Title: Raw Material Test Method

Material : Zinc Sulfate Monohydrate USP

Generic Name : Zinc Sulfate Monohydrate

Empirical Formula : ZnSO4 · H2O

Molecular weight : 179.46

CAS : [7446-19-7]

Method of Analysis:

  1. Appearance:

    Reference: USP

    Acceptance criteria: White crystalline powder.

    Procedure:

    Spread approximately 3.0 g of sample over a white paper and examine visually. Check the appearance for color, nature and any visible foreign particles. Record its appearance, extraneous matter, if any. The sample should be white, granular or crystalline, odorless powder.

  2. Solubility:

    Reference: USP

    Acceptance criteria: Freely soluble in water and practically insoluble in alcohol.

    Procedure:

    Freely soluble in water:

    Take about 0.1 g of test sample into a clean and dry test tube. Add 1 ml purified water and mix the content. The solution should be clear without any suspended particles.

    Practically insoluble in Alcohol:

    Take about 10 mg of the sample in 200 ml volumetric flask. To it add 100 ml of Alcohol and shake. The dispersion should not be clear (suspended particles will be observed).

  3. Identification:

    A. Test for zinc

    Reference: USP

    Acceptance criteria: Must comply with the test for Zinc.

    Ammonia TS:

    It contains between 9.5% and 10.5% of NH3. Prepare by diluting 350 ml of 25 % Ammonia , with water to make 1000 ml.

    Ammonium sulfide TS:

    Saturate ammonia TS with hydrogen sulfide by bubbling hydrogen sulfide gas through the solution for 1 minute. This solution must be freshly prepared. The solution is not rendered turbid either by magnesium sulfate TS or by calcium chloride TS (carbonate). This solution is unstable for use if an abundant precipitate of sulfur is present.

    Potassium ferrocyanide TS:

    Dissolve 1 g of potassium ferrocyanide in 10 ml of purified water. Prepare this solution fresh.

    Procedure:

    In the presence of sodium acetate, solutions of zinc salts yield a white precipitate with hydrogen sulfide. This precipitate is insoluble in acetic acid, but is dissolved by 3 N hydrochloric acid. Ammonium sulfide TS produces a similar precipitate in neutral and in alkaline solutions. With potassium ferrocyanide TS zinc salts in solution yield a white precipitate that is insoluble in 3 N hydrochloric acid.

    B. Test for sulfate:

    Reference: USP

    Acceptance criteria: Must comply with the test for sulfate.

    Barium chloride TS: Dissolve 12 g of barium chloride in purified water to make 100 ml.

    Lead Acetate TS:

    Dissolve 9.5 g of clear, transparent crystals of lead acetate in recently boiled water to make 100 ml. Store in well-stoppered bottles.

    Procedure:

    With barium chloride TS, solutions of sulfates yield a white precipitate that is insoluble in hydrochloric acid and in nitric acid. With lead acetate TS, neutral solutions of sulfates yield a white precipitate that is soluble in ammonium acetate. Hydrochloric acid produces no precipitate when added to solutions of sulfates (distinction from thiosulfates).

  4. Assay:

    Reference: USP

    Acceptance criteria: 99.0% to 100.5% of Zinc sulfate monohydrate (ZnSO4 · H2O)

    Ammonia--Ammonium Chloride Buffer TS:

    Dissolve 67.5 g of ammonium chloride in purified water, add 570 ml of ammonium hydroxide, and dilute with purified water to 1000 ml, mix.

    Eriochrome Black TS:

    Dissolve 200 mg of eriochrome black T and 2 g of hydroxylamine hydrochloride in methanol to make 50 ml, mix.

    Procedure:

    Dissolve about 188.7 mg of sample (zinc sulfate monohydrate) in 100 ml of purified water. Add 5 ml of ammonia--ammonium chloride buffer TS and 0.1 ml of eriochrome black TS and titrate with 0.05 M edetate disodium VS until the solution is deep blue in color.

    Each ml of 0.05 M edetate disodium is equivalent to 8.072 mg of Zinc sulfate.

    Calculate the content of Zinc sulfate monohydrate (ZnSO4 · H2O) in the sample taken in mg by equation given below.

