How to purify Sodium Alginate (NaC6H7O6) and Trisodium Phosphate (Na3PO4)?

Question

I tried to dissolve Sodium Alginate (SA) with Trisodium Phosphate (TSP). At first, it was successfully dissolved resulting clear, bright pink, thick liquid gel. Then I tried another experiment with TSP & SA from different source. They are more coarse & grainy than the first one. They results yellowish & unclear color. I don't know what caused this. Is it the TSP or SA? I also don't know whether they have same quality with the first ones. I suspected the purity level of both substances. Is there any methods to determine the purity? and the method to purify them?

I mixed the TSP with H2O and stirred it well. Then, I add SA gradually while I keep stirring it. SA normally won't dissolve quickly. The same technic I used for different source (mentioned above), but gives different results. The source 1 shows a beautiful clear pink color right after I pour in the SA and dissolve faster, but not the case with source 2. Source 2 tend to gum & has yellowish color. Is there any other methods?

Answer 1

The difference is the source of the Sodium alginate. Alginate is a linear co-polymer of beta-D-Mannuronic acid and alpha-L-Guluronic acid (often called the M and the G monomers).

It sounds like your source for Alginate have slightly different chemical compositions. It is not a matter of one of these being more pure than the other. If you want to repeat the first results exactly, you must use an Alginate from the same source (or with the exact same chemical composition.

Answer 2

The cause lies in the mixing conditions.