Carbon isotope analysis of bulk keratin and single amino acids from British and North American hair

Preparative HPLC Separation of Underivatized Amino Acids for Isotopic Analysis

Single-compound analysis of stable or radioactive isotopes has found application in a number of fields ranging from archaeology to forensics. Often, the most difficult part of these analyses is the development of a method for isolating the compound(s) of interest, which can derive from a wide range of sample types including the hair, nails, and bone.Here we describe three complementary preparative HPLC techniques suitable for separating and isolating amino acids from bone collagen and hair keratin. Using preparative reversed-phase, ion-pair, or mixed-mode chromatography in aqueous carbon-free mobile phases, or those from which carbon can easily be removed, underivatized single amino acids can be isolated and further analyzed using mass spectrometric techniques.

Carbon and nitrogen stable isotopic offsets between diet and hair/feces in captive chimpanzees

RATIONALE

Estimation of the stable isotopic offsets between tissue and diet is important for dietary reconstructions. Although stable isotopic studies of chimpanzees (Pan troglodytes) are increasing, the isotopic offsets in chimpanzees have never been studied. In this study, the carbon and nitrogen stable isotopic offset values in hair and feces were measured for 13 captive chimpanzees for the first time.

METHODS

All consumed food items and quantities were recorded for each individual for 1 week. Food samples were typically collected three times, hair was collected 3 weeks after the experimental week, and feces were collected ad libitum during the experimental week. The stable carbon and nitrogen isotope ratios were measured using elemental analyzer-isotope ratio mass spectrometry (EA-IRMS).

RESULTS

As the results of Monte Carlo analysis, the estimated carbon and nitrogen offsets between the hair and diet were +3.0 to +3.9‰ and +2.8 to +3.7‰, respectively, for the 95% confidence intervals (CIs). The 95% CIs of the carbon and nitrogen offset values between the feces and diet were -1.6 to 0.0‰ and +1.2 to +2.7‰, respectively.

CONCLUSIONS

These offset values are generally consistent with those of the other primate species reported in previous studies. However, potential variations in the offset values due to dietary and physiological factors should be studied in detail in the future. Copyright © 2016 John Wiley & Sons, Ltd.

Global spatial distributions of nitrogen and carbon stable isotope ratios of modern human hair

RATIONALE

Natural stable carbon (δ(13)C) and nitrogen isotope ratios (δ(15)N) of humans are related to individual dietary habits and environmental and physiological factors. In forensic science the stable isotope ratios of human remains such as hair and nail are used for geographical allocation. Thus, knowledge of the global spatial distribution of human δ(13)C and δ(15)N values is an essential component in the interpretation of stable isotope analytical results.

METHODS

No substantial global datasets of human stable isotope ratios are currently available, although the amount of available (published) data has increased within recent years. We have herein summarised the published data on human global δ(13)C andδ(15)N values (around 3600 samples) and added experimental values of more than 400 additional worldwide human hair and nail samples. In order to summarise isotope ratios for hair and nail samples correction factors were determined.

RESULTS

The current available dataset of human stable isotope ratios is biased towards Europe and North America with only limited data for countries in Africa, Central and South America and Southeast Asia. The global spatial distribution of carbon isotopes is related to latitude and supports the fact that human δ(13)C values are dominated by the amount of C4 plants in the diet, either due to direct ingestion as plant food, or by its use as animal feed. In contrast, the global spatial distribution of human δ(15)N values is apparently not exclusively related to the amount of fish or meat ingested, but also to environmental factors that influence agricultural production.

CONCLUSIONS

There are still a large proportion of countries, especially in Africa, where there are no available data for human carbon and nitrogen isotope ratios. Although the interpretation of modern human carbon isotope ratios at the global scale is quite possible, and correlates with the latitude, the potential influences of extrinsic and/or intrinsic factors on human nitrogen isotope ratios have to be taken into consideration.

