citric acid and sodium citrate having a ph between 3 5 and 7 application_number US 60784584 A description the inventive solutions are preferably prepared by mixing two solutions the first solution contains either citric acid monohydrate or anhydrous citric acid at a concentration of 0 002m the second solution contains either sodium citrate dihydrate or anhydrous sodium citrate at a concentration of 0 002m the two solutions are mixed together in selected volume ratios to yield a buffered solution having the desired ph as illustrated in the following table ______________________________________parts by volume of parts by volume of0 002 m citric acid 0 002 m sodium citrate resultingsolution solution ph______________________________________1 0 21 3 51 0 88 4 51 2 23 5 51 9 26 6 5______________________________________ next antimicrobial effective amounts of thimerosal and any active ingredients are added to the resulting mixture the resulting solution should have a ph in the range of 3 5 to 7 more preferably 3 5 to 5 and most preferably 4 5 to 5 ______________________________________ example 1 example 2ingredient mg ml mg ml______________________________________thimerosal 0 02 0 02citric acid monohydrate 0 22 0 23sodium citrate dihydrate 0 28 0 27purified distilled water q s ad 1 ml 1 mlph 4 4 5______________________________________ any active.