The EC50 has been determined by dose-dependent stimulation of the proliferation of murine CTLL-2 cells. The EC50 value can be used to determine activity. The EC50 value is listed on the lot specific Certificate of Analysis. Certificates of Analysis can accessed in the DOCUMENTATION section of the product detail page:
https://www.sigmaaldrich.com/product/sigma/i2644#product-documentation
The specific activity in Units/mg can be calculated by the following:
Activity = 1 × 106 / ED50 (in ng/ml).