Determination of purity of HPMC hydroxypropyl methyl cellulose

The principle

Hydroxypropyl methyl cellulose HPMC is insoluble in 80% ethanol. After dissolving and washing for many times, 80% ethanol dissolved in the sample is separated and removed to obtain pure hydroxypropyl methyl cellulose HPMC.


Unless otherwise stated, only reagents confirmed to be analytical pure and distilled or deionized water or water of comparable purity shall be used in the analysis.

95% ethanol (GB/T 679).

Ethanol, 80% solution, dilute 95% ethanol (E.2.1) 840mL with water to 1L.

BMI (GB/T 12591).

The instrument

Common laboratory instruments

Magnetic heating stirrer, stirring rod length about 3.5cm.

Filtration crucible, 40mL, aperture 4.5μm ~ 9μm.

Glass surface dish, φ10cm, central hole.

Beaker, 400mL.

Constant temperature water bath.

Oven, can control the temperature at 105℃±2℃.

The program

Accurately weigh the sample 3g (accurate to 0.001g) into a constant weight beaker, add 150mL 80% ethanol at 60℃ ~ 65℃, put the magnetic rod into the magnetic heating stirrers, cover the surface dish, insert a thermometer in the center hole, turn on the heating stirrers, adjust the stirring speed to avoid splashing, and maintain the temperature at 60℃ ~ 65℃. Stirring for 10 min.

Stop stirring, place the beaker in a constant temperature water bath of 60℃ ~ 65℃, stand still to settle insoluble matter, and pour the supernatant liquid as completely as possible into a constant weight filtration crucible.

Add 150mL 80% ethanol at 60℃ ~ 65℃ to the beaker, repeat the above stirring and filtering operations, and then wash the beaker, surface dish, stirring rod and thermometer carefully with 80% ethanol at 60℃ ~ 65℃, so that the insoluble matter is completely transferred to the crucible, and further wash the contents of the crucible. Suction should be used during this operation and drying of the cake should be avoided. If particles pass through the filter, suction should be slowed down.

Note: it should be ensured that the sodium chloride in the sample is completely washed away by 80% ethanol. If necessary, 0.1mol/L silver nitrate solution and 6mol/L nitric acid can be used to check whether the filtrate contains chloride ions.

At room temperature, the crucible contents were washed twice with 95% ethanol at 50mL, and finally with ethyl mi20mL for secondary washing. The filtration time should not be too long. The crucible was placed in a beaker and heated on the steam bath until no ethyl mi odor was found.

Note: washing with ethyl mi is necessary to completely remove the ethanol from the insoluble substance. If ethanol is not completely removed before oven drying, complete removal is not possible during oven drying.

The crucible and beaker were placed in an oven at 105℃±2℃ for drying for 2h, then transferred to the dryer for cooling for 30min and weighed, and dried for 1h and weighed for cooling until the mass change was not more than 0.003g. In case of mass increase during 1h drying, the lowest observed mass shall prevail.

The results calculated

The purity of HPMC hydroxypropyl methyl cellulose was calculated as mass fraction P, and the value was expressed as %

M1 — mass of dried insoluble matter, in grams (g);

M0 — Mass of the test component, in grams (g);

W0 — Moisture and volatile content of the sample, %.

The arithmetic mean value of the two parallel measurements is reduced to one decimal point as the measurement result.


The absolute difference between the two independent measurements obtained under repeatability conditions is not greater than 0.3%, provided that greater than 0.3% does not exceed 5%.

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