This product is a 1 – 10 mg/mL suspension in 3.0 M (NH4)2SO4 containing 0.1 mM zinc acetate. The volume varies from lot to lot and is reported in the product Certificate of Analysis. For example, a lot reporting a concentration of 5 mg protein/ml will have a volume of 200 uL for the 1 mg package size. Please see the link below to review a sample of lot specific Certificate:
https://www.sigmaaldrich.com/product/sigma/m7257#product-documentation
Please see the following link to review additional information available in the product datasheet:
https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/product/documents/217/622/m7257pis.pdf