    Content of Zinc sulfate monohydrate (% w/w) = (CO1 × CO2 × CO3 × CO4 × 1.1116) / COO

    Where

    CO1 = Volume of titre to titrate the sample

    CO2 = Factor of 0.05 M edetate disodium VS

    CO3 = 8.072

    CO4 = 100

    COO = Weight of test sample in mg

    1.1116 is the conversion factor of Zinc sulfate to Zinc sulfate monohydrate.

    Carry out two duplicate assays and take average.

    Alternative Liquid Chromatography Methods:

    Diluent, Mobile phase, post-column derivatization reagent, and System suitability:

    Proceed as directed in Zinc Determination á591ñ, Procedure, Ion Chromatographic Method.

    Standard solution: Equivalent to 40 μg/mL of zinc sulfate in Diluent from USP Zinc Sulfate RS

    Sample solution: 44 μg/mL of zinc sulfate monohydrate or 71 μg/mL of zinc sulfate heptahydrate, equivalent to 40 μg/mL of zinc sulfate, in Diluent from Zinc Sulfate

    Chromatographic system: Proceed as directed in Zinc Determination (591), Procedure, Ion Chromatographic Method, except for the Columns.

    Columns

    Guard: 4.0-mm × 5-cm; 9-μm packing L100.

    [NOTE---Alternatively, a 4.0-mm × 0.5-cm; 4.6-μm packing L91 column may be used.]

    Analytical: 4.0-mm × 25-cm; 9-μm packing L100.

    [NOTE---Alternatively, a 4.0-mm × 25-cm; 4.6-μm packing L91 column may be used.]

    Analysis

    Samples: Standard solution and Sample solution Calculate the percentage of zinc sulfate (ZnSO4) in the portion of Zinc Sulfate taken:

    Result = (ru/rs) × (Cs/Cu) × 100

    ru = peak response of zinc from the Sample solution

    rs = peak response of zinc from the Standard solution

    Cs = equivalent concentration of zinc sulfate in the Standard solution (μg/mL)

    Cu = concentration of Zinc Sulfate in the Sample solution (μg/mL)

  5. Limit of Arsenic:

    Reference: USP

    Acceptance criteria: NMT 14 ppm.

    Potassium Iodide TS:

    Dissolve 16.5 g of potassium iodide in purified water to make 100 ml. Store in light-resistant containers

    Stannous Chloride, Acid, Stronger, TS:

    Dissolve 40 g of stannous chloride in 100 ml of hydrochloric acid (37%). Store in glass containers, and use within 3 months.

    Silver Diethyldithiocarbamate TS:

    Dissolve 1 g of silver diethyldithiocarbamate in 200 ml of pyridine from a freshly opened bottle or that which has been recently distilled. Store in light-resistant containers, and use within 30 days.

    Arsenic Trioxide Stock Solution:

    Dissolve accurately about 132.0 mg of arsenic trioxide, previously dried at 105°C for 1 hour in 5 ml of sodium hydroxide solution (1 in 5) in a 1000 ml volumetric flask. Neutralize the solution with 2 N sulfuric acid, add 10 ml more of 2 N sulfuric acid, then add recently boiled and cooled purified water to volume, and mix.

    Standard Arsenic Solution:

    Transfer 10.0 ml of Arsenic Trioxide Stock Solution to a 1000 ml volumetric flask, add 10 ml of 2 N sulfuric acid, then add recently boiled and cooled purified water to volume, and mix. Keep this solution in an all-glass container, and use within 3 days.

    Standard Preparation:

    Pipet 3.0 ml of Standard Arsenic Solution into a generator flask, and dilute with purified water to 35 ml, mix.

    Test Preparation:

    Transfer about 239 mg of sample (zinc sulfate monohydrate) to the generator flask and dilute with purified water to 35 ml.

    Procedure:

    Treat the Standard Preparation and the Test Preparation similarly as follows.

