Xanthan Gum

» Xanthan Gum is a high molecular weight polysaccharide gum produced by a pure-culture fermentation of a carbohydrate with Xanthomonas campestris, then purified by recovery with Isopropyl Alcohol, dried, and milled. It contains d-glucose and d-mannose as the dominant hexose units, along with d-glucuronic acid, and is prepared as the sodium, potassium, or calcium salt. It yields not less than 4.2 percent and not more than 5.0 percent of carbon dioxide, calculated on the dried basis, corresponding to not less than 91.0 percent and not more than 108.0 percent of Xanthan Gum.

Packaging and storage— Preserve in well-closed containers.

Identification— To 300 mL of water in a 400-mL beaker, previously heated to 80

and stirred rapidly by mechanical means, add, at the point of maximum agitation, a dry blend of 1.5 g of Xanthan Gum and 1.5 g of locust bean gum. Stir until the mixture dissolves, and then continue stirring for 30 minutes longer. Do not allow the temperature of the mixture to drop below 60

during the stirring. Discontinue stirring, and allow the mixture to cool at room temperature for not less than 2 hours: a firm, rubbery gel forms after the temperature drops below 40

, but no such gel forms in a control solution prepared in the same manner with 3.0 g of Xanthan Gum and without locust bean gum.

Viscosity

911

— Place 250 mL of water in a 400-mL beaker, and add a dry blend of 3.0 g of Xanthan Gum and 3.0 g of potassium chloride slowly while stirring at 800 rpm, using a low-pitched propeller-type stirrer. Add an additional quantity of 44 mL of water, rinsing the walls of the beaker. Approximately 10 minutes after the addition of the dry blend of Xanthan Gum and the potassium chloride to the water, remove the beaker from the propeller-type stirrer, and vigorously stir the solution by hand to ensure that all the particles around the edge of the beaker are in solution. Return the beaker to the stirrer, and agitate at 800 rpm for a total mixing time of 2 hours. Then adjust the temperature to 24 ± 1

, and stir by hand in a vertical motion to eliminate any thixotropic effects or layering. [note—Each hand mixing should be not more than 15 to 30 seconds, and the last hand mixing should occur immediately prior to measuring the viscosity.] Equip a suitable rotational viscosimeter with a spindle having a cylinder 1.27 cm in diameter and 0.16 cm high attached to a shaft 0.32 cm in diameter, the distance from the top of the cylinder to the lower tip of the shaft being 2.54 cm, and the immersion depth being 5.00 cm (No. 3 spindle). With the spindle rotating at 60 rpm, immediately observe and record the scale reading. Convert the scale readings to centipoises by multiplying the readings by the constant for the viscosimeter spindle and speed employed. The viscosity at 24

is not less than 600 centipoises.

Microbial enumeration tests

and Tests for specified microorganisms

— It meets the requirements of the tests for Salmonella species and Escherichia coli.

Loss on drying

731

— Dry it at 105

for 2.5 hours: it loses not more than 15.0% of its weight.

Ash— Accurately weigh about 3 g in a tared crucible, and incinerate at about 650

until free from carbon. Cool the crucible and its contents in a desiccator, and weigh: the weight of the ash is between 6.5% and 16.0%, calculated on the dried basis.

Arsenic, Method II

211

: 3 µg per g.

Lead

251

— Prepare a Test Preparation as directed in the chapter, and use 5 mL of Diluted Standard Lead Solution (5 µg of Pb) for the test: the limit is 5 µg per g.

Heavy metals, Method II

231

— [note—Use a platinum crucible for the ignition.] The limit is 0.003%.

Limit of isopropyl alcohol—

Internal standard solution— Dissolve about 500 mg of tertiary butyl alcohol in about 500 mL of water, and mix.

Standard stock solution— Dissolve a suitable quantity of isopropyl alcohol, accurately weighed, in water to obtain a solution having a known concentration of about 1 mg of isopropyl alcohol per mL.

