Packaging and storage—
Preserve in tight containers.
Labeling—
Label it to indicate whether it is of apple or of citrus origin.
Identification—
A:
Heat 1 g with 9 mL of water on a steam bath until a solution is formed, replacing water lost by evaporation: it forms a stiff gel on cooling.
B:
To a solution (1 in 100) add an equal volume of alcohol: a translucent, gelatinous precipitate is formed (distinction from most gums).
C:
To 10 mL of a solution (1 in 100) add 1 mL of
thorium nitrate TS, stir, and allow to stand for 2 minutes: a stable precipitate or gel forms (
distinction from gums).
D:
To 5 mL of a solution (1 in 100) add 1 mL of 2 N sodium hydroxide, and allow to stand at room temperature for 15 minutes: a gel or semigel forms (distinction from tragacanth).
E:
Acidify the gel from the preceding test with 3 N hydrochloric acid, and shake: a voluminous, colorless, gelatinous precipitate forms, which upon boiling becomes white and flocculent (pectic acid).
Loss on drying 
731
—
Dry it at 105
for 3 hours: it loses not more than 10.0% of its weight.
Lead—
Add 2.0 g of Pectin to 20 mL of nitric acid in a 250-mL conical flask, mix, and heat the contents carefully until the Pectin is dissolved. Continue the heating until the volume is reduced to about 7 mL. Cool rapidly to room temperature, transfer to a 100-mL volumetric flask, and dilute with water to volume. A 50.0-mL portion of this solution contains not more than 5 µg of lead (corresponding to not more than 0.0005% of Pb) when tested according to the limit test for
Lead 251, 15 mL of ammonium citrate solution, 3 mL of potassium cyanide solution, and 500 µL of hydroxylamine hydrochloride solution being used. After the first dithizone extractions, wash the combined chloroform layers with 5 mL of water, discarding the water layer and continuing in the usual manner by extracting with 20 mL of dilute nitric acid (1 in 100).
Sugars and organic acids—
Place 1 g in a 500-mL flask, moisten it with 3 to 5 mL of alcohol, pour in rapidly 100 mL of water, shake, and allow to stand until solution is complete. To this solution add 100 mL of alcohol containing 0.3 mL of hydrochloric acid, mix, and filter rapidly. Measure 25 mL of the filtrate into a tared dish, evaporate the liquid on a steam bath and dry the residue in a vacuum oven at 50
for 2 hours: the weight of the residue does not exceed 20 mg.
Organic volatile impurities, Method IV 467:
meets the requirements.
Assay for methoxy groups—
Transfer 5.00 g of Pectin to a suitable beaker, and stir for 10 minutes with a mixture of 5 mL of hydrochloric acid and 100 mL of 60 percent alcohol. Transfer to a sintered-glass filter (30- to 60-mL crucible or Büchner type, coarse), and wash with six 15-mL portions of the hydrochloric acid—60 percent alcohol mixture, followed by 60 percent alcohol until the filtrate is free from chlorides. Finally wash with 20 mL of alcohol, dry for 1 hour at 105
, cool, and weigh. Transfer exactly one-tenth of the total net weight of the dried sample (representing 500 mg of the original unwashed sample) to a 250-mL conical flask, and moisten with 2 mL of alcohol. Add 100 mL of carbon dioxide-free water, insert the stopper, and swirl occasionally until the Pectin is completely dissolved. Add 5 drops of phenolphthalein TS, titrate with 0.5 N sodium hydroxide VS, and record the results as the
initial titer. Add 20.0 mL of 0.5 N sodium hydroxide VS, insert the stopper, shake vigorously, and allow to stand for 15 minutes. Add 20.0 mL of 0.5 N hydrochloric acid VS, and shake until the pink color disappears. Add
phenolphthalein TS, and titrate with 0.5 N sodium hydroxide VS to a faint pink color that persists after vigorous shaking: record this value as the
saponification titer. Each mL of 0.5 N sodium hydroxide used in the
saponification titer is equivalent to 15.52 mg of –OCH
3.
Assay for galacturonic acid—
Each mL of 0.5 N sodium hydroxide used in the total titration (the
initial titer added to the
saponification titer) in the
Assay for methoxy groups is equivalent to 97.07 mg of C
6H
10O
7.
