A method for maintaining stability in reaction of solutions during sterilization.

Abstract

Of the various means employed to prevent the marked changes in H-ion concentration which solutions undergo during sterilization, the use of relatively large quantities of Na or K phosphate has proved the most satisfactory. While this method may be suitable for certain types of solutions, the presence of large quantities of phosphate in solutions used for intravenous injection, and serological procedures, is undesirable. A very much smaller quantity of phosphate added to an adjusted solution after sterilization will maintain a stable reaction satisfactorily, but the disadvantage of adjustment after sterilization is obvious.

An attempt to adjust and buffer certain solutions before sterilization with an amount of phosphate as low as that found in the circulatory blood plasma, led to recognition of the fact that the chief variable in the solutions tested was their CO₂ content. The degree of CO₂ exchange between fluid and surrounding air during heating determined the reaction of the solution afterwards. Elimination of this variable by the use of CO₂ free water and CO₂ free reagents made it possible to autoclave 0.9 per cent NaCl solution, dilute gelatin solutions and water without changing, to more than a slight degree, their initial reaction. The method employed was as follows:

The water employed was twice distilled and rendered CO₂ free by boiling just before use or preferably by bubbling CO₂ free air through it for 24 hours. After the addition of the solute 1 per cent M/7.5 H₃PO₄ (previously boiled and kept in a bottle stoppered with a soda-lime trap) was added. Next, m/7.5 NaOH, prepared in the same way as the H₃PO₄, was added in sufficient quantity to bring the solution to the desired reaction. The solution was autoclaved at 14-15 lbs. steam pressure, care being taken not to let the steam escape during sterilization. The autoclave was not opened until the following morning.