in precipitation, thereby demonstrating API:IP interactions  are responsible for the phase formation (phase change). As  a general trend, the IPs that caused precipitation are higher  MW, more hydrophobic, and of a stronger acidic form  compared to IPs that did not cause precipitation. These  effects can be explained by the fact that more strongly  hydrophobic IPs produce more hydrophobic API:IP com› plexes, and that IPs that ionically interact more strongly with  the APis produce stronger API:IP complexes. In another  method of quantification, IPs that caused precipitation have  higher c Log P, and have acid forms with lower pKa. All IPs  that caused precipitation have c Log P greater than 0.11;  however one IP tested, sodium hexanoate, has a c Log P of  2.01 but did not cause precipitation. The acid form of  sodium hexanoate is a weak acid with a pKa of 4.88. The  comparatively poor ability of the acid form to ionize in  solution limits its ability to ion pair with the API, since  deprotonation of the acid is required for the required strong  electrostatic interaction with the amine on the APL These  results demonstrate that high IP hydrophobicity is a neces› sary, but not sufficient criteria of precipitating the APis. Both  hydrophobicity and strong ionic interactions are necessary.  [0083]  Out of the fifteen IPs tested with gentamycin, nine  IPs resulted in the formation of precipitates; six IPs did not  produce an observable precipitate (Tables 1 and 3).  [0084]  After successfully identifying water-insoluble API:  IP complexes, it was determined whether these new salt  forms could be dissolved in THF for NC processing. Pellets  formed from the previous step were incubated with THF at  a 1 x volume equal to the starting volume of API in water. Of  the eleven API:IP complexes tested, all complexes, except  sodium decanoate and sodium deoxycholate, dissolved in  THF. The IP sodium octanesulfonate, which has a hydro› phobic eight carbon chain pendant group, was sufficient for  API:IP dissolution into THF, whereas sodium decanoate,  which has a hydrophobic nine carbon chain pendant group,  was not. The  pKa  of the acid form of sodium octanesulfonate  is -0.40, while that of sodium decanoate is 4.0; this effect of  pKa  highlights differences in the ability of these two IPs to  charge interact with the APis. Thus, although sodium  decanoate is a more hydrophobic IP with a Log P of 2.01,  sodium octanesulfonate with a Log P of 0.85 is a better IP  agent due to its greater ability to ionically complex with  APis. As a control, APis prepared without IP complexation  were not soluble in THF, highlighting that association with  hydrophobic IPs is necessary for solubility in organic sol› vents. These results demonstrated that IP reagents that are  more hydrophobic are not necessarily better for API:IP  complex formation, and IPs with lower acid form pKa can  be better at forming hydrophobic salts.  [0085]  In the FNP process, API:IP complexes dissolved in  organic solvents must rapidly precipitate when mixed  against the water antisolvent. To assess whether the nine  remaining API:IP salt complexes would behave accordingly,  complexes dissolved from the previous step were rapidly  mixed and diluted tenfold into water.  [0086]  The results of the tests are shown in FIG.  4,  where  the axes are the pKa of the IP agent and the calculated Log  P of the compounds. Four of the IPs tested resulted in no  observable precipitation upon mixing (diamonds in FIG.  4).  Four of the IPs tested resulted in rapid precipitation and  successful NC formation (squares); those IPs were sodium  oleate (OA), pamoic acid disodium salt (PA), sodium dode› cylbenzene sulfonate (DBS), and sodium dodecyl sulfate  (SDS). The IPs that failed to produce precipitates at this  stage were the least hydrophobic among the group, with Log  US 2020/0268679 Al  11  Aug. 27, 2020  TABLE 3-continued  Swnmary of ion-pairing screening using gentarnicin APL  TABLE 2  Swnmary of ion-pairing screening using polymyxin B APL  TABLE 3  Swnmary of ion-pairing screening using gentamicin APL  Organic  Ion Pair  Precipitation Dissolution Reprecipitation  Sodium Hexanoate  n/a  n/a  Sodium Decanoate  ++  Sodium Myristate  ++  n/a  Sodium Oleate  +++  ++  +  Pamoic Acid Disodium Salt  ++  +  +  Benzenesulfonic Acid  n/a  n/a  Monohydrate  Sodium  ++  ++  2-Naphthalenesulfonate  (lR)-(-)-10-Camphorsulfonic  n/a  n/a  Acid  Sodium 1,2-Ethanedisulfonate  n/a  n/a  Sodium 1-Heptanesulfonate  +  +  Sodium 1-Octanesulfonate  +++  ++  Monohydrate  Sodium 1-Decanesulfonate  +++  ++  +  Sodium Dodecyl Sulfate  +++  ++  +  Sodium  +++  ++  +  Dodecylbenzenesulfonate  Sodium Deoxycholate  +++  n/a  Organic  Ion Pair  Precipitation Dissolution Reprecipitation  Sodium Hexanoate  n/a  n/a  Sodium Decanoate  +  n/a  Sodium Myristate  n/a  n/a  Sodium Oleate  n/a  n/a  Pamoic Acid Disodium Salt  +  +  +  Organic  Ion Pair  Precipitation Dissolution Reprecipitation  Benzenesulfonic Acid  Monohydrate  Sodium  2-Naphthalenesulfonate  (lR)-(-)-10-Camphorsulfonic  Acid  Sodium 1,2-Ethanedisulfonate  Sodium 1-Heptanesulfonate  ++  Sodium 1-Octanesulfonate  ++  Monohydrate  Sodium 1-Decanesulfonate  +++  Sodium Dodecyl Sulfate  +++  Sodium  +++  Dodecylbenzenesulfonate  Sodium Deoxycholate  ++  n/a  n/a  ++  n/a  n/a  n/a  n/a  n/a  n/a  ++  ++  +  ++  +  ++  +  n/a  In the precipitation step,  +  details qualitative observations of the amount of solid formed,  while - details no solids formed.  In the organic dissolution test,  ++  details complete dissolution, while  +  details non› complete dissolution.  In  the reprecipitation test,  +  details reprecipitation observed, and - details no reprecipi› tation observed.  In  the precipitation step,  +  details qualitative observations of the amount of solid formed,  while - details no solids formed.  In  the organic dissolution test,  ++  details complete dissolution, while  +  details non› complete dissolution.  In  the re-precipitation test,  +  details re-precipitation observed, and - details no re› precipitation observed. 