Gas leak into a flowing gas pipeline

Cenkoloji

Hi,

We have an experiment, in which we have gaseous detectors, and we pass a mixture of Argon + 2% Isobutan(C4H10) from them. The system is as follows:

Gas Mixture Bottle -> Detector -> Flowmeter

While the gas bottle is at 100bar, we have several layers of regulation, and in detector the pressure is reduced to 1.4 bar. The flow is kept more or less constant with the flowmeter to 3-4 l/h. All the pipes are copper, only just before the detector, the connection is made with a plastic pipe around 1 meters.

We installed O2 and H2O monitors just after the flowmeter, to measure the impurities of the gas. It measures in PPM(parts per million)

We made measurements with different flows: 1l/h, 3l/h and 6l/h

What we see is as we increase the flow, the percentage of O2 and H2O in the monitors decrease. My colleague's interpretation is as follows: There is a constant impurity of the bottle: C1, which doesn't change with the flow. And there is a leak into the system, that is constant per time C2(l/h), but when you increase the flow (F), the amount of gas per unit time gets higher, so contribution of the leak should be inversely proportional to the flow. We should have a formula more or less like:

Final PPM = C1 + C2 / F

Is it a good model? What other contributions one can consider?
(The fits have big errors with this formula)