Agar
»Agar is the dried,hydrophilic,colloidal substance extracted from Gelidium cartilagineum(Linné)Gaillon (Fam.Gelidiaceae),Gracilaria confervoides(Linné)Greville (Fam.Sphaerococcaceae),and related red algae (Class Rhodophyceae).
Botanic characteristics—
Agar—
Usually in bundles consisting of thin,membranous,agglutinated strips or in cut,flaked,or granulated forms.May be weak yellowish orange,yellowish gray to pale yellow,or colorless.Is tough when damp,brittle when dry.
Histology—
In water mounts Agar appears granular and somewhat filamentous;a few fragments of the spicules of sponges and a few frustules of diatoms may be present;in Japanese Agar,the frustules of Arachnoidiscus ehrenbergiiBaillon often occur,being disk-shaped and from 100µm to 300µm in diameter.
Powdered Agar—
White to yellowish white or pale yellow;in chloral hydrate TSits fragments are transparent,more or less granular,striated,and angular,and occasionally they contain frustules of diatoms.
Identification—
A:
Iodine TScolors some of the fragments of Agar bluish black,with some areas reddish to violet.
B:
When boiled with 65times its weight of water for 10minutes,with constant stirring,and adjusted to a concentration of 1.5%,by weight,with hot water,Agar forms a clear liquid which congeals at 32
to 39to form a firm resilient gel,which does not melt below 85.
to 39to form a firm resilient gel,which does not melt below 85.
Microbial limits á61ñ—
It meets the requirements of the test for absence of Salmonellaspecies.
Water,Method IIIá921ñ—
If necessary,cut it into pieces from 2mm to 5mm square,and dry at 105for 5hours:it loses not more than 20.0%of its weight.
for 5hours:it loses not more than 20.0%of its weight.
Total ash á561ñ:
not more than 6.5%,on a dry-weight basis.
Acid-insoluble ash á561ñ:
not more than 0.5%,on a dry-weight basis.
Foreign organic matter á561ñ:
not more than 1.0%.
Limit of foreign insoluble matter—
To 7.5g add sufficient water to make 500g,boil for 15minutes,and readjust to the original 500g.To 100g of the uniformly mixed material add hot water to make 200mL,heat almost to boiling,filter while hot through a tared filtering crucible,rinse the container with several portions of hot water,and pass these rinsings through the crucible.Dry the crucible and its contents at 105to constant weight:not more than 15mg (1.0%)remains.
to constant weight:not more than 15mg (1.0%)remains.
Arsenic,Method IIá211ñ:
3ppm.
Lead á251ñ:
0.001%.
Heavy metals,Method IIá231ñ:
0.004%.
Limit of foreign starch—
Asolution made by boiling 0.10g of it in 100mLof water does not,upon cooling,produce a blue color upon the addition of iodine TS.
Organic volatile impurities,Method IVá467ñ:
meets the requirements.
Gelatin—
Dissolve about 1g in 100mLof boiling water,and allow to cool to about 50.To 5mLof the solution add 2to 3drops of a mixture of 0.2Mpotassium dichromate solution and 3Nhydrochloric acid (4:1):no yellow precipitate is formed.
.To 5mLof the solution add 2to 3drops of a mixture of 0.2Mpotassium dichromate solution and 3Nhydrochloric acid (4:1):no yellow precipitate is formed.
Water absorption—
Place 5.0g in a 100-mLgraduated cylinder,fill to the mark with water,mix,and allow to stand at 25for 24hours.Pour the contents of the cylinder through moistened glass wool,allowing the water to drain into a second 100-mLgraduated cylinder:not more than 75mLof water is obtained.
for 24hours.Pour the contents of the cylinder through moistened glass wool,allowing the water to drain into a second 100-mLgraduated cylinder:not more than 75mLof water is obtained.
Auxiliary Information—
Staff Liaison:Catherine Sheehan,B.Sc.,Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 2951
Phone Number:1-301-816-8262