Photometric Titrations with Optical Endpoint Detection

The Optrode, a sensor from Metrohm for titrations with optical endpoint detection, was introduced in the last issue of Metrohm Information. Application specialists at Metrohm have worked out several applications for the Optrode from numerous fields and have documented them in the form of articles that can now be downloaded free of charge.

Automated Optical Endpoint Detection

In photometric titration, an change in color is used to detect the endpoint. This color change is due to either the sample solution itself or an incorporated indicator. Photometric titration is extensively used because it can be done easily and rapidly and offers a strong price advantage over techniques such as ICP and AAS.

Traditionally, the color change at the endpoint is established by eye. The eye can detect a quick change in color easily, but has difficulties when it requires qualitative evaluation of gradually changing color strength. By contrast, a photometric sensor can always monitor the relationship between the color and concentration of the sample solution very precisely.

Here, the optical endpoint can be established very precisely by a titrator, autonomously of the human eye and, what is more significant, in substantially smaller substance quantities (in this connection see also the following book: Jander, G. / Jahr, K. F. (2002). Massanalyse: Theorie und Praxis der Titrationen mit chemischen und physikalischen Indikationen (16th ed.). Berlin: De Gruyter.)

Eight Wavelengths for Each Application

The Optrode is a new photometric sensor designed and manufactured by Metrohm for titrations with optical endpoint detection. There are currently eight wavelengths to select from in a sensor; choosing the appropriate one for each application is easy. The sensor is slim, needs minimal maintenance and, because of its glass shaft, is chemically resistant. Power is delivered directly from the Metrohm instrument or with the aid of the optional USB power adapter.

Metrohm’s application laboratory can provide users with numerous application examples for the Optrode in the form of application notes. These articles can be found at

Pharmaceutical industry: selected titrations according to USP/Ph. Eur.:

  • Determination of zinc sulfate (AN-T-90)
  • Determination of manganese sulfate (AN-T-89)
  • Determination of bismuth nitrate (AN-T-88)
  • Determination of chondroitin sulfate (AN-T-83)

Oil analysis:

  • Fully automatic titrations of Ba, Ca, Mg, Pb, and Zn in unused lubricating oils (AN-T-91)
  • Fully automatic determination of TAN (AN-T-92) and TBN (AN-T-93)

Food analysis:

  • Determination of ascorbic acid / Vitamin C (AN-T-86)
  • Fully automatic determination of total, calcium and magnesium hardness in drinking water (AN-T-84)

Other applications:

  • Determination of nickel (AN-T-82)
  • Determination of aluminum (AN-T-78), calcium (AN-T-79), iron (AN-T-80), magnesium (AN-T-081) in cement
  • Determination of sulfate, aqueous (AN-T-77) or non-aqueous (AN-T-85)

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.


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