Bentonite

Bentonite.
Bentonite [1302-78-9].
»Bentonite is a native,colloidal,hydrated aluminum silicate.
Packaging and storage— Preserve in tight containers.
Labeling— Label it to indicate that absorption of atmospheric moisture should be avoided following the opening of the original package,preferably by storage of the remainder of the contents in a tight container.
Identification— Add 2g in small portions to 100mLof water,with intense agitation.Allow to stand for 12hours to ensure complete hydration.Place 2mLof the mixture so obtained on a suitable glass slide,and allow to air-dry at room temperature to produce an oriented film.Place the slide in a vacuum desiccator over a free surface of ethylene glycol.Evacuate the desiccator,and close the stopcock so that the ethylene glycol saturates the desiccator chamber.Allow to stand for 12hours.Record the X-ray diffraction pattern (see X-ray Diffraction á941ñ),and calculate the dvalues:the largest peak corresponds to a dvalue between 15.0and 17.2angstrom units.Prepare a random powder specimen of Bentonite,record the X-ray diffraction pattern,and determine the dvalues in the region between 1.48and 1.54angstrom units:the peak is between 1.492and 1.504angstrom units.
Microbial limits á61ñ— It meets the requirements of the test for absence of Escherichia coli.
pHá791ñ— Disperse 4.0g in 200mLof water,mixing vigorously to facilitate wetting.The pHof this suspension is between 9.5and 10.5.
Loss on drying á731ñ— Dry it at 105for 2hours:it loses between 5.0%and 8.0%of its weight.
Arsenic á211ñ—
Test preparation— Transfer 8.0g to a 250-mLbeaker containing 100mLof dilute hydrochloric acid (1in 25),mix,cover with a watch glass,and boil gently,with occasional stirring,for 15minutes without allowing excessive foaming.Filter the hot supernatant through a rapid-flow filter paper into a 200-mLvolumetric flask,and wash with four 25-mLportions of hot dilute hydrochloric acid (1in 25),collecting the washings in the volumetric flask.Cool the combined filtrates to room temperature,add dilute hydrochloric acid (1in 25)to volume,and mix.
Procedure— Use a 25-mLaliquot of Test preparationfor the Procedure.The absorbance due to any red color from the Test preparationdoes not exceed that produced by 5.0mLof Standard preparation(5µg of As)when treated with the same quantities of the same reagents and in the same manner:the limit is 5ppm.
Lead— [NOTE—The Standard preparation and the Test preparation may be modified,if necessary,to obtain solutions,of suitable concentrations,adaptable to the linear or working range of the instrument.It may be necessary to correct the value obtained for the Test preparation for interference from the test specimen matrix.]
Standard preparation— On the day of use,dilute 3.0mLof Lead Nitrate Stock Solution(see Heavy Metals á231ñ)with water to 100mL.Each mLof the Standard preparationcontains the equivalent of 3µg of lead.
Test preparation— Transfer 3.75g to a 250-mLbeaker containing 100mLof dilute hydrochloric acid (1in 25),stir,cover with a watch glass,and boil for 15minutes.Cool to room temperature,and filter through a rapid-flow filter paper into a 400-mLbeaker.Wash the filter with four 25-mLportions of hot water,collecting the washings in the 400-mLbeaker.Concentrate the combined extracts by gentle boiling to approximately 20mL.If a precipitate appears,add 2to 3drops of nitric acid,heat to boiling,and cool to room temperature.Filter the concentrated extracts through a rapid-flow filter paper into a 50-mLvolumetric flask.Transfer the remaining contents of the 400-mLbeaker through the filter paper and into the flask with water.Dilute with water to volume,and mix.
Procedure— Determine the absorbances of the Test preparationand the Standard preparationat 284nm in a suitable atomic absorption spectrophotometer equipped with a lead hollow-cathode lamp deuterium arc background correction,and a single-slot burner,using an oxidizing flame of air and acetylene.The absorbance of the Test preparationis not greater than that of the Standard preparation(0.004%).
Gel formation— Mix 6g with 300mg of magnesium oxide.Add the mixture,in several divided portions,to 200mLof water contained in a blender of approximately 500-mLcapacity.Blend thoroughly for 5minutes at high speed,transfer 100mLof the mixture to a 100-mLgraduated cylinder,and allow to remain undisturbed for 24hours:not more than 2mLof supernatant appears on the surface.
Swelling power— To 100mLof water contained in a glass-stoppered cylinder of 100-mLcapacity add 2g in portions,dropping it upon the surface of the water and allowing each portion to settle before adding the next.The mass at the bottom gradually swells until it occupies an apparent volume of not less than 24mLat the end of a 2-hour period.
Fineness of powder— Sprinkle 2g upon 20mLof water contained in a mortar.Allow to swell,disperse evenly with a pestle,and dilute with water to 100mL.Pour the suspension through a No.200standard sieve,and wash the sieve thoroughly with water.No grit is felt when the fingers are rubbed over the wire mesh of the sieve.
Auxiliary Information— Staff Liaison:Catherine Sheehan,B.Sc.,Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 2961
Phone Number:1-301-816-8262