Agar
Agar
Agar is the solid residue
obtained by freezing dehydration of a mucilage derived from Gelidium elegans Kuetzing, other species
of the same genus (Gelidiaceae), or other red algae (Rhodophyta).
Description:
White, translucent rectangular
column, string or flakes. Rectangular column about 26 cm in length, 4 cm square
in cross section; a string of about 35 cm in length and about 3 mm in width;
flakes about 3 mm in length; externally, with wrinkles and somewhat lustrous,
light and pliable.
Odorless; tasteless and
mucilagenous.
It is practically insoluble in
organic solvents.
A boiling solution of Agar (1
in 100) is neutral.
Identification:
(1) To a fragment of Agar add dropwise iodine TS: a dark blue to
reddish purple color develops.
(2) Dissolve 1 g of Agar in 65 mL of water by boiling for 10
minutes with constant stirring, and add a sufficient amount of hot water to
make up the water lost by evapora- tion: the solution is clear. Cool the
solution between 30oC and 39oC: the solution forms a
firm, resilient gel, which does not melt below 859C.
Purity:
(1) Sulfuric acid.Dissolve 1.0
g of Agar in 100 mL of water by boiling: the solution is not acidic.
(2) Sulfurous acid and starch.To 5 mL of the solution obtained in
(1) add 2 drops of iodine TS: the solution is not decolorized immediately, and
does not show a blue color.
(3) Insoluble matter.To 7.5 g of Agar add 500 mL of water, boil for
15 minutes, and add water to make exactly 500 mL. Measure exactly 100 mL of the
solution, add 100 mL of hot water, heat to boiling, filter while hot through a tared
glass filter (G3), wash the residue with a small amount of hot water, and dry
the residue at 105oC for 3 hours: the mass of the residue is not more than 15.0
mg.
(4) Water absorption.To 5.0 g of Agar add water to make 100 mL,
shake well, allow to stand at 25oC for 24 hours, and filter through
moistened glass wool in a 100 mL graduated cylinder: the volume of the filtrate
is not more than 75 mL.
Loss on drying:
Not more than 22.0z (6 hours).
Total ash:
Not more than 4.5z.
Acid-insoluble ash:
Not more than 0.5z.
Containers and storage:
Containers.Well-closed containers.
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