 1-5 cm soil horizons of a dung-treated temperate grassland soil to approximate percentage applied dung C incorporation over 372 days. Natural abundance 13C-labelled C4 dung (delta13C - 12.6%) and C3 dung (delta13C - 31.3% were produced in a monitored diet switch from ryegrass silage (delta13C - 30.1%) to maize silage (delta13C - 11.6%). The dung was applied to a C3 grassland (delta13C 0-1 cm - 29.9%, 1-5 cm - 30.6%), and dung remains and soil cores from beneath the treatments were sampled at intervals. delta13C values were used to estimate a maximum of 12% applied dung C incorporation in the top 5 cm of the soil after 112 days, which declined to around 8% at the end of the experiment. A significant increase in percentage applied dung C was observed in the top 1 cm of soil, compared with the 1-5 cm horizon, after a substantial rain event after 30 days. However, results of forage fibre analyses of the two dung types revealed significant differences in composition which may affect subsequent calculations of percentage dung incorporation based on bulk delta13C values.

Archaeology: formulation of a Roman cosmetic

The discovery of a small tin canister in London during archaeological excavations of a Roman temple precinct, dated to the middle of the second century AD, is a landmark in the study of this class of artefact. Such discoveries from the Roman world are rare and this is the only one to be found so far with its lid and contents--a whitish medicinal or cosmetic cream--providing a unique opportunity for us to study the ancient formulation.

Direct chemical evidence for widespread dairying in prehistoric Britain

Domesticated animals formed an important element of farming practices in prehistoric Britain, a fact revealed through the quantity and variety of animal bone typically found at archaeological sites. However, it is not known whether the ruminant animals were raised purely for their tissues (e.g., meat) or alternatively were exploited principally for their milk. Absorbed organic residues from pottery from 14 British prehistoric sites were investigated for evidence of the processing of dairy products. Our ability to detect dairy fats rests on the observation that the delta(13)C values of the C(18:0) fatty acids in ruminant dairy fats are approximately 2.3 per thousand lower than in ruminant adipose fats. This difference can be ascribed to (i) the inability of the mammary gland to biosynthesize C(18:0); (ii) the biohydrogenation of dietary unsaturated fatty acids in the rumen; and (iii) differences (i.e., 8.1 per thousand ) in the delta(13)C values of the plant dietary fatty acids and carbohydrates. The lipids from a total of 958 archaeological pottery vessels were extracted, and the compound-specific delta(13)C values of preserved fatty acids (C(16:0) and C(18:0)) were determined via gas chromatography-combustion-isotope ratio mass spectrometry. The results provide direct evidence for the exploitation of domesticated ruminant animals for dairy products at all Neolithic, Bronze Age, and Iron Age settlements in Britain. Most significantly, studies of pottery from a range of key early Neolithic sites confirmed that dairying was a widespread activity in this period and therefore probably well developed when farming was introduced into Britain in the fifth millennium B.C.

Organic chemistry of embalming agents in Pharaonic and Graeco-Roman mummies

Chemical treatments were an essential element of ancient Egyptian mummification. Although the inorganic salt natron is recognized as having a central role as a desiccant, without the application of organic preservatives the bodies would have decomposed in the humid environment of the tombs. The nature of the organic treatments remains obscure, because the ancient Egyptians left no written record of the process. Secondary textual evidence for mummification is provided by Herodotus, Diodorus Siculus, Strabo and Pliny. The most important account is that of Herodotus (about 450 yr bc), although archaeological evidence shows that by this time the process had declined significantly and the best results had been achieved centuries before. His account mentions myrrh, cassia, palm wine, 'cedar oil' (still widely disputed) and 'gum'; however, it is vague with respect to the specific natural products used. Here we report the results of chemical investigations of a substantial collection of samples of tissues, wrappings and 'resinous/bituminous' materials from provenanced and dated Egyptian mummies. We focused on examples of the 'classic' mummy-making culture of the Pharaonic or dynastic period, from which we can begin to track the development of mummification chronologically.

Computerised gas chromatographic-mass spectrometric analysis of complex mixtures of alkyl porphyrins

Computerised capillary gas chromatography-mass spectrometry (GC-MS) analysis of complex mixtures of alkyl porphyrins, as their bis-(trimethylsiloxy)silicon(IV) and bis(tert.-butyldimethylsiloxy)silicon(IV) derivatives, is described. The latter derivative is more suitable for routine GC-MS analysis. This computerised GC-MS approach, when applied to the alkyl porphyrins of two geological samples, a bitumen (Gilsonite, Eocene age, UT, U.S.A.) and a crude oil (Boscan, Cretaceous age, West Venezuela), has revealed the highly complex compositions of these fractions. Computer-aided data processing, using relative retention index (RRI) calculations, facilitated the classification of the chromatographic peaks according to structural type and membership of pseudo-homologous series. Computerised GC-MS is compared with, and contrasted to high-performance liquid chromatography as a means of petroporphyrin analysis.

