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Standard and Specification > Synthetic Additives > Sodium Alginate
156. Sodium Alginate  
[Compositional Specifications of Sodium Alginate]
Content Sodium Alginate when dried, contains not less than 90.0% of sodium alginate. 
Description Sodium Alginate occurs as a white to yellowish-white powder. It is tasteless and almost odorless. 
Identification (1) To 0.5 g of Sodium Alginate, add 50 ml of water in small portions while stirring, warm at 60~70° for 20 minutes while stirring occasionally to make the solution homogeneous, and cool. Use this solution as the test solution.

(A) To 5 ml of the test solution, add 1 ml of calcium chloride solution. A gelatinous precipitate is formed immediately.

(B) To 10 ml of the test solution, add 1 ml of diluted sulfuric acid (1→20). A gelatinous precipitate is formed immediately.

(C) To 1 ml of the test solution, add 1 ml of ammonium sulfate saturated solution. No precipitate is formed.

(2) The residue on ignition of Sodium Alginate responds to the test for Sodium Salt.  
Purity (1) pH : Weigh 0.5 g of Sodium Alginate, add in small portions to 50 ml of water while stirring, warm at 60~70° for 20 minutes while stirring occasionally to make the solution homogeneous, cool and measure. When pH of the solution is measured by the Free Electronic method, it should be pH 6.0 - 8.0.  

(2) Sulfate : To prepare Test Solution, weigh 0.1 g of Sodium Alginate, add 20 ml of water to make it pasty, add 1 ml of hydrochloric acid, shake well, heat in a water bath for several minutes, cool, and filter. Wash the container three times with 10 ml of water each time, filter the washings through the filter paper used above, combine the filtrates, and add water to make 50 ml. Measure 10 ml of this solution, and add water to make 50 ml. Test for Sulfates. To Prepare Reference solution To 0.4 ml of 0.01 N sulfuric acid, add 1 ml of diluted hydrochloric acid (1→4) and water to make 50 ml.

(3) Arsenic : 0.25 g of Sodium Alginate is placed in a platinum, quartz, or porcelain crucible. 10 ml solution of magnesium nitrate in ethyl alcohol (1→50) is added to the crucible and then alcohol is ignited. It is then reduced to ash by heating at 450∼550°. If carbonaceous substance persists, it is wetted with minute amount of nitric acid, which is further heat-treated at 450∼550°. After cooling, 3 ml of hydrochloric acid is added to the residue, which is then dissolved by heating in a water bath. When test for arsenic is carried out with this test solution, it should not be more than 4ppm.

(4) Heavy metals : Sodium Alginate is tested by (2) Purity for [Guar Gum] (not more than 20ppm).

(5) Phosphate : Weigh 0.1 g of Sodium Alginate, add in small portions to 20 ml of water while stirring, and warm at 60~70° for 20 minutes while stirring occasionally to make the solution homogeneous. Cool, add 5 ml of diluted nitric acid (1→4) and 20 ml of ammonium molybdate solution, and warm. No yellow precipitates are formed. 
Loss on Drying When Sodium Alginate is dried for 4 hours at 105°, the loss should not be more than 15%. 
Residue on Ignition Sodium Alginate is dried for 4 hours at 105°. When thermogravimetric analysis is done with approximately 1 g of dried material, weight the amount of residues should be 33~37%. 
Assay Glass filter (1G4) is dried for 30 minutes at 80° under vacuum, cooled in a desiccator, and weighed accurately. Approximately 0.5 g of dried material is accurately weighed and dissolved in 10 ml of sodium hydroxide solution (1→25), where 90 ml of water is added. It is filtered, if necessary. To this solution, 15 ml of hydrochloric acid (1→3) and 100 ml of 90% alcohol are added, which is well shaken and set-aside for 2 hours. It is centrifuged and the supernatant is discarded. 10 ml of 90% alcohol is added to the residues, which is well shaken and centrifuged. The supernatant is discarded. This is repeated until the supernatant does not show a reaction of chlorides. The resulting residues are filtered through the glass filter using 90% alcohol. The residue is washed with acetone, which is dried for 1 hour at 80° under vacuum. It is set-aside in a desiccator and accurately weighed. The content is calculated by the following equation.

                                                               1.125 x Weight of residue(g)
Content of Sodium Alginate(%) = ━━━━━━━━━━━━━━━ x 100
                                                                    Weight of sample(g)