Detection methods for trace NaHS and Na2S2O3 in desulfurization solution

“Can a small amount of sodium thiosulfate in a solution be detected by titration? Personally, I think it’s not possible! Although in theory sodium thiosulfate can be determined by the iodometric method, it is practically not feasible! First, there may be interference from other substances in the solution! Second, the desulfurization solution is very dark in color (I’m not sure if yours is the same), which makes it difficult to determine the endpoint!

Na2S2O3 in the desulfurization solution is a by-product of the desulfurization process. Its concentration not only reflects the desulfurization capacity of the solution but also serves as an important reference for operators when adding materials to the desulfurization solution. Therefore, it is crucial to analyze the concentration of Na2S2O3 in the desulfurization solution. Since reducing ions such as S2— in the desulfurization solution interfere with the determination of Na2S2O3, it is necessary to find an appropriate method to eliminate the interference from these reducing ions during the measurement. Generally, there are three methods for determining the content of Na2S2O3: (1) Adding a zinc carbonate suspension to the desulfurization solution to precipitate interfering ions such as S2−, filtering, and then using the iodometric method on the filtrate to back-titrate and analyze the content of Na2S2O3 ； (2) An excess of cadmium chloride is added to the desulfurization solution to precipitate interfering ions such as S2−, and the iodometric method is then used directly for titrimetric analysis of the Na2S2O3 content ； (3) An appropriate amount of boric acid is added to the desulfurization solution, and heating is applied to remove major interfering ions such as S2— from the solution. After cooling, acetic acid is added for acidification, followed by back-titration using the iodometric method to analyze the content of Na2S2O3. Acetic acid-sodium acetate buffer, pH≈4.5 ； Starch solution 5g/L ； Iodine standard solution c(1/2 I2) = 0.1 mol/L ； Sodium thiosulfate standard solution, c(Na2S2O3) = 0.1002 mol/L ； 10% acetic acid solution ； Boric acid solution 100 g/L ； The concentration of the Na2S standard solution is c(1/2Na2S) = 0.0952 mol/L. An accurate volume of the Na2S2O3 standard solution and the Na2S standard solution is taken, to which 10 mL of boric acid solution and 5 mL of acetic acid solution are added. The mixture is heated to boiling for 10 minutes; after cooling, another 5 mL of acetic acid solution is added, followed by 10 mL of acetic acid-sodium acetate buffer solution. Then 10.00 mL of iodine standard solution is added, and titration is carried out backwise using sodium thiosulfate standard solution, with starch as an indicator.

This method seems really complicated, but it can solve the problem, which is the most important thing. Thanks to the person who posted above :handshake