title: Determination of creatine and guanidinoacetate by GC-MS: study of their stability in urine at different temperatures.
abstract: OBJECTIVE
  Evaluation of a GC-MS method using N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA) as the silylating agent for GC-MS. Study of the stability of creatine and guanidinoacetate in urine.
  
  
  METHODS
  22 urines were kept at RT, 4 degrees C and -30 degrees C for 15 days.
  
  
  RESULTS
  MTBSTFA produces a single chromatographic peak in contrast with other derivatizing agents. Creatine concentration increases at room temperature (326% on average), and at 4 degrees C (75%). However, detection decreases after freezing (-37%). Guanidinoacetate is stable, but decreases after freezing (-37%). Sonication before analysis is crucial to obtain repetitive results.
  
  
  CONCLUSIONS
  A modified GC-MS method has been validated and the conditions for preservation of the urine have been established.
authors.affiliation: Division of Metabolism, Cruces Hospital, 48903 Barakaldo, Spain.
authors.forename: José Angel
authors.initials: JA
authors.lastname: Prieto
authors.forename: Fernando
authors.initials: F
authors.lastname: Andrade
authors.forename: Sergio
authors.initials: S
authors.lastname: Martín
authors.forename: Pablo
authors.initials: P
authors.lastname: Sanjurjo
authors.forename: Javier
authors.initials: J
authors.lastname: Elorz
authors.forename: Luís
authors.initials: L
authors.lastname: Aldámiz-Echevarría
mesh_terms: D000081:Acetamides; D003401:Creatine / Q000652:urine*; D005463:Fluoroacetates; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D005998:Glycine / Q000031:analogs & derivatives* / Q000652:urine; D006801:Humans; D017646:Organosilicon Compounds / Q000737:chemistry; D013696:Temperature; D014269:Trifluoroacetic Acid / Q000737:chemistry
chemical_list: D000081:Acetamides; D005463:Fluoroacetates; D017646:Organosilicon Compounds; C059151:N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide; D014269:Trifluoroacetic Acid; C004946:glycocyamine; D003401:Creatine; D005998:Glycine