Adopted in 1970, the rotating basket method of dissolution testing was the first official method. It essentially consists of an approximately 1 inch (25.4mm) × 1 3/8 inch (34.925mm) stainless steel, 40 mesh wire basket rotated at a constant speed between 25 and 150rpm. This method is now called Apparatus 1 (or Method 1).
The apparatus consists of a metallic drive shaft connected to the cylindrical basket. The basket is positioned inside a vessel made of glass or other inert, transparent material. The vessel contents are kept at a constant temperature by being placed inside a water bath or heating jacket. The solution in the vessel is stirred smoothly by the rotating basket.
The USP Method 1 requires a 40 mesh screen unless otherwise specified in the monograph. Other meshes can be used to solve individual problems.