Dynamic vs constant liquid flow calibrations down to 20 nL/min

Calibration of flow devices is important in several areas of pharmaceutical, flow chemistry, HPLC and microfluidic applications, where dosage of process liquids or accurate measurement of the flow rate are important. The process-oriented liquid itself might influence the performance of the flow device. Therefore, the calibration of the flow meter or microfluidic device with the process-oriented liquid is important and performing dynamic flow profile changes to simulate any dosing process gives important insight in the behaviour of these flow devices and their accuracies under non-constant flow conditions. Therefore, METAS has developed facilities with METAS piston provers to address the issue of measuring with process-oriented liquids non-constant flow profiles for flow rates down to 20 nL/min. The stated measurement uncertainties for the constant flow rate and for the dynamic flow profile changes are 1 % and 2 % at 20 nL/min. The piston provers, the new developed capillary beaker for the gravimetric reference method, validation measurements as well as response time characterization with incompressible and compressible liquids are discussed in this paper.