Rapid Readout from Dual Wavelength Spectrophotometers

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Abstract
Three methods are described for extending the time range of the dual wavelength spectrophotometric technique. First, a dual wavelength system employing interference filters (essentially a differential colorimeter) is described which employs no light modulation and thus gives operation down to the shortest time measurable in view of the system signal‐to‐noise (S/N) ratio. The second method employs dual wavelength light modulation and synchronizes the transient phenomena to the flash of the measuring light. While this method extends the time range down to that obtainable in view of S/N ratio of the optical system it is essentially a single beam method and does not compensate for optical artifacts that occur during a single flash of the measuring light. The third method extends the time range of the dual wavelength method by substituting for the vibrating mirror an air‐turbine‐driven mirror capable of rotating at several kilohertz and giving dual wavelength readout every 400 μsec or less. The three methods have been employed in time ranges of 40, 200, and 1000 μsec, respectively, in the measurement of the fast reaction of oxygen with cytochrome oxidase bound to mitochondrial membranes.