{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T15:55:55Z","timestamp":1790697355040,"version":"4.1.0"},"reference-count":90,"publisher":"American Chemical Society (ACS)","issue":"38","license":[{"start":{"date-parts":[[2026,9,14]],"date-time":"2026-09-14T00:00:00Z","timestamp":1789344000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"DOI":"10.13039\/100011033","name":"Thermo Fisher Scientific","doi-asserted-by":"publisher","id":[{"id":"10.13039\/100011033","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100013935","name":"Partnership for Clean Competition","doi-asserted-by":"publisher","id":[{"id":"10.13039\/100013935","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,9,29]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>Compound-specific stable isotope analysis (CSIA) is widely used to distinguish sources and transformation pathways of organic compounds. In steroid CSIA each analyte is represented by a single molecular-average isotope value, which can limit discrimination when sources overlap in isotopic composition. This limitation is especially important in anti-doping analysis, where molecular-average \u03b413C measurements can be inconclusive for compounds whose C-isotope composition falls within the endogenous range. Here, we present an Orbitrap-based method for fragment-resolved intramolecular isotope analysis of steroids. Using urinary androsterone as a model analyte, we measured \u03b413C values for four diagnostic ions and \u03b4D for one fragment following controlled administration of androstenedione and testosterone undecanoate. The resulting multidimensional isotope fingerprints reveal responses not evident from bulk \u03b413C measurements alone, including cases in which administered androgen lies near the endogenous \u03b413C range. Time-dependent differences among fragment ions further suggest sensitivity to changes in metabolic routing and pool mixing during steroid transformation. These results establish fragment-resolved isotope analysis by Orbitrap mass spectrometry as a promising extension of conventional steroid CSIA and a potential new tool for forensic steroid source discrimination, with possible applications to environmental steroids and geological sterols and steranes.<\/jats:p>","DOI":"10.1021\/acs.analchem.6c03178","type":"journal-article","created":{"date-parts":[[2026,9,15]],"date-time":"2026-09-15T04:01:51Z","timestamp":1789444911000},"page":"28201-28217","source":"Crossref","is-referenced-by-count":0,"title":["Fragment-Resolved\nCarbon and Hydrogen Isotope Analysis\nof Urinary Steroids by Orbitrap Mass Spectrometry"],"prefix":"10.1021","volume":"98","author":[{"ORCID":"https:\/\/orcid.org\/0009-0005-2618-9491","authenticated-orcid":true,"given":"Lubna","family":"Shawar","sequence":"first","affiliation":[{"name":"California Institute of Technology , , , ,","place":["Pasadena, California, United States, 91125"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thomas","family":"Piper","sequence":"additional","affiliation":[{"name":"German Sport University Cologne , , Am Sportpark Mu\u0308ngersdorf 6 , ,","place":["Ko\u0308ln, Germany, 50933"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"John M.","family":"Eiler","sequence":"additional","affiliation":[{"name":"California Institute of Technology , , , ,","place":["Pasadena, California, United States, 91125"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"316","published-online":{"date-parts":[[2026,9,14]]},"reference":[{"issue":"4","key":"2026092909095819900_cit1","doi-asserted-by":"publisher","first-page":"304","DOI":"10.1002\/rcm.1290080404","article-title":"Gas Chromatography\/Combustion\/Isotope-Ratio Mass Spectrometry Analysis\nof Urinary Steroids to Detect Misuse of Testosterone in Sport","volume":"8","author":"Becchi","year":"1994","journal-title":"Rapid Commun. Mass Spectrom."