I will try to know through my colleagues.  

If I know the answer I will try to pass it out to you! If I forget please send me a text remembering*

Usually I use MTS assay kit from Promega, it's a little bit expensive but really simple to use and also accurate. I have never prepared MTS manually, in the past I prepared MTT solution homemade but then I switched to kit because is easy and also the prize/ quality ratio was better in the kit compared to the homemade solution. Maybe is the same also for MTT.