I have run MTT for crude extract, pure compound and essential oil at the same time. I have used same batch of the cell, same number (0.8X 10,0000 cells/ml), same technique and at the same day, but got a quitely different results. Regarding the absorbance of untreated cells, both crude extract and pure compound gave me quietly stable and relevant results of about 1-1.2, while the absorbance of the oil for 72 hours is fluctuating and not consistent. I thought maybe the oil evaporated during the treatment and gave me this outcome. Any other advices and suggestions please. TQ