},{"issue":"2","key":"2026092909095819900_cit2","doi-asserted-by":"publisher","first-page":"83","DOI":"10.1016\/0146-6380(86)90089-6","article-title":"A Review\nof Sterol Markers for Marine and Terrigenous Organic Matter","volume":"9","author":"Volkman","year":"1986","journal-title":"Org. Geochem."},{"issue":"3","key":"2026092909095819900_cit3","doi-asserted-by":"publisher","first-page":"379","DOI":"10.1016\/j.steroids.2008.11.004","article-title":"Carbon\nIsotope Ratio (delta13C) Values of Urinary Steroids for Doping Control\nin Sport","volume":"74","author":"Cawley","year":"2009","journal-title":"Steroids"},{"issue":"7","key":"2026092909095819900_cit4","doi-asserted-by":"publisher","first-page":"854","DOI":"10.1002\/jms.1437","article-title":"The Application of\nCarbon Isotope Ratio Mass Spectrometry\nto Doping Control","volume":"43","author":"Cawley","year":"2008","journal-title":"J. Mass Spectrom."},{"issue":"4","key":"2026092909095819900_cit5","doi-asserted-by":"publisher","first-page":"645","DOI":"10.1016\/S0731-7085(00)00452-0","article-title":"13C\/12C Isotope Ratio MS Analysis of Testosterone,\nin Chemicals and Pharmaceutical Preparations","volume":"24","author":"de la Torre","year":"2001","journal-title":"J. Pharm. Biomed. Anal."},{"issue":"2","key":"2026092909095819900_cit6","doi-asserted-by":"publisher","first-page":"65","DOI":"10.1002\/dta.15","article-title":"13C\/12C Ratios\nof Endogenous Urinary Steroids Investigated for Doping Control Purposes","volume":"1","author":"Piper","year":"2009","journal-title":"Drug Test. Anal."},{"issue":"7","key":"2026092909095819900_cit7","doi-asserted-by":"publisher","first-page":"877","DOI":"10.1002\/jms.1457","article-title":"Factors Influencing\nthe Steroid Profile in Doping Control Analysis","volume":"43","author":"Mareck","year":"2008","journal-title":"J. Mass Spectrom. JMS"},{"issue":"Suppl 1","key":"2026092909095819900_cit8","doi-asserted-by":"publisher","first-page":"i21","DOI":"10.1136\/bjsm.2006.027482","article-title":"Testosterone and Doping\nControl","volume":"40","author":"Saudan","year":"2006","journal-title":"Br. J. Sports\nMed."},{"issue":"12","key":"2026092909095819900_cit9","doi-asserted-by":"publisher","first-page":"897","DOI":"10.1002\/dta.1378","article-title":"Complementary Stable\nCarbon Isotope Ratio and Amount\nof Substance Measurements in Sports Anti-Doping","volume":"4","author":"Cawley","year":"2012","journal-title":"Drug Test. Anal."},{"issue":"12","key":"2026092909095819900_cit10","doi-asserted-by":"publisher","first-page":"893","DOI":"10.1002\/dta.1399","article-title":"Isotope Ratio\nMass Spectrometry - History and Terminology in Brief","volume":"4","author":"Flenker","year":"2012","journal-title":"Drug Test. Anal."},{"issue":"3","key":"2026092909095819900_cit11","doi-asserted-by":"publisher","first-page":"514","DOI":"10.1002\/dta.3120","article-title":"Investigations in Carbon\nIsotope Ratios of Seized Testosterone\nand Boldenone Preparations","volume":"14","author":"Piper","year":"2022","journal-title":"Drug Test. Anal."},{"key":"2026092909095819900_cit12","doi-asserted-by":"publisher","first-page":"403","DOI":"10.1016\/bs.mie.2017.07.013","article-title":"Applications of Isotope\nRatio Mass Spectrometry in\nSports Drug Testing Accounting for Isotope Fractionation in Analysis\nof Biological Samples","volume":"596","author":"Piper","year":"2017","journal-title":"Methods Enzymol."},{"key":"2026092909095819900_cit13","doi-asserted-by":"publisher","first-page":"126","DOI":"10.1016\/j.ijms.2017.10.002","article-title":"Analysis of\nMolecular Isotopic Structures at High Precision and Accuracy by Orbitrap\nMass Spectrometry","volume":"422","author":"Eiler","year":"2017","journal-title":"Int. J. Mass Spectrom."},{"key":"2026092909095819900_cit14","doi-asserted-by":"publisher","first-page":"32","DOI":"10.1016\/j.orggeochem.2019.06.002","article-title":"Isotope Heterogeneity\nin Ethyltoluenes from Australian Condensates, and Their Stable Carbon\nSite-Specific Isotope Analysis","volume":"135","author":"Cesar","year":"2019","journal-title":"Org. Geochem."