Determination of creatine and guanidinoacetate by GC-MS: study of their stability in urine at different temperatures.
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.
Prieto
José Angel
JA
Division of Metabolism, Cruces Hospital, 48903 Barakaldo, Spain.
Andrade
Fernando
F
Martín
Sergio
S
Sanjurjo
Pablo
P
Elorz
Javier
J
Aldámiz-Echevarría
Luís
L
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
D000081:Acetamides; D005463:Fluoroacetates; D017646:Organosilicon Compounds; C059151:N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide; D014269:Trifluoroacetic Acid; C004946:glycocyamine; D003401:Creatine; D005998:Glycine