THE KINETICS AND MECHANISM OF THE HYDROLYSIS OF CREATININE IN URINE

Creatinine in urine concentrations are routinely measured at Aldermaston by an autoanalyser, using the Jaffe reaction, as an index of urinary excretion rates. These values are used in calculations to estimate the body content of radionuclides from their urinary excretion rates. Unfortunately, creatinine in urine concentrations gradually decrease with sample age due to pseudo first order hydrolysis of creatinine to give creatine in the presence of ammonia. This reaction may be arrested or reversed by mineral acid. After storage at ambient temperatures for several weeks the creatinine in urine concentration falls by around 20% so it is good practice to analyse samples soon after provision. The activation energy for the hydrolysis of creatinine in urine is around 60 KJ/mol over the range 20-70-degrees-C. Hence, raising the temperature by 10-degrees-C approximately doubles the reaction rate.