Uses of Retardation Plates in SpectrophotometryI Determination of Slit Shape and Slit Width

A retardation plate is used to make a “calibrator” having a known transmission curve. It is shown how the effect of slit width and slit shape on the plotted transmission of the calibrator can be predicted and conversely how the width and shape of an assumed slit may be evaluated from the performance of a spectrophotometer in plotting the transmission of the calibrator. If it is assumed that the slit is trapezoidal, it is recommended that it be described on an over-all performance basis in terms of two factors, H the slit width and f the shape factor. Regardless of the assumed slit geometry it is probable that two spectrophotometers that give similar transmission data for a calibrator will give similar curves for other types of samples.