It can be diluted with DMSO or water. I diluted with DMSO. if you want value of IC50, final concentration could be from 200 microgram per mili litre to 12.5 (100, 50, 25, 12.5) with serial dilution for 24 or 48 hours.
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Two years ago, I used cisplatin. I cultured cancer cells in a 96-well plate, and added cisplatin, viability of cells were determinate after 72 hours. It has done triplicate and Final concentrations of cisplatin in every well was 100, 50, 25, 12.5, and 6.25 µg.ml-1.