A pH 7 buffer devoid of nitrogen, sulfur, and phosphorus for use in bacteriological systems.

Apparent pK values were determined for a series of commercially available carboxylic acids in a search for a buffer suitable for bacterial studies at pH 7 in media free from nitrogen, sulfur, and phosphorus. Of the compounds possessing pK' values near pH 7,3,6-endomethylene-1,2,3,6-tetrahydrophthalic acid (EMTA) was chosen as possessing suitable physical properties, cost, and purity for biological use. Aerobacter aerogenes and Escherichia coli grew normally in its presence but did not utilize it as a sole source and energy. Although good turbidimetric data could not be obtained, Pseudomonas aeruginosa responded in the same qualitative way. Therefore, EMTA promises to be useful in work on endogenous metabolism and in nutritional studies.