Change of geographical location from Germany (Bavaria) to USA (Arizona) and its effect on H-C-N-S stable isotopes in human hair

To receive information about the duration of a person's stay abroad related to those questions in forensics, stable isotopes of H-C-N-S were analysed in beard hair samples from four young soldiers, who went from Fürstenfeldbruck (Bavaria, Germany) to Phoenix (Arizona, USA) on the same date for their pilot training over a time period of 3 months. All study subjects were almost of the same age, had similar physical constitutions and stayed at the same military bases for the whole study period. However, the results showed considerable individual variabilities. In Arizona, hair δ(13)C increased by 2.3‰ (±0.6) and δ(34)S decreased by 1.8‰ (±1.2). No remarkable shifts of hair δ(15)N and δ(2)H were observed. Significant shifts of δ(13)C or δ(34)S in the shaved beard hair samples occurred 8 or 9 days after arrival in Arizona, respectively. The time lag to receive the isotope signals in hair due to US diet correspond to the growth period that hair needs to cover the distance of 2-3 mm from its root to the surface of the skin. This implies that isotopic changes due to the consumption of food and drinks were incorporated almost immediately into the hair protein. Consequently, if connected with an isotopic change of the diet, short-term stays for only a few days might be clearly recognizable within the first millimetres of a scalp hair strand which includes the hair roots.

Stable isotope composition of human fingernails from Slovakia

Stable isotope composition of human fingernails has proven to be useful for documenting human dietary information and geographical patterns in archeological, forensic, anthropological and biological studies. Therefore, it is of interest to detect all factors influencing the stable isotopic composition in the certain regions in the world. Carbon and nitrogen isotope data of human fingernail keratin from 52 individuals from Slovakia were reported in this study. The online combustion and continuous flow isotope-ratio mass spectrometer Delta V Advantage was used for δ(13)C and δ(15)N analysis of fingernail keratin samples from 24 vegetarian and 28 omnivorous individuals. A group of people with frequent meat consumption showed enrichment in (13)C and (15)N isotopes in fingernails. A similar trend was observed with increasing seafood in an individual's diet. Moreover a significant difference was revealed between smokers and nonsmokers for both δ(13)C and δ(15)N values. These data were compared to previously published δ(13)C and δ(15)N fingernail values from across the globe. This study brings new information on the stable isotope signature of individuals from Slovakia and characterizes the Central European region for the first time. The stable isotope composition of fingernails is influenced by the frequency of meat and seafood consumption as well as smoking.

Hair for brain trade-off, a metabolic bypass for encephalization

Hair loss in humans is perplexing and raises many hypothetical explanations. This paper suggests that hair loss in humans is metabolically related to encephalization; and that hair covered hominids would have been unable to evolve large brains because of a dietary restriction of several amino acids which are essential for hair and brain development. We use simulations to imply that hair loss must have preceded increase in brain size & volume. In this respect we see hair loss as a major force in human evolution. We assume that hair reduction required favorable climatic conditions and must have been quick. Using evolutionary and ecological time scales, we pinpoint hair loss to a period around 2.2-2.4 million years ago. The dating is further supported by a rapid selection at that time of the sialic acid deletion mutation which may have protected growing human brains against calcium ion flux. In summary we view encephalization, in part, as a metabolic trade-off between hair and brain. Other biochemical changes may have intervened in the process too; and the deletion mutation of sialic acid hydroxylation may have been involved as well.

Isotopic investigation of niche partitioning among native carnivores and the non-native coyote (Canis latrans)

We employed stable carbon (δ(13)C) and nitrogen (δ(15)N) isotopes within a hypothetico-deductive framework to explore potential resource partitioning among terrestrial mammalian carnivores. Isotope values were acquired using guard hair samples from bobcat (Lynx rufus), coyote (Canis latrans), gray fox (Urocyon cinereoargenteus), and red fox (Vulpes vulpes) in the Adirondack Park, NY, USA. Enrichment along the δ(13)C axis was expected to reflect the use of human sources of food (reflecting a corn subsidy), and by extension tolerance for human-modified environments, whereas enrichment along the δ(15)N axis was expected to reflect a higher level of carnivory (i.e. amount of animal-based protein in the diet) - two mechanisms by which these now sympatric species may achieve a dynamic coexistence. Although bobcats were the only obligate carnivore, all four species shared a similar δ(15)N space. In contrast, bobcat had a lower and distinct δ(13)C signature compared to foxes, consistent with the a priori expectation of bobcats being the species least tolerant of human activities. Isotope signatures for coyotes, which colonized the region in the 1920s, overlapped all three native carnivores, bobcats the least, gray fox the most, indicating their potential competitive influence on this suite of native carnivores.

