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Record Information
Version5.0
StatusExpected but not Quantified
Creation Date2006-05-22 14:17:30 UTC
Update Date2021-09-07 16:45:31 UTC
HMDB IDHMDB0001973
Secondary Accession Numbers
  • HMDB01973
Metabolite Identification
Common Name9-Methyluric acid
Description9-Methyluric acid is a methyl derivative of uric acid, found occasionally in human urine. 9-Methyluracil is one of the purine components in urinary calculi. Methylated purines originate from the metabolism of methylxanthines (caffeine, theophylline and theobromine). Methyluric acids are indistinguishable from uric acid by simple methods routinely used in clinical laboratories, requiring the use of high-performance liquid chromatography (HPLC). Purine derivatives in urinary calculi could be considered markers of abnormal purine metabolism. The content of a purine derivative in stone depends on its average urinary excretion in the general population, similarity to the chemical structure of uric acid, and content of the latter in stone. This suggests that purines in stones represent a solid solution with uric acid as solvent. It is also plausible that methylxanthines, ubiquitous components of the diet and drugs, are involved in the pathogenesis of urolithiasis. Caffeine is metabolized via successive pathways mainly catalyzed by CYP1A2, xanthine oxidase or N-acetyltransferase-2 to give 14 different metabolites. CYP1A2 activity shows an inter-individual variability among the population. CYP1A2, an isoform of the CYP1A cytochrome P450 super-family, is involved in the metabolism of many drugs and plays a potentially important role in the induction of chemical carcinogenesis. (PMID:11712316 , 15833286 , 3506820 , 15013152 ).
Structure
Data?1582752220
Synonyms
ValueSource
9-MethylateGenerator
9-Methylic acidGenerator
7,9-dihydro-9-Methyl-1H-purine-2,6,8(3H)-trioneHMDB
9-Methyl-2,6,8-trihydroxypurineHMDB
MUAHMDB
9-Methyluric acidMeSH
9-Methyl urateGenerator, HMDB
Chemical FormulaC6H6N4O3
Average Molecular Weight182.1368
Monoisotopic Molecular Weight182.043990078
IUPAC Name9-methyl-2,3,6,7,8,9-hexahydro-1H-purine-2,6,8-trione
Traditional Name9-methyl uric acid
CAS Registry Number55441-71-9
SMILES
CN1C(=O)NC2=C1NC(=O)NC2=O
InChI Identifier
InChI=1S/C6H6N4O3/c1-10-3-2(7-6(10)13)4(11)9-5(12)8-3/h1H3,(H,7,13)(H2,8,9,11,12)
InChI KeyXJEJWDFDVPDMAS-UHFFFAOYSA-N
Chemical Taxonomy
Description Belongs to the class of organic compounds known as xanthines. These are purine derivatives with a ketone group conjugated at carbons 2 and 6 of the purine moiety.
KingdomOrganic compounds
Super ClassOrganoheterocyclic compounds
ClassImidazopyrimidines
Sub ClassPurines and purine derivatives
Direct ParentXanthines
Alternative Parents
Substituents
  • Xanthine
  • 6-oxopurine
  • Purinone
  • Alkaloid or derivatives
  • Pyrimidone
  • N-substituted imidazole
  • Pyrimidine
  • Azole
  • Imidazole
  • Heteroaromatic compound
  • Vinylogous amide
  • Lactam
  • Urea
  • Azacycle
  • Hydrocarbon derivative
  • Organic oxide
  • Organopnictogen compound
  • Organooxygen compound
  • Organonitrogen compound
  • Organic oxygen compound
  • Organic nitrogen compound
  • Aromatic heteropolycyclic compound
Molecular FrameworkAromatic heteropolycyclic compounds
External DescriptorsNot Available
Ontology
Disposition