Elucidation of the composition of bovine milk fat triacylglycerols using high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry

Bovine milk fat triacylglycerols (TAGs) have been characterised using high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry (HPLC-APCI-MS) and high-temperature gas chromatography-mass spectrometry (GC-MS). The complex nature of the fat meant that prefractionation was necessary to provide simpler fractions for more detailed molecular analyses. Silica thin-layer chromatography gave rise to two fractions, one of which contained predominantly butyric acid containing TAGs. Gel permeation chromatography (GPC) gave rise to 16 fractions, which were subsequently analysed using HPLC-APCI-MS. Twelve of the GPC fractions were also analysed by high-temperature GC-MS using a capillary column coated with a polarisable stationary phase. TAGs present in the fractions were correlated with those in the chromatogram of the whole milk fat through retention time comparison and the use of mass chromatograms. In total, 120 TAGs were identified.

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.

Detection of palm fruit lipids in archaeological pottery from Qasr Ibrim, Egyptian Nubia

In modern times, the trees of the palm family have been of great economic and social importance to the people in Egypt, as in other parts of the world. There are various species of palm and although different parts of the tree can be used, the fruit are of great value. In antiquity, it is expected that the palm fruit would also have been of great importance to people in the region. The chemical analysis of absorbed residues in archaeological pottery is well established, and through the investigation of ceramic vessels (via gas chromatography, gas chromatography-mass spectrometry and gas chromatography-combustion-isotope ratio mass spectrometry) saturated carboxylic acids in the range C12 to C18 have been detected (with an unusually high abundance of C12) from vessels from the Nubian site of Qasr Ibrim. This is mirrored in the saturated fatty acid distributions detected from the kernels of modern and ancient date palm (Phoenix dactylifera L.) and dom palm (Hyphaena thebaica (L.) Mart.). Mixing in some of the vessels of the palm fruit with another lipid source is indicated through the delta13C values. These results provide the first direct evidence for the exploitation of palm fruit in antiquity and the use of pottery vessels in its processing.

Practical and theoretical considerations in the gas chromatography/combustion/isotope ratio mass spectrometry delta(13)C analysis of small polyfunctional compounds

Carbohydrates and proteins are among the most abundant naturally occurring biomolecules and so suitable methods for their reliable stable isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) are required. Due to the non-volatile nature of these compounds they require hydrolytic cleavage to their lower molecular weight subunits and derivatisation prior to GC/C/IRMS analysis. The addition of carbon to the molecules and any kinetic isotopic fractionation associated with derivatisation must be accounted for in order to provide meaningful stable isotope values and estimates of propagated errors. To illustrate these points amino acid trifluoroacetate/isopropyl esters and alditol acetates were prepared from authentic amino acids and monosaccharides, respectively. As predicted from the derivatisation reaction mechanisms, a kinetic isotope effect was observed which precludes direct calculation of delta(13)C values of the amino acids and monosaccharides by simple mass balance equations. This study shows that the kinetic isotope effect associated with derivatisation is both reproducible and robust, thereby allowing the use of correction factors. We show how correction factors can be determined and accurately account for the addition of derivative carbon. As a consequence of the addition of a molar excess of carbon and the existence of a kinetic isotope effect during derivatisation, errors associated with determined delta(13)C values must be assessed. We illustrate how such errors can be quantified (for monosaccharides +/-1.3 per thousand and for amino acids between +/-0.8 per thousand and +/-1.4 per thousand). With the magnitude of the errors for a given delta(13)C value of a monosaccharide or amino acid quantified, it is possible to make reliable interpretations of delta(13)C values, thereby validating the determination of delta(13)C values of amino acids as TFA/IP esters and monosaccharides as alditol acetates.

