SUB-NANOMOL PER SECOND FLOW MEASUREMENT NEAR ATMOSPHERIC-PRESSURE

We present a measurement technique designed to accurately measure smal l flow rates near atmospheric pressure, and demonstrate the ability to measure flows on the order of 10(-10) mol/sec. The technique is based upon a modification of a constant-volume mass accumulation scheme whe re the flow rate is measured by monitoring the change in pressure of a known volume of gas. We identify two phenomena, thermally-induced flu ctuations and thermodynamically-induced fluctuations, which will affec t the resolution and dynamic range of the instrumentation and discuss how the problems associated with them can be mitigated. We estimate th e resolution to be approximately 2.0 X 10(-13) mol/s, and the maximum measurable flow rate to be to the order 2 X 10(-9) mol/s.