Method of Analysis for Ethyl Cellulose : Pharmaceutical Guidelines

Method of Analysis for Ethyl Cellulose

Procedure for analysis of Ethyl Cellulose in quality control laboratories in pharmaceuticals.

1. Description
Free flowing white to light tan powder.

2. Solubility
Insoluble in water in propylene glycol and in Glycerin

3. Identification
The infrared spectrum of the film so obtained exhibits maxima only at the same wavelength as that similar preparation of Ethyl cellulose (WRS).

4. Viscosity
Limit: Not less than 90% and Not more than 110%.
Procedure: Dissolve 5.0 gm sample in 95 gm in a mixture of 80 ml of toluene in 20 ml of alcohol. Adjust the temperature of the solution to 25 ± 0.1°

5. Loss on Drying
Limit: Not more than 3% of its weight.
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 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 – W1
% Loss on Drying = --------------- X 100
                                       W2 – W3
W1 = Weight of empty clean and dried LOD Bottle.
W2 = Weight of LOD Bottle + sample.
W3 = Weight of LOD Bottle + sample. (After drying)

6. Residue on Ignition
Limit: Not more than 0.4%
Ignite a clean platinum crucible at 900°c for 30 minutes, cool and weigh the crucible. Transfer about 1gm 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)

7. Lead
Limit: Not more than 10ppm
Test Preparation: Transfer 1.0 g of the sample to a suitable flask, add 5 ml of sulfuric acid and a few glass beads, and digest on a hot plate in a hood until charring begins. (Add additional sulfuric acid, if necessary, to wet the substance completely, but do not add more than a total of 10 ml.) Add, dropwise and with caution, 30 percent hydrogen Peroxide, allowing the reaction to subside and again heating between drops. Add the first few drops very slowly, mix carefully to prevent a rapid reaction, and discontinue heating if foaming becomes excessive. Swirl the solution in the flask to prevent the unreacted substance from taking on the walls of the flask. Continue the digestion until the substance is completely destroyed, copious fumes of sulfur trioxide is evolved, and the solution is colorless. Cool, cautiously add 10 ml of water,
Evaporate until sulfur trioxide again is evolved, and cool. Repeat this procedure with another 10ml of water to remove any traces of hydrogen peroxide. Cautiously dilute with 10 ml of water, and cool.
Transfer the Test Preparation, rinsing with 10 ml of water, or the volume of the prepared sample specified in the monograph to a separator, and, unless otherwise directed in the monograph, add 6 ml of Ammonium Citrate Solution and 2 ml of Hydroxylamine Hydrochloride Solution. Add 2 drops of phenol red, 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.

8. Heavy metals
Limit: Not more than 20 ppm
Standard solution: Into a 50 ml Nessler cylinder pipette 2.0 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 40 ml and mix.
Test solution: Weigh accurately about 1 gm of sample in a silica crucible, 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 500o to 600o, until the carbon is completely burnt off. Cool, 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 dropwise 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 with water to about 40 ml and mix.
To each of the tubes containing the Standard Preparation and the Test Preparation, add 2ml of pH 3.5 Acetate Buffer, then add 1.2ml of thioacetamide-glycerin base, dilute with water to 50ml, 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.

9. Organic Volatile Impurity
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 Preparation: Transfer 100 mg, accurately weighed, of the material under test to a vial, add 5.0ml of water, or the solvent specified in the monograph, and 1 g of anhydrous sodium sulfate, and seal with a septum and crimp cap. Heat the sealed vial at 80° 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 are mentioned in the limit.

10. Assay
Limit:: Not less than 44.0% and not more than 51.0% on anhydrous basis.

Prepare the apparatus by disconnecting the ball joint and pouring water into trap until it is half-full. Connect the two parts, using a minimal amount of a suitable silicone grease to seal the ball joint. Add 7 ml of Bromine-Acetic Acid Solution to absorption tube. Weigh 50mg accurately weighed sample in a tarred gelatin capsule, and add it to the boiling flask along with a few boiling chips. Finally add 6 ml of Hydriodic Acid and attach the flask to the column, using a minimal amount of a suitable silicone grease to seal thejunction. Bubble the carbon dioxide or nitrogen through the apparatus at the rate of 2 bubbles per second, place the boiling flask in an oil bath or heating mantle heated to 150°, and continue the reaction for 40 minutes for methoxy determination. Drain the contents of the absorption tube into a 500-mL conical flask containing 10 ml of sodium acetate solution (1 in 4). Rinse the tube with water, adding the rinsing to the flask, and finally dilute with water to about 125 ml. Add formic acid, drop wise, with swirling, until the reddish brown color of the bromine is discharged, then add 3 additional drops. A total of 12 to 15 drops usually is required. Allow to stand for 3 minutes, and add 15ml of diluted sulfuric acid and 3 g of potassium iodide, and titrate immediately with 0.1 N sodium thiosulfate, using 3ml of starch as the indicator. Perform a blank determination, including also a gelatin capsule, and make any necessary correction. Each ml of 0.1N sodium Thiosulphate is equivalent to 0.517 mg of (OCH 3).

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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