Dietary heterogeneity among Western industrialized countries reflected in the stable isotope ratios of human hair

Although the globalization of food production is often assumed to result in a homogenization of consumption patterns with a convergence towards a Western style diet, the resources used to make global food products may still be locally produced (glocalization). Stable isotope ratios of human hair can quantify the extent to which residents of industrialized nations have converged on a standardized diet or whether there is persistent heterogeneity and glocalization among countries as a result of different dietary patterns and the use of local food products. Here we report isotopic differences among carbon, nitrogen and sulfur isotope ratios of human hair collected in thirteen Western European countries and in the USA. European hair samples had significantly lower δ(13)C values (-22.7 to -18.3‰), and significantly higher δ(15)N (7.8 to 10.3‰) and δ(34)S (4.8 to 8.3‰) values than samples from the USA (δ(13)C: -21.9 to -15.0‰, δ(15)N: 6.7 to 9.9‰, δ(34)S: -1.2 to 9.9‰). Within Europe, we detected differences in hair δ(13)C and δ(34)S values among countries and covariation of isotope ratios with latitude and longitude. This geographic structuring of isotopic data suggests heterogeneity in the food resources used by citizens of industrialized nations and supports the presence of different dietary patterns within Western Europe despite globalization trends. Here we showed the potential of stable isotope analysis as a population-wide tool for dietary screening, particularly as a complement of dietary surveys, that can provide additional information on assimilated macronutrients and independent verification of data obtained by those self-reporting instruments.

Preparative HPLC separation of underivatized amino acids for isotopic analysis

Single-compound analysis of stable or radio-isotopes has found application in a number of fields ranging from archaeology to forensics. Often, the most difficult part of these analyses is the development of a method for isolating the compounds of interest.Here, we describe three complementary preparative HPLC procedures suitable for separating and isolating single amino acids from bone collagen or hair keratin with minimal isotopic contamination. Using preparative reversed-phase, ion-pair, or mixed-mode chromatography of underivatized amino acids in aqueous mobile phases, single amino acids can be isolated and further analyzed using mass spectrometric techniques.

Tracking cats: problems with placing feline carnivores on δO, δD isoscapes

Background

Several felids are endangered and threatened by the illegal wildlife trade. Establishing geographic origin of tissues of endangered species is thus crucial for wildlife crime investigations and effective conservation strategies. As shown in other species, stable isotope analysis of hydrogen and oxygen in hair (δD_h, δ¹⁸O_h) can be used as a tool for provenance determination. However, reliably predicting the spatial distribution of δD_h and δ¹⁸O_h requires confirmation from animal tissues of known origin and a detailed understanding of the isotopic routing of dietary nutrients into felid hair.

Methodology/Findings

We used coupled δD_h and δ¹⁸O_h measurements from the North American bobcat (Lynx rufus) and puma (Puma concolor) with precipitation-based assignment isoscapes to test the feasibility of isotopic geo-location of felidae. Hairs of felid and rabbit museum specimens from 75 sites across the United States and Canada were analyzed. Bobcat and puma lacked a significant correlation between H/O isotopes in hair and local waters, and also exhibited an isotopic decoupling of δ¹⁸O_h and δD_h. Conversely, strong δD and δ¹⁸O coupling was found for key prey, eastern cottontail rabbit (Sylvilagus floridanus; hair) and white-tailed deer (Odocoileus virginianus; collagen, bone phosphate).