    Add 20 ml of 7 N sulfuric acid, 2 ml of potassium iodide TS, 0.5 ml of stronger acid stannous chloride TS, and 1 ml of isopropyl alcohol to both preparations and mix. Allow to stand at room temperature for 30 minutes. Pack the scrubber tube with two pledgets of cotton that have been soaked in saturated lead acetate solution, freed from excess solution by expression, and dried in vacuum at room temperature, leaving a 2 mm space between the two pledgets. Lubricate the joints with suitable stopcock grease designed for use with organic solvents, and connect the scrubber unit to the absorber tube. Transfer 3.0 ml of silver diethyldithiocarbamate TS to the absorber tube. Add 3.0 g of granular zinc (No. 20 mesh) to the mixture in the flask, immediately connect the assembled scrubber unit, and allow the evolution of hydrogen and the color development to proceed at room temperature for 45 minutes, swirling the flask gently at 10 minutes intervals. Disconnect the absorber tube from the generator and scrubber units, and transfer the absorbing solution to a 1 cm absorption cell.

    Any red color produced by the Test Preparation does not exceed that produced by the Standard Preparation. If necessary or desirable, determine the absorbance at the wavelength of maximum absorbance between 535 and 540 nm, with a suitable spectrophotometer or colorimeter, using silver diethyldithiocarbamate TS as the blank.

  6. Limit of Lead:

    Reference: USP

    Acceptance criteria: NMT 20 ppm.

    Lead Nitrate Stock Solution (100 ppm):

    Dissolve 159.8 mg of lead nitrate in 100 ml of water to which has been added 1 ml of nitric acid, then dilute with water to 1000 ml, mix. Prepare and store this solution in glass containers free from soluble lead salts.

    Standard Lead Solution (10 ppm):

    On the day of use, dilute 10.0 ml of Lead Nitrate Stock Solution with purified water to 100.0 ml, mix.

    Sodium sulfide TS:

    Dissolve 1 g of s Sodium sulfide in purified water to make 10 ml, mix. Prepare this solution fresh.

    Preparation of Potassium cyanide Solution:

    [Note: Take necessary protection during this solution preparation. Try to avoid any kind of inhalation or ingestion.]

    Dissolve 50 g of potassium cyanide in sufficient water to make 100 ml. Remove the Lead from this solution by extraction with successive portions of Dithizone Extraction Solution, as described under Ammonium Citrate Solution above, then extract any Dithizon remaining in the cyanide solution by shaking with chloroform. Finally dilute the cyanide solution with sufficient water so that each 100 ml contains 10 g of potassium cyanide.

    Procedure:

    Dissolve 0.28 g of Zinc sulfate monohydrate (sample) in 5 ml of purified water, and transfer the solution to a color-comparison tube (A). Add 10 ml of Potassium Cyanide Solution (1 in 10), mix, and allow the mixture to become clear. In a similar, matched color-comparison tube (B) place 5 ml of purified water, and add 0.50 ml of Standard Lead Solution and 10 ml of Potassium Cyanide Solution (1 in 10). Add to the solution in each tube 0.1 ml of sodium sulfide TS. Mix the contents of each tube, and allow standing for 5 minutes.

    Observation:

    Viewed downward over a white surface, the solution in tube A is no darker than that in tube B.

    Or Alternative method:

    Test solution:

    Dissolve 5.00 g of sample in 20 ml of a 200 g/l solution of cadmium- and lead-free nitric acid and dilute to 25.0 ml with the same acid solution, mix.

    Reference solutions:

    Prepare the reference solutions of 10 ppm, 15 ppm, 20 ppm, 30 ppm, 40 ppm diluting with a 200 g/l solution of cadmium- and lead-free nitric acid.

    Measure the absorbance at 283.3 nm, using a lead hollow-cathode lamp as a source of radiation and an air-acetylene flame.

  7. Alkalies and alkaline earths:

    Reference: USP

    Acceptance criteria: The weight of the residue is NMT 5 mg (0.9%).

    Dissolve about 1.24 g of sample (zinc sulfate monohydrate) in about 150 ml of purified water in a 200 ml volumetric flask. Precipitate the zinc completely by means of ammonium sulfide TS, and dilute with purified water to volume. Mix, and filter through a dry filter, rejecting the first portion of the filtrate. To 100 ml of the subsequent filtrate add a few drops of sulfuric acid, evaporate to dryness in a tared dish (platinum crucible), and ignite.

  8. Acidity:

    Reference: USP

    Acceptance criteria: The sample solution is not colored pink by methyl orange TS.

    Methyl Orange TS:

    Dissolve 100 mg of methyl orange in 100 ml of purified water, and filter if necessary.

    Procedure:

    Dissolve about 310 mg of sample (Zinc sulfate monohydrate) in 10 ml of purified water, mix.