Evaluation of degradation of urinary catecholamines and metanephrines and deconjugation of their sulfoconjugates using stability-indicating reversed-phase ion-pair HPLC with electrochemical detection.

The possibility of the deconjugation of urinary catecholamine sulfates (CA-S) and metanephrine sulfates (MN-S) during storage was studied using a reversed-phase ion-pair HPLC method with electrochemical detection. Stability profiles of catecholamines (norepinephrine (NE), epinephrine (E) and dopamine (DA)) and metanephrines (normetanephrine (NM) and metanephrine (MN)) in preserved and unpreserved pooled urine and aqueous samples stored at 10 and 30 degrees C over 8 days were compared. Results showed that these compounds exhibited stable or declining profiles in aqueous samples but fluctuating profiles in pooled urine samples. It was concluded that deconjugation of CA-S and MN-S occurred in both preserved and unpreserved urine samples. Therefore, at 10 and 30 degrees C, levels of detected urinary catecholamines and metanephrines could be affected by both the degradation of the free amines and deconjugation of the CA-S and MN-S. Based on these findings, another batch of unpreserved urine and aqueous samples were prepared and stored at -80 degrees C. Under this condition, all compounds were found to be stable with less than 10% variations in both unpreserved urine and aqueous samples for at least 22 days. These indicated that urine samples could be stored unpreserved at -80 degrees C for at least 3 weeks without significant degradation of the free amines or deconjugation of their sulfoconjugates.