AOAC Official Method 940.05 Cream of Tartar and Free Tartaric Acid in Tartrate Powders
Total, Combined, and Free Tartaric Acid
First Action 1940
Final Action
A. Determination
To 2.5 g test portion in 250 mL volumetric flask add 100 mL H2O at ca 50°C, and hold at room temperature ca 30 min, shaking occasionally.
Cool, dilute to volume withH2O, shake vigorously, and filter through large fluted paper. Pipet 2 portions of 100 mL each of clear filtrate into 250 mL beakers, and evaporate to ca 20 mL. To 1 portion add 3.5 mL ca 1M KOH. Mix well, and add 2 mL CH3COOH. Again mix well and add 100 mL alcohol, stirring constantly.
Treat other portion similarly, but use 1M NaOH instead of KOH. Then treat each mixture separately as follows: Cool to ca 15°C, stir vigorously ca 1 min, and leave in refrigerator overnight. Collect precipitate in Gooch on thin, glass fiber pad. Rinse beaker with ca 75 mL ice-cold 80% alcohol, carefully washing down sides of beaker. Finally wash sides of crucible with 25 mL alcohol and suck dry. Transfer contents of crucible to original beaker with ca 100 mL hot H2O, and titrate with 0.1M NaOH, 936.16 (see A.1.12), using phenolphthalein. Designate titer of portion treated with KOH as “x” and that treated with NaOH as “y.”
B. Calculations
Total tartaric acid, % = 1.5(x + 0.6)
Cream of tartar, % = 1.88(y + 0.6)
Free tartaric acid, % = 1.5(x - y)
In above formulas “0.6” represents solubility of cream of tartar in reaction mixture in terms of 0.1M alkali.
