Method of Analysis for Sodium Carbonate Anhydrous : Pharmaceutical Guidelines

Method of Analysis for Sodium Carbonate Anhydrous

Procedure for analysis of Anhydrous Sodium Carbonate in pharmaceutical quality control laboratory.

1. Description
A white or almost white, slightly granular powder, hygroscopic.

2. Solubility
Freely soluble in water; practically insoluble in alcohol.

3. Identification
A. Dissolve 1gm of the Sodium Carbonate sample in water and dilute to 10 ml with the same solvent. The solution is strongly alkaline.
B. Test for Carbonates
Introduce into a test tube solution of Test A, Add 3 ml of 2M acetic acid, close the tube immediately using a stopper fitted with a glass tube bent at two right angles. The solution or suspension effervesces evolving a Colorless and odorless gas. Heat gently and collect the gas in 5 ml of 0.1M barium hydroxide. A white precipitate is produced which dissolves on addition of an excess of 7M hydrochloric acid.
C. Test for Carbonates
Treat the solution of the substance being examined with a solution of magnesium Sulphate. A white precipitate is produced (distinction form bicarbonates).
D. Reaction of Sodium
Solution of Test A, add 2 ml of a 15% w/v solution of potassium carbonate and heat to boiling; no precipitate is produced. Add 4 ml of freshly prepared potassium antimonate (V) solution and heat to boiling. Allow cooling in ice and if necessary scratching the inside of the tube with a glass rod; a dense, white precipitate is produced.

4. Appearance of the Solution
Limit: The solution is clear and not more intensely colored than reference solution Y6.
Into separate matched, flat-bottomed test tubes, 15 to 25 mm in internal diameter and of colorless, transparent, neutral glass, place sufficient of the solution being examined and of the appropriate reference suspension, freshly prepared as specified below, such that the test tubes are filled to a depth of 40 mm. Five minutes after preparation of the reference suspension, compare the contents of the test tube against a black background by viewing in diffused daylight down the vertical axes of the tubes.
Standard of opalescence: Dissolve 1.0 g of hydrazone sulphate in 100 ml of water and allow standing for 4 to 6 hours. Add 25 ml of this solution to a solution containing 2.5 g of hexamine in 25 ml of water mix well and allow standing for 24 hours. This suspension is stable for 2 months provided that it is stored in a glass container free from surface defects. The suspension must not adhere to the glass and must be well mixed before use.
To prepare the standard of opalescence, dilute 15 ml of the suspension to 1000 ml with water. This suspension must be used within 24 hours of preparation.
Reference suspensions 1: Take 5 ml standard opalescence and 95 ml of water.
Test solution: Dissolve 2.0 g of substance in 10 ml of water.
A liquid is clear if its clarity is the same as that of water or of reference suspensions 1.

Color of solution:
Yellow primary solution: Dissolve 46 g of iron (III) chloride hexahydrate in about 900 ml of a mixture of 25 ml of hydrochloric acid and 975 ml of water and dilute to 1000 ml with the same mixture.
Yellow primary solution   +   Red primary solution  + HCl (1% w/v)
Y  =             24                                         6                         70
            Standard solution       +    HCl (1% w/v) ml
Y6 =            5.0                              95.0

Using identical tubes of Colorless, transparent, neutral 12 mm in external diameter compare 2.0 ml of the liquid being examined with 2 ml of the reference solution Y6. Compare the colors in diffused daylight, viewing horizontally against a white background.
The solution is clear and not more intensely colored than reference solution Y6.

5. Alkali hydroxides and bicarbonates
Limit: The solution remains clear.
Dissolve 0.4gm in 20 ml of water. Add 20 ml of barium chloride solution and filter. To 10 ml of the filtrate add 0.1 ml of phenolphthalein solution. The solution does not become red. Boil the remainder of the filtrate for 2 minutes. The solution remains clear.

6. Chlorides
Limit: Not more than 125 ppm
Dissolve 0.4gm in water and 4 ml of dilute nitric acid and dilute to 15 ml with water. Pour the mixture as a single addition into 1 ml of silver nitrate solution and allow standing for 5 minutes protected from light. When viewed transversely against a black background any opalescence produced is not more intense than that obtained by treating a mixture of 10 ml of chloride standard solution (5 ppm Cl) and 5 ml of water in the same manner.

