pH-meter dissolution rate assay


pH-meter dissolution rate assay: GI (gastrointestinal) dissolution method³

This method is useful for neutral and ionizable substances showing a chromophore group and allows the following studies:

  • GI dissolution study: the experiment consists of four pH zones (pH 1.9, pH 3.8, pH 5.3 and pH 7.2)
  • Dissolution study using aqueous medium (1 – 6 pH zones)
  • Dissolution study using biorelevant media (e.g, FaSSiF or FeSSiF) and excipients

Samples are prepared in a tablet disk with a diameter of 3 mm where a controlled pressure is applied. The tablet is introduced in an appropriate vial and the dissolution medium at desirable pH is added. The solution is stirred at constant rate throughout the dissolution experiment. UV-visible absorption spectra are recorded via a fiber optic dip probe at fixed intervals for a specific period. Six pH zones can be investigated in one experiment. The desired pH zones, frequency of point collection and duration time in each zone can be easily modified to suit the needs of the experiment.

The knowlodge of molar extinction coefficients of the species are mandatory.


  • GlpKa titrator with D-PAS spectrometer (Sirius Analytical Instruments, East Sussex, UK) controlled from a computer running RefinementPro software.
  • pH electrode (Ag/AgCl, Sirius Analytical Instruments Ltd.).
  • Temperature probe to monitorize the temperature during the measurement


Required amount of substance:

To prepare a suitable tablet (Ø 3 mm), 6-10 mg of compound is necessary.


³ The ‘‘GI dissolution’’ method: a low volume, in vitro apparatus for assessing the dissolution/precipitation behaviour of an active pharmaceutical ingredient under biorelevant conditions Tom Gravestock, Karl Box, John Comer, Elizabeth Frake, Sam Judge and Rebeca Ruiz. Anal. Methods, 2011, 3, 560


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