{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,14]],"date-time":"2026-03-14T18:05:46Z","timestamp":1773511546149,"version":"3.50.1"},"reference-count":58,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2017,8,24]],"date-time":"2017-08-24T00:00:00Z","timestamp":1503532800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>The accurate assessment of racemic pharmaceuticals requires enantioselective analytical methods. This study presents the development and validation of an enantioselective liquid chromatography with a fluorescence detection method for the concomitant quantification of the enantiomers of tramadol and their metabolites, N-desmethyltramadol and O-desmethyltramadol, in wastewater samples. Optimized conditions were achieved using a Lux Cellulose-4 column 150 \u00d7 4.6 mm, 3 \u00b5m isocratic elution, and 0.1% diethylamine in hexane and ethanol (96:4, v\/v) at 0.7 mL min\u22121. The samples were extracted using 150 mg Oasis\u00ae mixed-mode cation exchange (MCX) cartridges. The method was validated using a synthetic effluent of a laboratory-scale aerobic granular sludge sequencing batch reactor. The method demonstrated to be selective, accurate, and linear (r2 &gt; 0.99) over the range of 56 ng L\u22121 to 392 ng L\u22121. The detection and the quantification limits of each enantiomer were 8 ng L\u22121 and 28 ng L\u22121 for tramadol and N-desmethyltramadol, and 20 ng L\u22121 and 56 ng L\u22121 for O-desmethyltramadol. The feasibility of the method was demonstrated in a screening study in influent and effluent samples from a wastewater treatment plant. The results demonstrated the occurrence of tramadol enantiomers up to 325.1 ng L\u22121 and 357.9 ng L\u22121, in the effluent and influent samples, respectively. Both metabolites were detected in influents and effluents.<\/jats:p>","DOI":"10.3390\/sym9090170","type":"journal-article","created":{"date-parts":[[2017,8,24]],"date-time":"2017-08-24T11:16:52Z","timestamp":1503573412000},"page":"170","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Enantiomeric Separation of Tramadol and Its Metabolites: Method Validation and Application to Environmental Samples"],"prefix":"10.3390","volume":"9","author":[{"given":"C\u00e1tia","family":"Silva","sequence":"first","affiliation":[{"name":"Laborat\u00f3rio de Qu\u00edmica Org\u00e2nica e Farmac\u00eautica, Departamento de Ci\u00eancias Qu\u00edmicas, Faculdade de Farm\u00e1cia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal"},{"name":"CESPU, Instituto de Investiga\u00e7\u00e3o e Forma\u00e7\u00e3o Avan\u00e7ada em Ci\u00eancias e Tecnologias da Sa\u00fade, Rua Central de Gandra, 1317, 4585-116 Gandra PRD, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7245-4552","authenticated-orcid":false,"given":"Cl\u00e1udia","family":"Ribeiro","sequence":"additional","affiliation":[{"name":"CESPU, Instituto de Investiga\u00e7\u00e3o e Forma\u00e7\u00e3o Avan\u00e7ada em Ci\u00eancias e Tecnologias da Sa\u00fade, Rua Central de Gandra, 1317, 4585-116 Gandra PRD, Portugal"},{"name":"Universidade Cat\u00f3lica Portuguesa, CBQF\u2014Centro de Biotecnologia e Qu\u00edmica Fina\u2014Laborat\u00f3rio Associado, Escola Superior de Biotecnologia, Rua Arquiteto Lob\u00e3o Vital, apartado 2511, 4202-401 Porto, Portugal"},{"name":"Centro Interdisciplinar de Investiga\u00e7\u00e3o Marinha e Ambiental (CIIMAR\/CIMAR), Universidade do Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal"}]},{"given":"Alexandra","family":"Maia","sequence":"additional","affiliation":[{"name":"CESPU, Instituto de Investiga\u00e7\u00e3o e Forma\u00e7\u00e3o Avan\u00e7ada em Ci\u00eancias e Tecnologias da Sa\u00fade, Rua Central de Gandra, 1317, 4585-116 Gandra PRD, Portugal"},{"name":"Universidade Cat\u00f3lica Portuguesa, CBQF\u2014Centro de Biotecnologia e Qu\u00edmica Fina\u2014Laborat\u00f3rio Associado, Escola Superior de Biotecnologia, Rua Arquiteto Lob\u00e3o Vital, apartado 2511, 4202-401 Porto, Portugal"}]},{"given":"Virg\u00ednia","family":"Gon\u00e7alves","sequence":"additional","affiliation":[{"name":"CESPU, Instituto de Investiga\u00e7\u00e3o e Forma\u00e7\u00e3o Avan\u00e7ada em Ci\u00eancias e Tecnologias da Sa\u00fade, Rua Central de Gandra, 1317, 4585-116 Gandra PRD, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3320-730X","authenticated-orcid":false,"given":"Maria","family":"Tiritan","sequence":"additional","affiliation":[{"name":"Laborat\u00f3rio de Qu\u00edmica Org\u00e2nica e Farmac\u00eautica, Departamento de Ci\u00eancias Qu\u00edmicas, Faculdade de Farm\u00e1cia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal"},{"name":"CESPU, Instituto de Investiga\u00e7\u00e3o e Forma\u00e7\u00e3o Avan\u00e7ada em Ci\u00eancias e Tecnologias da Sa\u00fade, Rua Central