Packaging and storage— Preserve in tight containers.

Labeling— Label it to indicate its type.

Identification— Add 2g in small portions to 100mLof water,with intense agitation.Allow to stand for 12hours to ensure complete hydration.Place 2mLof the resulting mixture 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 Magnesium Aluminum Silicate,record the X-ray diffraction pattern,and determine the dvalues in the region between 1.48and 1.54angstrom units:peaks are found between 1.492and 1.504angstrom units and between 1.510and 1.540angstrom units.

Viscosity— After determining the Loss on drying,weigh a quantity of Magnesium Aluminum Silicate 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 as specified below,operate the viscosimeter at 60rpm for 6minutes,accurately timed,and record the scale reading.For Type IA,use 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);if the scale reading is greater than 90%of full-scale,repeat the measurement,using a spindle similar to the No.2spindle but having the cylinder 1.27cm in diameter and 0.16cm high instead (No.3spindle).For Type IC,use a No.3spindle;if the scale reading is greater than 90%of full-scale,repeat the measurement using a spindle consisting of a cylindrical shaft 0.32cm in diameter and having an immersion depth of 4.05cm (No.4spindle).For Types IBand IIA,use a No.2spindle.

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.

Loss on drying á731ñ— Dry it at 110to constant weight:it loses not more than 8.0%of its weight.

Acid demand— After determining the Loss on drying,weigh a quantity of Magnesium Aluminum Silicate equivalent to 5.00g,and disperse in 500mLof water with the aid of a suitable blender fitted with a 1-liter jar.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.

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.

Lead— [NOTE—The Standard preparation and Test preparation may be modified if necessary,to obtain solutions,of suitable concentrations,adaptable to the linear or working range of the instrument.]

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.]

Expert Committee:(EMC)Excipients:Monograph Content

USP28–NF23Page 3028

Phone Number:1-301-816-8262