Isotope Ratio Mass Spectrometry Research Articles

Application of isotope ratio mass spectrometry (IRMS) in the geographical determination of selected herbs: A review

Application of isotope ratio mass spectrometry (IRMS) in the geographical determination of selected herbs: A review

Impact of Repeated Glucocorticoid Oral Administration on the Urinary Steroid Profile.

The detection of endogenous anabolic androgenic steroids (EAAS) is performed with the Steroidal Module of the Athlete Biological Passport (ABP). Glucocorticoids (GC) could be a confounding factor to the ABP Steroidal Module because they inhibit the hypothalamic-pituitary-adrenal axis, and ABP metabolites have partial adrenal origin. In previous studies, single-dose systemic GC administrations have been shown to reduce the urinary ratios A/T and 5αdiol/E. In this work, the impact of repeated oral doses of GCs on the urinary steroid profile (SP) has been evaluated. The treatments administered consisted of multiple oral administrations of methylprednisolone (12 mg/24 h for 3 days, n = 8) and dexamethasone (2 mg/12 h for 5 days, n = 8). Urine samples were collected before, during, and after the GC treatments, and the SP was measured in all samples using gas chromatography-tandem mass spectrometry. The multiple-dose oral administration of GCs resulted in a treatment-dependent reduction of the excretion rates of some urinary metabolites (5αAdiol, A, and Etio) and the urinary SP ratios A/T and 5αAdiol/E. The T/E ratio was not significantly affected. Overall, although the consumption of GC could result in atypical profiles for A/T and 5αAdiol/E ratios, according to the cost/benefit assessment, GC should not be considered a confounding factor to the urinary SP because misunderstandings would only take place in very specific situations and, in those cases, the analysis by isotope ratio mass spectrometry of the urine triggering the atypical profile would demonstrate the endogenous origin of the SP metabolites.

Rapid High-Sensitivity Analysis of Methane Clumped Isotopes (Δ13CH3D and Δ12CH2D2) Using Mid-Infrared Laser Spectroscopy.

Mid-infrared laser absorption spectroscopy enables rapid and nondestructive analysis of methane clumped isotopes. However, current analytical methods require a sample size of 20 mL STP (0.82 mmol) of pure CH4 gas, which significantly limits its application to natural samples. To enhance the performance of spectroscopic measurement of methane clumped isotopes, we established a laser spectroscopic platform with newly selected spectral windows for clumped isotope analysis: 1076.97 cm-1 for 12CH2D2 and 1163.47 cm-1 for 13CH3D, and a custom-built gas inlet system. These spectral windows were identified through an extensive spectral survey on newly recorded high-resolution Fourier transform infrared (FTIR) spectra across the wavelength range of 870-3220 cm-1, thereby addressing gaps for 12CH2D2 in existing spectral databases. In addition, we implemented several key technological advances, which result in superior control and performance of sample injection and analysis. We demonstrate that for small samples ranging from 3 to 10 mL (0.12-0.41 mmol) of CH4 gas, a measurement precision comparable to high-resolution isotope ratio mass spectrometry for Δ12CH2D2 (∼1.5‰) can be achieved through 3 to 8 repetitive measurements using a recycle-refilling system within a few hours. Samples larger than 10 mL can be quantified in under 20 min. At the same time, for Δ13CH3D analysis a repeatability of 0.05‰, superior to mass spectrometry, was realized. These advancements in reducing sample size and shortening analysis time significantly improve the practicality of the spectroscopic technique for determining the clumped isotope signatures of natural methane samples, particularly for applications involving low CH4 concentrations or requiring consecutive analyses, which are feasible in conjunction with an automated preconcentration system.

Unveiling diversity in amino acid stable isotope profiles for classifying rice varieties, refining types and cultivation systems.

