Stability of a dilute solution of tuberculin purified protein derivative at extreme temperatures

The stability of a dilute solution of tuberculin purified protein derivative (PPD) at extreme temperatures has been studied. It was found that tuberculin PPD retained its potency for a period of at least 91 days at −28°C. However, the same preparation stored at 60°C showed some evidence of a loss of potency as early as 5 days after storage, and its overall potency declined up to 47 days, and then remained constant. No loss of phenol was evinced at −28°C, whereas, at 60°C there was a significant loss of phenol.