Knowledge Bank

The bichromator is a device which measures the transmission of a sample at some wavelength, $\lambda 1$, relative to its transmission at a second wavelength, $\lambda 2$. An absorption maximum is normally chosen for $\lambda 1$, and $\lambda 2$ is preferably an adjacent wavelength at which the sample has little or no absorption. The instrument employs the conventional Littrow arrangement with a horizontally split Littrow mirror pair to cause the two wavelengths to overlap at the exit slit. A unique advantage over double beam systems is the use of only one typical path and sampling cell. Simultaneous comparison of the two wavelengths is made by a sector placed at a conjugate to the Littrow mirrors. Operation of a laboratory model is described. It is shown that analysis is possible in the presence of interfering components. The process control applications of the instrument are discussed.