Polarimetric stopped-flow apparatus

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Abstract
A stopped‐flow apparatus is described for the measurement of millidegree changes in optical rotation and absorbance changes at wavelengths between 230 and 800 nm. The design utilizes Faraday modulation at 2.5 kHz and signal processing by selective filtering and phase sensitive detection. Observed rms noise levels are reported for the wavelength range 230–450 nm: representative values for nonabsorbing solutions are 0.2 mdeg at 450 nm (15 nm bandpass, 9 msec time constant) and 3 mdeg at 260 nm (8 nm bandpass, 9 msec time constant). It is shown that these figures correspond to the theoretical shot‐noise limited performance of the instrument. The use of the apparatus is exemplified by studies of the hydroxide ion‐catalyzed mutarotation of glucose, and the displacement of NADH by NAD+ from the NADH‐liver alcohol dehydrogenase complex.
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