Titration titration results are poorly reproducible

For any titration analysis, it is important to understand what kind of accuracy requirements are meaningful and necessary. Then if you find that some of the results are still beyond the error range, you have to find the reason from the following points:

1. Is the sample to be tested representative of the entire sample? In other words, you should start looking for possible errors from the moment you sample. "The results of the analysis only represent the results of the actual sample being analyzed." Perhaps before the actual measurement, the sample may come from a container that is not well-mixed. Or after sampling, the sample is exposed to different environmental conditions. For example, if the sample is placed in different time periods before titration, it will absorb different amounts of carbon dioxide in the air. This should be taken into consideration when using an open titration vessel on the sample changer. Therefore, we recommend that the titration vessel be closed first, and then be opened (Cover-UpTM) with a special device just before the titration starts, just like on the Rondo sample changer.

2. How many samples are used for analysis? For extremely small sample analysis, the performance of the balance is crucial. Then a minimum sample test can be used to understand whether the balance meets the requirements.

3. If it is a problem with the titrator itself, check from the following aspects:

a) Is there a siphon titration tip at the end of the feed tube and is it working properly? The titration head is designed to prevent the titrant from diffusing into the sample. If the titration head is lost, the titrant will flow into the titration cell and react with the sample. However, this part of the consumption is not counted, so it can lead to a relatively large standard deviation.

b) The burette should be checked for leaks. If the connector is not tightened or the valve does not work properly, liquid leakage may occur. In this case, not all titrants fed by the titrator are added to the sample. Because this effect is not repetitive, it will lead to a large standard deviation.

c) There are air bubbles in the burette. This is usually caused by dissolved gases such as CO2, SO2 or O2 in the titrant. Therefore, the titrant should have a degassing process before use, such as placing it in an ultrasonic bath. The titration vessel holder as an add-on to the titrator can be used to raise the titration bottle to the same height as the burette. This ensures that no decompression can occur due to negative pressure when the burette is filled. The reagents used in the Karl Fischer titration are extremely sensitive to the dissolved SO2. Therefore, in the DL31/DL38 Karl Fischer titrator, the filling rate can be appropriately reduced.