At first I am very grateful for every one who will read this topic
and deeply indebted for those who will share their experience, thoughts with me

Today was my first MTT assay on Tongue squamous cell carcinoma
I used a cytotoxic agent which is ZnCl2 to establish standard curve.
I used 10 microliter of the following concentration :
2 mg/ml
1mg/ml
0.5 mg/ml
0.1 mg/ml
0.01 mg/ml
0,001 mg/ml
0.0001 mg/ml
I followed the protocol of MTT assay as widely present online
what was strange that higher concentration showed a stronger purple color ( higher viability).
While low concentration showed a lower absorbance.
I wonder if any one could share his experience regarding using standard cytotoxic agents ( Not drugs ).
Best Regards