Please do not use buffer containing milk powder to block the Western Blot. This will reduce sensitivity. QIAGEN recommends use 3% BSA in TBS-buffer to block the membrane and for incubation of the Anti His Antibody on the membrane. For the binding of the secondary Antibody BSA does not sufficiently block and therfore 10% milk powder in TBS-buffer should be used at this step only. Alternatively, if alkali-soluble casein (Merck, Cat. No. 1.02241) is available in your country it can be used as a blocking reagent throughout the chemiluminescent detection protocol. Please see Table 9 of the QIAxpress Detection and Assay Handbook for additional information.