Effects of long-term storage on the concentrations of the unconjugated acidic metabolites of the trace amines, indoleamines and catecholamines.

The concentrations of urinary phenylacetic, m- and p-hydroxyphenylacetic, mandelic (MA), p-hydroxymandelic, indoleacetic, homovanillic, vanillylmandelic, 5-hydroxyindoleacetic and 3,4-dihydroxyphenylacetic (DOPAC) acids and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and the concentrations of the above plasma acids (except MA, MHPG and DOPAC) were determined by gas chromatography-mass spectrometry with selected-ion monitoring at the time of receipt of the samples and after three, six and nine months storage at -18 degrees C. The samples were not treated in any way before storage. The concentrations of most of the urinary metabolites declined significantly (analysis of variance) over the nine-month storage period, whereas most of the plasma metabolites did not.