Detection and classification of atmospheric methane oxidizing bacteria in soil

Well-drained non-agricultural soils mediate the oxidation of methane directly from the atmosphere, contributing 5 to 10% towards the global methane sink. Studies of methane oxidation kinetics in soil infer the activity of two methanotrophic populations: one that is only active at high methane concentrations (low affinity) and another that tolerates atmospheric levels of methane (high affinity). The activity of the latter has not been demonstrated by cultured laboratory strains of methanotrophs, leaving the microbiology of methane oxidation at atmospheric concentrations unclear. Here we describe a new pulse-chase experiment using long-term enrichment with 12CH4 followed by short-term exposure to 13CH4 to isotopically label methanotrophs in a soil from a temperate forest. Analysis of labelled phospholipid fatty acids (PLFAs) provided unambiguous evidence of methane assimilation at true atmospheric concentrations (1.8-3.6 p.p.m.v.). High proportions of 13C-labelled C18 fatty acids and the co-occurrence of a labelled, branched C17 fatty acid indicated that a new methanotroph, similar at the PLFA level to known type II methanotrophs, was the predominant soil micro-organism responsible for atmospheric methane oxidation.

Evidence for demethylation of syringyl moieties in archaeological wood using pyrolysis-gas chromatography/mass spectrometry

Archaeological oak (Quercus sp.) wood samples, ranging from 16(th) C. AD to 6000 BP, were studied using flash pyrolysis-gas chromatography/mass spectrometry to obtain insight into angiosperm lignin degradation. The pyrolysates revealed evidence of a number of 3-methoxy-1,2-benzenediol derivatives, methoxycatechols, directly related to 2,6-dimethoxyphenol, syringyl, moieties which are characteristic building blocks of angiosperm lignin. Mass spectra and mass chromatograms of these compounds are reported. The finding of these characteristic pyrolysis products in well-preserved archaeological wood provides unequivocal evidence that demethylation of syringyl units occurs very early in wood degradation. It is highly likely that the absence of abundant 3-methoxy-1, 2-benzenediols in degrading plant materials containing angiosperm lignin relates to the lability of these newly formed moieties.

Interpreting early land management through compound specific stable isotope analyses of archaeological soils

Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd.

Studies of organic residues from ancient Egyptian mummies using high temperature-gas chromatography-mass spectrometry and sequential thermal desorption-gas chromatography-mass spectrometry and pyrolysis-gas chromatography-mass spectrometry

The techniques of gas chromatography-mass spectrometry (GC-MS) and sequential thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) have been utilised to characterise the constituents of tissue-derived or applied organic material from two Pharaonic Egyptian mummies with a view to identifying embalming practices/substances. The results obtained using TD-GC-MS revealed a series of monocarboxylic acids with the C16:0, C18:1 and C18:0 components dominating in both mummies. The thermal desorption products related to cholesterol, i.e., cholesta-3,5,7-triene and cholesta-3,5-diene (only in Khnum Nakht), were detected in both mummies. Khnum Nakht also contained a number of straight chain alkyl amides (C16-C18) and an alkyl nitrile (C18). Other products included the 2,5-diketopiperazine derivative (DKP) of proline-glycine (pro-gly) which was a major component (7.9%) in Khnum Nakht but only a very minor component in Horemkenesi. Py-GC-MS of samples of both specimens yielded a series of alkene/alkane doublets (Horemkenesi C6-C18, Khnum Nakht C6-C24) which dominated their chromatograms. Series of methyl ketones in the C9-C19 chain length range were also present, with C5-C7 cyclic ketones occurring in Horemkenesi only. These ketones are indicative of covalent bond cleavage, probably of polymerised acyl lipids. Nitrogenous products included nitriles (C9-C18) which were significant in both samples, and amides which were only detected in Khnum Nakht. Also present amongst the pyrolysis products were three steroidal hydrocarbons, cholest-(?)-ene, cholesta-3,5,7-triene and cholesta-3,5-diene. High temperature-GC-MS of trimethylsilylated lipid extracts yielded similar monocarboxylic acids to that obtained using TD-GC-MS, while a series of alpha, omega-dicarboxylic acids and a number of mono- and di-hydroxy carboxylic acids not seen in the thermal desorption or pyrolysis GC-MS analyses were significant constituents in both mummy samples. Overall, the use of GC-MS and sequential TD-GC-MS and Py-GC-MS has demonstrated in both mummies the presence of a complex suite of lipids and proteinaceous components whose compositions indicates extensive alteration via oxidative and hydrolytic processes during long-term interment. None of the classical embalming resins was detected but an exogenous origin for at least a proportion of these components cannot be discounted since fats, oils and gelatin have been proposed as embalming agents in mummification. The combined approach of sequential TD- and Py-GC-MS has potential for application to the characterisation of embalming materials in mummies. Most importantly these techniques virtually eliminate any destruction of the mummified bodies thereby allowing the scope of investigations of ancient Egyptian funerary practices to be significantly extended.

