Stability of human blood serum aminoacids after storage at different pH and temperature conditions

The stability of the aminoacids in human blood serum ultrafiltrates and in an aminoacid standard solution was investigated under different pH and storage conditions. At close to neutral pH values the aminoacid concentrations remained constant for at least 12 months at -50 degrees C (n = 6), except for lysine. With acid but particularly with alkaline conditions a time- and temperature-dependent decrease was observed for glutamine and asparagine with concomitant increases of glutamate and aspartate. Similar, but less prominent alterations were noted for the concentrations of methionine, glycine, tyrosine, histidine, arginine and ornithine. Almost independent of pH, there was an effect of temperature; after 24 h at 55 degrees C a significant increase of several per cent in a number of serum aminoacid concentrations was observed, presumably due to the hydrolysis of small proteins and peptides. For the purpose of aminoacid analysis it is recommended that samples be stored deproteinized, deep-frozen and at neutral pH.