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Learn how to do a pre-titration to measure drift or background moisture before running a batch of volumetric Karl Fischer titrations on a Metrohm instrument. Follow along with this video series to ensure you get correct measurement results when doing Karl Fischer titrations.
This video shows how to determine the titer of a volumetric Karl Fischer Titrant using a Metrohm instrument.
In this video, I’m going to show you how to perform a pre-titration or conditioning in a volumetric Karl Fischer titration.
My name is Eyla Reuss. I’m a lab scientist.
First, we have to rinse our system at least twice to ensure there are no air bubbles in our tube or the burette. The concentration of the reagent may change due to incoming humidity or evaporating solvent.
Now we will see the new reagent pumping through the tubes into the burette and then pumping into the cell.
Now we empty the cell and add fresh solvent. If additional solvent is needed for the determination, add it now and then perform the pre-titration in the solvent mixture. When fresh solvent is added into our titration cell, we gently have to swing it to bring down the drops of water which are on the side of the wall and the electrode.
To dry the solvent and the titration cell, we now start the pre-titration. The titration cell is never really tight, that’s why we have a drift. And the drift shows us the amount of water that comes from the environment into our titration cell. The drift should be below 20 µL per minute and stable.
Today I’m going to show you how to do the determination of the volumetric Karl Fischer titration. This is important because concentration of our reagents may change over time and to receive right results we have to determine the titer.
I’m going to show you how to do it in a few steps afterward.
My name is Eyla Reuss. I’m a lab scientist.
First thing I do is pick all the things I need for the titer determination, which is the liquid water standard 1% which is easy to use and has a high purity but you also could use pure water as a standard. In this case you have to weigh in very small amounts which makes it hard to handle and also the weighing error is quite big. The other option is to use a solid, sodium tartrate dihydrate, which has a very high water content but a limited solubility in our solvent. Then [you’ll need] a syringe with a needle in the right size, an ampoule opener to open the ampoule safely, a waste beaker, and a tissue to wipe the last droplet off the needle.
To open the ampoule, we have to find the blue spot and then break away from the blue spot. For our safety, we apply the ampoule opener, which also has a spot on it. We [align the blue spot on the opener with] the blue spot on the ampoule. And then we’re going to break it.
To prepare the syringe with the standard, we have to first rinse the syringe. Therefore we pull up 1 mL of our water standard 1% and then we pull up the rest of the syringe with air and shake it a little bit to get all the water from the syringe out and then we put that 1 mL in the waste and repeat this again to rinse the syringe again. We pull up about 1 mL again and shake it again to get the water from the syringe out and put it in the waste.
After this, we pull up the rest of the ampoule into the syringe and in the end we also pull up a little bit of air to make sure there is no liquid in the needle. Afterwards, we wipe the needle to ensure there is no liquid on the outside. You cannot use the leftover in the ampoule again because the water content will change. That’s why we throw it away.
The titration cell is never really tight, [resulting in] a drift. The drift shows the amount of water that comes from our environment into the titration cell. The drift should be under 20 uL per minute and stable.
If additional solvent is needed for a sample, make sure to perform the titer determination in the solvent mixture.
Now we weigh the syringe with the water standard before we apply it into the titration cell. We apply about 1 mL of our standard into the titration cell. It is very important to pull back the last drop into the needle. Now we weigh the syringe back to see what weight we applied in our titration cell. We recommend performing the titer determination 3-6 times so that you have an average you can use for the calculation. Regular standard deviation should be below 1% but each laboratory needs to define it for itself.
Thank you for watching this video about titer determination. We hope this information was helpful for you.
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