Method of Analysis for Calcium Silicate : Pharmaceutical Guidelines

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Method of Analysis for Calcium Silicate

Learn how to analyse Calcium Silicate in pharmaceuticals.

1. Description

White to off-white free-flowing powder.

2. Solubility

Insoluble in water.

3. Identification

A. Reaction of Calcium Salt

Reagents required
3N Hydrochloric acid
6N Ammonium Hydroxide
Ammonium oxalate 2% w/v solution
6N acetic acid
Procedure: Mix 0.5 g with 10 mL of 3 N hydrochloric acid, filter, and neutralize the filtrate to litmus paper with 6 N ammonium hydroxide. To the neutralized filtrate so obtained add 2 drops of methyl red, and neutralize with 6 N ammonium hydroxide. Add 3 N hydrochloric acid, dropwise, until the solution is acid to the indicator.Upon the addition of ammonium oxalate, a white precipitate is formed. This precipitate is insoluble in 6 N acetic acid but dissolves in hydrochloric acid. Calcium salts moistened with hydrochloric acid impart a transient yellowish red color to a nonluminous flame.

B. Mix 25gm with 200ml of hot water, add 60ml of 2N sulfuric acid and Prepare a bead by fusing a few crystals of sodium ammonium phosphate on a platinum loop in the flame of a gas burner. Place the hot, transparent bead in contact with the specimen of Calcium Silicate, and again fuse. Silica floats about in the bead, producing, upon cooling, an opaque bead having a web-like structure.

4. Loss on Ignition

Limit: It loses not more than 20.0% of its weight.
Procedure: Ignite a clean platinum crucible at 900°C for 30 minutes, cool and weigh the crucible. Transfer about 1.0 gm. of the sample into the crucible and record the weight. Ignite the crucible along with the sample at 900°c for 2 hours. Cool the crucible to room temperature in a desiccator and record the weight.
                                   W2 – W3
%Loss on ignition = ------------------- X 100
                                   W2 – W1
W1 = Weight of empty platinum crucible.
W2 = Weight of crucible + sample.
W3 = Weight of crucible + sample. (After ignite)

5. pH

Limit: Between 8.4 and 10.2
Procedure: Take 1gm of the sample and mix it properly with 20ml of water. Then take the pH of the solution using pH meter

6. Lead

Limit: Not more than 0.001%
Test Preparation: Dissolve 1.0 g in 20 mL of 3 N hydrochloric acid, evaporate on a steam bath to about 10 ml, dilute with water to about 20 mL, and cool.
Procedure: Transfer the Test Preparation, rinsing with 10 mL of water, or the volume of the prepared sample specified add 6 mL of Ammonium Citrate Solution and 2 mL of Hydroxylamine Hydrochloride Solution. Add 2 drops of phenol red TS, and make the solution just alkaline (red in color) by the addition of ammonium hydroxide. Cool the solution if necessary, and add 2 mL of Potassium Cyanide Solution. Immediately extract the solution with 5-mL portions of Dithizone Extraction Solution, draining off each extract into another separator, until the dithizone solution retains its green color. Shake the combined dithizone solutions for 30 seconds with 20 mL of dilute nitric acid (1 in 100), and discard the chloroform layer. Add to the acid solution 5.0 mL of Standard Dithizone Solution and 4 mL of Ammonia-Cyanide Solution, and shake for 30 seconds: the color of the chloroform layer is no deeper shade of violet than that of a control made with a volume of Diluted Standard Lead Solution equivalent to the amount of lead permitted in the sample under examination, and the same quantities of the same reagents and in the same manner as in the test with the sample.

7. Heavy metals

Limit: Not more than 20 ppm.
Test solution preparation: Boil 4.0 g with a mixture of 50 ml of water and 10 ml of hydrochloric acid for 20 minutes, adding water to maintain the volume during the boiling. Add ammonium hydroxide until the mixture is only slightly acid to litmus paper. Filter with the aid of suction, and wash with 15 ml to 20 ml of water, combining the washing with the original filtrate. Add 2 drops of phenolphthalein, then add a slight excess of 6 N ammonium hydroxide. Discharge the pink color with dilute hydrochloric acid (1 in 100). Dilute with water to 100 ml. Into a 50-mL color-comparison tube place 25 mL of the solution prepared then adjust with 1 N acetic acid or 6 N ammonium hydroxide to a pH between 3.0 and 4.0, using short-range pH indicator paper as an external indicator, dilute with water to 40 ml, and mix.
Standard Preparation: Into a 50-mL color-comparison tube pipet 2 mL of Standard Lead Solution (20 µg of Pb), and dilute with water to 25 mL. Adjust with 1 N acetic acid or 6 N ammonium hydroxide to a pH between 3.0 and 4.0, using short-range pH indicator paper as an external indicator, dilute with water to 40 mL, and mix.
Procedure: To each of the three tubes containing the Standard Preparation and the Test Preparation, add 2 ml of pH 3.5 Acetate Buffer, then add 1.2 ml of thioacetamide-glycerin base, dilute with water to 50 ml, mix, allow to stand for 2 minutes, and view downward over a white surface: the color of the solution from the Test Preparation is not darker than that of the solution from the Standard Preparation.

