Karl Fischer method for determination of water con

2022-07-23
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Karl Fischer method for moisture determination of ethyl acetate solvent in composite (Part 2)

IV. precautions for purchasing moisture measuring instruments

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

1. It is best to consider automatic instruments 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. When selecting, it is necessary to consider purchasing full closed system test. The exposed Karl Fischer reagent is very easy to absorb water due to the existence of iodine. The ethyl ester sample to be tested and methanol solvent should also try to avoid the trouble of water dissolving in the air

3. The service life of metering pump shall be considered. The metering pump is a key part of the volumetric moisture meter. Karl Fischer FMS ⑴ metal material corrosion and wear tester is a free abrasive wear tester. The reagent is also a highly corrosive reagent. Try to choose a metering pump made of fluoroplastic and other corrosion-resistant materials to prevent the new type of regenerating plastic granulator from being optimized, renewed and leaked, resulting in the scrapping of the instrument

4. Electrode problems. 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 select an instrument equipped with high-quality platinum electrode to maintain the electrode life

v. the process of Karl Fischer volumetric moisture determination

there are several kinds of Karl Fischer volumetric moisture meters to choose from, and their connection and determination are also different, but the basic process is similar. Taking zd-2 automatic moisture analyzer of Beijing landmaker company as an example, its measurement process can meet the standard and get normal production as follows: 1. Eliminate the blank of the solution

add 10-15ml of anhydrous methanol reagent (immersed 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 alarms

2, 2. Calibrate Karl Fischer Reagent

press the reset key, use a 10ul sampler to take 10mg (10ul) distilled water into the reaction pool, 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 of water, from which the Mg amount of each M1 Karl Fischer is equivalent to water can be calculated

f=10/a

in the formula: F - the Mg amount of each ml of Karl Fischer solution equivalent to water

10 - the Mg number of weighed water

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

3, 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 torque, press the electromechanical output multiplied by the deceleration ratio start key to carry out titration. When the end point is reached, 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 equivalent to water per M1

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 landmark equipment and instrument development center

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