Preparation of Stable Sodium Thiosulfate Solutions JARIES L. KASSNER AND ESTHER E. K.ISSSER University of Alabama, University, M a .
A
GREAT many investigations (1-8, 10, 11) of the preservation of sodium thiosulfate solutions have been made. Stable solutions of sodium thiosulfate are generally prepared (3) b y dissolving sterile sodium thiosulfate crystals in freshly boiled and cooled distilled water. Many solutions prepared b y this procedure maintain a constant titer over a long period of time, while other solutions prepared in exactly the same way decompose. Since sulfur-eating bacteria, Thioban’llus thioparus, are present in the air, the stopper may become contaminated before the bottle is closed or later when the bottle is opened. As a result, not all solutions prepared by using freshly boiled water are sterile. The present investigation was started in a n effort to find a better method for preparing stable solutions of sodium thiosulfate. It seemed logical to assume that some poison could be found t h a t would prevent the growth of the sulfur-eating
OF TABLE I. EFFECT
CHClP Ml./l.
CHLOROFORM ON
NORNALITT
Dec., 1936 h l a y , 1937 luov , 1938 Nov., 1939 h l a r . , 1940 ,\T
.v
s
.v
0.1054 0.1055 0,1057 0,1056 0.07 0.0963 0,0963 0.0963 0.30 0.0963 0.0852 0.0852 0.0852 0.15 0.0852 a N o more chloroform was added after t h e first day.
s
0.1054 0.0963 0.0852
The data for the more concentrated d u t i o n s are summarized in Table I. The solutions were not protected from the light but were not exposed to the direct rays of the sun. Unfortunately, the first dilute solutions (0.05 to 0.006 N) mere prepared and stored in clear glass, glass-stoppered bottles. These solutions maintained their titer to within less than 0.3 per cent from December, 1937, to May, 1938, but their normality had decreased so much by Sovember, 1938, that they were discarded and a new series was started. This time 3 liters of each solution were prepared and divided into three portions. Series A contained only water plus the sodium thiosulfate and was stored in ordinary glass, rubber-stoppered bottles. A white precipitate formed in each bottle within 6 months. Tests showed that the normality had decreased. T o each portion of series B and C 0.4 ml. of chloroform per liter was added. Series B was stored in clear glass, rubberstoppered bottles and series C was stored in dark brown (1,4) rubber-stoppered bottles. The data are summarized in Table 11. Chloroform has been used as a bactericide in the preservation of sodium thiosulfate solutions in this laboratory for the past 5 years. TABLE Series
bacteria and would not interfere with t’he subsequent use of the solution. -4preliminary investigation showed that chloroform offered the most promise of preventing the growth of these bacteria. It is a good germicide, practically insoluble in water, and soluble in rubber. K h e n a few drops are added to a solution in a rubber-stoppered bottle, the chloroform diffuses u p through the solution and dissolves in the stopper. It later diffuses out of the stopper into the air space above the solution, and keeps the solution sterile over a long period of time, even though the bottle is opened frequently. To see whether the addition of chloroform to a solution affected its titer, an approximately 0.05 N solution of sodium thiosulfate, containing 3 drops of chloroform per liter, was prepared and standardized. More chloroform was then added in 0.1-ml. por-
tions and the solution was restandardized until 0.5 ml. of chloroform had been added to 1 liter. The addition of 0.5 ml. of chloroform to 1 liter (the total time that elapsed during this addition was 3 days) of sodium thiosulfate did not affect the fourth significant figure in the normality of the solution. In all this work the solutions were standardized with a solution of potassium iodate (9) of approximately the same normality as the thiosulfate solution. The first st’andardization was made each time within less than 2 hours after the solution was prepared. Bureau of Standards potassium iodate, calibrated weights, and calibrated volumetric apparatus were used throughout this investigation. The solutions were prepared from ordinary distilled water and had a pH of 6.2 to 6.8. If the pH of the distilled water is unknown, it is advisable to add about 0.01 gram of sodium carbonate per liter. The pH of distilled water can be changed from 5.2 to 9.3 by adding 0.01 gram of sodium carbonate per liter. The sodium thiosulfate used in this work was not recrystallized or sterilized in any way before use. The solutions were stored in clear glass, rubber-stoppered bottles. The rubber stoppers were cleaned by boiling in dilute caustic solution. Further sterilization is not necessary because the chloroform dissolves in the stoppers.
11. EFFECTOF CHLOROFORM^
Nov., 1938
May, 1939
N
N
Nov., 1939 AV
Mar., 1940 N
0.05252 0.02643 0.01405 0.006695
0.05232 0.02875 0.01378 0.006663
0.05207 0.02556 0.01364 0.006640
B
0.05262
C
0,05252
0,02646 0.01406 0.006778
0.05251 0.02647 0.01406 0.006778 0.006776 (1 N o more chloroform wasi added in series B first prepared. 0.02646 0.01406
0 .05250 0.02645
0.05251 0.02646 0.01405 0.006772 0.006774 and C after t h e solutions were 0.01404
Summary Small amounts of chloroform prevent the decomposition of sodium thiosulfate stored in rubber-stoppered bottles. Solutions of approximately 0.05 N or less should be stored in brown glass, rubber-stoppered bottles. Sterile sodium thiosulfate solutions that have a p H of 6.2 or more maintain their titer over a long period of time. Literature Cited (1) Bellucci, Italo, and Damiani, I., Gaze. chim. ital., 64, 69 (1934). (2) Campbell, F. H., and Xatson, F. J., Chem. Eng. Mining Reu., 22, 340 (1930). (3) Xilpatrick, M., Jr., and Kilpatrick, >I. L., J. Am. Chem. Soc., 45. 2132 (1923). (4) Kolthoff, I: M.; Pharm. Teekblad, 56, 878 (1919); 2. anal. Chem., 60, 344 (1921). (5) La Mer, V. K., and Tomlinson, H. M., IND.ENO.CHEM.,Anal. Ed., 9, 588 (1937). (6) Rice, F. A,, Kilpatrick, M.,Jr., and Lemkin, K m . , J . Am. Chem. Soc., 45, 1361 (1923). (7) Topf, G., 2. anal. Chem., 26, 137 (1887). (8) Katson, F. J., SOC.Chem. I n d . Vzctorza P I O C .32, , 679 (1932). (9) Willard and Furman, “Elementary Quantitative Analysis”, 3rd ed., p. 269, New York, D . Van Nostrand Co. (1940). (10) Winkler, L. W., Pharm. Zentralhalle, 69, 369 (192s). (11) Yoshida, I., J. Chem. SOC.Japan., 48, 26 (1927).
