A four-channel temperature-controlled stop-flow mixing apparatus adapted for the Beckman model DU spectrophotometer

Abstract

Each of 4 syringes empties into a 3-way stopcock. One stopcock limb is used for filling the syringe and the other limb empties into the mixer via a small jet. Mixing is completed within the mixing chamber before the reagents are emptied into the reaction vessel. Accuracy of mixing exceeds the limit of resolution of the spectrophotometer. The reaction vessel consists of a cylindrical quartz tube held in position with unstretched nylon bushings in a brass block adjacent to the cuvette housing unit. The flow of material is controlled by a needle valve at the exit of the reaction-vessel housing unit. Approximately 6 ml of fluid is required to flush out the reaction vessel. Temperature control is maintained with a water jacket around the 4 syringes and with cooling channels within the reaction-vessel housing unit. Steady-state temperature is reached in the syringes in a maximum of 6 minutes. The signal from the density-scale slide-wire potentiometer of the spectrophotometer is fed through a potential divider into a Brown stripchart recorder. As the operator tracks the changes in optical density of the reaction mixture the percentage transmission is recorded continuously. By means of a mixing switch the temperature of the reaction vessel measured with a thermopile is recorded at intervals during the reaction time. The percentage error (standard deviation) of the velocity constant of decomposition of H2O2 by bacterial catalase measured with this apparatus is less than +- 2%.