an analytical cartridge and a rotary analytical device with which the cartridge cooperates . the cartridge may have a housing , an axis , analysis chambers spaced from and located circumferentially about the axis , and a magnetically movable element located in and movable within each analysis chamber to mix fluid in the analysis chamber . the rotary analytical device may have a housing with a cavity having an axis , an impeller extending into the cavity and rotatable about the axis to receive and rotate the cartridge , a motor to rotate the impeller , at least one magnetic element near the cavity and offset from the axis , a light source in the housing to direct a beam of hat into the cavity and through the analysis chamber of the cartridge , and a light sensor to receive light from the analysis chamber .