de Gandra, 1317, 4585-116 Gandra PRD, Portugal"},{"name":"Centro Interdisciplinar de Investiga\u00e7\u00e3o Marinha e Ambiental (CIIMAR\/CIMAR), Universidade do Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5731-5789","authenticated-orcid":false,"given":"Carlos","family":"Afonso","sequence":"additional","affiliation":[{"name":"Laborat\u00f3rio de Qu\u00edmica Org\u00e2nica e Farmac\u00eautica, Departamento de Ci\u00eancias Qu\u00edmicas, Faculdade de Farm\u00e1cia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal"},{"name":"Centro Interdisciplinar de Investiga\u00e7\u00e3o Marinha e Ambiental (CIIMAR\/CIMAR), Universidade do Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2017,8,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"61","DOI":"10.1016\/j.envint.2015.07.020","article-title":"The significance of different health institutions and their respective contributions of active pharmaceutical ingredients to wastewater","volume":"85","author":"Herrmann","year":"2015","journal-title":"Environ. Int."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"381","DOI":"10.1007\/s10311-015-0524-4","article-title":"Pharmaceuticals and personal care products in waters: Occurrence, toxicity, and risk","volume":"13","author":"Cizmas","year":"2015","journal-title":"Environ. Chem. Lett."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"8","DOI":"10.1016\/j.jchromb.2014.02.049","article-title":"Enantioseparation of chiral pharmaceuticals in biomedical and environmental analyses by liquid chromatography: An overview","volume":"968","author":"Ribeiro","year":"2014","journal-title":"J. Chromatogr. B"},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Lichtfouse, E., Schwarzbauer, J., and Robert, D. (2012). Environmental fate of chiral pharmaceuticals: Determination, degradation and toxicity. Environmental Chemistry for a Sustainable World, Springer.","DOI":"10.1007\/978-94-007-2442-6"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"239","DOI":"10.1007\/s10311-011-0352-0","article-title":"Chiral pharmaceuticals in the environment","volume":"10","author":"Ribeiro","year":"2012","journal-title":"Environ. Chem. Lett."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"9","DOI":"10.1016\/j.chemosphere.2007.04.080","article-title":"Enantiospecific sublethal effects of the antidepressant fluoxetine to a model aquatic vertebrate and invertebrate","volume":"69","author":"Stanley","year":"2007","journal-title":"Chemosphere"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1780","DOI":"10.1897\/05-298R1.1","article-title":"Enantiospecific toxicity of the beta-blocker propranolol to daphnia magna and pimephales promelas","volume":"25","author":"Stanley","year":"2006","journal-title":"Environ. Toxicol. Chem."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"36884","DOI":"10.1038\/srep36884","article-title":"Completely chiral optical force for enantioseparation","volume":"6","author":"Rukhlenko","year":"2016","journal-title":"Sci. Rep."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"9516","DOI":"10.1021\/acsami.5b00755","article-title":"Role of chirality and macroring in imprinted polymers with enantiodiscriminative power","volume":"7","author":"Kupai","year":"2015","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1003","DOI":"10.1002\/bmc.2894","article-title":"Simultaneous quantification of tramadol and O-desmethyltramadol in hair samples by gas chromatography-electron impact\/mass spectrometry","volume":"27","author":"Pinho","year":"2013","journal-title":"Biomed. Chromatogr."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"84","DOI":"10.1016\/j.chroma.2016.02.015","article-title":"Enantiomeric profiling of chiral drug biomarkers in wastewater with the usage of chiral liquid chromatography coupled with tandem mass spectrometry","volume":"1438","author":"Castrignano","year":"2016","journal-title":"J. Chromatogr. A"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"486","DOI":"10.1002\/chir.22048","article-title":"Chiral separation of cathinone derivatives used as recreational drugs by HPLC-UV using a CHIRALPAK\u00ae AS-H column as stationary phase","volume":"24","author":"Mohr","year":"2012","journal-title":"Chirality"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"589","DOI":"10.1016\/j.chemosphere.2013.09.118","article-title":"Enantioselective quantification of fluoxetine and norfluoxetine by HPLC in wastewater effluents","volume":"95","author":"Ribeiro","year":"2014","journal-title":"Chemosphere"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"41729","DOI":"10.1039\/C5RA04764A","article-title":"Chiral liquid membrane for enantioselective separation of racemic ibuprofen by l-tartaric acid derivatives","volume":"5","author":"Zhang","year":"2015","journal-title":"RSC Adv."