PhD Scientific Days 2023

Budapest, 22-23 June 2023

Pharmaceutical Sciences - Posters F

Influence of Centrifugation on Solubility Measurements

Rita Szolláth
Department of Pharmaceutical Chemistry, Semmelweis University, Budapest
Dóra Csicsák
Department of Pharmaceutical Chemistry, Semmelweis University, Budapest

Text of the abstract

The bioavailability of a drug is greatly influenced by its solubility, therefore it is important to know the solubility of a drug in an early state of drug development. The validated method for solubility measurement is the saturation shake-flask (SSF) method, which has a phase separating step. This can be done with sedimentation, filtration or centrifugation. Phase separation is a critical step, as it can have a significant impact on our measured result, thereby questioning its validity.
Our aim was to investigate the effect of centrifugation and its parameters on the results of the solubility measurements. The changed paramaters were the time and rotation speed of centrifugation. Furthermore our goal was to investigate if there is a difference among samples that were continuously stirred for 24 hours before centrifugation and samples that were sedimented for 18 hours after being stirred for 6 hours. Molecules of different acid-base characteristics were chosen as model compunds, and were measured at 3 different pH values: where the molecule is in neutral form, where 50% is ionized and unionized, and where 100% is in ionized state.
We used the SSF method to determine the solubility of our compounds. In the presence of excess solid in the chosen buffer the suspensions were vigorously stirred, and after 1 hour the pH was checked and reseted if needed. As mentioned above, there was a difference between samples in the stirring time and whether sedimentation was applied before centrifugation or not. The centrifugation time was either 5, 10 or 20 minutes, and the rotation speed was either 5000 or 10000 rpm. We carried out three parallel measurements with each combination of these variables, at different pH values.
In most cases, the solubility of the samples that were sedimented before centrifugation was closer to the literature data, which we considered as 100% and used as reference. The solubility of the continuously stirred samples were higher than 100%. The longer the centrifugation time, the more it diverged from the reference. The discrepancies were different for each pH. The standard deviation was the smallest when shorter and slower centrifugation was applied.
Choosing the right type of phase separation is a crucial step in determining solubility values. These results show, how important it is to know the different attributes that can influence our results.

Doctoral School: Semmelweis University, Doctoral School of Pharmaceutical Sciences
Supervisor: Dr. Gergely Völgyi