Magnesium Aluminum Silicate
(mag nee' zee um a loo' mi num sil' i kate).
» Magnesium Aluminum Silicate is a blend of colloidal montmorillonite and saponite that has been processed to remove grit and nonswellable ore components.
The requirements for viscosity and ratio of aluminum content to magnesium content differ for the several types of Magnesium Aluminum Silicate, as set forth in the accompanying table.
Packaging and storage Preserve in tight containers.
Labeling Label it to indicate its type.
Identification Add 2 g in small portions to 100 mL of water, with intense agitation. Allow to stand for 12 hours to ensure complete hydration. Place 2 mL of 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 12 hours. Record the X-ray diffraction pattern (see X-ray Diffraction 941), and calculate the d values: the largest peak corresponds to a d value between 15.0 and 17.2 angstrom units. Prepare a random powder specimen of Magnesium Aluminum Silicate, record the X-ray diffraction pattern, and determine the d values in the region between 1.48 and 1.54 angstrom units: peaks are found between 1.492 and 1.504 angstrom units and between 1.510 and 1.540 angstrom units.
Viscosity After determining the Loss on drying, weigh a quantity of Magnesium Aluminum Silicate test specimen equivalent to 25.0 g on the dried basis. Over a period of a few seconds, transfer the undried test specimen to a suitable 1-L blender jar containing an amount of water, maintained at a temperature of 25 ± 2, that is sufficient to produce a mixture weighing 500 g. Blend for 3 minutes, accurately timed, at 14,000 to 15,000 rpm (high speed). [noteHeat generated during blending causes a temperature rise to above 30. ] Transfer the contents of the blender to a 600-mL beaker, allow to stand for 5 minutes, 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 60 rpm for 6 minutes, accurately timed, and record the scale reading. For Type IA, use a spindle having a cylinder 1.87 cm in diameter and 0.69 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. 2 spindle); if the scale reading is greater than 90% of full-scale, repeat the measurement, using a spindle similar to the No. 2 spindle but having the cylinder 1.27 cm in diameter and 0.16 cm high instead (No. 3 spindle). For Type IC, use a No. 3 spindle; if the scale reading is greater than 90% of full-scale, repeat the measurement using a spindle consisting of a cylindrical shaft 0.32 cm in diameter and having an immersion depth of 4.05 cm (No. 4 spindle). For Types IB and IIA, use a No. 2 spindle.
Microbial enumeration tests 61 and Tests for specified microorganisms 62 Its total aerobic microbial count does not exceed 1000 cfu per g, and it meets the requirements of the test for absence of Escherichia coli.
pH 791: between 9.0 and 10.0, in a suspension (5 in 100) in water.
Loss on drying 731 Dry it at 110 to 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 5.00 g, and disperse in 500 mL of 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-mL portions of 0.100 N hydrochloric acid at 5, 65, 125, 185, 245, 305, 365, 425, 485, 545, 605, 665, and 725 seconds, and add a 1.0-mL portion at 785 seconds. Determine the pH potentiometrically at 840 seconds: the pH is not more than 4.0.
Arsenic, Method I 211 Prepare the Test Preparation as follows. Transfer 13.3 g to a 250-mL beaker containing 100 mL of dilute hydrochloric acid (1 in 25), mix, cover with a watch glass, and boil gently, with occasional stirring, for 15 minutes without allowing excessive foaming. Allow the insoluble material to settle, and decant the hot supernatant through a rapid-flow filter paper into a 200-mL volumetric flask, retaining as much sediment as possible in the beaker. Add 25 mL of hot dilute hydrochloric acid (1 in 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-mL volumetric flask. Repeat the extraction with four additional 25-mL portions of hot dilute hydrochloric acid (1 in 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 (1 in 25) to volume, and mix.
Procedure Use a 25-mL aliquot of Test Preparation for the Procedure. The absorbance due to any red color from the Test Preparation does not exceed that produced by 5.0 mL of Standard Preparation (5 µg of As) when treated with the same quantities of the same reagents and in the same manner. The limit is 3 ppm.
Lead [noteThe 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. ]
Standard preparation On the day of use, dilute 3.0 mL of Lead Nitrate Stock Solution (see Heavy Metals 231) with water to 100 mL. Each mL of the Standard preparation contains the equivalent of 3 µg of lead.