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1016\/S0379-0738(00)00374-1","article-title":"Fatality due to ingestion of tramadol alone","volume":"116","author":"Musshoff","year":"2001","journal-title":"Forensic Sci. Int."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"879","DOI":"10.2165\/00003088-200443130-00004","article-title":"Clinical pharmacology of tramadol","volume":"43","author":"Grond","year":"2004","journal-title":"Clin. Pharmacokinet."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"240","DOI":"10.1002\/anie.201508646","article-title":"Synthetic origin of tramadol in the environment","volume":"55","author":"Kusari","year":"2016","journal-title":"Angew. Chem. Int. Ed."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"9","DOI":"10.1016\/j.jchromb.2013.02.019","article-title":"Simultaneous determination of tramadol, O-desmethyltramadol and n-desmethyltramadol in human urine by gas chromatography-mass spectrometry","volume":"926","author":"Mohamed","year":"2013","journal-title":"J. Chromatogr. B"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"354","DOI":"10.1016\/j.jpba.2008.10.030","article-title":"An accurate, rapid and sensitive determination of tramadol and its active metabolite O-desmethyltramadol in human plasma by LC\u2013MS\/MS","volume":"49","author":"Patel","year":"2009","journal-title":"J. Pharm. Biomed. Anal."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/S0378-8741(01)00310-5","article-title":"The effect of nigella sativa oil against the liver damage induced by schistosoma mansoni infection in mice","volume":"79","author":"Mahmoud","year":"2002","journal-title":"J. Ethnopharmacol."},{"key":"ref_21","first-page":"90","article-title":"Histopathological and molecular studies on tramadol mediated hepato-renal toxicity in rats","volume":"10","author":"Awadalla","year":"2015","journal-title":"IOSR J. Pharm. Biol. Sci."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"165","DOI":"10.1016\/S0378-4347(01)00388-7","article-title":"Gas chromatographic method using nitrogen\u2013phosphorus detection for the measurement of tramadol and its O-desmethyl metabolite in plasma and brain tissue of mice and rats","volume":"763","author":"Tao","year":"2001","journal-title":"J. Chromatogr. B Biomed. Sci. Appl."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1168","DOI":"10.1016\/j.jpba.2007.04.012","article-title":"Improved liquid chromatographic method for the simultaneous determination of tramadol and its three main metabolites in human plasma, urine and saliva","volume":"44","author":"Ardakani","year":"2007","journal-title":"J. Pharm. Biomed. Anal."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"2013","DOI":"10.1097\/00029330-200612010-00012","article-title":"Simultaneous analysis of tramadol, metoprolol and their metabolites in human plasma and urine by high performance liquid chromatography","volume":"119","author":"Li","year":"2006","journal-title":"Chin. Med. J."},{"key":"ref_25","first-page":"458","article-title":"Determination of tramadol and its active metabolite O-desmethyltramadol in plasma and amniotic fluid using LC\/MS\/MS","volume":"39","author":"Zhao","year":"2004","journal-title":"Acta Pharm. Sin."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"161","DOI":"10.1016\/S0378-4347(97)00267-3","article-title":"Automated determination of tramadol enantiomers in human plasma using solid-phase extraction in combination with chiral liquid chromatography","volume":"698","author":"Ceccato","year":"1997","journal-title":"J. Chromatogr. B Biomed. Sci. Appl."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"83","DOI":"10.1016\/S0378-4347(98)00547-7","article-title":"Simultaneous determination of tramadol and its major active metabolite O-demethyltramadol by high-performance liquid chromatography with electrochemical detection","volume":"724","author":"Valle","year":"1999","journal-title":"J. Chromatogr. B Biomed. Sci. Appl."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"65","DOI":"10.1016\/S0378-4347(00)00318-2","article-title":"Enantiomeric determination of tramadol and its main metabolite O-desmethyltramadol in human plasma by liquid chromatography-tandem mass spectrometry","volume":"748","author":"Ceccato","year":"2000","journal-title":"J. Chromatogr. B Biomed. Sci. Appl."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"295","DOI":"10.1016\/S0021-9673(99)01257-1","article-title":"Simultaneous stereoselective analysis of tramadol and its main phase I metabolites by on-line capillary zone electrophoresis-electrospray ionization mass spectrometry","volume":"868","author":"Ruda","year":"2000","journal-title":"J. Chromatogr. A"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"469","DOI":"10.1016\/S0731-7085(99)00310-6","article-title":"The determination of RWJ-38705 (tramadol N-oxide) and its metabolites in preclinical pharmacokinetic studies using LC\u2013MS\/MS","volume":"22","author":"Juzwin","year":"2000","journal-title":"J. Pharm. Biomed. Anal."