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In all the tutorials I found online, the tip of the burette (containing the titrant - NaOH) was immersed into the analyte solution. My question is: shouldn't the tip be out of the solution? Isn't there a possibility for the analyte to crawl up the tip and react with the NaOH inside the burette that hasn't been dispensed yet?.

Everyone does that... Even in the official tutorials of the company

burette tip

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    $\begingroup$ I would think that the tip of the burette should never be in the liquid being analyzed. If it is then an indeterminate amount of the titrant in the tip can diffuse into the liquid. $\endgroup$ – MaxW Feb 26 at 16:58
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    $\begingroup$ I quess it's a question of the diameter and lenght of the burette tip, and the speed in which the automatic system can finish the titration. If the former is thin, and the latter is fast, then you can probably neglect the diffusive backflow, or calibrate and deduct it from the result. $\endgroup$ – Karl Feb 26 at 20:21
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In classical titrimetry you would avoid dipping the burette into the sample. However, for autotitrators, the electronic dispenser tip (electronic burette) should be dipped in the sample. This is to avoid any error due to the a drop clinging to the tip. In manual titration one would wash it. Most autotitrators are like this design including Karl Fischer system. Your concern can be alleviated by the fact that you need pressure to cause a back flow of the sample into the tip of the dispensor.

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    $\begingroup$ Just to quibble you wouldn't wash the tip of the burette in classic titrimetry. You touch the tip to the side of the flask, and then wash down the side of the flask. $\endgroup$ – MaxW Feb 26 at 17:18
  • $\begingroup$ Chemists are in general Sceptical Chymists ! $\endgroup$ – M. Farooq Feb 26 at 20:25
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I have tried either inside or outside and they both worked fine. Since I deliver very small volumes at a time (20 μL), I validated the dispensed volume using a balance and dipping the tip inside the analyte was more precise. My system dispenses through a small micropipette tip (jerry-rigged).

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  • $\begingroup$ This is the way to go as an analytical chemist! Calibration with 20 micoliters is not so trivial. Both deliveries should have been identical, however, there are tons of weighing errors with small weights such as evaporation issues and buoyancy errors. Once you dipped the tip in solution, evaporation error is minimized. $\endgroup$ – M. Farooq Feb 27 at 4:51

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