Dear Sirs,
Kind time of day. 
We somehow for a long time with you worked. We now plan 
purchase Magnesium Sulphate hept in quantity of 100 tons. 
The technical grade is necessary for us. I ask you to give cost on 
FOB (port of shipment) , the certificate of quality. For us it is still 
necessary Magnesium Sulphate hept with the following parameters: 

Mass share of magnesium sulphate, not less 99, 5% min 
Insoluble in water of substances no more of 0, 005% min
Iron (Fe) 0, 0005% max
Copper (Cu) 0, 005% max

That you can offer.
I wait for your answer. 
Best regards,