Evaluation of various substances to prevent adsorption of tuberculin purified protein derivative (PPD) to glass surfaces.

It is well known that a dilute tuberculin PPD solution (1 IU or 5 IU per dose) very rapidly loses its potency owing to adsorption of tuberculoprotein to the wall of the container into which it is dispensed. The amount of tuberculoprotein adsorbed per cm(2) of glass surface has been measured for phosphate-buffered saline over a wide pH range (pH 1 to pH 10). The maximum adsorption was found at pH 4 (0.31 mug/cm(2)) and the least at between pH 6 and pH 10 (0.15 mug/cm(2)). The rate of adsorption of tuberculoprotein to glass was not changed when the phosphate-buffered saline was replaced by borate-buffered saline. Tuberculin PPD prepared by the ammonium sulfate precipitation method, by the trichloroacetic acid precipitation method and by a combination of both methods adsorbed equally well to glass and no difference in the rate of adsorption for these tuberculoproteins was found.Forty-two substances in addition to Tween 80 were tested for their property to prevent adsorption of tuberculoprotein to glass in dilute tuberculin PPD solutions (50 IU/ml of (14)C-labelled PPD). The most efficient anti-adsorption agents were found to be nonionic surfactants, some ionic surfactants and some colloidal substances; polypeptides and non-surface-active substances of low molecular weight showed little or no anti-adsorption property.The labelling of PPD with (14)C has proved to be a valuable tool, particularly for long-term adsorption studies and for screening substances to be used as efficient anti-adsorption agents. These studies have permitted the selection of agents which could be added to dilute solutions of tuberculin PPD (10 IU/ml to 500 IU/ml or 0.2 mug/ml to 10 mug/ml respectively) in order to avoid loss of potency due to adsorption.