Isotope Ratio Mass Spectrometry (IRMS) is a promising tool in organic authentication cases. Premium-priced Italian rice varieties (Carnaroli, Arborio, Baldo) are used in cuisines worldwide for their unique qualitative properties. Organic authentication of rice by morphological assessment is unfeasible, while its market availability at different refining stages (brown, white) further increases the data variability. In this study, bulk and compound-specific (CS) - IRMS analysis of nine rice amino acids (AAs), by elemental analyser (EA) - IRMS and gas chromatography (GC) - combustion (C) - IRMS, respectively, were applied in order to explore their organic authentication potential in cases involving different rice varieties and refining types. The individual and interactive effects of the different variables were assessed on the δ13CAAs, δ15NAAs, δ13Cbulk and δ15Nbulk, and the sample classification was attempted by linear discriminant analysis (LDA) and decision tree analysis (DTA). Organic authentication of brown rice was achieved by CS-IRMS. Generic rice was differentiated from all Italian organic and conventional varieties (δ15Nleucine<2.5‰). The δ13C values of glutamic acid, glycine, phenylalanine and proline, significantly contributed to the complete LDA separation of conventional Arborio, conventional Carnaroli and organic Carnaroli samples. This study showcases the interplay between refining type, variety and cultivation, which should be considered in cases of organic authentication by IRMS methods.

Recent uses and applications of nuclear magnetic resonance, isotope ratio mass spectrometry and high-resolution mass spectrometry for authenticity and geographical origin of wines

Recent uses and applications of nuclear magnetic resonance, isotope ratio mass spectrometry and high-resolution mass spectrometry for authenticity and geographical origin of wines

A simple and cost-effective sample preparation and storage method for stable isotope analysis of atmospheric CO2 for GasBench II/continuous flow isotope ratio mass spectrometry.

The stable isotope compositions of atmospheric CO2 can provide useful insight into various geochemical processes and carbon cycles on Earth, which is critical for understanding of Earth's changing climate. Here, we present a simple and cost-effective analytical method for the collection and measurement of carbon and oxygen isotope compositions of atmospheric CO2. Air samples of ~150 mL were collected individually or collectively using our simple active air collection system and then extracted on a vacuum purification line to remove noncondensable gases and atmospheric water vapor. The efficiency of removing atmospheric water vapor was tested by using a magnesium perchlorate desiccant trap and a dry ice/ethanol trap. Lastly, a "J-Cut tube sealing/cracking method" was developed to store and transfer purified atmospheric CO2 to the GasBench II and CF-IRMS system for δ13C and δ18O measurements. The collective active air collection method combined with the full sample air extraction method for a 3-min transfer time or "Full 3m TE" yields the best analytical precision of 0.07‰ (δ13C) and 0.04‰ (δ18O). Removing atmospheric water vapor from air samples is not necessary for δ13C, but essential for δ18O measurements. The J-Cut tube sealing/cracking method shows a near 100% effectiveness for the storage and transfer of atmospheric or any CO2. A simple and cost-effect method was developed for the collection, purification, storage, and isotopic analysis of indoor/outdoor atmospheric CO2 samples for general users. This method utilizes a popular headspace gas sample preparation system for CF-IRMS and an easy-to-build vacuum purification line without involving complex and high-cost devices for the preparation of atmospheric CO2.

Compound-Specific Isotope Analysis as a Potential Approach for Investigation of Cerebral Accumulation of Docosahexaenoic Acid: Previous Milestones and Recent Trends.

Docosahexaenoic acid (DHA, C22:6 n-3), a predominant omega-3 polyunsaturated fatty acid in brain, plays a vital role in cerebral development and exhibits functions with potential therapeutic effects (synaptic function, neurogenesis, brain inflammation regulation) in neurodegenerative diseases. The most common approaches of studying the cerebral accretion and metabolism of DHA involve the use of stable or radiolabeled tracers. Although these methods approved kinetic modeling of ratios and turnovers for fatty acids, they are associated with excessive costs, restrictive studies, and singular dosing effects. Compound-specific isotope analysis (CSIA) is recognized as a cost-effective alternative approach for investigating DHA metabolism in vitro and in vivo. This method involves determining variations in 13C content to identify the sources of specific compounds. This review comprehensively discusses a summary of different methods and recent advancements in CSIA application in studying DHA turnover in brain. Following, the ability and applications of CSIA by using gas-chromatography combined with isotope ratio mass-spectrometry to differentiate between natural endogenous DHA in brain and exogenous DHA are also highlighted. In general, the efficiency of CSIA has been demonstrated in utilizing natural 13C enrichment to distinguish between the incorporation of newly synthesized or pre-existing DHA into the brain and other body tissues, eliminating the need of tracers. This review provides comprehensive knowledge, which will have potential applications in both academia and industry for advancing the understanding in neurobiology and enhancing the development of nutritional strategies and pharmaceutical interventions targeting brain health.