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"325","DOI":"10.1016\/S0378-4347(01)00237-7","article-title":"Validation of a high-performance liquid chromatography method for tramadol and O-desmethyltramadol in human plasma using solid-phase extraction","volume":"759","author":"Gan","year":"2001","journal-title":"J. Chromatogr. B Biomed. Sci. Appl."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"11","DOI":"10.1016\/S0021-9673(01)01567-9","article-title":"High-performance liquid chromatographic determination of tramadol and its O-desmethylated metabolite in blood plasma: Application to a bioequivalence study in humans","volume":"949","author":"Nobilis","year":"2002","journal-title":"J. Chromatogr. A"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"219","DOI":"10.1016\/j.chroma.2003.11.034","article-title":"Simultaneous stereoselective analysis of tramadol and its primary phase I metabolites in plasma by liquid chromatography: Application to a pharmacokinetic study in humans","volume":"1031","author":"Campanero","year":"2004","journal-title":"J. Chromatogr. A"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"109","DOI":"10.1016\/j.jchromb.2008.01.038","article-title":"Enantioselective determination of tramadol and its main phase I metabolites in human plasma by high-performance liquid chromatography","volume":"864","author":"Ardakani","year":"2008","journal-title":"J. Chromatogr. B"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"240","DOI":"10.1016\/j.jchromb.2005.05.003","article-title":"Improved HPLC method for the simultaneous determination of tramadol and O-desmethyltramadol in human plasma","volume":"821","author":"Gu","year":"2005","journal-title":"J. Chromatogr. B"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"207","DOI":"10.1016\/j.jchromb.2005.10.039","article-title":"Development and validation of a rapid HPLC method for simultaneous determination of tramadol, and its two main metabolites in human plasma","volume":"830","author":"Rouini","year":"2006","journal-title":"J. Chromatogr. B"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"152","DOI":"10.1016\/j.jchromb.2007.01.004","article-title":"Stereospecific high-performance liquid chromatographic analysis of tramadol and its O-demethylated (M1) and N,O-demethylated (M5) metabolites in human plasma","volume":"852","author":"Mehvar","year":"2007","journal-title":"J. Chromatogr. B"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1304","DOI":"10.1016\/j.jprot.2008.01.012","article-title":"Optimized HPLC method for tramadol and O-desmethyl tramadol determination in human plasma","volume":"70","author":"Curticapean","year":"2008","journal-title":"J. Biochem. Biophys. Methods"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"1104","DOI":"10.1016\/j.talanta.2008.01.006","article-title":"Determination of tramadol and O-desmethyltramadol in human plasma by high-performance liquid chromatography with mass spectrometry detection","volume":"75","author":"Vlase","year":"2008","journal-title":"Talanta"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"112","DOI":"10.1016\/j.aca.2015.03.039","article-title":"Determination of chiral pharmaceuticals and illicit drugs in wastewater and sludge using microwave assisted extraction, solid-phase extraction and chiral liquid chromatography coupled with tandem mass spectrometry","volume":"882","author":"Evans","year":"2015","journal-title":"Anal. Chim. Acta"},{"key":"ref_41","unstructured":"ICH Steering Committee (1996). ICH Q2B Validation of Analytical Procedures: Methodology, European Agency for the Evaluation of Medicinal Products, International Commission on Harmonisation. (CPMP\/ICH\/281\/95)."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"814","DOI":"10.1016\/j.chroma.2009.10.022","article-title":"Chiral recognition by enantioselective liquid chromatography: Mechanisms and modern chiral stationary phases","volume":"1217","year":"2010","journal-title":"J. Chromatogr. A"},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"2155","DOI":"10.1590\/S0100-40422010001000028","article-title":"Fases estacion\u00e1rias quirais para cromatografia l\u00edquida de alta efici\u00eancia","volume":"33","author":"Cassiano","year":"2010","journal-title":"Quim. Nova"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"4712","DOI":"10.1021\/ac1010926","article-title":"Chiral separations: Fundamental review 2010","volume":"82","author":"Ward","year":"2010","journal-title":"Anal. Chem."