Pumps, constant-pressure drive mechanism

For active flow delivery, pumps must be used in pressure drive systems. Flow splitting from constant flow rate pumps, such as was done by Bjorkman et al. [58, 59], is not desirable when such small flows are demanded because of inaccuracies and fluctuations. Nowadays, mechanical pump technology has advanced to the point of providing split-less nanoliter per minute flows. Constant flow mechanical pumps, such as the Agilent 1100 series nanoflow pumps and NanoFlow pump from Scivex work in the nanoliter per minute range, are of course commercially available, delivering stable constant flows as low as 20 nL min h These pumps are not amenable to miniaturization, however, and if used would need to be operated... 

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