Titrations

Potentiometric

Any normal acid-base titration can also be done potentiometrically, where a pH probe is used to make a plot of pH vs. titrant volume added. Potentiometric titrations can also be used for dark samples or titrations in solvents other than water which may not be suitable for color-based methods. In addition, use of other electrode types allows potentiometric titrations beyond acid-base chemistry, such as the chloride analysis described above.

Finally, potentiometric titrations can be automated, reducing the technician time (and therefore cost) of a measurement significantly, and allowing more complicated experiments.

Applications:

Chloride in isocyanates

Acid-neutralization

Amine endgroups in nylon

Alcohol endgroups in polymers

Neutralization of strong acid samples

Hydroxyl content

Acid endgroups of PLA

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Work We've Done

Potentiometric Titrations

A client had three samples of isocyanate used for production of urethane plastics. The three samples had similar specifications from the manufacturers, but the final product produced from each isocyanate had notably different physical properties. The hydrolysable chloride contents of the three samples were measured by potentiometric titration with a silver electrode. This value is a measure of the amount of residual starting materials from isocyanate manufacture which remain in the materials.

One of the isocyanate samples was found to have a chloride content 30 times that of the other samples, which is a likely cause of the material problems observed with urethanes produced using that material.

We also did NMR and found no major chemical differences, and did isocyanate titration colorimetrically, and found that the same sample has a lower isocyanate content than the other two samples, though that does not involve potentiometric titration.