Direct demonstration of milk as an element of archaeological economies

The stable carbon isotope (delta13C) compositions of individual fatty acid components of remnant fats preserved in archaeological pottery vessels show that dairying was a component of archaeological economies. Characteristic delta13C values arise from biases in the biosynthetic origins of the C18:0 fatty acids in milk and adipose fat. Milk and adipose fat from animals raised on similar pastures and fodders have distinct isotopic signatures.

Molecular coproscopy: dung and diet of the extinct ground sloth Nothrotheriops shastensis

DNA from excrements can be amplified by means of the polymerase chain reaction. However, this has not been possible with ancient feces. Cross-links between reducing sugars and amino groups were shown to exist in a Pleistocene coprolite from Gypsum Cave, Nevada. A chemical agent, N-phenacylthiazolium bromide, that cleaves such cross-links made it possible to amplify DNA sequences. Analyses of these DNA sequences showed that the coprolite is derived from an extinct sloth, presumably the Shasta ground sloth Nothrotheriops shastensis. Plant DNA sequences from seven groups of plants were identified in the coprolite. The plant assemblage that formed part of the sloth's diet exists today at elevations about 800 meters higher than the cave.

delta 13C analyses of vegetable oil fatty acid components, determined by gas chromatography--combustion--isotope ratio mass spectrometry, after saponification or regiospecific hydrolysis

The delta 13C values of the major fatty acids of several different commercially important vegetable oils were measured by gas chromatography--combustion--isotope ratio mass spectrometry. The delta 13C values obtained were found to fall into two distinct groups, representing the C3 and C4 plants classes from which the oils were derived. The delta 13C values of the oils were measured by continuous flow elemental isotope ratio mass spectrometry and were found to be similar to their fatty acids, with slight differences between individual fatty acids. Investigations were then made into the influence on the delta 13C values of fatty acids of the position occupied on the glycerol backbone. Pancreatic lipase was employed to selectively hydrolyse fatty acids from the 1- and 3-positions with the progress of the reaction being followed by high-temperature gas chromatography in order to determine the optimum incubation time. The 2-monoacylglycerols were then isolated by thin-layer chromatography and fatty acid methyl esters prepared. The delta 13C values obtained indicate that fatty acids from any position on the glycerol backbone are isotopically identical. Thus, whilst quantification of fatty acid composition at the 2-position and measurement of delta 13C values of oils and their major fatty acids are useful criteria in edible oil purity assessment, measurement of delta 13C values of fatty acids from the 2-position does not assist with oil purity assignments.

Assessment of bog-body tissue preservation by pyrolysis-gas chromatography/mass spectrometry

Flash pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) was used to assess the quality and mechanism of protein preservation in the tissue of Iron Age bog bodies from Lindow, UK, and south-eastern Drenthe, The Netherlands. Abundant pyrolysis products of the fresh skin tissue, including 2,5-diketopiperazines of Pro-Gly, Pro-Ala, Pro-Val, Pro-Pro and Hyp, were readily assigned to specific amino acid or dipeptide moieties. Comparison of the pyrolysates of the bog-body tissues with that of modern samples revealed qualitative similarities suggesting good preservation of the collagen and non-collagenous proteins in the ancient tissues. Examination of the pyrolysates of samples of fresh calf skin, which had been treated with various vegetable tanning agents, clearly revealed markers of non-hydrolysable tannins including 1,2-benzenediol, 1,3-benzenediol and 1,2,3-benzenetriol, although chromatographic quality inevitably diminished with increasing functionalization of the compounds. Such markers were not detected in the pyrolysates of the bog-body tissues. Instead 4-isopropenylphenol, a characteristic pyrolysis product of Sphagnum moss, was detected in both solvent-extracted and base-treated samples of tissue. The presence of 4-isopropenylphenol in the pyrolysates of the bog-body tissues provides evidence that their preservation involves reactions of amino acids with sphagnum acid, and possibly other agents derived from the peat. The study constitutes the first chemical characterization of the pyrolysis products of modern and ancient collagen.