Biological location

Source

Physical Properties
StateSolid
Experimental Molecular Properties
PropertyValueReference
Melting PointNot AvailableNot Available
Boiling PointNot AvailableNot Available
Water Solubility0.021 mg/mL at 25 °CNot Available
LogPNot AvailableNot Available
Experimental Chromatographic PropertiesNot Available
Predicted Molecular Properties
PropertyValueSource
Water Solubility3.6 g/LALOGPS
logP-1ALOGPS
logP-1.3ChemAxon
logS-1.7ALOGPS
pKa (Strongest Acidic)7.25ChemAxon
pKa (Strongest Basic)-6.2ChemAxon
Physiological Charge0ChemAxon
Hydrogen Acceptor Count3ChemAxon
Hydrogen Donor Count3ChemAxon
Polar Surface Area90.54 ŲChemAxon
Rotatable Bond Count0ChemAxon
Refractivity50.53 m³·mol⁻¹ChemAxon
Polarizability15.67 ųChemAxon
Number of Rings2ChemAxon
BioavailabilityYesChemAxon
Rule of FiveYesChemAxon
Ghose FilterNoChemAxon
Veber's RuleNoChemAxon
MDDR-like RuleNoChemAxon
Predicted Chromatographic Properties

Predicted Collision Cross Sections

PredictorAdduct TypeCCS Value (Å2)Reference
DarkChem[M+H]+138.88131661259
DarkChem[M-H]-136.6931661259
AllCCS[M+H]+137.6532859911
AllCCS[M-H]-134.57632859911
DeepCCS[M+H]+129.25330932474
DeepCCS[M-H]-126.50430932474
DeepCCS[M-2H]-163.03130932474
DeepCCS[M+Na]+138.19730932474

Predicted Kovats Retention Indices

Underivatized

MetaboliteSMILESKovats RI ValueColumn TypeReference
9-Methyluric acidCN1C(=O)NC2=C1NC(=O)NC2=O2924.5Standard polar33892256
9-Methyluric acidCN1C(=O)NC2=C1NC(=O)NC2=O2042.5Standard non polar33892256
9-Methyluric acidCN1C(=O)NC2=C1NC(=O)NC2=O2444.0Semi standard non polar33892256

