An absorption spectroscopy method comprising providing a sample in a container, rotating the container, while rotating the container, directing a beam of electromagnetic radiation through the container, the beam comprising one or more wavelengths selected from the group consisting of visible wavelengths, infrared wavelengths, and ultraviolet wavelengths, and measuring characteristics of the beam after it passes through the container. Also an absorption spectroscopy apparatus comprising a container holder, a drive rotating the container holder, means for, while rotating the container, directing a beam of electromagnetic radiation through the container, the beam comprising one or more wavelengths selected from visible wavelengths, infrared wavelengths, and ultraviolet wavelengths, and means for receiving the beam after passage through the container.