8. Limit of Fluorides

Limit: Not more than 10 ppm
Buffer solution: Add 800 mL of hot water to 74.4 g of edetate disodium and 24.2 g of tris(hydroxymethyl) aminomethane, and stir until dissolved. Adjust with 5 N sodium hydroxide to a pH of 7.5 to 7.6. Allow the solution to cool, and adjust with 5 N sodium hydroxide to a pH of 8.0. Dilute with water to 1000 ml, and mix.
Electrode system: Use a fluoride-specific, ion-indicating electrode and a calomel reference electrode connected to a pH meter capable of measuring potentials with a reproducibility of ±0.2 mV
Standard stock solution: Dissolve an accurately weighed quantity of USP Sodium Fluoride RS quantitatively in water to obtain a solution containing 221 µg per ml. Each ml of this stock solution contains 100 µg of fluoride ion.
Standard solutions: Transfer 10.0 ml of Standard stock solution to a 100-ml volumetric flask, dilute with water to volume and mix. This solution contains 10 µg of fluoride ion per ml (Standard solution A). Transfer 1.0 ml of Standard stock solution to a second 100- ml volumetric flask, dilute with water to volume, and mix. This solution contains 1.0 µg of fluoride ion per ml ( Standard solution B).
Test solution: Transfer 5.0 g of Calcium Silicate to a 150-ml polytef beaker. Add 40 ml of water and 20ml of 1 N hydrochloric acid. Heat to near boiling for 1 minute, stirring continuously. Cool in an ice bath, transfer the suspension to a 100-ml volumetric flask, dilute with water to volume, and mix.
Procedure: Transfer 20.0 ml of Standard solution A, Standard solution B, and the Test solution to separate polytef beakers, add 10.0 mL of Buffer solution to each beaker, and stir with a plastic-coated stirring bar. Concomitantly measure the potentials, in mV, of the solutions. Plot the logarithms of the fluoride ion concentrations, in µg per mL, of the Standard solutions versus potential, in mV. From the measured potential of the test solution and the standard response line, determine the concentration, C, in µg per mL, of fluoride ion in the Test solution. Calculate the quantity, in µg of fluoride per g of Calcium Silicate by multiplying C by 20.

9. Assay for Silicon Dioxide

Limit: The percentage of silicon dioxide in the Calcium Silicate not less than 45%
Procedure: Transfer about 400 mg of Calcium Silicate, accurately weighed, to a beaker, add 5 ml of water and 10 mL of perchloric acid, and heat until dense white fumes of perchloric acid is evolved. Cover the beaker with a watch glass, and continue to heat for 15 minutes longer. Allow to cool, add 30 ml of water, filter, and wash the precipitate with 200 ml of hot water. Transfer the filter paper and its contents to a platinum crucible, heat slowly to dryness, then heat sufficiently to char the filter paper. After cooling, add a few drops of sulfuric acid, and ignite at about 1300° to constant weight. Moisten the residue with 5 drops of sulfuric acid, add 15 ml of hydrofluoric acid, heat cautiously on a hot plate until all of the acid is driven off, and ignite at a temperature not lower than 1000° to constant weight. Cool in a desiccator, and weigh: the loss in weight represents the weight of SiO2.
                                   W2 – W3
%Loss on ignition = ------------------- X 100
                                   W2 – W1
W1 = Weight of empty platinum crucible.
W2 = Weight of crucible + sample.
W3 = Weight of crucible + sample. (After ignition)

10. Assay of Calcium Oxide

Limit: The percentage of CaO in the Calcium Silicate is not less than 4.0%
Procedure: Neutralize the combined filtrate and washings retained from the Assay for silicon dioxide to litmus with 1 N sodium hydroxide. Add, while stirring, about 30 ml of 0.05 M edetate disodium VS from a 50-ml buret. Add 15 ml of 1 N sodium hydroxide and 300 mg of hydroxy naphthol blue, and continue the titration to a blue endpoint. Each mL of 0.05 M edetate disodium is equivalent to 2.804 mg of CaO.
                                                     V X M X F            100
% Assay on dried basis. = -----------------------x--------------
                                                    0.05 X W            (100-LOD)

= _____________________% Assay on dried basis

V = Consumed volume of 0.05M Disodium EDTA
M= Molarity of 0.05M Disodium EDTA
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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