},{"issue":"2","key":"2026092909095819900_cit15","doi-asserted-by":"publisher","first-page":"1092","DOI":"10.1021\/acs.analchem.1c04141","article-title":"Simultaneous,\nHigh-Precision Measurements of \u03b42H and \u03b413C in Nanomole\nQuantities of Acetate Using Electrospray Ionization-Quadrupole-Orbitrap\nMass Spectrometry","volume":"94","author":"Mueller","year":"2022","journal-title":"Anal. Chem."},{"issue":"18","key":"2026092909095819900_cit16","doi-asserted-by":"publisher","DOI":"10.1002\/rcm.9347","article-title":"Position-Specific Carbon Isotope\nAnalysis of Serine by Gas Chromatography\/Orbitrap Mass Spectrometry,\nand an Application to Plant Metabolism","volume":"36","author":"Wilkes","year":"2022","journal-title":"Rapid\nCommun. Mass Spectrom."},{"key":"2026092909095819900_cit17","doi-asserted-by":"publisher","first-page":"210","DOI":"10.1016\/j.gca.2023.06.010","article-title":"Position-Specific\nCarbon Isotopes\nof Murchison Amino Acids Elucidate Extraterrestrial Abiotic Organic\nSynthesis Networks","volume":"355","author":"Zeichner","year":"2023","journal-title":"Geochim. Cosmochim. Acta"},{"key":"2026092909095819900_cit18","doi-asserted-by":"publisher","DOI":"10.1016\/j.ijms.2022.116848","article-title":"Methods\nand Limitations of Stable\nIsotope Measurements via Direct Elution of Chromatographic Peaks Using\nGas Chromotography-Orbitrap Mass Spectrometry","volume":"477","author":"Zeichner","year":"2022","journal-title":"Int. J. Mass Spectrom."},{"issue":"8","key":"2026092909095819900_cit19","doi-asserted-by":"publisher","first-page":"2435","DOI":"10.1038\/s41596-024-00981-5","article-title":"A Guide to Precise Measurements of\nIsotope Abundance\nby ESI-Orbitrap MS","volume":"19","author":"Kantnerova\u0301","year":"2024","journal-title":"Nat. Protoc."},{"issue":"9","key":"2026092909095819900_cit20","doi-asserted-by":"publisher","first-page":"717","DOI":"10.1002\/dta.1416","article-title":"Investigations on Hydrogen\nIsotope Ratios of Endogenous Urinary Steroids: Reference-population-based\nThresholds and Proof-of-concept","volume":"4","author":"Piper","year":"2012","journal-title":"Drug Test.\nAnal."},{"issue":"14","key":"2026092909095819900_cit21","doi-asserted-by":"publisher","first-page":"2161","DOI":"10.1002\/rcm.3601","article-title":"Determination of 13C\/12C Ratios of\nEndogenous Urinary Steroids: Method Validation, Reference Population\nand Application to Doping Control Purposes","volume":"22","author":"Piper","year":"2008","journal-title":"Rapid Commun. Mass Spectrom."},{"issue":"3","key":"2026092909095819900_cit22","doi-asserted-by":"publisher","first-page":"369","DOI":"10.1016\/j.steroids.2008.10.001","article-title":"Steroid\nIsotopic Standards for Gas\nChromatography-Combustion Isotope Ratio Mass Spectrometry (GCC-IRMS)","volume":"74","author":"Zhang","year":"2009","journal-title":"Steroids"},{"issue":"26","key":"2026092909095819900_cit23","doi-asserted-by":"publisher","first-page":"9139","DOI":"10.1021\/acs.analchem.1c00944","article-title":"Exploring the Potential\nof Electrospray-Orbitrap for Stable Isotope Analysis Using Nitrate\nas a Model","volume":"93","author":"Hilkert","year":"2021","journal-title":"Anal. Chem."},{"issue":"1\u20133","key":"2026092909095819900_cit24","doi-asserted-by":"publisher","first-page":"234","DOI":"10.1016\/j.ijms.2010.11.001","article-title":"Characterization\nof Nonpolar Lipids\nand Selected Steroids by Using Laser-Induced Acoustic Desorption\/Chemical\nIonization, Atmospheric Pressure Chemical Ionization, and Electrospray\nIonization Mass Spectrometry","volume":"301","author":"Jin","year":"2011","journal-title":"Int. J. Mass Spectrom."