the present invention relates to preparation of biodegradable microparticles formed from polylactide - polyglycolide copolymers polymer and how to achieve sigmoidal release of active pharmaceutical compound from the microparticles . in particular , the present invention relates to emulsification of an inner / oil phase to an outer / water phase followed by quenching and a single drying step for the preparation of microparticles having a preferred release profile of preferably basic / nucleophilic compounds such as risperidone . alternatively the present invention is also suitable for hydrophobic compounds that have poor water - solubility and a high drug loading of & gt ; 20 % w / w is required . the release profile can be controlled by adjusting the degree of saturation of the outer / water phase with the organic solvent used in the inner / oil phase , the polymer concentration of the inner / oil phase and the temperature at the quenching step . in particular , an initial lag phase and a substantially sigmoidal release profile are achieved by using an outer aqueous phase over saturated with the solvent used in the inner phase at emulsification step , in combination with a low temperature during quenching .