Axial fluctuations in carrier concentrations cause detection noise during chemical analysis using flowing carrier streams. Here, we report a method of axial mixing using serially cascaded microchannel units with branches and junctions. Two branched channels in one unit differ in liquid residence time, and the time lags between the two branched channels are different for each unit. Each unit decreases the fluctuations in carrier concentration of the frequency associated with the time lag. The branched channels are in the form of spirals to induce the secondary flow that decreases axial dispersion and enhances the cancelling effect of the axial fluctuations from the branched channels. We evaluated the effect of secondary flow on the reduction in axial dispersion as a function of the Dean number in computational fluid dynamics simulations. Axial mixing in the prototype mixer was the most effective at a Dean number of 10. A prototype mixer whose volume was 52.5 mm 3 reduced absorbance fluctuations from 27.2 to 5.0 mAU in a 0.1% trifluoroacetate aqueous: acetonitrile stream under these conditions. The frequency characteristics of the reduced absorbance fluctuations were evaluated through numerical simulations within a deviation of 20%.

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