The Half-Life of 11α-Hydroxy-9, 15-Dioxo-2,3,4,5,20-Pentanor-19-Carboxyprostanoic Acid (PGE-M) in Human Urine

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Abstract
A GC-MS-SIM assay for PGE-M recently developed by us (Analyt. Biochem. 128:351-358, 1983) is based on the use of the diethyl ester of the analyte as the internal standard (IS). Because the decay rate of this IS and that of the underivatized metabolite cannot be assumed to be identical, we determined the half-lives of both species so that data can be adjusted accordingly when the urine specimens are stored for a prolonged time. At -22.degree. C the first-order rate constant of PGE-M decomposition and that of its diethyl ester are 3.120 .times. 10-3 day-1 (t1/2 222 days) and 2.422 .times. 10-3 day-1 (t1/2 286 days), respectively. Thus, if the storage time is less than 60 days data adjustment can be omitted, the consequent error being less than 4.3%.