GB 5009.232-2016Fruit and vegetable products -- Determination of formic acid content -- Gravimetric method (English PDF)

3.1 Reagents

3.1.1 Barium carbonate (BaCO3) or calcium carbonate (CaCO3).

3.1.2 Mercury chloride (HgCl2).

3.1.3 Sodium chloride (NaCl).

3.1.4 Sodium acetate (CH3COONa).

3.1.5 Hydrochloric acid (HCl): the concentration is 37% (mass fraction) and the density

is 1.19 g/mL.

3.1.6 Tartaric acid (C4H6O6).

3.1.7 Ethanol (CH3CH2OH).

3.1.8 Diethyl ether (CH3OCH3).

so that the solution volume in flasks A and B do not vary by more than 5 mL. When the distillate in the conical flask is 1 000 mL ~ 1 500 mL, stop heating and discard the distillate.

5.2.3 Use a F15 cm rapid quantitative filter paper to filter the hot solution in the flask

into a 500 mL conical flask; use hot water to wash flask B of Figure 1 for 3 ~ 4 times;

collect the washing solution which is filtered through the filter paper, to make the final solution in the conical flask at about 250 mL; transfer the filtrate to an evaporating dish and place it on an electric furnace for heating; after the solution is evaporated to about 100 mL, transfer it to another 500 mL conical flask.

5.2.4 Add 10 mL of 500 g/L sodium acetate solution, 2 mL of 10% hydrochloric acid

solution and 25 mL of mercuric chloride-sodium chloride mixture to the conical flask;

install the reflux condenser in the water bath for boiling water bath for 2h; take out for cooling (the barium formate quantitatively reduce the mercury chloride to mercurous chloride precipitate).

5.2.5 Wash and dry the crucible-style filter; balance it in a dryer for 0.5 h; weigh and accurate to 0.000 2 g. Use cold water to wash all the precipitate into the filter; suction filter; use ethanol and diethyl ether respectively to wash the precipitate.

5.2.6 Place the crucible-style filter that contains mercurous chloride precipitate in an oven at 100°C ± 2°C for 1 h; then take it out and place it in a dryer for cooling; weigh and accurate to 0.000 2 g.