Identification method of sodium alginate

　　Alginate is light yellow powder; Odorless; Almost tasteless, insoluble in water, methanol, ethanol, acetone and chloroform, soluble in sodium hydroxide alkali solution. It is helpful for suspension, thickening, emulsification and adhesion. Can be used as microcapsule material, or as coating and film-forming material.

　　Physical and chemical properties: relative density: 1.67g/cm3.

　　Alginic acid is a polysaccharide formed by linear polymerization of mono-uronic acid, and the monomer is β -1,4-D- mannuronic acid (m) and α -1,4-L- guluronic acid (g). M and G units are connected by 1,4 glycosidic bonds in the form of M-M, G-G or M-G to form a block copolymer. The experimental formula of alginic acid is (C6H8O6)n, and its molecular weight ranges from 10,000 to 600,000.

　　(1) Take about 30mg of this product, add 5 ml of sodium hydroxide solution (0.1 mol/L), shake it to dissolve, add 1ml of calcium chloride test solution, and stir it with a glass rod to produce colloidal precipitate that sticks to the glass rod.

　　(2) Take about 30mg of this product, add 5 ml of sodium hydroxide solution (0.1 mol/L), shake it to dissolve, and add 1ml of dilute sulfuric acid to produce colloidal precipitation.

　　(3) Take about 10mg of this product, add 5ml of water, add 1ml of 1%1,3- dihydroxynaphthalene ethanol solution and 5ml of hydrochloric acid, shake well, boil for 5 minutes, let cool, transfer to a 60ml separatory funnel, wash the container with 5ml of water, add 15ml of isopropyl ether into the separatory funnel, shake and extract, separate the ether layer, and make a blank control at the same time.

　　【 Inspection 】 Take 1.5g of this product for acidity, add 50ml of water and shake for 5min.

　　Take 0.1g of starch and add sodium hydroxide solution (1→ 2500)100ml, shake to dissolve, take 5ml, add 1 drop of iodine test solution, and do not produce transient blue.

　　Loss on drying takes this product and dries it at 105℃ for 4 hours. The weight loss shall not exceed 15.0%.

　　Take 0.5g of this product for ignition residue, and the residual residue shall not exceed 5.0%.

　　Take 1g of iron salt, slowly ignite until it is completely carbonized, and ignite until it is completely ashed at 500 ~ 600℃. Add 3ml of hydrochloric acid to dissolve the residue, then move it into a 50ml volumetric flask, add water to the scale, shake well, accurately measure 5ml, put it into a Nessler colorimetric tube, and add water to make 25ml. If it is colored, it shall not be deeper than the control solution made of 5ml of standard iron solution (0.05%).

　　The heavy metal is taken from the residue left under the ignition residue, and the heavy metal content shall not exceed 40 parts per million according to the law.

　　Take 0.5g of arsenic salt, add 0.5g of anhydrous sodium carbonate, mix well, add a small amount of water to moisten it, slowly ignite it with a small fire until it is completely ashed, let it cool, add a small amount of hydrochloric acid until the residue no longer produces bubbles, add 5ml of hydrochloric acid, and dissolve it with 23ml of water. The arsenic content shall not exceed three parts per million.

　　When the viscosity is 20℃, take 1% aqueous solution of this product, adjust it to neutrality with sodium hydroxide test solution, and the viscosity should be less than 50×10<-3>Pa<[0]>s as measured by rotary viscometer (choose No.2 rotor, rotating speed is 30n/min or 60n/min).

　　Take 0.5g of this product, weigh it accurately, add 50ml of water and 30ml of calcium acetate solution (0.25mol/L)30ml), shake it evenly, stand for 1h, add 5 drops of phenolphthalein indicator solution, titrate with sodium hydroxide solution (0.1mol/L), and correct the titration result with blank test.