Heat index flow monitoring in capillaries with interferometric backscatter detection

Independent control of fluid is important for small volume fluid applications including separation science techniques and analytical microchip devices. To effectively control fluid, a monitoring system is necessary to ensure proper response to the control input. Proof of principle for a new online technique for flow monitoring is demonstrated here. It offers near real-time measurements of small-volume flows in a noninvasive, simple, and robust design. The measurement is accomplished by the introduction of a plug of heat into the fluid and detection of the time of its appearance a short distance downstream. Using heat indexing and laser induced interferometric backscatter as the detector, flow monitoring is demonstrated in 184-microm diameter capillary tubing over a range of 2-25 cm/s (500 nL/s to 7 mL/s.).