Test preparation Transfer 10.0 g of Magnesium Aluminum Silicate to a 250-mL beaker containing 100 mL of dilute hydrochloric acid (1 in 25), stir, cover with a watch glass, and boil for 15 minutes. Cool to room temperature, and allow the insoluble matter to settle. Decant the supernatant through a rapid-flow filter paper into a 400-mL beaker. Add 25 mL of hot water to the insoluble matter in the 250-mL beaker, stir, allow the insoluble matter to settle, and decant the supernatant through the filter into the 400-mL beaker. Repeat the extraction with two additional 25-mL portions of water, decanting each supernatant portion through the filter into the 400-mL beaker. Wash the filter with 25 mL of hot water, collecting this filtrate in the 400-mL beaker. Concentrate the combined extracts by gentle boiling to approximately 20 mL. If a precipitate appears, add 2 to 3 drops of nitric acid, heat to boiling, and cool to room temperature. Filter the concentrated extracts through a rapid-flow filter paper into a 50-mL volumetric flask. Transfer the remaining contents of the 400-mL beaker through the filter paper and into the flask with water. Dilute with water to volume, and mix.
Procedure Determine the absorbances of the Test preparation and the Standard preparation at 284 nm 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 preparation is not greater than that of the Standard preparation (0.0015%).
Assay for aluminum and magnesium content [noteThe 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 88.30 g of lanthanum chloride (LaCl3) with 500 mL of 6 N hydrochloric acid until solution is complete, transfer with the aid of water to a 1000-mL volumetric flask, and dilute with water to volume.
Specimen preparation Transfer 0.200 g of Magnesium Aluminum Silicate to a 25-mL platinum crucible containing 1.0 g of lithium metaborate, and mix. Using a muffle furnace or a suitable burner, heat slowly at first, and ignite at 1000 to 1200 for 15 minutes. Cool, place the crucible in a 100-mL beaker containing 25 mL of dilute nitric acid (1 in 20), and add an additional 50 mL of 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-mL beaker, and remove the crucible. Warm the solution, and transfer through a rapid-flow filter paper with the aid of water into a 200-mL volumetric flask, dilute with water to volume, and mix.
Aluminum standard preparations Dissolve 1.000 g of aluminum in a mixture of 10 mL of hydrochloric acid and 10 mL of water by gentle heating. Transfer the solution to a 1000-mL volumetric flask, dilute with water to volume, and mix. This solution contains the equivalent of 1 mg of aluminum per mL. Transfer 2-, 5-, and 10-mL aliquots to separate 100-mL volumetric flasks containing 200 mg of sodium chloride, dilute each with water to volume, and mix.
Aluminum assay preparation Pipet 20 mL of Specimen preparation into a 100-mL volumetric flask. Add 20 mL of a solution of sodium chloride (1 in 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 acetyleneairnitrous oxide flame, determine the absorbances of the Aluminum assay preparation and each of the Aluminum standard preparations at 309 nm. From a linear regression equation calculated from the absorbances and concentrations of the Aluminum standard preparations, determine the aluminum content of the Magnesium Aluminum Silicate.
Magnesium standard preparations Place 1.000 g of magnesium in a 250-mL beaker containing 20 mL of water, and carefully add 20 mL of hydrochloric acid, warming, if necessary, to complete the reaction. Transfer the solution to a 1000-mL volumetric flask, dilute with water to volume, and mix. This solution contains the equivalent of 1 mg of magnesium per mL. Transfer 10.0 mL of this solution to a 1000-mL volumetric flask, dilute with water to volume, and mix. Transfer 5-, 10-, 15-, and 20-mL aliquots to separate 100-mL volumetric flasks. To each flask add 20.0 mL of Lanthanum solution, dilute with water to volume, and mix.
Magnesium assay preparation Transfer a 25-mL aliquot of Specimen preparation to a 50-mL volumetric flask, dilute with water to volume, and mix. Transfer a 5.0-mL aliquot of this dilution to a 100-mL volumetric flask, add 20.0 mL of 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 acetyleneair flame, determine the absorbances of the Magnesium assay preparation and each of the Magnesium standard preparations at 285 nm. From a linear regression equation calculated from the absorbances and concentrations of the Magnesium standard preparations, determine the magnesium content of the Magnesium Aluminum Silicate.
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USP35NF30 Page 1845