Derivatized

Derivative Name / StructureSMILESKovats RI ValueColumn TypeReference
9-Methyluric acid,1TMS,isomer #1CN1C(=O)N([Si](C)(C)C)C2=C1[NH]C(=O)[NH]C2=O2013.9Semi standard non polar33892256
9-Methyluric acid,1TMS,isomer #1CN1C(=O)N([Si](C)(C)C)C2=C1[NH]C(=O)[NH]C2=O2156.5Standard non polar33892256
9-Methyluric acid,1TMS,isomer #1CN1C(=O)N([Si](C)(C)C)C2=C1[NH]C(=O)[NH]C2=O2971.0Standard polar33892256
9-Methyluric acid,1TMS,isomer #2CN1C(=O)[NH]C2=C1N([Si](C)(C)C)C(=O)[NH]C2=O1989.9Semi standard non polar33892256
9-Methyluric acid,1TMS,isomer #2CN1C(=O)[NH]C2=C1N([Si](C)(C)C)C(=O)[NH]C2=O2177.4Standard non polar33892256
9-Methyluric acid,1TMS,isomer #2CN1C(=O)[NH]C2=C1N([Si](C)(C)C)C(=O)[NH]C2=O3075.5Standard polar33892256
9-Methyluric acid,1TMS,isomer #3CN1C(=O)[NH]C2=C1[NH]C(=O)N([Si](C)(C)C)C2=O2053.8Semi standard non polar33892256
9-Methyluric acid,1TMS,isomer #3CN1C(=O)[NH]C2=C1[NH]C(=O)N([Si](C)(C)C)C2=O2248.9Standard non polar33892256
9-Methyluric acid,1TMS,isomer #3CN1C(=O)[NH]C2=C1[NH]C(=O)N([Si](C)(C)C)C2=O3086.6Standard polar33892256
9-Methyluric acid,2TMS,isomer #1CN1C(=O)N([Si](C)(C)C)C2=C1[NH]C(=O)N([Si](C)(C)C)C2=O2069.2Semi standard non polar33892256
9-Methyluric acid,2TMS,isomer #1CN1C(=O)N([Si](C)(C)C)C2=C1[NH]C(=O)N([Si](C)(C)C)C2=O2262.0Standard non polar33892256
9-Methyluric acid,2TMS,isomer #1CN1C(=O)N([Si](C)(C)C)C2=C1[NH]C(=O)N([Si](C)(C)C)C2=O2537.5Standard polar33892256
9-Methyluric acid,2TMS,isomer #2CN1C(=O)N([Si](C)(C)C)C2=C1N([Si](C)(C)C)C(=O)[NH]C2=O1953.7Semi standard non polar33892256
9-Methyluric acid,2TMS,isomer #2CN1C(=O)N([Si](C)(C)C)C2=C1N([Si](C)(C)C)C(=O)[NH]C2=O2235.6Standard non polar33892256
9-Methyluric acid,2TMS,isomer #2CN1C(=O)N([Si](C)(C)C)C2=C1N([Si](C)(C)C)C(=O)[NH]C2=O2511.2Standard polar33892256
9-Methyluric acid,2TMS,isomer #3CN1C(=O)[NH]C2=C1N([Si](C)(C)C)C(=O)N([Si](C)(C)C)C2=O2012.0Semi standard non polar33892256
9-Methyluric acid,2TMS,isomer #3CN1C(=O)[NH]C2=C1N([Si](C)(C)C)C(=O)N([Si](C)(C)C)C2=O2298.8Standard non polar33892256
9-Methyluric acid,2TMS,isomer #3CN1C(=O)[NH]C2=C1N([Si](C)(C)C)C(=O)N([Si](C)(C)C)C2=O2620.6Standard polar33892256
9-Methyluric acid,3TMS,isomer #1CN1C(=O)N([Si](C)(C)C)C2=C1N([Si](C)(C)C)C(=O)N([Si](C)(C)C)C2=O2114.0Semi standard non polar33892256
9-Methyluric acid,3TMS,isomer #1CN1C(=O)N([Si](C)(C)C)C2=C1N([Si](C)(C)C)C(=O)N([Si](C)(C)C)C2=O2249.2Standard non polar33892256
9-Methyluric acid,3TMS,isomer #1CN1C(=O)N([Si](C)(C)C)C2=C1N([Si](C)(C)C)C(=O)N([Si](C)(C)C)C2=O2292.7Standard polar33892256
9-Methyluric acid,1TBDMS,isomer #1CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1[NH]C(=O)[NH]C2=O2167.0Semi standard non polar33892256
9-Methyluric acid,1TBDMS,isomer #1CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1[NH]C(=O)[NH]C2=O2396.0Standard non polar33892256
9-Methyluric acid,1TBDMS,isomer #1CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1[NH]C(=O)[NH]C2=O2916.1Standard polar33892256
9-Methyluric acid,1TBDMS,isomer #2CN1C(=O)[NH]C2=C1N([Si](C)(C)C(C)(C)C)C(=O)[NH]C2=O2164.2Semi standard non polar33892256
9-Methyluric acid,1TBDMS,isomer #2CN1C(=O)[NH]C2=C1N([Si](C)(C)C(C)(C)C)C(=O)[NH]C2=O2428.1Standard non polar33892256
9-Methyluric acid,1TBDMS,isomer #2CN1C(=O)[NH]C2=C1N([Si](C)(C)C(C)(C)C)C(=O)[NH]C2=O3009.9Standard polar33892256
9-Methyluric acid,1TBDMS,isomer #3CN1C(=O)[NH]C2=C1[NH]C(=O)N([Si](C)(C)C(C)(C)C)C2=O2248.7Semi standard non polar33892256
9-Methyluric acid,1TBDMS,isomer #3CN1C(=O)[NH]C2=C1[NH]C(=O)N([Si](C)(C)C(C)(C)C)C2=O2457.8Standard non polar33892256
9-Methyluric acid,1TBDMS,isomer #3CN1C(=O)[NH]C2=C1[NH]C(=O)N([Si](C)(C)C(C)(C)C)C2=O3031.2Standard polar33892256
9-Methyluric acid,2TBDMS,isomer #1CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1[NH]C(=O)N([Si](C)(C)C(C)(C)C)C2=O2438.3Semi standard non polar33892256
9-Methyluric acid,2TBDMS,isomer #1CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1[NH]C(=O)N([Si](C)(C)C(C)(C)C)C2=O2654.7Standard non polar33892256
9-Methyluric acid,2TBDMS,isomer #1CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1[NH]C(=O)N([Si](C)(C)C(C)(C)C)C2=O2614.4Standard polar33892256
9-Methyluric acid,2TBDMS,isomer #2CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1N([Si](C)(C)C(C)(C)C)C(=O)[NH]C2=O2325.5Semi standard non polar33892256
9-Methyluric acid,2TBDMS,isomer #2CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1N([Si](C)(C)C(C)(C)C)C(=O)[NH]C2=O2637.5Standard non polar33892256
9-Methyluric acid,2TBDMS,isomer #2CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1N([Si](C)(C)C(C)(C)C)C(=O)[NH]C2=O2589.0Standard polar33892256
9-Methyluric acid,2TBDMS,isomer #3CN1C(=O)[NH]C2=C1N([Si](C)(C)C(C)(C)C)C(=O)N([Si](C)(C)C(C)(C)C)C2=O2413.7Semi standard non polar33892256
9-Methyluric acid,2TBDMS,isomer #3CN1C(=O)[NH]C2=C1N([Si](C)(C)C(C)(C)C)C(=O)N([Si](C)(C)C(C)(C)C)C2=O2688.7Standard non polar33892256
9-Methyluric acid,2TBDMS,isomer #3CN1C(=O)[NH]C2=C1N([Si](C)(C)C(C)(C)C)C(=O)N([Si](C)(C)C(C)(C)C)C2=O2658.8Standard polar33892256
9-Methyluric acid,3TBDMS,isomer #1CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1N([Si](C)(C)C(C)(C)C)C(=O)N([Si](C)(C)C(C)(C)C)C2=O2594.9Semi standard non polar33892256
9-Methyluric acid,3TBDMS,isomer #1CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1N([Si](C)(C)C(C)(C)C)C(=O)N([Si](C)(C)C(C)(C)C)C2=O2865.7Standard non polar33892256
9-Methyluric acid,3TBDMS,isomer #1CN1C(=O)N([Si](C)(C)C(C)(C)C)C2=C1N([Si](C)(C)C(C)(C)C)C(=O)N([Si](C)(C)C(C)(C)C)C2=O2602.3Standard polar33892256
Spectra

