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 4.2percent and not more than 5.0percent of carbon dioxide,calculated on the dried basis,corresponding to not less than 91.0percent and not more than 108.0percent of Xanthan Gum. Packaging and storage— Preserve in well-closed containers. Identification— To 300mLof water in a 400-mLbeaker,previously heated to 80and stirred rapidly by mechanical means,add,at the point of maximum agitation,a dry blend of 1.5g of Xanthan Gum and 1.5g of locust bean gum.Stir until the mixture dissolves,and then continue stirring for 30minutes longer.Do not allow the temperature of the mixture to drop below 60during the stirring.Discontinue stirring,and allow the mixture to cool at room temperature for not less than 2hours: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 3.0g of Xanthan Gum and without locust bean gum. Viscosity á911ñ Place 250mLof water in a 400-mLbeaker,and add a dry blend of 3.0g of Xanthan Gum and 3.0g of potassium chloride slowly while stirring at 800rpm,using a low-pitched propeller-type stirrer.Add an additional quantity of 44mLof water,rinsing the walls of the beaker.Approximately 10minutes 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 800rpm for a total mixing time of 2hours.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 15to 30seconds,and the last hand mixing should occur immediately prior to measuring the viscosity.]Equip a suitable rotational viscosimeter with a spindle having a cylinder 1.27cm in diameter and 0.16cm high attached to a shaft 0.32cm in diameter,the distance from the top of the cylinder to the lower tip of the shaft being 2.54cm,and the immersion depth being 5.00cm (No.3spindle).With the spindle rotating at 60rpm,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 24is not less than 600centipoises. Microbial limits á61ñ It meets the requirements of the tests for Salmonellaspecies and Escherichia coli. Loss on drying á731ñ Dry it at 105for 2.5hours:it loses not more than 15.0%of its weight. Ash— Accurately weigh about 3g in a tared crucible,and incinerate at about 650until 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 IIá211ñ: 3µg per g. Lead á251ñ Prepare a Test Preparationas directed in the chapter,and use 5mLof Diluted Standard Lead Solution(5µg of Pb)for the test:the limit is 5µg per g. Heavy metals,Method IIá231ñ [NOTE—Use a platinum crucible for the ignition.]The limit is 0.003%. Limit of isopropyl alcohol— Internal standard solution— Dissolve about 500mg of tertiary butyl alcohol in about 500mLof 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 1mg of isopropyl alcohol per mL. Standard solution— Pipet 4mLof the Standard stock solutionand 4mLof the Internal standard solutioninto a 100-mLvolumetric flask,dilute with water to volume,and mix. Test solution— Disperse 1mLof a suitable antifoam emulsion in 200mLof water contained in a 1000-mL,round-bottom distilling flask having a 24/40standard taper ground joint.Add about 5g of Xanthan Gum,accurately weighed,and shake for 1hour on a wrist-action mechanical shaker.Connect the flask to a fractionating column,and distill about 100mL,adjusting the heat so that foam does not enter the column.Add by pipet 4mLof the Internal standard solution,and mix. Chromatographic system(see Chromatography á621ñ)— 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 4to 5µL)of the Standard solutionand the Test solutioninto 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 1.5relative 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 Cis the concentration,in mg per mL,of isopropyl alcohol in the Standard stock solution;and RUand RSare the peak response ratios of isopropyl alcohol to tertiary butyl alcohol obtained from the Test solutionand the Standard solution,respectively:not more than 0.075%is found. Pyruvic acid— Standard preparation— Transfer 45mg of pyruvic acid,accurately weighed,to a 500-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.Transfer 10.0mLof this solution to a glass-stoppered,50-mLflask,and proceed as directed under Test preparation,beginning with “Add 20.0mLof 1Nhydrochloric acid.” Test preparation— Dissolve 600mg of Xanthan Gum,accurately weighed,in water to make 100.0mL,and transfer 10.0mLof the solution to a glass-stoppered,50-mLflask.Add 20.0mLof 1Nhydrochloric acid,weigh the flask,and reflux for 3hours,taking precautions to prevent loss of vapors.Cool,and add water to make up for any weight loss during refluxing.Transfer 2.0mLof this solution to a 30-mLseparator containing 1.0mLof a solution of 2,4-dinitrophenylhydrazine in 2Nhydrochloric acid (1in 200),mix,and allow to stand for 5minutes.Extract the mixture with 5mLof ethyl acetate,and discard the aqueous layer.Extract the hydrazone from the ethyl acetate with three 5-mLportions of sodium carbonate TS,collect the extracts in a 50-mLvolumetric flask,dilute with sodium carbonate TSto volume,and mix. Procedure— Determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 375nm,with a suitable spectrophotometer,using sodium carbonate TSas the blank.The absorbance of the Test preparationis not less than that of the Standard preparation,corresponding to not less than 1.5%of pyruvic acid. Organic volatile impurities,Method IVá467ñ: meets the requirements.[NOTE—A G16column has been shown to be an appropriate secondary column.] Assay— Proceed with Xanthan Gum as directed for Procedureunder Alginates Assay,using about 1.2g of Xanthan Gum,accurately weighed. Auxiliary Information— Staff Liaison:Ravi Ravichandran,Ph.D.,Senior Scientist Expert Committee:(EMC)Excipients:Monograph Content USP28–NF23Page 3108 Pharmacopeial Forum:Volume No.29(6)Page 2021 Phone Number:1-301-816-8330