Packaging and storage—
Preserve in well-closed containers.
Identification—
A:
Place about 2 g in a 400-mL beaker, moisten it with about 4 mL of isopropyl alcohol, add 200 mL of cold water with vigorous stirring, and continue stirring until the gum is completely and uniformly dispersed: an opalescent, viscous solution results.
B:
Place about 100 mL of the solution prepared in Identification test A in a 400-mL beaker, heat in a boiling water bath for about 10 minutes, and cool: no appreciable increase in viscosity is produced (distinction from locust bean gum—see Reagents in the section Reagents, Indicators, and Solutions).
Loss on drying 
731
—
Dry it at 105
for 5 hours: it loses not more than 15.0% of its weight.
Acid-insoluble matter—
Transfer about 1.5 g of Guar Gum, accurately weighed, to a 250-mL beaker containing 150 mL of water and 1.5 mL of sulfuric acid. Cover the beaker with a watch glass, and heat the mixture on a steam bath for 6 hours, rubbing down the wall of the beaker frequently with a rubber-tipped stirring rod, and replacing any water lost by evaporation. At the end of the 6-hour heating period add about 500 mg of a suitable filter aid, accurately weighed, and filter through a suitable tared, ashless filter. Wash the residue several times with hot water, dry the filter and its contents at 105
for 3 hours, cool in a desiccator, and weigh: the amount of acid-insoluble matter, determined by subtracting the weight of filter aid from that of the residue, is not more than 7.0% of the Guar Gum taken.
Lead 251—
Prepare a
Test Preparation as directed in the chapter, and use 10 mL of
Diluted Standard Lead Solution (10 µg of Pb) for the test: the limit is 0.001%.
Heavy metals, Method II 231:
0.002%.
Protein—
Transfer about 1.0 g of Guar Gum, accurately weighed, to a 500-mL Kjeldahl flask, and proceed as directed for
Method I under
Nitrogen Determination 461: the amount of protein, obtained by multiplying by 6.25 the percentage of nitrogen determined, is not more than 10.0% of the Guar Gum taken.
Starch—
To a 1 in 10 solution of Guar Gum add a few drops of
iodine TS: no blue color is produced.
Content of galactomannans—
Subtract from 100.0 the total percentages of Loss on drying, Total ash, Acid-insoluble matter, and Protein: the content of galactomannans is not less than 66.0%.
