Figure 11. Response surface and contour plots of the ζ -potential versus: ( a ) drug–diluent and drug–stabilizer ratio, ( b ) inlet Figure 11. Response surface and contour plots of the ζ -potential versus: ( a ) drug–diluent and drug–stabilizer ratio, ( b ) temperature and drug–stabilizer ratio, ( c ) operating temperature and drug–mannitol inlet temperature and drug–stabilizer ratio, ( c ) operating temperature and drug–mannitol ratio.