Transmittance ratio spectrometry as a stray radiant energy test method for optical-null spectrophotometers

Abstract

A stray radiant energy (SRE) test method for optical-null double-beam spectrophotometers is described based on transmittance ratio measurements made on an absorbing species placed in a pair of matched cuvettes whose path-length ratio is maintained constant while the said path-length is gradually increased. A theoretical expression is derived which relates the coordinates of the minimum of the resulting characteristic transmittance ratio versus reference transmittance plot, to the relative SRE level, and to the sample cell to reference cell path-length ratio employed. The effect of sample absorption of the SRE on transmittance ratio measurements is also explored. The result obtained with a Perkin-Elmer 297 spectrophotometer is compared with that obtained by applying the SRE test method of Mielenz et al. to the same instrument.