Large-Volume Injection and Assessment of Reference Standards for n-Alkane δD and δ13C Analysis via Gas Chromatography Isotope Ratio Mass Spectrometry.

Compound-specific stable isotope analysis of hydrogen (δD) and carbon (δ13C) in organic compounds is a valuable tool in biogeochemical research. A key limitation of this method is the relatively large amount of sample required to achieve desirable precision. We developed a large-volume (20 μL) injection method that allows for high throughput analysis of less concentrated samples and tested it for δ13C and δD measurements of n-alkanes. We also conducted a comparison of reference standards and assessed several methods to normalize and correct n-alkane δD and δ13C measurements. The mean precision of the δD method based on 233 environmental n-alkane samples (two to three replications per sample) is 4.0‰ (1σ, estimated from the weighted mean of the pooled unbiased standard deviations) and 0.46‰ (1σ) for δ13C from 37 environmental samples (two to three replications per sample). The evaluation of reference standards shows that the use of n-alkane standards with large offsets in δD values in adjacent n-alkane chains can lead to biases in measurement correction. The large-volume injection method shows good reproducibility of δ13C and δD measurements of n-alkanes and reduces the required sample concentration by about 80%. We propose that for δD measurements, a reference standard set should be used in which each reference standard has a limited range of δD values and no adjacent n-alkane chains, to minimize memory effects.

Using stable oxygen isotope dual-inlet isotope-ratio mass spectrometry to elucidate uranium transport and mixed 230Th/U calcite formation ages at the seminal Devils Hole, Nevada, natural laboratory.

Vein calcite in Devils Hole has been precipitating continuously in oxygen-isotope equilibrium at a constant temperature for over 500 000years, providing an unmatched δ18O paleoclimate time series. A substantial issue is that coeval calcite (based on matching δ18O values) has uranium-series ages differing by 12 000years. An unparalleled high-accuracy δ18O chronology series from continuously submerged calcite was used to correct the published uranium-series ages of non-continuously formed calcite in two cores, cyclically exposed by water-table decline during glacial-interglacial transitions. This method relies on the premise that the δ18O values of coevally precipitated calcite are identical, allowing matching calcite δ18O values to establish formation ages. Exposed calcite can have apparent ages that are 12 000years too young due to unrecognized uranium mobility and resulting mixed ages identified in over 50 mixed uranium-series ages from previous studies. Secondary uranium in fluids, sourced from the formation or dissolution of porous carbonate deposits (folia) with high uranium-238 (238U) concentrations, has migrated up to 10mm into vein calcite. The continuously submerged Devils Hole δ18O chronology is not explained by orbital forcing. Rather, this chronology represents a regional climate record in the southern Great Basin of sea-surface-temperature (SST) variations off California, variations that preceded the last and penultimate deglaciations by 5000 to approximately 10 000years. Temporal discrepancies between the continuously submerged Devils Hole chronology and other regional δ18O records (e.g., the Leviathan chronology) can be explained by unrecognized cryptic, pernicious uranium mobility, leading to model estimations that may be thousands of years younger than actual ages. Consequently, paleo-moisture availability, water-table, and groundwater recharge models based on these mixed uranium-series ages are too young by as much as 12 000years. The potential for post-formation uranium addition in subaerial cores and speleothems underscores the need for caution in uranium-series dating, highlighting δ18O time-series comparisons as a method for identifying mixed ages.

Supporting a more sustainable future for determining the bio-carbon content of products from the co-processing of bio-based feedstock

Renewable fuels have been widely developed in recent decades. Products derived from the processing of biological feedstocks have a lower carbon footprint than conventional petroleum products due to the absorption of carbon dioxide during the cultivation phase. Technologies for co-processing petroleum and renewable feedstocks are of particular interest due to their ease of integration into refineries. However, renewable feedstocks are not necessarily allocated to products according to the material balance of processing products separately. There is a problem in determining which part of the renewable carbon has gone into which fractions. This paper provides a comparative description of the methods for determining bioorganic carbon in petroleum products. The article considers the accuracy, technical and technical-economic parameters of both standardized and experimental methods for determining the biocarbon content. The Alpha Magnetic Spectrometer (AMS) method is characterized by high accuracy and a shorter analysis time. However, the cost of the necessary equipment is significantly higher than that of other methods. The Liquid-Solid Chromatography (LSC) method is less precise and more cost-effective but requires a longer analysis time. The Isotope-Ratio Mass Spectrometry (IRMS) method offers a combination of the advantages, yet it is constrained by notable limitations in terms of the identified feedstocks. An assessment of the possibility of introducing such methods at enterprises engaged in co-processing is given, as a result of which the most optimal method for determining biocarbon is the direct LSC method.

