Reason analysis and solution for Karl Fischer titration not reaching the end point for a long time
What should I do if Karl Fischer titrates for a long time?
First, observe the color of the solution in the reaction cup of Karl Fischer Moisture Analyzer . If it is dark brown or obviously overdose, please check: http://?content/help/6/index. Html
If the color is light yellow, it may be the following.
1. Reason: The test environment is not well sealed and the external moisture continues to enter.
Solution: Check the seal and check if there is external water entering the titration cell;
2. Reason: Karl Fischer reagent is invalid, or the titer is too low;
Treatment: Replace the Karl Fischer reagent and recalibrate the titer;
3. Reason: Due to the voltage of the electrode, the adsorption of dirt or the viscosity of the sample causes the surface of the electrode to be contaminated and passivated;
Handling: Take out the electrode and short the two pins of the electrode. Normally, it should reach the end point immediately. If the end point or slow reaction is not possible, the electrode should be cleaned, ultrasonically cleaned with a weak acid solvent, and chromic acid ultrasonic cleaning with severe contamination; if the sample adheres, it should be ultrasonically cleaned with a reagent that dissolves the sample, washed and rinsed with pure water. Use it later.
4. Cause: The solvent contains too much water and the pH of the solvent is incorrect;
Treatment: replace the solvent and restart the titration; use the solvent pH value in the range of 5.5-8;
5. Cause: The sample reacts side by side with Karl Fischer reagent to form water continuously; some samples such as active aldehydes and ketones react with methanol in Karl Fischer reagent to form acetal and ketal with water to consume iodine, making titration reaction No end. Some weak oxyacid salts, such as carbonates, borates, and metal oxides and hydroxides, react with HI to form water, resulting in no end.
Treatment: Check the contents of the sample components. If there is a side reaction, you need to replace the reagents or perform sample processing before testing.
6. Cause: After the sample is added to the titration cell, the pH value in the titration cell changes, which is not conducive to detecting the reaction;
Treatment: The sample was neutralized with a reagent such as imidazole benzoic acid before titration to give a pH of 5.5-8.
7. Cause: The drift is too large, and the end delay time is too long, causing the drift value to be greater than the end point judgment value;
Handling: check the sealing condition and shorten the end point delay time;
8. Reason: The water content in the sample is very high, and the amount of sample added is too large;
Treatment: Reduce the sample injection volume so that the water content in each sample does not exceed 10 mg.
If the above methods still do not solve your doubts, please call our technical department, we will be happy to help you.
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