},{"key":"ref_45","first-page":"450","article-title":"Recentchiral selectors for separation in HPLC and CE","volume":"10","year":"2012","journal-title":"Cent. Eur. J. Chem."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"815","DOI":"10.1007\/s10337-012-2261-1","article-title":"Chiral recognition mechanisms in analytical separation sciences","volume":"75","author":"Scriba","year":"2012","journal-title":"Chromatographia"},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"871","DOI":"10.1007\/s10337-013-2469-8","article-title":"Small molecules as chromatographic tools for HPLC enantiomeric resolution: Pirkle-type chiral stationary phases evolution","volume":"76","author":"Fernandes","year":"2013","journal-title":"Chromatographia"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"12","DOI":"10.1016\/j.jchromb.2008.05.022","article-title":"Recent progresses in protein-based chiral stationary phases for enantioseparations in liquid chromatography","volume":"875","author":"Haginaka","year":"2008","journal-title":"J. Chromatogr. B"},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"69","DOI":"10.1016\/S0021-9673(01)01573-4","article-title":"Screening approach for chiral separation of pharmaceuticals: Part I. Normal-phase liquid chromatography","volume":"947","author":"Perrin","year":"2002","journal-title":"J. Chromatogr. A"},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"83","DOI":"10.1016\/S0021-9673(03)00888-4","article-title":"Evaluation of generic chiral liquid chromatography screens for pharmaceutical analysis","volume":"1005","author":"Andersson","year":"2003","journal-title":"J. Chromatogr. A"},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"445","DOI":"10.1016\/S0021-9673(02)01451-6","article-title":"Enantiomeric resolution of a series of chiral sulfoxides by high-performance liquid chromatography on polysaccharide-based columns with multimodal elution","volume":"987","author":"Cass","year":"2003","journal-title":"J. Chromatogr. A"},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"89","DOI":"10.1002\/chir.22112","article-title":"Enantioresolution of chiral derivatives of xanthones on (S,S)-whelk-O1 and l-phenylglycine stationary phases and chiral recognition mechanism by docking approach for (S,S)-whelk-O1","volume":"25","author":"Fernandes","year":"2013","journal-title":"Chirality"},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"481","DOI":"10.1016\/j.jchromb.2009.12.005","article-title":"Enantiomeric determination of tramadol and O-desmethyltramadol in human plasma by fast liquid chromatographic technique coupled with mass spectrometric detection","volume":"878","author":"Chytil","year":"2010","journal-title":"J. Chromatogr. B"},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"463","DOI":"10.1093\/jat\/30.7.463","article-title":"Enantiomeric determination of tramadol and O-desmethyltramadol by liquid chromatography-mass spectrometry and application to postoperative patients receiving tramadol","volume":"30","author":"Musshoff","year":"2006","journal-title":"J. Anal. Toxicol."},{"key":"ref_55","unstructured":"ICH, M. (1996, January 6). Q2b\u2014Validation of analytical procedures: Methodology. Proceedings of the International Conference on Harmonization Expert Working Group, Geneva, Switzerland."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1038\/sj.clpt.6100152","article-title":"Concentrations of tramadol and O-desmethyltramadol enantiomers in different CYP2D6 genotypes","volume":"82","author":"Stamer","year":"2007","journal-title":"Clin. Pharmacol. Ther."},{"key":"ref_57","first-page":"109","article-title":"Pharmacokinetics of oral tramadol drops for postoperative pain relief in children aged 4 to 7 years\u2014A pilot study","volume":"49","author":"Payne","year":"2002","journal-title":"Anesth. Prog."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"235","DOI":"10.1007\/s002280050368","article-title":"Polymorphic CYP2D6 mediates O-demethylation of the opioid analgesic tramadol","volume":"53","author":"Paar","year":"1997","journal-title":"Eur. J. Clin. Pharmacol."}],"container-title":["Symmetry"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-8994\/9\/9\/170\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T18:43:14Z","timestamp":1760208194000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-8994\/9\/9\/170"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2017,8,24]]},"references-count":58,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2017,9]]}},"alternative-id":["sym9090170"],"URL":"https:\/\/doi.org\/10.3390\/sym9090170","relation":{},"ISSN":["2073-8994"],"issn-type":[{"value":"2073-8994","type":"electronic"}],"subject":[],"published":{"date-parts":[[2017,8,24]]}}}