Photometric linearity test for IR spectrophotometers by means of a rotating sector disk attenuator.

An important aspect in spectrophotometry is the reliability of precise absorbance measurements. For a brand-new instrument with an optical null balancing system (made by a mechanical comb attenuator), the ordinate accuracy usually ranges between ±0.5 and ±1%. Environmental effects, sample characteristics, electromechanical and optical features of the instrument, aging effects, and finally comb nonlinearity may degrade photometric accuracy to ±5%. A decalogue to be fulfilled for an effective linearity calibration has been specified by Hawes. A review of the various possible calibration methods has been reported by Reule.