Determination of creatine and guanidinoacetate by GC-MS: Study of their stability in urine at different temperatures

ObjectivesEvaluation 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.Design and methods22 urines were kept at RT, 4 °C and − 30 °C for 15 days.ResultsMTBSTFA produces a single chromatographic peak in contrast with other derivatizing agents. Creatine concentration increases at room temperature (326% on average), and at 4 °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.ConclusionsA modified GC-MS method has been validated and the conditions for preservation of the urine have been established.