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Method of Analysis for Hydroxypropyl Methylcellulose (HPMC) K100


Procedure for chemical analysis for the Hydroxypropyl Methylcellulose k100 in pharmaceutical quality control.
1. Description
White or yellowish white, fibrous or granular powder, almost odourless, hygroscopic after drying.

2. Solubility
Practically insoluble in hot water, in acetone, in ethanol, in ether, toluene and in chloroform. It swells in water forming an opalescent, viscous colloidal solution.

3. Identification
A) With constant stirring add a quantity equivalent to 1.0 g of the dried substance into 50 ml of carbon dioxide-free water previously heated to 90°. Allow to cool, dilute to 100 ml with carbon dioxide- free water and continue stirring until solution is complete (Solution A). Heat 10 ml of solution A in a water-bath with stirring. At temperatures above 50° the solution becomes cloudy or a flocculent precipitate is formed. On cooling, the solution becomes clear or slightly opalescent.
B) To 10 ml of solution A add 10 ml of 1M sodium hydroxide or 1M hydrochloric acid; in either case the mixture remains stable.
C) To 10 ml of solution A add 0.3 ml of 2M acetic acid and 2.5 ml of a 10.0% w/v solution of tannic acid; a yellowish white, flocculent precipitate is produced which dissolves in 6M ammonia.
D) Without heating completely dissolve 0.2 g in 15 ml of a 70% w/w solution of sulphuric acid, pour the solution with stirring into 100 ml of iced water. In a test tube kept in ice, mix thoroughly 1 ml of the solution with 8 ml of sulphuric acid, added drop wise. Heat in a water bath for exactly 3 minutes and cool immediately in ice. When the mixture is cool, carefully add 0.6 ml of a solution containing 3 g of ninhydrin in 100 ml of a 4.55% w/v solution of sodium metabisulphite, mix well and allow to stand at 25°; a pink color is produced immediately which becomes violet within 100 minutes.
E) Place 1 ml of solution A on a glass plate, After evaporation of the water a thin film is produced.

4. pH
Limit: Between 5.5 and 8.0.
Procedure
The pH value of a solution is determined potentiometrically.
Immerse the pH meter electrodes in the 1.0% w/v solution being examined in a carbon dioxide free water and measure the pH at the 25° ± 2°, record the pH of the solution (use earlier calibrated pH meter).

5. Clarity and Color of Solution
Limit: Solution A is not more opalescent than opalescence standard OS3, and not more intensely color than reference solution YS6.
Procedure for Clarity of Solution:
Test Solution: Use Solution A
OS3 Solution: 30.0 ml (standard suspension) + 70.0 ml (Water)
Examine both the test tube in diffused light by viewing down the vertical axis of the tubes against a white background.
Procedure for Color of Solution:
Test Solution: Use Solution A
Reference solution YS6: Mix 1.6 ml of FCS, 0.4 ml of CCS and 98 ml of Hydrochloric acid (1% w/v).
Examine both the test tube in diffused light by viewing down the vertical axis of the tubes against a white background.

6. Apparent viscosity
Limit: Between 75% to 140% of the label claim. (Between 75000 cps to 140000 cps)
Procedure
Weigh accurately an equivalent to 5 g of the dried substance and add, with constant stirring, to 50 ml of water previously heated to 90°. Allow cool, diluting to 250 ml with water and continuing stirring until solution is complete. Adjust the weight of the solution to 250 g and centrifuge the solution to expel any trapped air. Adjust the temperature of test solution at 20° C. Take viscosity on Brook field viscometer using Spindle LV-4. Find out the factor using factor finder as per applied speed. Note down the dial reading on instrument and calculate the viscosity using given formulas.
Viscosity (in cps) = Dial reading x factor

7. Heavy metals
Limit: Not more than 10 ppm
Standard solution: Into a 50 ml Nessler cylinder pipette 1 ml of lead standard solution (20 ppm Pb) and dilute with water to 25 ml. Adjust with dilute acetic acid or dilute ammonia solution to a pH between 3.0 and 4.0, dilute with water to about 35 ml and mix.
Test solution: Weigh in a suitable crucible the 2 g of the substance, add sufficient sulphuric acid to wet the sample, ignite carefully at a low temperature until thoroughly charred. Add to the charred mass 2 ml of nitric acid and 5 drops of sulphuric acid and heat cautiously until white fumes are no longer evolved. Ignite, preferably in a muffle furnace, at 500° to 600°, until the carbon is completely burnt off. Cool, add 1 ml of hydroxylamine hydrochloride solution (1 in 5) and add 4 ml of hydrochloric acid, cover, digest on a water-bath for 15 minutes, uncover and slowly evaporate to dryness on a water bath. Moisten the residue with 1 drop of hydrochloric acid, add 10 ml of hot water and digest for 2 minutes, Add ammonia solution drop wise until the solution is just alkaline to litmus paper, dilute to 25 ml with water and adjust with dilute acetic acid to a pH between 3.0 and 4.0. Filter, if necessary, rinse the crucible and the filter with 10 ml of water, combine the filtrate and washings in a 50 ml Nessler cylinder, dilute water to about 35 ml and mix.
Procedure
To each of the cylinders containing the standard solution and test solution respectively add 10 ml of freshly prepared hydrogen sulphide solution, mix, dilute to 50 ml with water, allow to stand for 5 minutes and view downwards over a white surface; the color produced with the test solution is not more intense than that produced with the standard solution.

8. Chloride
Limit: Not more than 0.5%
Procedure:
Test solution: Dilute 5 ml of solution A to 15 ml with water.
Transfer a test solution in Nessler cylinder. Add 10 ml of dilute nitric acid dilute to 50 ml with water and add 1 ml of 0.1M silver nitrate. Stir immediately with a glass rod 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 (25 ppm Cl) and 5 ml of water in the same manner.

9. Sulphated Ash
Limit: Not more than 1.0%.
Procedure:
Heat a silica crucible to redness for 10 min., allow to cool in a desiccator and weigh. Place about 1 g of accurately weighed substance being examined in the silica crucible, moisten with sulphuric acid, ignite gently, again moisten with sulphuric acid and ignite at about 800o, cool, weigh again, ignite for 15 min. and repeat this procedure until two successive weighing do not differ by more than 0.5 mg.           
Calculation: 
                                          W3– W1
% Sulphated Ash =    ---------------- x 100
                                         W2 – W1
Where:   
W1 = Weight of empty platinum crucible.
W2 = Weight of crucible + sample.
W3 = Weight of crucible + residue.  (After ignition)

10. Loss on drying
Limit: Not more than 10 %.
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 oven and remove cover and leave it also inside the oven. Dry the 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.  
Calculation:
                                       W2 – W1
% Loss on Drying = --------------- X 100
                                       W2 – W3
Where: 
W1 = Weight of empty clean and dried LOD Bottle.
W2 = Weight of LOD Bottle + sample.
W3 = Weight of LOD Bottle + sample. (After drying)



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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