},{"issue":"8","key":"2026092909095819900_cit25","doi-asserted-by":"publisher","first-page":"722","DOI":"10.1016\/S1044-0305(00)00135-5","article-title":"Electrospray\nand Atmospheric Pressure Chemical Ionization Tandem Mass Spectrometric\nBehavior of Eight Anabolic Steroid Glucuronides","volume":"11","author":"Kuuranne","year":"2000","journal-title":"J. Am. Soc. Mass Spectrom."},{"key":"2026092909095819900_cit26","doi-asserted-by":"publisher","first-page":"276","DOI":"10.1016\/j.ijms.2018.08.001","article-title":"Scanning\nthe Isotopic Structure of Molecules by Tandem\nMass Spectrometry","volume":"434","author":"Neubauer","year":"2018","journal-title":"Int. J. Mass Spectrom."},{"key":"2026092909095819900_cit27","doi-asserted-by":"publisher","DOI":"10.3389\/fendo.2022.1059473","article-title":"Anabolic\u2013Androgenic\nSteroids: How Do They Work and What Are the Risks?","volume":"13","author":"Bond","year":"2022","journal-title":"Front. Endocrinol."},{"issue":"8","key":"2026092909095819900_cit28","doi-asserted-by":"publisher","first-page":"3654","DOI":"10.1210\/jcem.86.8.7705","article-title":"Metabolism of Orally Administered\nAndrostenedione in\nYoung Men","volume":"86","author":"Leder","year":"2001","journal-title":"J. Clin. Endocrinol. Metab."},{"issue":"2","key":"2026092909095819900_cit29","doi-asserted-by":"publisher","first-page":"133","DOI":"10.17925\/EE.2022.18.2.133","article-title":"Testosterone Replacement Therapy: A Narrative Review\nwith a Focus on New Oral Formulations","volume":"18","author":"Bhat","year":"2022","journal-title":"TouchREVIEWS\nEndocrinol."},{"issue":"3","key":"2026092909095819900_cit30","doi-asserted-by":"publisher","first-page":"925","DOI":"10.1124\/jpet.103.052522","article-title":"Contribution of\nLymphatically Transported\nTestosterone Undecanoate to the Systemic Exposure of Testosterone\nafter Oral Administration of Two Andriol Formulations in Conscious\nLymph Duct-Cannulated Dogs","volume":"306","author":"Shackleford","year":"2003","journal-title":"J. Pharmacol. Exp.\nTher."},{"issue":"8","key":"2026092909095819900_cit31","doi-asserted-by":"publisher","first-page":"2515","DOI":"10.1210\/clinem\/dgaa238","article-title":"A New Oral\nTestosterone Undecanoate Formulation Restores Testosterone to Normal\nConcentrations in Hypogonadal Men","volume":"105","author":"Swerdloff","year":"2020","journal-title":"J. Clin.\nEndocrinol. Metab."},{"issue":"4","key":"2026092909095819900_cit32","doi-asserted-by":"publisher","first-page":"161","DOI":"10.1016\/j.jsbmb.2006.06.024","article-title":"Metabolism and Excretion of Anabolic\nSteroids in Doping Control\u2500New Steroids and New Insights","volume":"101","author":"Van Eenoo","year":"2006","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"2026092909095819900_cit33","doi-asserted-by":"publisher","DOI":"10.1155\/2012\/530121","article-title":"The 5 Alpha-Reductase\nIsozyme Family: A Review of Basic Biology and Their Role in Human\nDiseases","volume":"2012","author":"Azzouni","year":"2012","journal-title":"Adv. Urol."},{"key":"2026092909095819900_cit34","unstructured":"The Human Protein Atlas.\n          . Tissue expression of SRD5A1\u2500Summary\u2500The Human Protein\nAtlas, https:\/\/www.proteinatlas.org\/ENSG00000145545-SRD5A1\/tissue (accessed\nDec 16, 2025)."},{"key":"2026092909095819900_cit35","unstructured":"NCBI, H.\n          . HSD17B3 hydroxysteroid\n17-beta dehydrogenase 3 [Homo sapiens (human)]\u2500Gene\u2500NCBI, https:\/\/www.ncbi.nlm.nih.gov\/gene\/3293 (accessed Dec 16, 2025)."},{"key":"2026092909095819900_cit36","unstructured":"The Human Protein Atlas, H.\n          . Tissue expression of HSD17B3\u2500Summary\u2500The Human Protein\nAtlas, https:\/\/www.proteinatlas.org\/ENSG00000130948-HSD17B3\/tissue (accessed Dec 16, 2025)."},{"key":"2026092909095819900_cit37","doi-asserted-by":"publisher","DOI":"10.1016\/j.jsbmb.2019.105493","article-title":"Evaluation of 17\u03b2-Hydroxysteroid Dehydrogenase\nActivity Using Androgen Receptor-Mediated Transactivation","volume":"196","author":"Yazawa","year":"2020","journal-title":"J. Steroid Biochem. Mol. Biol."