For beta glucuronidase inhibitory assay, I'm using Silymarin as positive control. However, it has solubility issue. I've prepared the Silymarin stock in DMSO(100%) . No ppt are observed after double dilution with buffer/water...but on subsequent dilutions ppt start appearing. I want to have [DMSO] less than 1 % in final assay system. The same condition is observed with Ethanol. Please suggest what can be done.