Acacia
Gummi Arabicum
Acacia is the secretions
obtained from the stems and branches of Acacia senegal Willdenow or other
species of the same genus (Leguminosae).
Description:
Colorless or light
yellow-brown, translucent or somewhat opaque spheroidal tears, or angular
fragments with numerous fissures on the surface; very brittle; the fractured
surface glassy and occasionally iridescent.
Odorless; tasteless, but
produces a mucilaginous sensation on the tongue.
Pulverized Acacia (1.0 g)
dissolves almost completely in 2.0 mL of water, and the solution is acid.
It is practically insoluble in
ethanol (95).
Identification:
To 1 g of powdered Acacia add 25 mL of water
and 1 mL of sulfuric acid, and heat under a reflux condenser in a boiling water
bath for 60 minutes. After cooling, add gently 2.0 g of anhydrous sodium
carbonate. To 1 mL of this solution add 9 mL of methanol, mix well, centrifuge,
and use the supernatant liquid as the sample solution. Separately, dissolve 10
mg of D-galactose in 1 mL water, add methanol to make 10 mL, and use this solution
as the standard solution (1). Proceed with L-arabinose and with L-rhamnose
monohydrate in the same manner as for the preparation of the standard solution
(1), and use so obtained solutions as the standard solution (2) and the
standard solution (3), respectively. Perform the test with these solutions as
directed under Thin-layer chromatography.
Spot 10 mL each of the sample solution and standard solutions (1), (2) and (3) on
a plate of silica gel for thin-layer chromatography. Develop the plate with a
mixture of acetone and water (9:1) to a distance of about 10 cm, and air-dry
the plate. Spray evenly 1-naphthol-sulfuric acid TS on the plate, and heat at 1050C for 5 minutes: the three spots from the sample solution are the same with
the spots of D-galactose, L-arabinose and L-rhamnose from the standard solution
in the color tone and the Rf value, respectively.
Purity:
(1) Insoluble residue.To 5.0 g of pulverized Acacia add 100 mL of
water and 10 mL of dilute hydrochloric acid, and dissolve by gentle boiling for
15 minutes with swirling. Filter the warm mixture through a tared glass filter (G3),
wash the residue thoroughly with hot water, and dry at 1050C for 5 hours: the
mass of the residue does not exceed 10.0 mg.
(2) Tannin-bearing gums.To 10 mL of a solution of Acacia (1 in 50)
add 3 drops of iron (III) chloride TS: no dark green color is produced.
(3) Glucose.Dissolve 10 mg of glucose in 1 mL of water, add methanol
to make 10 mL, and use this solution as the standard solution. Proceed with the
sample solution obtained in the Identification and the standard solution obtained
here as directed in the Identification: any spot at the Rf value
corresponding to glucose from the standard solution does not appear from the
sample solution.
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