delta 13C analysis of cholesterol preserved in archaeological bones and teeth

Cholesterol preserved in archaeological bones and teeth constitutes an important new source of palaeodietary information. A method is described here for the isotopic (delta 13C) determination of cholesterol employing a semiautomated sample preparation procedure and the technique of isotope ratio monitoring/gas chromatography/ mass spectrometry (irm/GC/MS). High-temperature gas chromatography (HT-GC) and high-temperature gas chromatography/mass spectrometry (HT-GC/MS) were used to identify the lipids and quantify the cholesterol present in the total lipid extracts. delta 13C values are then readily obtained from nanogram amounts (approximately 50 ng) of cholesterol resolved and determined directly by high-resolution capillary irm/GC/MS of trimethylsilylated total lipid extracts. The protocol developed allows effective processing of the large numbers of samples essential for palaeodietary determinations. Analytical precision and reproducibility have been assessed through multiple sampling of the same skeleton (femur, 9th century). Comparable delta 13C values have been obtained from different skeletal members from the same individual. The utility of the approach is demonstrated through a study of the delta 13C values of cholesterol isolated from sections of femoral bones of individuals excavated from cemeteries (dated Saxon to 18th century) at a coastal site in the U.K. The mean delta 13C value (-22.2 +/- 0.3/1000, sigma = 0.9) determined for cholesterol in 50 different individuals indicates a strong preference for marine foods by the members of the community extending back over the last approximately 1500 years. A minority of individuals exhibited delta 13C values as low as -26/1000, indicating preferences for terrestrial rather than marine foodstuffs.

Measurement of the turnover of glycogen phosphorylase by GC/MS using stable isotope derivatives of pyridoxine (vitamin B6)

The majority of vitamin B6 in the body is in skeletal muscle, bound as the cofactor pyridoxal 5'-phosphate to one abundant protein, glycogen phosphorylase. Previous work has established that radiolabelled vitamin B6 can be used as a turnover label for glycogen phosphorylase. In this study, a stable isotope derivative of pyridoxine {dideuterated pyridoxine; 3-hydroxy-4-(hydroxymethyl) -5-[hydroxymethyl-2H2]-2-methylpyridine} ([2H2]PN) has been used as a metabolic tracer to study the kinetics of labelling of the body pools of vitamin B6 in mice. A non-invasive method was developed in which the isotope abundance of the urinary excretory product of vitamin B6 metabolism, 4-pyridoxic acid, was analysed by GC/MS. The change in isotope abundance of urinary 4-pyridoxic acid following administration of [2H2]PN reflects the kinetics of labelling of the body pools of vitamin B6, and yields, non-invasively, the rate of degradation of glycogen phosphorylase.

Remarkable preservation of biomolecules in ancient radish seeds

Desiccated seeds from a 6th century AD storage vessel recovered from Qasr Ibrîm, Egypt, were examined for the presence of lipids and nucleic acids. A remarkable degree of lipid preservation was discovered, the fatty acid and sterol profiles being very similar to those of modern radish seeds. The only significant differences were hydrolysis of triacylglycerols and depletion of the polyunsaturated fatty acids (C18:2 and C18:3). The delta 13 C values of the principal fatty acids were in the range -25.4 to -29.2/1000, which is congruent with modern radish (C3 seeds) taking account of isotopic shifts caused by recent changes in atmospheric CO2. Deoxyribonucleosides and nucleic acid bases were detected by direct chemical analysis, and polymerase chain reactions gave products with sequences comparable to those from modern radish. The degree of lipid preservation, which was much greater than that reported for other archaeological remains, suggests that the microenvironment within desiccated seeds retards biomolecular decay. The results illustrate the utility of combined lipid-nucleic acid analysis in chemotaxonomic and genotypic studies of archaeobotanical remains.

Molecular heterogeneity in the Major Urinary Proteins of the house mouse Mus musculus

Major Urinary Proteins (MUPs) from different inbred strains of mouse have been analysed by high-resolution ion-exchange chromatography and mass spectrometry. MUPs from six strains were resolved chromatographically into four major protein peaks which characterized two distinct phenotypes, typified by the profiles obtained from the Balb/c and C57BL/6 inbred strains. A combination of ion-exchange chromatography and electrospray ionization mass spectrometry analysis of the MUPs from each strain identified five proteins, only one of which was common to both strains. The charge and mass data, together with N-terminal sequence analyses, were correlated with the masses of the proteins inferred from published cDNA sequences. Several members of the family of MUP sequences differ in only four positions, and in some circumstances the substitutions elicit a minimal change in protein mass (Lys/Gln; Lys/Glu). Peptide mapping with endopeptidase Lys-C, followed by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry permitted identification of new MUPs that were correlated with partial cDNA sequence data. In the two strains there are at least 13 different MUPs, either observed or predicted, indicating the heterogeneity of expression of this group of proteins.

