I am extracting an analyte that perciptated to form light weight crystal like particles. Almost looks like fine table salt (or white creatine crystals). If the analyte is low in concentration, upon centrifuging for 30mins at 4200xg, I get a nice pellet on the bottom side wall in a fixed angle rotor. However, when there is more sample, it doesn't form a tight pellet. Bits of salt like precipitate will stick all over the tube. I have to sonicate it briefly to release the crystals which drop down to the bottom. This would be fine, but when trying to pipette off the liquid, the pellets (crystals get sucked up). I try carefully and slowly and re-centrifuge it between liquid phase removal, but some particles won't pellet properly and are really light weight. It is extremely time consuming per sample. It can take a few hours to try get the liquid off carefully.

I have tried filtering the solution instead on an acetate type filter but I can't wash the crystals off. It sticks on. I even tried leaving the crystals on the filter and adding the colouring reagent which contains phosphoric acid to it in a tube. The filter digest a bit but the solutions is gloopy and it doesn't colour up correctly. I need to read it on a spec so this doesn't work. Any ideas on how to form a strong pellet. Is there anything I can add to aid the pellets forming that won't react badly to phosphoric acid?

Thank you.