Associations of Food Group Intakes with Serum Carbon Isotope Ratio Values in Youth: Results from 2 Prospective Pediatric Cohort Studies

BackgroundThe carbon isotope ratio (CIR) is a candidate biomarker for sugar-sweetened beverage (SSB) intake in the United States. However, research specific to youth, who differ in their physiology and dietary patterns compared with adults, is lacking. ObjectivesWe evaluated longitudinal associations of SSB intakes across childhood/adolescence with serum CIR. We also explored the relationship between other dietary intakes and serum CIR. MethodsData were from participants in two longitudinal, pediatric cohorts in Colorado: Exploring Perinatal Outcomes among CHildren (EPOCH) study (visits at median 10 and 16 y, n = 150) and Healthy Start Study (visits at median 5 and 9 y, n = 166). Serum CIR was measured using isotope ratio mass spectrometry. Diet was assessed by food-frequency questionnaires (EPOCH) or 24-h diet recalls (Healthy Start). We assessed associations of longitudinal dietary intakes (log2-transformed, standardized) with serum CIR using linear mixed models adjusted for age, sex, and energy intake, and associations of change values between visits using linear regression models. ResultsIn linear mixed models, higher SSB intake across visits was associated with higher serum CIR in both cohorts [β (95% confidence interval (CI)): 0.11 (0.06, 0.15) in EPOCH and 0.14 (0.07, 0.21) in Healthy Start]. Higher meat intake and a higher dietary animal protein ratio were also positively associated with serum CIR in both cohorts [β (95% CI): 0.08 (0.05, 0.12) and 0.18 (0.13, 0.23) in EPOCH; 0.08 (0.01, 0.16) and 0.28 (0.21, 0.35) in Healthy Start]. In change analyses, there were positive associations for changes in the dietary animal protein ratio between visits with changes in serum CIR in both cohorts, but not for changes in SSB intake. ConclusionsOur findings support serum CIR as a potential biomarker of SSB intake in youth cross-sectionally; however, there was not a strong link between change values over longer-term follow-up. Meat/animal protein intake was also consistently and, at times, more strongly associated with serum CIR.

Authenticating the Geographical Origin of Jingbai Pear in Northern China by Multiple Stable Isotope and Elemental Analysis.

The Jingbai pear is one of the best pear species in China with high quality and nutrition values which are closely linked to its geographical origin. With the purpose of discriminating the PGI Mentougou Jingbai pear from three other producing regions, the stable isotope ratios and elemental profiles of the pears (n = 52) and the corresponding soils and groundwater were determined using isotope ratio mass spectrometry (IRMS) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. The results revealed that δ15N, δ18OJ, and Li were significantly different (p < 0.05) in samples from different regions, which indicated their potential to be used in the geographical origin classification of the Jingbai pear. The nitrogen isotopic values of the pear pulp were positively correlated with the δ15N value and nitrogen content of the corresponding soils, whilst the B, Na, K, Cr, and Cd contents of the pear pulps were positively correlated with their corresponding soils. Orthogonal partial least squares discriminant analysis (OPLS-DA) was performed in combination with analysis of the stable isotopes and elemental profiles, making it possible to distinguish the cultivation regions from each other with a high prediction accuracy (a correct classification rate of 92.3%). The results of this study highlight the potential of stable isotope ratios and elemental profiles to trace the geographical origin of pears at a small spatial scale.

Magnesite hosted by the Neoarchean ultramafic rocks in Attappadi, southern India: Insights from spectral and stable isotope investigation

