standard testing procedure magnesium hydroxide

B. It complies with the test for loss on ignition (see Tests).

Using identical tubes of colourless, transparent, neutral glass with a flat base and an internal diameter of 15 mm to 25 mm, compare the liquid to be examined with water or the solvent or the reference solution (see Tables of reference solutions) prescribed in the monograph, the depth of the layer being 40 mm. Compare the colours in diffused daylight, viewing vertically against a white background.

Volumes in milliliters

Reference solution      Standard solution           B Hydrochloric acid

                                                                               (10 g/L HCl)

B1                                      75.0                                    25.0

B2                                      50.0                                    50.0

B3                                      37.5                                    62.5

B4                                     25.0                                    75.0

B5                                      12.5                                    87.5

B6                                      5.0                                      95.0

B7                                     2.5                                      97.5

B8                                     1.5                                      98.5

B9                                     1.0                                      99.0

Mix 2.00 g with 100 ml of water and boil for 5 min. Filter whilst hot through a sintered-glass filter (40), allow to cool and dilute to 100 ml with water. Evaporate 50 ml of the filtrate to dryness and dry at 100-105 °C. The residue weighs not more than 20 mg.

Any residue obtained during the preparation of solution S, washed, dried, and ignited at 600 ± 50 °C, weighs not more than 5 mg

1 ml of solution S diluted to 15 ml with water  complies with the limit test for chlorides.

To 15 ml of the prescribed solution add 1 ml of dilute nitric acid  and pour the mixture as a single addition into a test-tube containing 1 ml of silver nitrate solution. Prepare a standard in the same manner using 10 ml of chloride standard solution (5 ppm Cl) and 5 ml of water. Examine the tubes laterally against a black background. After standing for 5 min protected from light, any opalescence in the test solution is not more intense than that in the standard.

0.6 ml of solution S diluted to 15 ml with distilled water complies with the limit test for sulphates.

All solutions used for this test must be prepared with distilled water.

Add 3 ml of a 250 g/L solution of barium chloride to 4.5 ml of sulfate standard solution (10 ppm SO4). Shake and allow to stand for 1 min. To 2.5 ml of this solution, add 15 ml of the solution to be examined and 0.5 ml of acetic acid. Prepare a standard in the same manner using 15 ml of sulfate standard solution (10 ppm SO4) instead of the solution to be examined. After 5 min, any opalescence in the test solution is not more intense than that in the standard.

5 ml of solution S complies with limit test A.

Dissolve the prescribed quantity of the substance to be examined in 14 ml of water in a test-tube, make alkaline if necessary by the addition of dilute sodium hydroxide solution  and dilute to 15 ml with water. To the solution add 0.3 ml of alkaline potassium tetraiodomercurate solution. Prepare a standard by mixing 10 ml of ammonium standard solution (1 ppm NH4) with 5 ml of water  and 0.3 ml of alkaline potassium tetraiodomercurate solution. Stopper the test-tubes. After 5 min, any yellow colour in the test solution is not more intense than that in the standard.

Dilute 1.3 ml of solution S to 150 ml with distilled water. 15 ml of the solution complies with the limit test for calcium

To 0.2 ml of alcoholic calcium standard solution (100 ppm Ca), add 1 ml of ammonium oxalate solution. After 1 min, add a mixture of 1 ml of dilute acetic acid and 15 ml of a solution containing the prescribed quantity of the substance to be examined and shake. Prepare a standard in the same manner using a mixture of 10 ml of aqueous calcium standard solution (10 ppm Ca), 1 ml of dilute acetic acid  and 5 ml of distilled water. After 15 min, any opalescence in the test solution is not more intense than that in the standard.

Dissolve 0.15 g in 5 ml of dilute hydrochloric acid and dilute to 10 ml with water. 1 ml of this solution diluted to 10 ml with water complies with the limit test for iron.

Dissolve the prescribed quantity of the substance to be examined in water and dilute to 10 ml with the same solvent or use 10 ml of the prescribed solution. Add 2 ml of a 200 g/L solution of citric acid and 0.1 ml of thioglycollic acid. Mix, make alkaline with ammonia and dilute to 20 ml with water. Prepare a standard in the same manner, using 10 ml of iron standard solution (1 ppm Fe). After 5 min, any pink colour in the test solution is not more intense than that in the standard.

Dissolve 2.0 g in 20 ml of hydrochloric acid and shake with 25 ml of methyl isobutyl ketone for 2 min. Allow to stand, separate the aqueous layer and evaporate to dryness. Dissolve the residue in 30 ml of water. 12 ml of the solution complies with limit test A. Prepare the standard using lead standard solution (2 ppm Pb) methyl isobutyl ketone for 2 min. Allow to stand, separate the aqueous layer and evaporate to dryness. Dissolve the residue in 30 ml of water. 12 ml of the solution complies with limit test A. Prepare the standard using lead standard solution (2 ppm Pb).

Test solution. 12 ml of the prescribed aqueous solution of the substance to be examined. Reference solution (standard). A mixture of 10 ml of lead standard solution (1 ppm Pb)  or lead standard solution (2 ppm Pb), as prescribed, and 2 ml of the prescribed aqueous solution of the substance to be examined. Blank solution. A mixture of 10 ml of water and 2 ml of the prescribed aqueous solution of the substance to be examined. To each solution, add 2 ml of buffer solution pH 3.5. Mix and add to 1.2 ml of thioacetamide reagent. Mix immediately. Examine the solutions after 2 min. System suitability: the reference solution shows a slight brown colour compared to the blank solution. Result: any brown colour in the test solution is not more intense than that in the reference solution.

This procedure is provided for the purpose of determining the percentage of test material that is volatilized and driven off under the conditions specified. The procedure, as generally applied, is nondestructive to the substance under test; however, the substance may be converted to another form such as an anhydride.

Perform the test on finely powdered material, and break up lumps, if necessary, with the aid of a mortar and pestle before weighing the specimen. Weigh the specimen to be tested without further treatment, unless a preliminary drying at a lower temperature, or other special pretreatment, is specified in the individual monograph. Unless other equipment is designated in the individual monograph, conduct the ignition in a suitable muffle furnace or oven that is capable of maintaining a temperature within 25 of that required for the test, and use a suitable crucible, complete with cover, previously ignited for 1 hour at the temperature specified for the test, cooled in a desiccators, and accurately weighed.

Unless otherwise directed in the individual monograph, transfer to the tarred crucible an accurately weighed quantity, in g, of the substance to be tested, about equal to that calculated by the formula:

10 / L

in which L is the limit (or the mean value of the limits) for Loss on ignition, in percentage. Ignite the loaded uncovered crucible, and cover at the temperature (±25) and for the period of time designated in the individual monograph. Ignite for successive 1-hour periods where ignition to constant weight is indicated. Upon completion of each ignition, cover the crucible, and allow it to cool in a desiccator to room temperature before weighing.

1 ml of 0.1 M sodium edetate is equivalent to 5.832 mg of Mg(OH)₂.

Calculation                                               Limit 95.0 – 100.5%

  Volume x 5.832 x M x 100

———————————————-

0.1 x wt of spl