I have been using 5% Acetonitrile to extract pregabalin INN from crushed samples in the assay method. So far, I have not been able to extract more than 95% of pregabalin contents. I have uses mechanically shaking & ultrasound sonication alone or in combination with vortex, water bath, and magnetic stirring for a longer duration but to no avail.

Have also used Phosphate buffer (pH7.0), Ethanol, Methanol, 0.1N HCl, and 0.06N HCl as co-solvent, respectively yielding not more than 95%.

Are there any other techniques or solvent that I can use to get better extraction?