Extract
First Action 1942
Indicator Method (Final Action 1965)
Titratable acidity can be expressed conventionally in g acid per 100 g or per 100 mL product, as appropriate, by using the factor appropriate to the acid; for malic acid use 0.067 as factor; oxalic acid, 0.045; citric acid monohydrate, 0.070; tartaric acid, 0.075; sulfuric acid, 0.049; acetic acid, 0.060; lactic acid, 0.090.
...
Glass Electrode Method (Final Action 1980)
Before use, check apparatus with standard buffer solutions, 964.24 (seeA.1.04) and Table 964.24 (seeA.1.04). Rinse glass electrode in H2O several times until reading is ca pH 6. Immerse electrodes in test solution contained in beaker. (Test solution should titrate 10–50 mL 0.1M NaOH and be contained in initial volume of 100–200 mL.) Stir moderately. Add alkali quite rapidly until near pH 6. Then add alkali slowly to pH 7. After pH 7 is reached, finish titration by adding 0.1M alkali 4 drops at time, and record total volume and pH reading after each addition. (Add whole drops, so that fraction of drop does not remain on buret tip.) Continue titration ≥4 drops beyond pH 8.1, and interpolate data for titration corresponding to pH 8.1. pH values used for interpolation should lie in range 8.10 ± 0.2.