Magnesite is an economically important mineral commonly found in ultramafic complexes worldwide, primarily in Archean to Proterozoic ultramafic complexes. This study focuses on the chemical and spectral characterization of magnesite found in the Neoarchean ultramafic rocks in the Attappadi region in the Southern Granulite Terrane of southern India. The research utilizes x‐ray diffraction analysis, hyperspectral, laser Raman, Fourier Transform Infrared, and Isotope Ratio Mass Spectrometry. The studied ultramafic rocks are part of a well‐exposed ophiolitic suite known as the Agali ophiolitic complex. Magnesite primarily occurs as veins, veinlets, and lenses within weathered ultramafic rocks. The hyperspectral analysis of the magnesite samples shows absorption bands in the shortwave infrared region, particularly around 2.3 and 2.5 μm, which correspond to the stretching and bending of the CO bond in the (CO3)2− ion in MgCO3. The laser Raman spectra show intensity peaks at 1095, 738, and 330 cm−1, which may be attributed to the translational and librational vibrations. The Fourier transform infrared data reveal transmittance at 1434, 880, and 747 cm−1, corresponding to MgO bond stretching and asymmetrical CO stretching. The x‐ray powder diffraction spectra exhibit diffraction peaks at 32°, 35°, 42°, 46° and 53°, characteristic of pure magnesite. The spectroscopic parameters derived from various analyses indicate that the magnesite is high quality and free from gangue minerals. Stable isotope analysis of the magnesite samples yielded δ13C values ranging from −5‰ to −9‰ and δ18O values in the range of 21‰–25‰. The estimated water temperature from which the magnesite has been precipitated is ~59 ± 3.9°C. Based on the field relations, mode of occurrence and isotopic signatures, the mineralization is considered to have been formed by the low‐temperature alteration of ultramafic rocks facilitated by CO2‐rich fluids in the near‐surface environment. This study compares the characteristics of magnesite from the study area with a few Neoproterozoic serpentinite‐hosted magnesite veins in the ophiolitic sequence of the Egyptian Eastern Desert, which is part of the Arabian Nubian shield. The research aims to contribute to understanding magnesite formation in Archaean to Proterozoic mafic–ultramafic rocks on the Earth's crust. It also provides insights into the geological processes that govern the genesis of ultramafic‐hosted magnesite globally, particularly in East Gondwana fragments. This information can enhance mineral exploration and resource evaluation in these regions, helping to identify economic prospects and assess the feasibility of magnesite resource extraction and utilization in East Gondwana fragments.

Анализ отношений стабильных изотопов легких элементов в отдельных компонентах мёда

Honey possesses excellent sensory and nutritional properties, which makes it a valuable food ingredient. However, the same qualities make it one of the most often adulterated products in the world. Constant violations of processing technology threaten the beekeeping industry. In this regard, new authenticity criteria are a popular area of honey studies. The article introduces a method for establishing ratios of light stable isotopes in honey. The study featured 36 samples of honey of various geographical origins and botanical profiles, as well as five samples of sugar syrups from various raw materials. The quantitative profiles were obtained using a Delta Advantage V isotope mass spectrometer (USA – Germany) with additional Flash IRMS and Conflo IV modules. The experiment involved the ratios of stable carbon isotopes in honey δ13C (gross) and nitrogen δ15N in its protein fraction, as well as the values of δ13C, δ18O, and δ2H of ethanol isolated from fermented honey. The values of δ13C (gross) and δ13C of honey proteins made it possible to calculate the amount of added sugar of corn and cane origin. Exogenous sugars in the amounts of 6.5% and 18% cane sugar were detected in two samples. Isotope mass spectrometry was able to identify honey samples with exogenous sugars of C4-plant origin. However, the method failed to detect sugar-containing substances from C3-type plants. The δ18O index demonstrated some prospects as an identification criterion for sugars from C3-plants in honey. Nitrogen isotope ratios in honey proteins proved to be an efficient tool for determining honey authenticity and an additional criterion for identifying bee products. The research resulted in a patent (RU2809285C1) for a new method of determining exogenous sugar-containing substances in honey

Establishment of a method for cultivating tomatoes using the method of isotope mass spectrometry

Establishment of a method for cultivating tomatoes using the method of isotope mass spectrometry

Effects of inhibitors and slit incorporation on NH3 and N2O emission processes after urea application

