This invention is a stirrer, impeller or stirrer paddle used for mixing small volumes of liquid in a vessel having a small capacity for liquid, said impeller being characterized by an impeller blade connected to the bottom portion of a support, where the blade has an opening extending through the blade from the front to the back surface of the blade said opening extending across the rotational axis of the impeller. The invention is also an apparatus comprising that blade, a method of mixing components using the apparatus and an array of two or more of the apparatuses.