Preferential adsorption of polysorbate 20 molecular species in aqueous paliperidone palmitate suspensions

This work investigates the adsorption of polysorbate (Tween) 20 to paliperidone palmitate using the depletion technique, which analyzes the residual surfactant concentration in the aqueous continuous phase of the solid/liquid suspension. Total organic carbon determination was used to study the overall Tween concentration, whereas 1H NMR was applied to differentiate between hydrophilic and amphiphilic ethoxylated sorbitan species. The investigation revealed that Tween 20 adsorption was proportional to the specific surface area of paliperidone palmitate particles, and can be approximated by the Langmuir model. The alkyl-chain-bound (amphiphilic) sorbitans were found to be more effectively adsorbed than the alkyl-chain-free (hydrophilic) sorbitan species, which indicates that the adsorption was driven by hydrophobic interactions. Temperature (room temperature versus 40 °C) was found to have an increasing effect on adsorption.