The use of urea fertilizers in agriculture is associated with many negative environmental impacts and is a source of ammonia (NH3) and nitrous oxide (N2O) emissions. Such losses from urea fertilizer can be avoided by different mitigation techniques. Three different mitigation principles, urease inhibitor (N-(2-Nitrophenyl) phosphoric triamide, 2-NPT) (UI) alone and urease inhibitor in combination with nitrification inhibitors (N-[3(5)-methyl-1 H-pyrazol-1-yl) methyl] acetamide, MPA) (NI) and closed slit incorporation of urea fertilizer into the soil, were compared on a sandy loam soil at a soil water level of 70 % water-holding capacity. An in vitro microcosm approach with open dynamic incubation chambers was used to monitor NH3 emissions over two weeks with NH3 sampling by washing bottles. N2O emissions were studied over ten weeks in slow throughflow mesocosms with continuous gas chromatographic (GC) measurements. To get insights into N2O production and consumption processes, gas samples were taken after six weeks and N2O isotopocules were analyzed by isotope ratio mass spectrometry (IRMS). Slit injection showed the greatest effect on NH3 emission reduction by 79.6 % (40.6 % by UI, and 46.7 % by UINI) compared to surface applied urea. Minor pollution swapping to N2O was observed at the beginning of the trial due to incorporation but not in the cumulative emissions over the entire incubation time. The reduction effect of UINI on N2O emissions decreased over time with no cumulative emission reduction at the end of experimentation. N2O isotopocules confirmed the high contribution of nitrification to N2O production. In contrast and bacterial denitrification, nitrifier denitrification and fungal denitrification were involved on a much lower level and N2O reduction to N2 was not pronounced. All NH3 mitigation measurements where effective to decrease NH3 emissions while their effects on N2O emission varied over time. Factors as crop N uptake and rainfall would further modify the overall effect on N2O emissions and need to be considered for final pollution swapping assessment. Further research on the impact of NI on non-target microbial communities is warranted to elucidate potential environmental consequences and long-term efficacy of inhibitor compounds.

Improving the Determination of Carbon Isotope Ratios of Endogenous Steroids Found in Human Serum.

The determination of serum concentrations of testosterone (T) and 4-androstenedione (A4) was implemented into the steroidal module of the Athlete Biological Passport in 2023. Monitoring T, A4, and the ratio of T/A4 in a longitudinal manner enables the detection of the misuse of low-dose T administrations especially in female athletes, whereas urinary markers of the steroid profile may not be influenced significantly. In contrast to the urinary steroid profile, knowledge on confounding factors regarding serum concentrations of T and A4 is yet comparably scarce, and corroborating exogenous sources of the target analytes by isotope ratio mass spectrometry (IRMS) is desirable. In a recent study, it was demonstrated that carbon isotope ratios (CIRs) of serum steroids can be determined if analyte concentrations permit. The therein-employed method utilized 2D-GC/IRMS, and only a limited number of potential endogenous reference compounds were available. The here-presented approach uses complementary analyte purification strategies, addressing previous limitations. A high-performance liquid chromatography cleanup was developed and fully validated for serum steroids in order to enable all doping control laboratories to potentially implement this method alongside existing protocols for urinary steroids. Besides the already-investigated endogenous steroids cholesterol, dehydroepiandrosterone sulfate, androsterone sulfate, and epiandrosterone sulfate, two additional steroids were included in the test menu, namely, pregnenolone sulfate and 5-androstene-3β,17β-diol sulfate. Serum steroid concentrations down to 25 ng/mL were found to allow robust CIR determinations, and a reference population encompassing 124 male and female athlete samples was investigated to enable the calculation of population-based thresholds for all relevant steroid combinations.

Isotopic Composition of C, N, and S as an Indicator of Endometrial Cancer.

The metabolic pathway of cancerous tissue differs from healthy tissue, leading to the unique isotopic composition of stable isotopes at their natural abundance. We have studied if these changes can be developed into diagnostic or prognostic tools in the case of endometrial cancer. Measurements of stable isotope ratios were performed using isotope ratio mass spectrometry for nitrogen, carbon, and sulfur isotopic assessment. Uterine tissue and serum samples were collected from patients and the control group. At a natural abundance, the isotopic compositions of all three of the studied elements of uterus cancerous and healthy tissues are different. However, no correlation of the isotopic composition of the tissues with that of serum was found. Differences in the isotopic composition of the tissues might be a potential prognostic tool. However, the lack of a correlation between the differences in the isotopic composition of the tissues and serum seems to exclude their application as diagnostic biomarkers, which, however, might be possible if a position-specific isotopic analysis is performed.

