Purified Bentonite
»Purified Bentonite is a colloidal montmorillonite that has been processed to remove grit and nonswellable ore components.
Packaging and storage— Preserve in tight containers.
Identification— It responds to the Identificationtest under Bentonite.
Viscosity— After determining the Loss on drying,weigh a quantity of Purified Bentonite test specimen equivalent to 25.0g on the dried basis.Over a period of a few seconds,transfer the undried test specimen to a suitable 1-Lblender jar containing an amount of water,maintained at a temperature of 25±2,that is sufficient to produce a mixture weighing 500g.Blend for 3minutes,accurately timed,at 14,000to 15,000rpm (high speed).[NOTE—Heat generated during blending causes a temperature rise to above 30.]Transfer the contents of the blender to a 600-mLbeaker,allow to stand for 5minutes,and adjust,if necessary,to a temperature of 33±3.Using a suitable rotational viscosimeter equipped with a spindle having a cylinder 1.87cm in diameter and 0.69cm 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.2spindle),operate the viscosimeter at 60rpm for 6minutes,accurately timed,and record the scale reading:the viscosity is between 40centipoises and 200centipoises.
Microbial limits á61ñ— Its total aerobic microbial count does not exceed 1000cfu per g,and it meets the requirements of the test for absence of Escherichia coli.
pHá791ñ: between 9.0and 10.0,in a suspension (5in 100)in water.
Acid demand— After determining the Loss on drying,weigh a quantity of Purified Bentonite equivalent to 5.00g,and disperse in 500mLof water with the aid of a suitable blender fitted with a 1-Ljar.Using a stopwatch,designate zero time.With constant mixing,add 3.0-mLportions of 0.100Nhydrochloric acid at 5,65,125,185,245,305,365,425,485,545,605,665,and 725seconds,and add a 1.0-mLportion at 785seconds.Determine the pHpotentiometrically at 840seconds:the pHis not more than 4.0.
Loss on drying á731ñ— Dry it at 110to constant weight:it loses not more than 8.0%of its weight.
Arsenic,Method Iá211ñ— Prepare the Test Preparationas follows.Transfer 13.3g 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.Allow the insoluble material to settle,and decant the hot supernatant through a rapid-flow filter paper into a 200-mLvolumetric flask,retaining as much sediment as possible in the beaker.Add 25mLof hot dilute hydrochloric acid (1in 25)to the residue in the beaker,stir,heat to boiling,allow the insoluble material to settle,and decant the supernatant through the filter into the 200-mLvolumetric flask.Repeat the extraction with four additional 25-mLportions of hot dilute hydrochloric acid (1in 25),decanting each hot supernatant through the filter into the volumetric flask.At the last extraction,transfer as much of the insoluble material as possible onto the filter.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 3ppm.
Lead— [NOTE—The Standard preparationand the Test preparationmay be modified,if necessary,to obtain solutions of suitable concentrations,adaptable to the linear or working range of the instrument.]
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 10.0g of Purified Bentonite 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 allow the insoluble matter to settle.Decant the supernatant through a rapid-flow filter paper into a 400-mLbeaker.Add 25mLof hot water to the insoluble matter in the 250-mLbeaker,stir,allow the insoluble matter to settle,and decant the supernatant through the filter into the 400-mLbeaker.Repeat the extraction with two additional 25-mLportions of water,decanting each supernatant portion through the filter into the 400-mLbeaker.Wash the filter with 25mLof hot water,collecting this filtrate 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(0.0015%).
Assay for aluminum and magnesium content— [NOTE—The Standard preparations and Assay preparations may be diluted quantitatively with water,if necessary,to obtain solutions of suitable concentrations,adaptable to the linear or working range of the instrument.]
Lanthanum solution— Stir 88.30g of lanthanum chloride (LaCl3)with 500mLof 6Nhydrochloric acid until solution is complete,transfer with the aid of water to a 1000-mLvolumetric flask,and dilute with water to volume.
Specimen preparation— Transfer 0.200g of Purified Bentonite to a 25-mLplatinum crucible containing 1.0g of lithium metaborate,and mix.Using a muffle furnace or a suitable burner,heat slowly at first,and ignite at 1000to 1200for 15minutes.Cool,place the crucible in a 100-mLbeaker containing 25mLof dilute nitric acid (1in 20),and add an additional 50mLof the dilute acid,filling and submerging the upright crucible.Place a polyfluorocarbon-coated magnetic stirring bar into the crucible,and stir gently with a magnetic stirrer until solution is complete.Pour the contents into a 250-mLbeaker,and remove the crucible.Warm the solution,and transfer through a rapid-flow filter paper with the aid of water into a 200-mLvolumetric flask,dilute with water to volume,and mix.
Aluminum standard preparations— Dissolve 1.000g of aluminum in a mixture of 10mLof hydrochloric acid and 10mLof water by gentle heating.Transfer the solution to a 1000-mLvolumetric flask,dilute with water to volume,and mix.This solution contains the equivalent of 1mg of aluminum per mL.Transfer 2-,5-,and 10-mLaliquots to separate 100-mLvolumetric flasks containing 200mg of sodium chloride,dilute each with water to volume,and mix.
Aluminum assay preparation— Pipet 20mLof Specimen preparationinto a 100-mLvolumetric flask.Add 20mLof a solution of sodium chloride (1in 100),dilute with water to volume,and mix.
Procedure for aluminum— In a suitable atomic absorption spectrophotometer equipped with an aluminum hollow-cathode lamp and a single-slot burner,using an oxidizing air–acetylene–nitrous oxide flame,determine the absorbances of the Aluminum assay preparationand each of the Aluminum standard preparationsat 309nm.From a linear regression equation calculated from the absorbances and concentrations of the Aluminum standard preparations,determine the aluminum content of the Purified Bentonite.
Magnesium standard preparations— Place 1.000g of magnesium in a 250-mLbeaker containing 20mLof water,and carefully add 20mLof hydrochloric acid,warming,if necessary,to complete the reaction.Transfer the solution to a 1000-mLvolumetric flask,dilute with water to volume,and mix.This solution contains the equivalent of 1mg of magnesium per mL.Transfer 5-,10-,15-,and 20-mLaliquots to separate 100-mLvolumetric flasks.To each flask add 20.0mLof Lanthanum solution,dilute with water to volume,and mix.
Magnesium assay preparation— Transfer a 25-mLaliquot of Specimen preparationto a 50-mLvolumetric flask,dilute with water to volume,and mix.Transfer a 5.0-mLaliquot of this dilution to a 100-mLvolumetric flask,add 20.0mLof Lanthanum solution,dilute with water to volume,and mix.
Procedure for magnesium— In a suitable atomic absorption spectrophotometer equipped with a magnesium hollow-cathode lamp and a single-slot burner,using a reducing acetylene–air flame,determine the absorbances of the Magnesium assay preparationand each of the Magnesium standard preparationsat 285nm.From a linear regression equation calculated from the absorbances and concentrations of the Magnesium standard preparations,determine the magnesium content of the Purified Bentonite:the ratio of the aluminum content to the magnesium content is between 3.5and 5.5.
Auxiliary Information— Staff Liaison:Catherine Sheehan,B.Sc.,Scientist
Expert Committee:(EMC)Excipients:Monograph Content
USP28–NF23Page 2962
Phone Number:1-301-816-8262