Conclusions/Significance

Puma and bobcat hairs do not adhere to expected pattern of H and O isotopic variation predicted by precipitation isoscapes for North America. Thus, using bulk hair, felids cannot be placed on δ¹⁸O and δD isoscapes for use in forensic investigations. The effective application of isotopes to trace the provenance of feline carnivores is likely compromised by major controls of their diet, physiology and metabolism on hair δ¹⁸O and δD related to body water budgets. Controlled feeding experiments, combined with single amino acid isotope analysis of diets and hair, are needed to reveal mechanisms and physiological traits explaining why felid hair does not follow isotopic patterns demonstrated in many other taxa.

Spatial distributions of carbon, nitrogen and sulfur isotope ratios in human hair across the central United States

We present data on the carbon (δ(13)C), nitrogen (δ(15)N) and sulfur (δ(34)S) isotope ratios of human hair collected in the central portions of the USA. These elements are incorporated into hair from the diet and thus provide a record of dietary inputs that may also document geospatial patterns. We detected regional differences in hair δ(34)S values across the USA, with the lowest values in the northern Great Plains and increasing values towards the east, west and south. In contrast, no statistically significant patterns were detected in the spatial variation of human hair δ(13)C and δ(15)N values. Using δ(34)S values and a Geographic Information System approach, we created a map ('sulfur isoscape'). The accuracy of the map was tested using hair samples not included in its generation. We conclude that sulfur isotope analysis may represent a new tool to investigate the movements and/or region-of-origin of humans.

Advances in natural stable isotope ratio analysis of human hair to determine nutritional and metabolic status

PURPOSE OF REVIEW

We review the literature on the use of stable isotope ratios at natural abundance to reveal information about dietary habits and specific nutrient intakes in human hair protein (keratin) and amino acids. In particular, we examine whether hair isotopic compositions can be used as unbiased biomarkers to provide information about nutritional status, metabolism, and diseases.

RECENT FINDINGS

Although the majority of research on the stable isotope ratio analysis of hair has focused on bulk protein, methods have been recently employed to examine amino acid-specific isotope ratios using gas chromatography or liquid chromatography coupled to an isotope ratio mass spectrometer. The isotopic measurement of amino acids has the potential to answer research questions on amino acid nutrition, metabolism, and disease processes and can contribute to a better understanding of the variations in bulk protein isotope ratio values. First results suggest that stable isotope ratios are promising as unbiased nutritional biomarkers in epidemiological research. However, variations in stable isotope ratios of human hair are also influenced by nutrition-dependent nitrogen balance, and more controlled clinical research is needed to examine these effects in human hair.

SUMMARY

Stable isotope ratio analysis at natural abundance in human hair protein offers a noninvasive method to reveal information about long-term nutritional exposure to specific nutrients, nutritional habits, and in the diagnostics of diseases leading to nutritional stress and impaired nitrogen balance.

Black and white--does melanin change the bulk carbon and nitrogen isotope values of feathers?

Bird feathers are employed in a wide range of carbon and nitrogen isotope studies relating to diet and migration. Feathers are chemically inert with respect to carbon and nitrogen, after synthesis. It has always been assumed that feathers show isotope values characteristic of keratin, a fibrous structural protein from which they are formed. Little attention has been paid to other components of feathers such as melanin or carotenoids. Melanin is synthesized from tyrosine, which is depleted in both (13)C and (15)N. We compared isotope values of coeval black and white feathers in four different species. Black feather parts were in all cases significantly depleted in (13)C relative to white feather parts but in most species no clear trend was discernable for (15)N. We suggest that additional evaluation may be required to characterize the carbon and nitrogen isotope contribution of feather pigments like carotenoids. Care should be taken in future stable isotope studies when comparing differently coloured feathers.

Stable isotope analysis of the bioelements: an introduction

The abundances of the stable isotopes of the bioelements are not constant. Subtle, but significant, variations may be induced by physical, physiological and biochemical processes. These variations may be detected and quantified. Often, isotope fingerprints are characteristic of certain processes and may reveal information concerning the sources and origins of compounds of interest. Moreover, natural variabilities of stable isotopes may be exploited in order to perform tracer experiments. The most accurate technology to perform stable isotope analysis is (gas) isotope ratio MS (IRMS). Compound-specific approaches employ hyphenation of GC and LC to IRMS. In these approaches, complete conversion to simple gases prior to MS is required. Analysis by stable isotope ratio spectroscopy currently approaches the accuracy of IRMS. However, for bioanalytical projects, it is still predominantly confined to material synthetically enriched with stable isotopes.

