Design and uncertainty assessment of a setup for calibration of microfluidic devices down to 5 nL min^-1

This work focuses on the design and characterization of a system for measuring and calibration of liquid micro-flows down to 5 nL min^-1. The experimental setup relies on a telecentric imaging system mounted on a high-precision, computer controlled linear stage to track a moving liquid meniscus in a glass capillary. The position of the linear stage can be automatically adjusted to track the motion of the liquid front over distances of up to 15 cm. All fluidic components were placed inside a temperature regulated chamber at 36.0 ± 1.1 °C with a maximum variability ΔT = ± 0.1 °C for time intervals shorter than 1 h. The combined flow-rate uncertainty has been evaluated for measurement times from 15 s to 1 h and nominal flow rates between 5 and 50 nL min^-1. At 5 nL min ^-1, an extended flow-rate uncertainty better that 8.3% can be attained for measurement times equal to or longer than 60 s. The uncertainty approaches asymptotically 5.4% for measurement times longer than 300 s or flow rates higher than 50 nL min^-1.