Edition: BP 2025 (Ph. Eur. 11.6 update)
General Notices
Manganese Sulphate
MnSO4,4H2O 223.1 7785-87-7
DEFINITION
Manganese Sulfate is manganese(II) sulfate tetrahydrate. It contains not less than 98.0% and not more than 100.5% of MnSO4, calculated with reference to the substance ignited at 450° to 500°.
CHARACTERISTICS
Pale pink crystals or crystalline powder.
Freely soluble in water; practically insoluble in ethanol (96%).
IDENTIFICATION
A. Dissolve 0.5 g in 10 mL of water and add 1 mL of sodium sulfide solution. A pink precipitate is produced which is soluble in 6M acetic acid.
B. To 0.1 g add 2 g of lead(IV) oxide and 5 mL of nitric acid, boil gently for a few minutes, add 100 mL of water and filter. A purple solution is produced.
C. Yields the reactions characteristic of sulfates, Appendix VI.
TESTS
Arsenic
0.25 g complies with the limit test for arsenic, Appendix VII (4 ppm).
Heavy metals
Dissolve 0.50 g in 50 mL of water, add 1 mL of 1M acetic acid and pass hydrogen sulfide through the solution for 20 seconds. The colour produced within 2 minutes is not more intense than that obtained by treating 10 mL of lead standard solution (2 ppm Pb) diluted to 50 mL in the same manner (40 ppm).
Iron
Dissolve 1.0 g in 10 mL of water and add 2 mL of 1M hydrochloric acid and, dropwise, 0.05M potassium permanganate until a permanent pink colour is produced. Add 5 mL of a 10% w/v solution of ammonium thiocyanate and 20 mL of a mixture of equal volumes of isoamyl alcohol and amyl acetate, shake well and allow to separate. Any colour in the upper layer is not more intense than that obtained by treating 2 mL of iron standard solution (20 ppm Fe) diluted to 10 mL in the same manner (40 ppm).
Zinc
Dissolve 2.0 g in 10 mL of water, add 3 mL of 1M hydrochloric acid and 0.3 mL of a freshly prepared 3% w/v solution of potassium hexacyanoferrate(II), mix and allow to stand for 15 minutes. Any turbidity produced is not more intense than that obtained by treating 10 mL of zinc standard solution (100 ppm Zn) in the same manner (500 ppm).
Chloride
15 mL of a 1.0% w/v solution complies with the limit test for chlorides, Appendix VII (330ppm).
Loss on ignition
When ignited to constant weight at 450° to 500°, loses 31.0 to 34.0% of its weight. Use 1 g.
ASSAY
Dissolve 0.15 g in 40 mL of water, add 8 mL of freshly boiled and cooled nitric acid, cool, add 1.5 g of sodium bismuthate and shake for 2 minutes. Add 25 mL of a mixture of 3 volumes of nitric acid and 97 volumes of water, filter, wash the residue with 40 mL of the mixture, collecting the filtrate and washings in 50 mL of 0.1M ammonium iron(II) sulfate VS, and titrate immediately with 0.02M potassium permanganate VS. Repeat the operation without the substance being examined. The difference between the titrations represents the amount of ammonium iron(II) sulfate required. Each mL of 0.1M ammonium iron(II) sulfate VS is equivalent to 3.020 mg of MnSO4.