},{"issue":"11","key":"2026092909095819900_cit38","doi-asserted-by":"publisher","first-page":"13228","DOI":"10.3390\/molecules181113228","article-title":"11\u03b2-Hydroxyandrostenedione\nReturns to the Steroid Arena: Biosynthesis, Metabolism and Function","volume":"18","author":"Bloem","year":"2013","journal-title":"Molecules"},{"issue":"1","key":"2026092909095819900_cit39","doi-asserted-by":"publisher","DOI":"10.1038\/s41467-020-20675-2","article-title":"Crystal Structure\nof Steroid Reductase SRD5A Reveals Conserved Steroid Reduction Mechanism","volume":"12","author":"Han","year":"2021","journal-title":"Nat. Commun."},{"key":"2026092909095819900_cit40","doi-asserted-by":"publisher","first-page":"4","DOI":"10.1016\/j.mce.2017.08.016","article-title":"Intracrine Androgen\nBiosynthesis,\nMetabolism and Action Revisited","volume":"465","author":"Schiffer","year":"2018","journal-title":"Mol. Cell.\nEndocrinol."},{"issue":"23","key":"2026092909095819900_cit41","doi-asserted-by":"publisher","first-page":"17404","DOI":"10.1016\/S0021-9258(19)85349-8","article-title":"Characterization of Chinese Hamster\nOvary Cell Lines Expressing Human Steroid 5 Alpha-Reductase Isozymes","volume":"268","author":"Thigpen","year":"1993","journal-title":"J. Biol. Chem."},{"issue":"10","key":"2026092909095819900_cit42","doi-asserted-by":"publisher","first-page":"3640","DOI":"10.1073\/pnas.87.10.3640","article-title":"Structural and Biochemical\nProperties of Cloned and\nExpressed Human and Rat Steroid 5 Alpha-Reductases","volume":"87","author":"Andersson","year":"1990","journal-title":"Proc. Natl. Acad. Sci. U. S. A."},{"issue":"7","key":"2026092909095819900_cit43","doi-asserted-by":"publisher","first-page":"559","DOI":"10.1016\/S0039-128X(02)00005-3","article-title":"Effects\nof Androstenedione Administration on Epitestosterone Metabolism in\nMen","volume":"67","author":"Catlin","year":"2002","journal-title":"Steroids"},{"issue":"24","key":"2026092909095819900_cit44","doi-asserted-by":"publisher","first-page":"16830","DOI":"10.1074\/jbc.M801778200","article-title":"Crystal\nStructure of Human Liver Delta4-3-Ketosteroid 5beta-Reductase (AKR1D1)\nand Implications for Substrate Binding and Catalysis","volume":"283","author":"Di Costanzo","year":"2008","journal-title":"J. Biol. Chem."},{"issue":"51","key":"2026092909095819900_cit45","doi-asserted-by":"publisher","first-page":"13537","DOI":"10.1021\/bi801276h","article-title":"Crystal Structures\nof Human Delta4-3-Ketosteroid 5beta-Reductase (AKR1D1) Reveal the\nPresence of an Alternative Binding Site Responsible for Substrate\nInhibition","volume":"47","author":"Faucher","year":"2008","journal-title":"Biochemistry"},{"issue":"27","key":"2026092909095819900_cit46","doi-asserted-by":"publisher","first-page":"19548","DOI":"10.1016\/S0021-9258(18)41809-1","article-title":"Tissue Distribution\nand Kinetic Characteristics of\nRat Steroid 5 Alpha-Reductase Isozymes. Evidence for Distinct Physiological\nFunctions","volume":"267","author":"Normington","year":"1992","journal-title":"J. Biol. Chem."},{"key":"2026092909095819900_cit47","doi-asserted-by":"publisher","DOI":"10.1038\/s41467-020-19249-z","article-title":"Structure\nof Human Steroid 5\u03b1-Reductase 2 with the Anti-Androgen Drug\nFinasteride","volume":"11","author":"Xiao","year":"2020","journal-title":"Nat. Commun."},{"issue":"5","key":"2026092909095819900_cit48","doi-asserted-by":"publisher","first-page":"2135","DOI":"10.1172\/JCI117569","article-title":"17 Beta-Hydroxysteroid Dehydrogenase\nType 2: Chromosomal Assignment and Progestin Regulation of Gene Expression\nin Human Endometrium","volume":"94","author":"Casey","year":"1994","journal-title":"J. Clin. Invest."