Effect of a controlled dietary change on carbon and nitrogen stable isotope ratios of human hair

The carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) stable isotope ratios of human hair can be used for the interpretation of dietary habits and nutritional status in contemporary or past populations. Although the results of bulk or segmental isotope ratio analysis of human hair have been used for the reconstruction of an individual's diet for years, only limited data of controlled dietary changes on the carbon and nitrogen isotopic composition of human hair are available. Hair of four individuals, two males and two females, who participated in a dietary change experiment for 28 days was segmentally analysed for delta(13)C and delta(15)N. The dietary change included a change from C3 to C4 plant enriched diets and a simultaneous replacement of terrestrial animal products by marine products. This resulted in an increase in delta(13)C(diet) of +8.5 to +9.9 per thousand and in delta(15)N(diet) of +1.5 to +2.2 per thousand. All subjects showed significant increases in delta(13)C(hair) and delta(15)N(hair) during the dietary change period, although no subject reached a new steady state for either carbon or nitrogen. The change in delta(15)N(hair) was faster than the change in delta(13)C(hair) for all individuals. The magnitude of change of the isotopic composition during the dietary change period could be attributed to the degree of physical activity of the individuals, with a higher physical activity resulting in a faster change.

Hair protein and amino acid 13C and 15N abundances take more than 4 weeks to clearly prove influences of animal protein intake in young women with a habitual daily protein consumption of more than 1 g per kg body weight

A high protein or meat intake might be a risk factor for metabolic disorders. Stable isotopic abundances (SIA) of hair can be used as biomarkers for animal protein intake due to characteristic isotopic patterns of food proteins. We investigated if an additional meat intake (M, 200 g pork fillet/day) or an omission of meat and meat products (NOM) can influence the natural (15)N and (13)C SIA within 4 weeks in hair and plasma of young women. The daily protein intake (means +/- SD) was 1.40 +/- 0.29, 2.25 +/- 0.35, and 1.15 +/- 0.26 g/kg at baseline, during M, and during NOM, respectively. At baseline the animal protein intake correlated with bulk SIA of hair ((15)N: R(2) = 0.416; (13)C: R(2) = 0.664; n = 14). However, isotope ratio mass spectrometry (IRMS) analyses have not shown that hair and plasma SIA were changed significantly after M or NOM. Possible reasons were discussed. Urinary SIA were significantly lower after M than after NOM ((15)N: p = 0.039; (13)C: p = 0.006) and close to those of pork fillet. Characteristic patterns of SIA were measured in individual amino acids (AA) by gas chromatography/combustion isotope ratio mass spectrometry (GC/C/IRMS). The results confirmed considerable differences in SIA between AA (delta(15)N, up to 22 per thousand; delta(13)C, up to 31 per thousand). Plots of (15)N versus (13)C abundances in hair revealed characteristic differences between indispensable and dispensable AA. The intervention-dependent changes of AA-specific SIA were not as clear as expected. Although the AA-specific SIA may reveal more detailed characteristics of physiological conditions, further methodological research is required. We suggest that the SIA of leucine can be potential markers of protein intake. The reliability of SIA as biomarkers of protein intake still have to be tested in longer lasting intervention studies in humans. The results may have implications in the assessment for possible benefits and risks of protein consumption.