High-resolution triacylglycerol mixture analysis using high-temperature gas chromatography / mass spectrometry with a polarizable stationary phase, negative ion chemical ionization, and mass-resolved chromatography

High-temperature gas chromatography/mass spectrometry (HT-GC/MS) has been employed to study the behavior of mixtures of triacylglycerol molecular species on a polarizable stationary phase (immobilized 65% phenyl methyl silicone). The use of negative ion chemical ionization (NICI) at an ion source block temperature of 300 °C overcomes problems with interpretation of electron ionization (EI) mass spectra produced during the HT-GC/MS. The NICI spectra of triacylglycerols produced under these conditions contain abundant [RCO2](-), [RCO2 - 18](-), and [RCO2 - 19](-) ions, believed to be produced by nucleophilic gas-phase ammonolysis, that are used to identify the individual fatty acid moieties associated with peaks in triacylglycerol total ion chromatograms. The polarizable stationary phase produces significantly enhanced resolution of triacylglycerol molecular species compared to hightemperature stable apolar stationary phases, such as immobilized dimethyl polysiloxanes. The resolution of complex natural mixtures of triacylglycerols can be further improved by use of the Biller-Biemann enhancement technique to produce mass-resolved chromatograms. Investigation of the mass-resolved chromatograms provides important information with regard to the factors that affect elution orders of individual triacylglycerol molecular species. The analysis of mixtures of authentic triacylglycerols by HT-GC/MS via NICI provides data that relate to the analytical limits of the technique for the analysis of triacylglycerols that bear both saturated and polyunsaturated fatty acyl moieties.

Recognition of chitin and proteins in invertebrate cuticles using analytical pyrolysis/gas chromatography and pyrolysis/gas chromatography/mass spectrometry

Flash pyrolysis/gas chromatography (py/GC) and py/GC/mass spectrometry (MS) have been utilized to characterize the cuticles of invertebrates chemically. Pyrolysis products have been identified and assigned to specific cuticular components. Acetylpyridones, acetamidofuran, 3-acetamido-5-methylfuran and 3-acetamido-(2 and 4)-pyrones are proposed as characteristic pyrolysis markers for chitin. Pyrolysis products displaying ions of m/z 70, 154, 168, 194 are thought to derive from diketopiperazine structures and provide potential markers for proteins and peptides in which proline, alanine, valine, arginine and glycine are the dominant amino acids. These products, constituting specific pyrolysis markers for invertebrate cuticles, may reflect the amino acid composition of their constituent structural proteins. The source of the various pyrolysis products of proteins has been verified by pyrolysis of reference proteins, peptides and amino acid mixtures. The presence of additional pyrolysis products related directly to histidine and catechol moieties is consistent with the chemical structure and composition proposed for arthropod cuticles based on recent work utilizing solid state 13C and 15N nuclear magnetic resonance. This study constitutes the first comprehensive chemical characterization of the pyrolysis products of invertebrate cuticles and provides the basis for future investigations requiring qualitative screening for cross-linked chitin and proteins in modern and fossil cuticles and in materials, e.g. geopolymers, that may be derived from them.

Application of electrospray ionization mass spectrometry with maximum-entropy analysis to allelic 'fingerprinting' of major urinary proteins

Mixtures of a specific group of proteins, the major urinary proteins (MUPs), believed to have a role in odorant binding, have been analysed by electrospray ionization mass spectrometry. The data obtained from conventional transformed electrospray data confirm that the molecular weights of the protein mixtures, deduced from published sequences, lie in the molecular weight range 18,600 to 19,000 Da. Application of maximum-entropy analysis to the raw electrospray data has confirmed a heterogeneity in MUP composition, consistent with allelic similarities (and differences) between the different mouse strains. This work demonstrates the use of maximum entropy in the assessment of protein content and in the subsequent resolution enhancement of naturally occurring protein mixtures containing components of closely similar molecular mass.

Application of gas chromatography-mass spectrometry with selected ion monitoring to the urinanalysis of 4-pyridoxic acid

An analytical protocol has been developed for the analysis of urinary 4-pyridoxic acid (4-PA) by gas chromatography-mass spectrometry (GC-MS) for use in metabolic studies. Aliquots of urine were deproteinised and fractionated by isocratic reversed-phase high-performance liquid chromatography. The eluent fraction containing the 4-PA was collected, freeze-dried and silylated using N-methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide. Derivatisation produced the mono-tert.-butyldimethylsilyl derivative of 4-PA lactone. This derivative was readily amenable to GC-MS analysis in the electron ionisation (70 eV) mode, yielding a prominent fragment ion at m/z 222 ([M-57]+; base peak). A heavy isotope-labelled derivative of pyridoxine [dideuteriated pyridoxine; 3-hydroxy-4-(hydroxymethyl)-5-[hydroxymethyl-2H2]-2-methylpyridine] has been synthesised and is being employed to determine the kinetics of labelling of the body pools of vitamin B6. Kinetic measurements are based on the determination of the relative proportions of metabolically produced deuterium-labelled and non-labelled 4-PA in urine, obtained from stable isotope ratios determined by low-resolution selected ion monitoring using a bench-top quadrupole GC-MS system.

