According to the USP method:
Dissolve 26 grams of sodium thiosulfate 5 A along with 200 milligrams of sodium carbonate Na2CO3 in one liter of freshly boiled and cooled distilled water.
The reason for increasing sodium carbonate is that thiosulfate becomes slightly alkaline and becomes more stable. Acidic pH is not suitable for thiosulfate.
Important:
Thiosulfate is sensitive to microorganisms. Therefore, it is better to prevent contamination in the solution as much as possible. This is one of the reasons for boiling water before making the solution.
If you want to increase this level of accuracy, you can sterilize your thiosulfate container inside it.
It is recommended to keep the thiosulfate solution in a glass container with a screw cap and keep it cool (if possible in the refrigerator). Because not closing the lid of the container well and keeping it in a place with high temperature will increase the possibility of evaporation during the next few days and the molarity of the solution will change.
The prepared thiosulfate solution should be standardized at least once a week.