PSIX-13 Methionine requirements across the life cycle of working Labrador Retrievers using the indicator amino acid oxidation (IAAO) technique

Abstract Methionine is a limiting amino acid in canine diets, but few requirement studies have been conducted across life stages in large-breed dogs. The objective of this study was to determine the minimum requirement (MR) for methionine (Met) in Labrador retrievers at 4 life stages using the indicator amino acid (AA) oxidation (IAAO) technique. In total, 24 dogs were used: 6 puppies aged 10 to 14 wk, 6 puppies aged 14 wk to 9 mo, 6 adults aged 2 to 5 yr, and 6 seniors aged over 8 yr in feeding studies to evaluate the changing requirements of methionine (Met) as canines age. After 2-d adaptation to Met-adequate basal diet (Met = 0.56% dry matter), dogs underwent individual IAAO studies. In brief, all dogs were randomly fed one of six test diets with varying levels of Met ranging from deficient to sufficient (final Met content in experimental diets was 0.1982, 0.2386, 0.279, 0.49, 0.525, 0.56% dry matter, with indispensable amino acids formulated at 1.6x NRC values. Test diet was divided into 13 equal meals; at the 5th meal, a tracer amino acid was supplied (a bolus L-[1-13C]phenylalanine based on body weight was first given, followed by [1-13C]Phe doses every 30 min spanning a 4-h period), and breath samples were collected via respiration mask every 30 min. Total production of 13CO2 during isotopic steady state was determined by enrichment of 13CO2 in breath samples and total CO2 production measured via indirect calorimetry and isotope ratio mass spectrometry (IRMS). Results for IRMS were converted to atom percent excess (APE) and analyzed using segmented linear regression. The Four Rivers mean and population requirements for Met were estimated to be 0.84 ± 0.05 g/1000 kcal (mean ± 2SD) for puppies 10 to 14 wk, 0.78 ± 0.16 g/1,000kcal (mean ± 2SD) for puppies 14 wk to -9 mo, 0.68 ± 0.19 g/1,000kcal (mean ± 2SD) for adults 2 to 5 yr, and 0.62 ± 0.17 g/1,000kcal (mean ± 2SD) for seniors. This research provides important information to assist in accurate formulation of diets that contain appropriate methionine for large breed dogs at all life stages.

PSLBI-17 Total sulfur amino acid requirements across the canine life cycle in Labrador Retrievers using the indicator amino acid oxidation (IAAO) technique

Abstract Methionine and cysteine are the principal sulfur-containing amino acids that are incorporated into proteins, although homocysteine and taurine also have important physiological roles in canines. As limited studies have been conducted for total sulfur-containing amino acids (TSAA) requirements across the canine life cycle, our objective was to determine the minimum requirements (MR) for TSAA at 4 life stages using the indicator amino acid oxidation (IAAO) technique. Labrador Retrievers (n = 24) were used in feeding studies to evaluate the changing requirements of TSAA as dogs mature: 6 puppies aged 10 to 14 wk, 6 puppies &amp;gt;14 wk to 9 mos, 6 adults 2 to 5 yr (yr), and 6 seniors &amp;gt; 8yr. Following a 2-d adaptation to a TSAA-adequate basal diet (TSAA = 1.12% dry matter), dogs underwent individual IAAO studies. In brief, all dogs were randomly fed one of six test diets with varying levels of TSAA ranging from deficient to sufficient (final TSAA content in experimental diets were 0.41, 0.46, 0.51, 0.98, 1.05, and 1.12% dry matter, with indispensable amino acids formulated at 1.6x NRC values). The test diet was divided into 13 equal meals; at the 5th meal, a tracer amino acid was included (a bolus L-[1-13C] phenylalanine based on body weight was first given, followed by [1-13C] Phe doses every 30 spanning 4 h). Breath samples were collected via a respiration mask every 30 min. Total CO2 production was determined via indirect calorimetry and production of 13CO2 at each dose was measured by enrichment of 13C in breath samples via isotope ratio mass spectrometry (IRMS). Results for IRMS data were converted to atom percent excess (APE) and analyzed using segmented linear regression. The Four Rivers mean and population requirements for TSAA were estimated to be 1.55 ± 0.069 g/1,000 kcal (mean ± 2 SD) for puppies 10 to 14 wk, 1.53 ± 0.21 g/1,000 kcal (mean ± 2 SD) for puppies 14 wk to 9 mo, 1.4 ± 0.30 g/1000 kcal (mean ± 2 SD) for adults 2 to 5 yr, and 1.27 ± 0.23 g/1,000 kcal (mean ± 2 SD) for seniors. These results may contribute to the formulation of diets that meet the age-appropriate requirements of TSAA for large-breed dogs at all life stages.