},{"issue":"5","key":"2026092909095819900_cit49","doi-asserted-by":"publisher","first-page":"485","DOI":"10.1042\/cs1010485","article-title":"17 Beta-Hydroxysteroid\nDehydrogenase\nType 2 Expression and Enzyme Activity in the Human Gastrointestinal\nTract","volume":"101","author":"Sano","year":"2001","journal-title":"Clin. Sci. London Engl. 1979"},{"key":"2026092909095819900_cit50","doi-asserted-by":"publisher","DOI":"10.1016\/j.jsbmb.2019.105439","article-title":"Human Steroid Biosynthesis,\nMetabolism and Excretion Are Differentially Reflected by Serum and\nUrine Steroid Metabolomes: A Comprehensive Review","volume":"194","author":"Schiffer","year":"2019","journal-title":"J. Steroid Biochem. Mol. Biol."},{"issue":"5","key":"2026092909095819900_cit51","doi-asserted-by":"publisher","first-page":"364","DOI":"10.1016\/j.steroids.2005.11.004","article-title":"Use of Isotope Ratio\nMass Spectrometry\nto Detect Doping with Oral Testosterone Undecanoate: Inter-Individual\nVariability of 13C\/12C Ratio","volume":"71","author":"Baume","year":"2006","journal-title":"Steroids"},{"key":"2026092909095819900_cit52","doi-asserted-by":"publisher","first-page":"377","DOI":"10.1146\/annurev.bi.58.070189.002113","article-title":"MULTIPLE\nISOTOPE EFFECTS ON ENZYME-CATALYZED REACTIONS","volume":"58","author":"O\u2019Leary","year":"1989","journal-title":"Annu. Rev. Biochem."},{"key":"2026092909095819900_cit53","doi-asserted-by":"publisher","first-page":"67","DOI":"10.1042\/bj3510067","article-title":"Human 3\u03b1-Hydroxysteroid\nDehydrogenase Isoforms (AKR1C1\u2013AKR1C4) of the Aldo-Keto Reductase\nSuperfamily: Functional Plasticity and Tissue Distribution Reveals\nRoles in the Inactivation and Formation of Male and Female Sex Hormones","volume":"351","author":"Penning","year":"2000","journal-title":"Biochem J"},{"issue":"11","key":"2026092909095819900_cit54","doi-asserted-by":"publisher","first-page":"10784","DOI":"10.1074\/jbc.M313308200","article-title":"Human Cytosolic\n3\u03b1-Hydroxysteroid Dehydrogenases of the Aldo-Keto Reductase\nSuperfamily Display Significant 3\u03b2-Hydroxysteroid Dehydrogenase\nActivity: IMPLICATIONS FOR STEROID HORMONE METABOLISM AND ACTION *","volume":"279","author":"Steckelbroeck","year":"2004","journal-title":"J. Biol. Chem."},{"issue":"9","key":"2026092909095819900_cit55","doi-asserted-by":"publisher","first-page":"2326","DOI":"10.1021\/ja01542a075","article-title":"Kinetic Isotope\nEffects in the Acetolyses of Deuterated Cyclopentyl Tosylates1,2","volume":"80","author":"Streitwieser","year":"1958","journal-title":"J. Am. Chem. Soc."},{"issue":"16","key":"2026092909095819900_cit56","doi-asserted-by":"publisher","first-page":"5455","DOI":"10.1007\/s00216-013-6949-3","article-title":"Combination\nof Carbon Isotope Ratio with Hydrogen Isotope Ratio Determinations\nin Sports Drug Testing","volume":"405","author":"Piper","year":"2013","journal-title":"Anal. Bioanal. Chem."},{"issue":"1","key":"2026092909095819900_cit57","doi-asserted-by":"publisher","first-page":"2","DOI":"10.1016\/j.abb.2004.08.027","article-title":"The Use\nof Isotope Effects to Determine Enzyme Mechanisms","volume":"433","author":"Cleland","year":"2005","journal-title":"Arch. Biochem. Biophys."},{"issue":"27","key":"2026092909095819900_cit58","doi-asserted-by":"publisher","first-page":"7295","DOI":"10.1021\/bi800308q","article-title":"Isotope\nSensitive Branching and Kinetic Isotope Effects\nin the Reaction of Deuterated Arachidonic Acids with Human 12- and\n15-Lipoxygenases","volume":"47","author":"Jacquot","year":"2008","journal-title":"Biochemistry"},{"issue":"6","key":"2026092909095819900_cit59","doi-asserted-by":"publisher","first-page":"426","DOI":"10.1093\/jat\/28.6.426","article-title":"Urinary Analysis of\nFour Testosterone Metabolites and Pregnanediol by Gas Chromatography-Combustion-Isotope\nRatio Mass Spectrometry after Oral Administrations of Testosterone","volume":"28","author":"Mai\u0302tre","year":"2004","journal-title":"J. Anal. 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