[Studies on the recovery of pharmaceutical drug substances from surfaces made of defined stainless-steel alloys]

Facilities for the manufacturing of pharmaceutical drug substances on the pilot-plant and the industrial scale as well as chemical reactors and vessels used for chemical work-up mainly consist of alloyed stainless steel. The influence of the alloy composition and the surface condition, i.e. of the roughness of the stainless-steel materials, on the adsorption of structurally diverse steroidal substances and, hence, on the quality of the products was studied. In general, stainless-steel alloys with smooth, not so rough surfaces are to be favored as reactor material. However, it was demonstrated in this study that, on account of the weak interaction between active substances and steel materials, mechanically polished materials of a medium roughness up to approx. 0.4 microm can be employed instead of the considerably more cost-intensive electrochemically polished stainless-steel surfaces. The type of surface finishing up to a defined roughness, then, has no influence on the quality of these pharmaceutical products. Substances that, because of their molecular structure, can function as "anions" in the presence of polar solvents, are adsorbed on very smooth surfaces prepared by electrochemical methods, forming an amorphous surface film. For substances with this structural characteristics, the lower-cost mechanically polished reactor materials of a medium roughness up to approx. 0.5 microm should be used exclusively.