MTT problems (Seeking advice) - (Jan/17/2012 )

Dear guys,
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

Guys I figured it out....
I will write the answer perhaps someone else face the same problem.
The problem was I didn't filter my MTT solution (I weighted the powder and dissolve it in PBS), so it was not sterile which lead to inaccurate results.
So sterilization of your MTT solution is very important to consider during your experiment as contamination lead to inaccurate results

hi
which filter have you used?? what was the size??

are you sure that the MTT solution should be filtered, while you add the MTT solution, means you are killing the cell any way, and cross contamination does not give any sense...