Standard solution— Pipet 4 mL of the Standard stock solution and 4 mL of the Internal standard solution into a 100-mL volumetric flask, dilute with water to volume, and mix.

Test solution— Disperse 1 mL of a suitable antifoam emulsion in 200 mL of water contained in a 1000-mL, round-bottom distilling flask having a 24/40 standard taper ground joint. Add about 5 g of Xanthan Gum, accurately weighed, and shake for 1 hour on a wrist-action mechanical shaker. Connect the flask to a fractionating column, and distill about 100 mL, adjusting the heat so that foam does not enter the column. Add by pipet 4 mL of the Internal standard solution, and mix.

Chromatographic system (see Chromatography

621

)— The gas chromatograph is equipped with a flame-ionization detector and a 3.2-mm × 1.8-m stainless steel column packed with 80- to 100-mesh surface silanized packing S3, or equivalent. The column temperature is maintained at 165

, the injection port and detector block temperatures are maintained at 200

, and helium is used as the carrier gas.

Procedure— Separately inject equal volumes (about 4 to 5 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and determine the peak responses of isopropyl alcohol and tertiary butyl alcohol in each chromatogram. [note—The retention time of tertiary butyl alcohol is about 1.5 relative to that of isopropyl alcohol.] Calculate the weight, in mg, of isopropyl alcohol in the quantity of Xanthan Gum taken by the formula:

4C(RU / RS)

in which C is the concentration, in mg per mL, of isopropyl alcohol in the Standard stock solution; and RU and RS are the peak response ratios of isopropyl alcohol to tertiary butyl alcohol obtained from the Test solution and the Standard solution, respectively: not more than 0.075% is found.

Pyruvic acid—

Standard preparation— Transfer 45 mg of pyruvic acid, accurately weighed, to a 500-mL volumetric flask, dissolve in and dilute with water to volume, and mix. Transfer 10.0 mL of this solution to a glass-stoppered, 50-mL flask, and proceed as directed under Test preparation, beginning with “Add 20.0 mL of 1 N hydrochloric acid.”

Test preparation— Dissolve 600 mg of Xanthan Gum, accurately weighed, in water to make 100.0 mL, and transfer 10.0 mL of the solution to a glass-stoppered, 50-mL flask. Add 20.0 mL of 1 N hydrochloric acid, weigh the flask, and reflux for 3 hours, taking precautions to prevent loss of vapors. Cool, and add water to make up for any weight loss during refluxing. Transfer 2.0 mL of this solution to a 30-mL separator containing 1.0 mL of a solution of 2,4-dinitrophenylhydrazine in 2 N hydrochloric acid (1 in 200), mix, and allow to stand for 5 minutes. Extract the mixture with 5 mL of ethyl acetate, and discard the aqueous layer. Extract the hydrazone from the ethyl acetate with three 5-mL portions of sodium carbonate TS, collect the extracts in a 50-mL volumetric flask, dilute with sodium carbonate TS to volume, and mix.

Procedure— Determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 375 nm, with a suitable spectrophotometer, using sodium carbonate TS as the blank. The absorbance of the Test preparation is not less than that of the Standard preparation, corresponding to not less than 1.5% of pyruvic acid.

Assay— Proceed as directed under Alginates Assay

311

using about 1.2 g of Xanthan Gum, accurately weighed.

Auxiliary Information— Please check for your question in the FAQs before contacting USP.

Topic/Question	Contact	Expert Committee
Monograph	Hong Wang, Ph.D. Scientist 1-301-816-8351	(EM205) Excipient Monographs 2
61	Radhakrishna S Tirumalai, Ph.D. Senior Scientist 1-301-816-8339	(MSA05) Microbiology and Sterility Assurance
62	Radhakrishna S Tirumalai, Ph.D. Senior Scientist 1-301-816-8339	(MSA05) Microbiology and Sterility Assurance

USP32–NF27 Page 1378

Pharmacopeial Forum: Volume No. 31(3) Page 821

Chromatographic Column—

XANTHAN GUM

Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.