7. Sulphate
Limit: Not more than 250 ppm
Solution S: Dissolve 2gm in portions in a mixture of 5 ml of hydrochloric acid and 25 ml of distilled water. Heat the solution to boiling and cool. Add dilute sodium hydroxide solution until the solution is neutral and dilute to 50 ml with distilled water. (Solution S)
Add 1 ml of a 25% w/v solution of barium chloride to 1.5 ml of Sulphate standard solution in ethanol (30 %) (10 ppm SO4), shake and allow standing for 1 minute. Add 15 ml of the solution S and 0.5 ml 5M acetic acid allow standing for 5 minutes. Any opalescence produced is not more intense than that of a standard prepared in the same manner but using 15 ml of Sulphate standard solution (10 ppm SO4).

8. Arsenic
Limit:  Not more than 5 ppm
The apparatus consists of a 100 ml conical flask closed with a ground glass stopper through which passes a glass tube about 200 mm long and 5 mm in internal diameter. The lower part of the tube is drawn to an internal diameter of 1.0 mm and 15 mm from its tip is a lateral orifice 2 to 3 mm in diameter. When the tube is in position in the stopper the lateral orifice should be at least 3 mm below the lower surface of the stopper. The upper end of it has a perfectly flat, ground surface at right angles to the axis of the tube.
A second glass tube of the same internal diameter and 30 mm long, with a similar flat ground surface, is placed in contact with the first and is held in position by two spiral springs. Into the lower tube insert 50 to 90 mg of lead acetate cotton, loosely packed, or a small plug of cotton and a rolled piece of lead acetate paper weighing 50 to 60 mg. Between the flat surfaces of the tubes place a disc or a small square of mercury (II) bromide paper large enough to cover the orifice of the tube (15 mm x 15 mm) In the conical flask 5 ml of solution S, dilute the prescribed volume to 25 ml with water. Add 15 ml of hydrochloric acid, 0.1 ml of tin (II) chloride solution and 5 ml of potassium iodide solution, allow standing for 15 minutes and adding 5 g of activated zinc. Immediately assemble the two parts of the apparatus and immerse the flask in a water bath at a temperature such that a uniform evolution of gas is maintained. After not less than 2 hours any stain produced on the mercury (II) bromide paper is not more intense than that obtained by treating 1 ml of arsenic standard solution (1 ppm As) diluted to 25 ml with water in the same manner.

9. Heavy metals
Limit: Not more than 50 ppm,
Reagent required
Acetate buffer pH 3.5
Lead standard solution (2 ppm Pb)
Sodium Carbonate sample Preparation: To 12 ml of solution S add 2ml of acetate buffer pH 3.5, mix, add to 1.2 ml of thioacetamide, mix immediately and allow standing for 2 minutes
Standard Solution: Take 10ml of lead standard solution (2 ppm Pb), a  add 2ml of acetate buffer pH 3.5, mix, add to 1.2 ml of thioacetamide, mix immediately and allow to stand for 2 minutes.
Allow to stand for 5 min. and view downwards over a white surface. The color produced with test solution is not more intense than produced with the standard solution

10. Iron
Limit: Not more than 50 ppm
Reagent required
20% w/v of citric acid
Mercaptoacetic acdi
10M ammonia
Iron standard solution (1 ppm)
Dilute 5ml Solution S to 10 ml with water to transfer in Nessler cylinder. Add 2ml of a 20% w/v solution of citric acid and 0.1 ml of mercaptoacetic acid, mix, make alkaline with 10M ammonia, dilute to 20 ml with water and allow standing for 5 minutes. Any pink color produced is not more intense than that obtained by treating 10 ml of iron standard solution (1 ppm Fe) in the same manner.

11. Loss on drying
Limit: Not more than 1.0 %.
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 oven and remove cover and leave it also inside the oven. Dry the Sodium Carbonate sample at 300° C for 3 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 – W1
% Loss on Drying = --------------- X 100
                                      W2 – W3
W1 = Weight of empty clean and dried LOD Bottle
W2 = Weight of LOD Bottle + Sodium Carbonate sample
W3 = Weight of LOD Bottle + Sodium Carbonate sample (After drying)

12. Assay
Limit: Not less than 99.5 % and Not more than 100.5 % on dried basis
Reagent required
1M Hydrochloric acid
Methyl orange
Dissolve 1 g in 25 ml of water. Add 0.2 ml of methyl orange solution as indicator. Titrate with 1M hydrochloric acid until the color changes from yellow to red or potentiometrically (up to second point of inflexion)
Each ml of 1M hydrochloric acid is equivalent to 52.99 mg of Na2CO3.

% Assay = B.R. x Molarity of HCl x 52.99 x 100 x 100
                    1 x wt. of Sodium Carbonate sample in mg x (100- LOD)

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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