The vial content and EC50 values are lot-specific and reported on the product Certificate of Analysis. The vial content will range from 20-26 µg and the EC50 will be a maximum of 0.2 ng/mL. An EC50 of 0.2 ng/ml corresponds to 5,000,000 units/mg.
Please see the link below to review the product datasheet:
https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/product/documents/347/154/i0523dat.pdf
Please see the link below to access a lot specific or sample Certificate of Analysis:
https://www.sigmaaldrich.com/product/sigma/I0523#product-documentation