Correspondence between human diet, body composition and stable isotopic composition of hair and breath in Fijian villagers

The main aim of this work was to describe the relationship between diet, and hair and breath isotopic composition. From one Fijian rural village, hair and breath samples were procured from 20 women. Physical anthropometrics were made, and hair (13)C/(12)C and (15)N/(14)N and breath (13)C/(12)C were measured. Individual diet diaries were kept for two of the four preceding weeks, and isotopic compositions of items which accounted for most of the diet were measured. Individual average diets were analysed for macronutrient and energy content and conform to reasonable nutritional expectation. Characteristics of the diet are described in terms of protein and energy, their patterning with respect to different clusters of food items and their relationship to individuals' anthropometry. Breath CO(2) is depleted in (13)C by 1-2 per thousand on average with respect to the total diet. Hair was enriched on average by 4.1 per thousand in nitrogen and 4.5 per thousand in carbon with respect to the total diet. There was insufficient population variation in hair isotopic composition to establish individual hair-diet isotopic differences. The definite relationship that we establish in this work, between dietary and tissue isotopic values for a human community, provides a basis for determining and validating dietary regimes more generally within non-industrial, non-global-'supermarket' economies.

Trophy heads from Nawinpukio, Perú: physical and chemical analysis of Huarpa-era modified human remains

Rescue excavations at the site of Nawinpukio in Perú's Ayacucho Valley exposed a cache of fragmented skulls dating to the Huarpa-era, about AD 400-700. Physical analysis of these remains revealed that they belonged to individuals of both sexes and a range of ages (MNI = 8), and that four crania had been modified through drilling, cutting, and scraping. The occipital and parietal bones of one cranium had been modified to form a shallow basin. Carbon stable isotope analysis of these remains revealed that five individuals had isotopic signatures consistent with maize consumption and one individual exhibited a carbon isotope value indicative of a C(3) plant based diet. Such a nonmaize diet distinguishes this individual from all other prehistoric humans analyzed from the Ayacucho Valley and is consistent with an origin a different ecozone of the valley. On the basis of their physical properties it is argued that these remains represent trophies obtained during raiding. Drawing on the formal properties of the specimens as well as ethnographic and archaeological analogies, it is suggested that the cranial basin served as a vessel for liquid.

Using hooves for high-resolution isotopic reconstruction of bovine dietary history

The objective of this study was to ascertain whether sequential sampling and isotopic analysis of bovine hooves could be used to reconstruct the dietary history of cattle. A controlled, on-farm experiment was conducted in which cattle were switched from a barley-based diet to an isotopically different diet incorporating maize, urea and seaweed (the isotopic spacing between diets was 13.6 per thousand for delta(13)C and 8.0 per thousand for delta(15)N) and maintained on that diet for 168 days. Postmortem sampling of the cleaned anterior wall of the lateral, left front claw was carried out on five individuals using a micro-drilling technique. From the first 60 mm of each claw, up to 41 samples with a spacing between them of less than 1 mm were collected. Bands were less than 1 mm deep and had a mean width of 1.2 mm. The hoof keratin showed a rapid increase followed by a slower increase in its delta(13)C and delta(15)N values following the diet switch, suggesting that C and N in hoof keratin originate from more than one pool. However, the response of the N isotope composition of the hoof was somewhat delayed compared with that of C. Estimated mean hoof growth rates for these cattle were 10.5 +/- 2.3 mm per month and 6.7 +/- 1.0 mm per month (+/-SD, n = 5) when receiving the barley-based transition diet and the maize-based experimental diet, respectively. These values are considerably higher than previous estimates obtained by visual methods and they suggest that diet may have a greater influence on hoof growth rates than seasonality. These results demonstrate that hooves are a suitable incremental tissue for high-resolution isotopic reconstruction of the dietary history of bovine animals.

Preparative separation of underivatized amino acids for compound-specific stable isotope analysis and radiocarbon dating of hydrolyzed bone collagen

Analysis of stable and radioactive isotopes from bone collagen provides useful information to archaeologists about the origin and age of bone artifacts. Isolation and analysis of single amino acids from the proteins can provide additional and more accurate information by removing contamination and separating a bulk isotope signal into its constituent parts. In this paper, we report a new method for the separation and isolation of underivatized amino acids from bone collagen, and their analysis by isotope ratio MS and accelerator MS. RP chromatography is used to separate the amino acids with nonpolar side chains, followed by an ion pair separation to isolate the remaining amino acids. The method produces single amino acids with little or no contamination from the separation process and allows for the measurement of accurate stable isotope ratios and pure samples for radiocarbon dating.

