Sensitive Absorption Spectrophotometer for Use as a Split Beam or as a Dual Wavelength Instrument

The spectrophotometer described in this paper is constructed to operate either as a spectrum-scanning or as a dual wavelength instrument. The advantages of combining these two modes of operation in a single instrument are discussed. The described spectrophotometer has a limit of detectibility as (1) dual wavelength spectrophotometer of 1 to 2×10−4 O.D. (O.D. is optical density) in the visible range (400–650 mμ), (2) as spectrum scanning instrument of 2×10−4 O.D. in the same wavelength range. A dynamic correction system using magnetic tape memory for obtaining a baseline flat within ±2×10−4 O.D. is described. The instrument is designed to measure optical densities with an accuracy of 2% in the range −0.3 to +1.0 O.D.