Method of Analysis for Calcium Stearate : Pharmaceutical Guidelines

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Method of Analysis for Calcium Stearate

Learn how to analyse Calcium Stearate in pharmaceutical laboratory.

1. Description

Fine, white to a yellowish white bulky powder having a slight, characteristic odor.

2. Solubility

Insoluble in water, in alcohol and in the ether.

3. Identification

A. Reaction of Calcium Salt

Reagents required
Hydrochloric acid
Ammonium oxalate 2% w/v solution
Dilute acetic acid
Procedure: Heat 1gm with a mixture of 25ml of water and 5ml of hydrochloric acid: fatty acids are liberated and appear as an oily layer floating on the surface of the liquid. To 5 ml of water, layer add 0.2 ml of a 2% w/v solution of ammonium oxalate; a white precipitate is obtained that is only sparingly soluble in dilute acetic acid but is soluble in hydrochloric acid.

B. Mix 25gm with 200ml of hot water, add 60ml of 2N sulfuric acid, and heat the mixture with frequent stirring until the separated fatty acid layer is clear. Wash the fatty acids with boiling water until free from sulfate, collect them in a small beaker, and warm on a steam bath until the water has separated and the fatty acids are clear. Allow the acids to cool, pour off the water layer, melt the acids, filter into a dry beaker, and dry at 105°C for 20 minutes. The fatty acid so obtained congeal at a temperature not below 54°C.

4. Loss on Drying

Limit: Not more than 4.0%.
Procedure: Weigh 1.000 g of substance in a clean and dried pre-weighed LOD Bottle. Cover the stopper and gently shake to distribute material to not more than 10 MM height. Place the LOD Bottle in the oven and remove the cover and leave it also inside the oven. Dry the Calcium Stearate sample at 105° C for 2 hr. On opening the chamber, immediately close the LOD Bottle, transfer it to desiccators and bring it to room temperature. Weigh up to constant weight.
                                 W2 – W3
%Loss on ignition = --------------- X 100
                                 W2 – W1
W1 = Weight of empty LOD bottle.
W2 = Weight of LOD bottle + Calcium Stearate sample.
W3 = Weight of LOD bottle + Calcium Stearate sample. (After drying)

5. Heavy metals

Limit: Not more than 10 ppm.
Test solution preparation: Place 2.5 gm of Calcium Stearate sample in a porcelain dish, add 5 ml of a 1 in 4 solution of magnesium nitrate in alcohol. Cover the dish with 7.5 cm short-stem funnels so that the stems are straight up. Heat on a hot plate at low heat for 30 minutes, then heat at medium heat for 30 minutes, and cool. Heat the dish over a suitable burner until most of the carbon is burned off. Cool add 10ml of nitric acid, and transfer the solutions into 250ml beakers. Add 5 ml of 70% Perchloric acid, cautiously evaporate to dryness, add 2ml of hydrochloric acid to the residues, and wash down the insides of the beaker with water. Evaporate carefully to dryness again, swirling near the dry point to avoid spattering. Repeat the hydrochloric acid treatment then cool, and dissolve the residues in about 10 ml of water. Add 1 drop of phenolphthalein and add sodium hydroxide until the solutions just turn pink, then add 3N hydrochloric acid until the solutions become colorless. Add 1 ml of 1N acetic acid and a small amount of charcoal to the solution, and filter through filter paper into 50ml color comparison tube.
Standard Preparation: Place 500mg Calcium Stearate sample in a porcelain dish, to it add 5ml of 1 in 4 solution of magnesium nitrate in alcohol. Cover the dishes with 7.5 cm short-stem funnels so that the stems are straight up. Heat on the hot plate at low heat for 30 minutes, then heat at medium heat for 30 minutes and cool. Remove the funnel and add 2ml of standard lead solution (20 mg of Pb). Then follow the procedure as per test solution starting from heat the dish over a suitable burner until most of the carbon is burned off.
Procedure: Each of the color comparison tubes dilute with water up to 40 ml. Then add 1.2 ml of thioacetamide-glycerin base TS and 2 ml of pH 3.5 Acetate buffer to each tube and allow standing for 5 minutes. The color of the test solution does not exceed that of the standard solution.

6. Organic Volatile Impurities

Chloroform: Not more than 60 ppm
1,4-Dioxane: Not more than 380 ppm
Methylene chloride: Not more than 600 ppm
Trichloroethylene: Not more than 80 ppm
Standard solution preparation: Prepare a solution in organic free water containing in each ml, 12mg of Methylene chloride, 7.6mg of 1,4-dioxane, 1.6mg of Trichloroethylene, and 1.2mg of chloroform. Pipette 5ml of this solution into a vial fitted with a septum and crimp-cap, containing 1g of anhydrous sodium sulfate, and seal. Heat a sealed vial at 80°C for 60 minutes.
Test Solution: Transfer 100mg, accurately weighed Calcium Stearate sample to a vial, add 5.0ml of water, and 1gm of anhydrous sodium sulfate, and seal with a septum and crimp cap. Heat the sealed vial at 80°C for 60 minutes.
Chromatographic conditions
Column: 0.53mm X 30m fused silica analytical column coated with a 3.0 mm G43 stationary phase, and a 0.53mm X 5m silica guard column deactivated with phenyl methyl siloxane.
Carrier gas
Carrier flow
Column Int. Temp
Column Pro. Rate
Column Pro. Rate
Injector temp.
Injection volume
Detector temp
Flame ionization detector

40°C for 20 minutes

Procedure: Separately inject equal volumes (about 1ml) of the standard solution and the test solution into the chromatograph, record the chromatograms, and measure the peak responses. Identify based on retention time, any peaks present in the chromatogram of the test solution. The identity and the peak response in the chromatogram may be established as being from any of the organic volatile impurities that is mentioned in the limit.
                                                                       Rt       WS       P   
 Content of each components (ppm)     = ----- x ----- x ----- x D x 106
                                                                       RS       Wt      100
Rt = Ratio of the detector response of the component to IS in test preparation.
RS = Ratio of the detector response of the component to IS in std.preparation.
WS= weight of the component in standard in gms.
Wt= weight Calcium Stearate samples taken in gms
P = % purity of component.
D = Dilution factor 0.01 for methanol and THF, 0.001 for n-hexane and toluene).

7. Assay

Limit: Not less than 9.0% and Not more than 10.5% of Calcium oxide.
Reagent Required
1N sulfuric acid
1N sodium hydroxide
0.05M Disodium Edetate
Hydroxy naphthol blue
Procedure: Boil about 1.2gm of Calcium Stearate sample accurately weighed with 50ml of 1N sulfuric acid for about 3 hours using a watch glass cover to avoid splattering, or until the separated fatty acid layer is clear, adding water, if necessary to maintain the original volume. Cool, filter and wash the filter and flask thoroughly with water until the last washing is not acid to litmus. Neutralize the filtrate with 1N sodium hydroxide to litmus. While stirring, preferably with a magnetic stirrer, titrate with 0.05M Disodium Edetate VS as follows. Add about 30ml from a 50ml burette, then add 15ml of 1N sodium hydroxide and 300mg of Hydroxy naphthol blue, and continue the titration to a blue endpoint.
Each ml of 0.05M Disodium Edetate is equivalent to 2.804mg of CaO.
                                                    V X M                        F
% Assay on the dried basis. = -----------------------x--------------
                                                   0.05 X W              (100-LOD)

 = _____________________% Assay on dried basis

V = Consumed volume of 0.1 M Perchloric Acid
M= Molarity of 0.1 M Perchloric Acid
F= Factor
W= Weight of substance

Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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