Determination of Moisture in Chinese Medicine (2)

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(1) Brief description

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(2) Determination method

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(3) Matters needing attention

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(4) Calculation

In the formula, W ₁ is the weight of the sample (g); W ₂ is the weight (g) of the constant weight of the bottle; W ₃ is the weight (g) of the constant weight (weighing bottle + the test product)

Three, toluene method

(1) Brief description

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(2) Operation method

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Place the round bottom flask in an electric heating mantle and slowly heat it.
When the toluene starts to boil, adjust the temperature to distill out 2 drops per second.
When the water is completely distilled out, that is, when the volume of water in the graduated part of the measuring tube no longer increases , Rinse the inside of the condenser tube with toluene, then use a long brush saturated with toluene or other suitable methods to push down the toluene attached to the tube wall, continue to distill for 5 minutes, and let it cool to room temperature
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(3) Disassembly device

If water adheres to the wall of the moisture measuring tube, it can be pushed down with a copper wire dipped in toluene and placed to completely separate the moisture from the toluene (a small amount of methylene blue powder can be added to make the water dye blue for separation and observation) , Check the water volume (Figure 13-1)
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Figure 13-1 Toluene method equipment

(4) Matters needing attention

1.
The moisture analyzer should be cleaned until there is no water on the inner wall before use, and placed in an oven for drying
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2.
The toluene used for the measurement must be added with a small amount of water first, shaken thoroughly and then placed, the water layer is separated and discarded, and the toluene is used after being distilled
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3.
The test product used in the determination of Chinese medicine is generally broken into particles or fragments with a diameter of no more than 3mm
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Diameter and length below 3mm can not be broken
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4.
When heating with an electric heating mantle, the heating temperature should be strictly controlled
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5.
The scale part of the moisture measuring tube should be calibrated and qualified
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(5) Calculation

Check the water volume and calculate it as the water content (%) of the test product
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In the formula, W is the weight of the sample (g); V is the volume of water (ml) read
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Four, gas chromatography

(1) Brief description

This method uses gas chromatography, with purified water as the control, absolute ethanol as the solvent, and thermal conductivity detector to determine the water content (%) of precious medicinal materials
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(2) Chromatographic conditions and system suitability test

Use divinylbenzene-ethylvinylbenzene type polymer porous beads with a diameter of 0.
18～0.
25mm as the carrier, or use a capillary column with compatible polarity, the column temperature is 140～150℃, and the thermal conductivity detector detects
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Inject absolute ethanol and determine according to gas chromatography (general rule 0521), which should meet the following requirements:

(1) The number of theoretical plates calculated by the water peak should be greater than 1000, and the number of theoretical plates calculated by the ethanol peak should be greater than 150;

(2) The resolution of the two peaks of water and ethanol should be greater than 2;

(3) Inject 5 times with absolute ethanol, and the relative standard deviation of the water peak area shall not be greater than 3.
0%
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(3) Operation method

1.
Preparation of the control solution Take about 0.
2g of purified water, accurately weigh it, place it in a 25ml measuring flask, add absolute ethanol to the mark, and shake it up to get it
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2.
Preparation of the test product solution Take an appropriate amount of the test product (water content about 0.
2g), cut or grind it into fine pieces, accurately weigh it, and place it in a stoppered conical flask, add 50ml of absolute ethanol, tightly stopper, and mix.
Evenly, sonicate for 20 minutes, let it stand for 12 hours, then sonicate for 20 minutes, and place it tightly.
After clarification, pour the supernatant to get it
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3.
The system suitability test is tested in accordance with gas chromatography (see the gas chromatography and gas chromatograph standard operating procedures for details).
Take an appropriate amount of absolute ethanol, inject it into the gas chromatograph, and inject 5 consecutive samples.
The number of theoretical plates is based on the water peak.
The calculation should be greater than 1000, the resolution of the water and ethanol peaks should be greater than 2, and the relative standard deviation of the water peak area should not be greater than 3.
0%
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4.
Determination Take 1~5ul each of absolute ethanol, control solution and test solution, inject into the gas chromatograph, measure, and get it
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(4) Matters needing attention

1.
To prepare the control solution and the test solution, use the same newly opened bottle of absolute ethanol
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2.
After adding absolute ethanol to the test product, it should be sealed tightly and ultrasonically processed to prevent moisture in the air from entering the solvent
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(5) Calculation

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Calculate K value

Peak area of ​​water in absolute ethanol

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Use the external standard method to calculate the water content in the test product when calculating the water content in absolute ethanol
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In the formula, sample A is the water peak area in the test product; sample A is the total water peak area in the test product solution-K×the ethanol peak area in the test product solution ; A is the actual water peak area added to the control solution ;A mark = the total water peak area in the control solution-K×the ethanol peak area in the control solution; W sample is the weight of the test product (g); W standard reference substance (purified water) weight (g); V sample is the test The injection volume of the product solution (ul); V indicates the injection volume of the control solution (ul)
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Related Links: Chinese Medicine Moisture Determination Method (1)