GC-MS Spectra

Spectrum TypeDescriptionSplash KeyDeposition DateSourceView
Predicted GC-MSPredicted GC-MS Spectrum - 9-Methyluric acid GC-MS (Non-derivatized) - 70eV, Positivesplash10-0gwr-1900000000-ad4ab961fb153ec968f02017-08-28Wishart LabView Spectrum
Predicted GC-MSPredicted GC-MS Spectrum - 9-Methyluric acid GC-MS (Non-derivatized) - 70eV, PositiveNot Available2021-10-12Wishart LabView Spectrum
Predicted GC-MSPredicted GC-MS Spectrum - 9-Methyluric acid GC-MS (Non-derivatized) - 70eV, PositiveNot Available2021-10-12Wishart LabView Spectrum

MS/MS Spectra

Spectrum TypeDescriptionSplash KeyDeposition DateSourceView
Experimental LC-MS/MSLC-MS/MS Spectrum - 9-Methyluric acid Quattro_QQQ 10V, Positive-QTOF (Annotated)splash10-001i-0900000000-03ab1b745dbb16bf82cf2012-07-25HMDB team, MONAView Spectrum
Experimental LC-MS/MSLC-MS/MS Spectrum - 9-Methyluric acid Quattro_QQQ 25V, Positive-QTOF (Annotated)splash10-05o0-4900000000-37b0feef423309da3c702012-07-25HMDB team, MONAView Spectrum
Experimental LC-MS/MSLC-MS/MS Spectrum - 9-Methyluric acid Quattro_QQQ 40V, Positive-QTOF (Annotated)splash10-0gb9-9800000000-967f7da2548d78a94b572012-07-25HMDB team, MONAView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 10V, Negative-QTOFsplash10-001i-0900000000-fc29b0fd4d9a83e9e06c2017-07-26Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 20V, Negative-QTOFsplash10-0006-9500000000-62d351e045a1e54e9a7f2017-07-26Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 40V, Negative-QTOFsplash10-0006-9200000000-15682730273e8e61333b2017-07-26Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 10V, Negative-QTOFsplash10-001i-0900000000-35d70442060a47f4840b2021-09-25Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 20V, Negative-QTOFsplash10-0fl3-1900000000-05cdb031cf04c4eb174e2021-09-25Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 40V, Negative-QTOFsplash10-0006-9200000000-a0cec5036ddb470e74d72021-09-25Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 10V, Positive-QTOFsplash10-001i-0900000000-9cb11ef3bf1ef22898e82017-07-26Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 20V, Positive-QTOFsplash10-001l-0900000000-2f1b0c821176367c5f412017-07-26Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 40V, Positive-QTOFsplash10-0aor-9700000000-06fd51df30b167ff1cf92017-07-26Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 10V, Positive-QTOFsplash10-001i-0900000000-fa33d1f90dc5e1d6cf642021-09-25Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 20V, Positive-QTOFsplash10-001i-0900000000-c75e3994fddbcfa2cd2e2021-09-25Wishart LabView Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 9-Methyluric acid 40V, Positive-QTOFsplash10-0bt9-9700000000-a1642fde92db4b9ec4612021-09-25Wishart LabView Spectrum

