Determination of water content of ethyl acetate so

2022-05-25
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Karl Fischer method for determining the water content of ethyl acetate solvent in composite (Part 2)

IV. precautions for purchasing moisture measuring instrument

for various commercially available Karl Fischer volumetric moisture measuring instruments, it is suggested that flexible packaging manufacturers should pay attention to the following points when purchasing them according to the cost performance:

1. Automatic instruments should be considered when selecting. The manual moisture meter requires the tester to visually inspect the reagent in the glass burette, and it also needs to be manually closed after reaching the end point. Delay due to different action habits will bring unnecessary errors

2. The purchase of fully closed system test shall be considered during selection. The exposed Karl Fischer reagent is very easy to absorb water because of the existence of iodine. The ethyl ester sample to be tested and methanol solvent should also try to avoid the trouble of water dissolution in the air

3. The service life of metering pump should be considered. The metering pump is a key part of the volumetric moisture meter. Karl Fischer FMS (1) metal material corrosion and wear tester is a free abrasive wear tester, and the reagent is highly corrosive. Try to choose a metering pump made of fluoroplastic and other corrosion-resistant materials to prevent the new type of plastic granulator from being optimized and renewed, resulting in leakage and scrapping of the instrument

4. Electrode problem. This part is the core part of the instrument. On the one hand, it should have high sensitivity. On the other hand, because it is immersed in the test cell during the test, it is best to choose an instrument equipped with high-quality platinum electrode to maintain the service life of the electrode

v. Karl Fischer volumetric moisture determination process

in the Karl Fischer volumetric moisture meter, there are several kinds to choose from, and their connection and determination are also different, but the basic process is similar. Take zd-2 automatic moisture analyzer of Beijing landmec company as an example. The measurement process is as follows: 1. Eliminate the blank of the solution

add 10-15ml of anhydrous methanol reagent (immersion electrode) into the reaction tank, turn on the titration and start liquid injection, and inject Karl Fischer Reagent into the reaction tank until the reaction of trace moisture in methanol is completed, and the instrument automatically stops and gives an alarm

2, 2. Calibrate Karl Fischer Reagent

press the reset key, use a 10ul sampler to take 10mg (10ul) distilled water into the reaction tank, press the titration start key, and the instrument starts automatic titration. When it reaches the end point, the buzzer rings and the end point indicator light is on. At this time, the digital tube displays the M1 number of Karl Fischer solution consumed by 10mg water, from which the Mg amount of Karl Fischer per M1 can be calculated

F = 10/a

in the formula: f-the amount of mg per ml of Karl Fischer solution equivalent to water

10-The number of Mg weighed by water

a-the number of Mg (UL) of Karl Fischer Reagent consumed by titration

3. Determine the water content

press the reset key, take 10ml of ethyl acetate (or toluene) measured with a sampler and add it to the reaction tank. According to the output ratio of titration opening torque, press the start key of electromechanical output multiplied by deceleration ratio to carry out titration. When reaching the end point, the buzzer rings and the end point indicator light is on. The result is calculated according to the following formula:

moisture content = A1 × F/10000

in the formula: A1 - M1 amount of Karl Fischer solution consumed by the sample

F - Mg amount of Karl Fischer solution per M1 is equivalent to water

10000 refers to the Mg amount by adding 10ml of ethyl acetate (or toluene)

comprehensive calculation of the above 2 and 3 steps: ethyl ester moisture content =

it can be seen that the above test process is fast, the calculation is simple and the principle is easy to understand

accurate determination of moisture in ethyl acetate solvent can not only avoid the quality problems in compounding in advance and minimize the loss, but also negotiate with the solvent manufacturer to return the unsuitable solvent

source -- Beijing landmec equipment and instrument development center

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