Serial analysis of stable nitrogen and carbon isotopes in hair: monitoring starvation and recovery phases of patients suffering from anorexia nervosa

Stable nitrogen and carbon isotopic ratios of hair strands of six patients suffering from anorexia nervosa were measured to monitor a dietary change from near starvation to recovery. This paper presents the results of a first-time study of nitrogen and carbon balance of the patients prior to and after admittance to a hospital and therapy. Sequential analysis of the isotopic ratios of hair strands of all patients could be related to the respective body mass index (BMI) of each patient. Our hypothesis concerning the diachronic change in delta15N and delta13C during therapy was met: The delta15N values were inversely related to the BMI, indicating a slow-down in catabolism of bodily protein due to the process of gluconeogenesis during the starvation phase. In contrast, the delta13C values and BMI were in phase: an increase in BMI resulted in an increase in the delta13C values. This rise in delta13C ratios is best interpreted by an increased supply of protein in the diet. Furthermore, delta15N and delta13C were inversely related. We conclude that hair, which is easily and non-traumatically sampled, is an adequate monitor that reflects dietary change and nitrogen balance within days. This isotopic method may also be applied in forensic studies with regard to cases of deprivation, and starvation, and may be a method for investigating starvation in historic populations.

Analysis of amino acid 13C abundance from human and faunal bone collagen using liquid chromatography/isotope ratio mass spectrometry

The scope of compound-specific stable isotope analysis has recently been increased with the development of the LC IsoLink which interfaces high-performance liquid chromatography (HPLC) and isotope ratio mass spectrometry (IRMS) to provide online LC/IRMS. This enables isotopic measurement of non-volatile compounds previously not amenable to compound-specific analysis or requiring substantial modification for gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS), which results in reduced precision. Amino acids are an example of such compounds. We present a new chromatographic method for the HPLC separation of underivatized amino acids using an acidic, aqueous mobile phase in conjunction with a mixed-mode stationary phase that can be interfaced with the LC IsoLink for compound-specific delta13C analysis. The method utilizes a reversed-phase Primesep-A column with embedded, ionizable, functional groups providing the capability for ion-exchange and hydrophobic interactions. Baseline separation of 15 amino acids and their carbon isotope values are reported with an average standard deviation of 0.18 per thousand (n = 6). In addition delta13C values of 18 amino acids are determined from modern protein and archaeological bone collagen hydrolysates, demonstrating the potential of this method for compound-specific applications in a number of fields including metabolic, ecological and palaeodietary studies.

A measuring system for the fast simultaneous isotope ratio and elemental analysis of carbon, hydrogen, nitrogen and sulfur in food commodities and other biological material

The isotope ratio of each of the light elements preserves individual information on the origin and history of organic natural compounds. Therefore, a multi-element isotope ratio analysis is the most efficient means for the origin and authenticity assignment of food, and also for the solution of various problems in ecology, archaeology and criminology. Due to the extraordinary relative abundances of the elements hydrogen, carbon, nitrogen and sulfur in some biological material and to the need for individual sample preparations for H and S, their isotope ratio determination currently requires at least three independent procedures and approximately 1 h of work. We present here a system for the integrated elemental and isotope ratio analysis of all four elements in one sample within 20 min. The system consists of an elemental analyser coupled to an isotope ratio mass spectrometer with an inlet system for four reference gases (N(2), CO(2), H(2) and SO(2)). The combustion gases are separated by reversible adsorption and determined by a thermoconductivity detector; H(2)O is reduced to H(2). The analyser is able to combust samples with up to 100 mg of organic material, sufficient to analyse samples with even unusual elemental ratios, in one run. A comparison of the isotope ratios of samples of water, fruit juices, cheese and ethanol from wine, analysed by the four-element analyser and by classical methods and systems, respectively, yielded excellent agreements. The sensitivity of the device for the isotope ratio measurement of C and N corresponds to that of other systems. It is less by a factor of four for H and by a factor of two for S, and the error ranges are identical to those of other systems.