NMR Spectra

Spectrum TypeDescriptionDeposition DateSourceView
Experimental 1D NMR1H NMR Spectrum (1D, 600 MHz, 100%_DMSO, experimental)2012-12-05Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 100 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 100 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 1000 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 1000 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 200 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 200 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 300 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 300 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 400 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 400 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 500 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 500 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 600 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 600 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 700 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 700 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 800 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 800 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR13C NMR Spectrum (1D, 900 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Predicted 1D NMR1H NMR Spectrum (1D, 900 MHz, D2O, predicted)2021-09-25Wishart LabView Spectrum
Experimental 2D NMR[1H, 13C]-HSQC NMR Spectrum (2D, 600 MHz, 100%_DMSO, experimental)2012-12-05Wishart LabView Spectrum
Biological Properties
Cellular Locations
  • Cytoplasm
Biospecimen Locations
  • Blood
  • Urine
Tissue Locations
  • Kidney
  • Liver
Pathways
Normal Concentrations
BiospecimenStatusValueAgeSexConditionReferenceDetails
BloodExpected but not QuantifiedNot QuantifiedNot AvailableNot AvailableNormal
      Not Available
details
UrineExpected but not QuantifiedNot QuantifiedNot AvailableNot AvailableNormal
      Not Available
details
Abnormal Concentrations
Not Available
Associated Disorders and Diseases
Disease ReferencesNone
Associated OMIM IDsNone
DrugBank IDDB03293
Phenol Explorer Compound IDNot Available
FooDB IDFDB022772
KNApSAcK IDNot Available
Chemspider ID97755
KEGG Compound IDNot Available
BioCyc IDNot Available
BiGG IDNot Available
Wikipedia LinkNot Available
METLIN IDNot Available
PubChem Compound108714
PDB IDMUA
ChEBI IDNot Available
Food Biomarker OntologyNot Available
VMH IDNot Available
MarkerDB IDNot Available
Good Scents IDNot Available
References
Synthesis ReferenceBiilman, Einar; Bjerrum, Johanne. Methyl- and ethyluric acids. Journal of the Chemical Society, Abstracts (1917), 112(I), 588-9.
Material Safety Data Sheet (MSDS)Download (PDF)
General References
  1. Morris GS, Simmonds HA, Davies PM: Use of biological fluids for the rapid diagnosis of potentially lethal inherited disorders of human purine and pyrimidine metabolism. Biomed Chromatogr. 1986 Jun;1(3):109-18. [PubMed:3506820 ]
  2. Safranow K, Machoy Z: Simultaneous determination of 16 purine derivatives in urinary calculi by gradient reversed-phase high-performance liquid chromatography with UV detection. J Chromatogr B Analyt Technol Biomed Life Sci. 2005 May 25;819(2):229-35. [PubMed:15833286 ]
  3. Safranow K: [Identification and quantitation of purine derivatives in urinary calculi as markers of abnormal purine metabolism by using high-performance liquid chromatography (HPLC)]. Ann Acad Med Stetin. 2000;46:35-49. [PubMed:11712316 ]
  4. Caubet MS, Comte B, Brazier JL: Determination of urinary 13C-caffeine metabolites by liquid chromatography-mass spectrometry: the use of metabolic ratios to assess CYP1A2 activity. J Pharm Biomed Anal. 2004 Feb 4;34(2):379-89. [PubMed:15013152 ]