Quantitative determination of cholesterol sulphate in plasma by stable isotope dilution fast atom bombardment mass spectrometry

A stable isotope dilution assay has been developed for the quantitative determination of cholesterol sulphate in plasma using negative ion fast atom bombardment (FAB) mass spectrometry. The assay is highly selective and avoids problems of contamination from free cholesterol and other conjugates of cholesterol present in plasma. (6,7,7-2H3)Cholesterol sulphate is used as the internal standard and solvent extraction and silica Sep-Paks are employed to isolate plasma cholesterol sulphate. Limited-range acceleration voltage scanning in FAB mass spectrometric analyses leads to sub-microgram detection limits. Comparison of results obtained by FAB mass spectrometry of the intact cholesterol sulphate, and by gas chromatography/mass spectrometry selected ion monitoring of the free cholesterol, released by solvolysis of the cholesterol sulphate, showed that the latter approach probably overestimates plasma levels of cholesterol sulphate.

Detection of unconjugated and conjugated steroids in the ovary, eggs, and haemolymph of the decapod crustacean Nephrops norvegicus

Gas chromatography/mass spectrometry with selected ion monitoring has been employed to examine extracts from the ovary, eggs, and haemolymph of the marine prawn, Nephrops norvegicus, to demonstrate the presence of steroids. Both free and conjugated steroids were isolated by solvent partitioning and chromatography (lipophilic Sephadex, reversed-phase Sep Pak, and normal phase medium-pressure liquid chromatography) and steroidal conjugates were cleaved enzymatically. Steroids were determined as their methyloxime derivatives, trimethylsilyl (TMS) ethers or methyloxime-TMS ethers. All assignments were based on the detection of characteristic ions and cochromatography with the authentic steroid derivatives. 5 alpha-Dihydrotestosterone, testosterone, pregnenolone, and 20 alpha-hydroxypregn-4-en-3-one were detected in unconjugated form in the ovary. The eggs and haemolymph were found to contain unconjugated 17 beta-estradiol. Conjugated 5 alpha-dihydrotestosterone was detected in both the ovary and haemolymph, but no conjugated steroids were found in the eggs.

Negative ion ammonia chemical ionization and electron impact ionization mass spectrometric analysis of steryl fatty acyl esters

Synthesis of steryl palmitates, varied in the nature of the steryl moiety, provided model compounds for investigation of the mass spectrometric behavior of steryl long-chain fatty acyl esters. The structure of the steryl moiety was varied according to: (i) position and degree of unsaturation in the steroid nucleus and C-17 side-chain, (ii) position and degree of methylation, (iii) presence or absence of a 9 beta, 19-cyclopropane ring. Compounds were chosen so as to be representative of biochemically important steryl esters. Electron impact (EI) behavior of steryl palmitate esters closely resembles that of their short-chain (e.g. acetate) counterparts. M+.ions were generally weak or absent and the major high mass ions arose from characteristic fragmentations of the steroid nucleus following loss of the acyl moiety ([M-RCO2H]+.). Fragment ions characteristic of the acyl moiety were lacking. Negative ion chemical ionization (NICI) using ammonia as reagent gas, on the other hand, afforded spectra containing characteristic fragment ions [RCO2]-, [RCO2-18]-, and [RCO2-19]- from which the nature of the fatty acyl moiety can be readily deduced. Hence, NICI and EI provide complementary means of ionization for the mass spectrometric determination of structures of steryl esters.

Capillary gas chromatography/mass spectrometry of intact fatty acyl esters of pregnane steroids

Synthetic long-chain fatty acyl esters of pregnenolone and 3 beta-hydroxy-5 alpha-pregnan-20-one (5 alpha-pregnanolone) were submitted to gas chromatography (GC) and GC/mass spectrometry (GC/MS). Analyses were readily performed using short (8-12 m) flexible fused-silica capillary columns coated with thin films of immobilized apolar stationary phase (e.g. OV-1 type). The electron impact (EI) mass spectra were found to be of limited value for structure investigations, as molecular ions (M+.) were either weak or absent. EI spectra also lacked characteristic fatty acyl fragment ions. In contrast, negative ion ammonia chemical ionization produced characteristic [M-H]- ions and diagnostic fragment ions. The application of the above methods to biochemical investigations is exemplified by GC/MS analysis of the steroidal fatty acyl esters in extracts of bovine adrenal tissue, and the metabolites produced by incubating starfish (Asterias rubens) testicular tissue with exogenous progesterone.

