Apatite in-situ restoration

A method of purifying a target analyte with an apatite solid surface wherein resin mass and particle strength are increased, the method comprising:

• (a) contacting the apatite solid surface with the target analyte, thereby separating the target analyte from one or more contaminants;
• (b) collecting the target analyte;
• and
• (c) after the collecting and before subsequent loading of additional target analyte, regenerating the apatite solid surface, the regenerating comprising:
• (i) contacting the apatite solid surface with a buffered calcium solution comprising a calcium ion at a concentration of at least about 5 mM and a zwitterionic buffer, wherein the ratio of zwitterionic buffer concentration to calcium ion concentration is at least about 2, and the pH of the buffered calcium solution is at least about 5;
• (ii) after (i), contacting the apatite solid surface with a phosphate buffered solution at a pH of at least about 6.5;
• and
• (iii) after (ii), contacting the apatite solid surface with a solution comprising an hydroxide wherein step (c) increases the resin mass and particle strength of said apatite solid surface.