(mag nee' zee um fos' fate).
Phosphoric acid, magnesium salt (2:3), pentahydrate;
Magnesium phosphate (3:2) pentahydrate [10233-87-1].
Mg3(PO4)2 262.86 [7757-87-1].
Magnesium Phosphate, ignited at 425 to constant weight, contains NLT 98.0% and NMT 101.5% of Mg3(PO4)2.
Sample: 200 mg
Analysis: Dissolve the Sample in 10 mL of 2 N nitric acid, and add, dropwise, ammonium molybdate TS.
Acceptance criteria: A greenish-yellow precipitate of ammonium phosphomolybdate is formed, and it is soluble in 6 N ammonium hydroxide.
• B. Identification TestsGeneral, Magnesium 191
Sample solution: Dissolve 0.1 g in 0.7 mL of 1 N acetic acid and 20 mL of water. Add 1 mL of ferric chloride TS, allow to stand for 5 min, and filter. Use 5 mL of the filtrate.
Acceptance criteria: Meets the requirements
Sample: 200 mg, previously ignited at 425 to constant weight
Analysis: Dissolve the Sample in a mixture of 25 mL of water and 10 mL of 2 N nitric acid. Filter, if necessary. Wash any precipitate, add sufficient 6 N ammonium hydroxide to the filtrate to produce a slight precipitate, and then dissolve the precipitate by the addition of 1 mL of 2 N nitric acid. Adjust the temperature to 50, add 75 mL of ammonium molybdate TS, and maintain the temperature at 50 for 30 min, stirring occasionally. Wash the precipitate once or twice with water by decantation, using 3040 mL each time and passing the washings through a filter. Transfer the precipitate to the filter, and wash with potassium nitrate solution (1 in 100) until the last washing is not acid to litmus. Transfer the precipitate and filter to the precipitation vessel. Add 50 mL of water and 40.0 mL of 1 N sodium hydroxide VS, and agitate until the precipitate is dissolved. Add phenolphthalein TS, and then titrate the excess alkali with 1 N sulfuric acid VS. Each mL of 1 N sodium hydroxide is equivalent to 5.716 mg of Mg3(PO4)2.
Acceptance criteria: 98.0%101.5% on the previously ignited basis
• Acid-Insoluble Substances
[NotePerform if an insoluble residue remains in the test for Carbonate. ]
Analysis: Filter the solution, wash well with hot water until the last washing is free from chloride, and ignite the residue.
Acceptance criteria: The weight of the residue does not exceed 4 mg (NMT 0.2%).
• Soluble Substances
Sample: 2.0 g
Analysis: Digest the Sample with 100 mL of water on a steam bath for 30 min. Cool, add sufficient water to restore the original volume, mix, and filter. Evaporate 50 mL of the filtrate to dryness, and ignite gently to constant weight.
Acceptance criteria: The weight of the residue does not exceed 15 mg (NMT 1.5%).
Sample: 2.0 g
Analysis: Mix the Sample with 20 mL of water, and add hydrochloric acid, dropwise, to dissolve.
Acceptance criteria: No effervescence occurs when the acid is added.
• Chloride and Sulfate, Chloride 221
Sample: 0.50 g
Analysis: Dissolve the Sample in 50 mL of 2 N nitric acid, and add 1 mL of silver nitrate TS.
Acceptance criteria: The turbidity does not exceed that produced by 1.0 mL of 0.020 N hydrochloric acid (NMT 0.14%).
• Chloride and Sulfate, Sulfate 221
Sample: 0.50 g
Analysis: Dissolve the Sample in the smallest possible amount of 3 N hydrochloric acid, dilute with water to 48 mL, and add 2 mL of barium chloride TS.
Acceptance criteria: The turbidity does not exceed that produced by 3.0 mL of 0.020 N sulfuric acid (NMT 0.6%).
• Limit of Nitrate
Sample: 0.20 g
Analysis: Mix the Sample with 5 mL of water, and add just sufficient hydrochloric acid to dissolve. Dilute with water to 10 mL, add 0.1 mL of indigo carmine TS, then add, with stirring, 10 mL of sulfuric acid.
Acceptance criteria: The blue color persists for NLT 5 min.
• Arsenic, Method I 211
Test preparation: Prepare as directed in the chapter, using 1.0 g and dissolving it first in just a sufficient amount of 3 N hydrochloric acid (about 9 mL).
Acceptance criteria: NMT 3 ppm
Sample: 2.0 g
Analysis: Mix the Sample with 40 mL of water. Heat, add hydrochloric acid, dropwise, to dissolve, and then add 1 mL of acid in excess. Cool, dilute with water to 50 mL, and filter. To 5 mL of the filtrate add 1 mL of potassium sulfate TS.
Acceptance criteria: No turbidity is produced within 15 min.
Sample: 0.50 g
Analysis: Mix the Sample with 15 mL of water. Heat, and add sufficient hydrochloric acid, in small portions, to dissolve. Cool, add 6 N ammonium hydroxide, in small portions, to produce a slight permanent precipitate, then add 2 mL of 6 N acetic acid. Dilute with water to 25 mL, and filter. To 10 mL of the filtrate add 2 mL of ammonium oxalate TS.
Acceptance criteria: NMT a slight turbidity is produced within 5 min.
• Dibasic Salt and Magnesium Oxide
Sample: Ignite about 2.5 g to constant weight and use 2 g of the ignited salt.
Analysis: Dissolve the Sample by warming with 50.0 mL of 1 N hydrochloric acid VS. Cool, add 1 or 2 drops of methyl orange TS, and slowly titrate the excess 1 N hydrochloric acid VS with 1 N sodium hydroxide VS to a yellow color, vigorously shaking the mixture during the titration.
Acceptance criteria: 14.815.4 mL of 1 N hydrochloric acid is consumed for each g of the ignited salt.
• Lead 251
Test preparation: Dissolve 1.0 g in 20 mL of 3 N hydrochloric acid, evaporate on a steam bath to 10 mL, dilute with water to 20 mL, and cool.
Analysis: Proceed as directed in the chapter, using 5 mL of Diluted Standard Lead Solution (5 µg of Pb).
Acceptance criteria: NMT 5 ppm
• Heavy Metals, Method I 231
Test preparation: Dissolve 0.67 g in 4.5 mL of 3 N hydrochloric acid, and dilute with water to 25 mL.
Acceptance criteria: NMT 30 ppm
• Microbial Enumeration Tests 61 and Tests for Specified Microorganisms 62: It meets the requirements of the test for the absence of Escherichia coli.
• Loss on Ignition 733: Ignite a sample at 425 to constant weight; it loses 20.0%27.0% of its weight.
• Packaging and Storage: Preserve in well-closed containers.
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