Strategy for the analysis of steryl esters from plant and animal tissues

Methods are described for the analysis of intact steryl esters present in complex mixtures isolated from plant or animal tissues. A preliminary examination by analytical thin-layer chromatography (TLC) and capillary column gas chromatography-mass spectrometry (GC-MS) under electron impact (EI) ionisation reveals the complexity of the mixture and the nature of the steryl moieties. Preparative TLC is then utilised to separate the steryl esters into two broad groups, containing fatty acyl moieties of shorter (C2-C8) or longer chain length (C10-C22). The shorter-chain fatty acyl steryl esters are separated by adsorption high-performance liquid chromatography (HPLC) on a LiChrosorb Silica-60 column. The steryl esters with longer-chain fatty acyl moieties are analysed by reversed-phase HPLC on either an Ultrasphere ODS, 5-micron, or a S3 Spherisorb ODS, 3-micron, column. Steryl esters with unsaturated fatty acyl moieties are eluted with the shorter-chain fatty acyl steryl esters. The presence of the unsaturated fatty acyl esters can be monitored by analytical argentation TLC, which will also reveal the degree of unsaturation. The steryl esters are fractionated into the saturated, mono-, di-, tri- and polyene acyl types by preparative medium-pressure liquid chromatography on a column of 10% AgNO3-silica gel. Each of these steryl ester types can then be resubmitted to reversed-phase HPLC or analysed by GC-MS on a short fused-silica capillary column with a bonded phase of the OV-1 type. GC-MS on a magnetic-sector instrument under negative-ion chemical ionisation conditions with ammonia as the reagent gas produces fragment ions for both the steryl and fatty acyl moieties, thus permitting identification of the individual intact steryl esters. These various methods are illustrated by analyses of the steryl ester mixtures obtained from human plasma, barley seedlings, palm oil and rape seed oil.

Capillary gas chromatography-mass spectrometry of ecdysteroids

Fully trimethylsilylated ecdysteroids have been analysed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) using flexible fused-silica capillary columns. Best results were obtained using columns coated with cross-bonded apolar (OV-1 type) stationary phases. By employing capillary GC-MS with selected-ion monitoring (SIM), very sensitive and selective analyses for ecdysteroids are possible. Detection limits of 10 and 100 pg have been determined for 20-hydroxyecdysone and ecdysone, respectively. At this level of sensitivity, capillary GC-SIM-MS constitutes a complementary means of ecdysteroid analysis to high-performance liquid chromatography (HPLC) with monitoring of the eluent fractions by radioimmunoassay (RIA), but with the advantage of enhanced selectivity. Examples are given of the application of capillary GC-SIM-MS and HPLC-RIA in combination to investigate the nature and concentration of ecdysteroids at the picogram level in three helminth species.

Capillary gas chromatography/mass spectrometry of cholesteryl esters with negative ammonia chemical ionization

Mixtures of both synthetic and naturally occurring (human plasma cholesteryl esters have been examined by capillary gas chromatography/mass spectrometry (GC/MS). A magnetic sector mass spectrometer was used and a variety of ionization modes were assessed with a view to obtaining structural information on intact cholesteryl esters. By employing ammonia as reagent gas, with negative ion scanning, spectra were produced from which the nature of steryl and fatty acyl moieties could be readily deduced. Analyses were performed at an ion source temperature of 300 degrees C in order to maintain the integrity of the gas chromatographic profile. The technique described is of general use for the GC/MS analysis of steryl esters, particularly in conjunction with magnetic sector instruments.

Identification of ecdysone 22-long-chain fatty acyl esters in newly laid eggs of the cattle tick Boophilus microplus

The five major apolar ecdysone esters present in newly laid eggs of the cattle tick Boophilus microplus have been purified by h.p.l.c. The quantities of the apolar esters present in the eggs were increased by administration of ecdysone to the mature females. G.c.-m.s. analysis, as their methyl esters, of the fatty acids released from the apolar ecdysone derivatives by alkali, coupled with positive-ion fast-atom-bombardment m.s. of the intact ecdysone esters, showed that the compounds consisted of a series of fatty acyl esters of ecdysone. The position of esterification of the ecdysone was established by p.m.r. spectroscopy. The combined data show that the novel apolar derivatives of ecdysone consist of the 22-palmitate, -palmitoleate, -stearate, -oleate, and -linoleate esters respectively. Confirmation was obtained by comparison with synthetic ecdysone 22-palmitate. The significance of the ecdysone fatty acyl esters as a possible source of free hormone during embryogenesis is discussed.