Working principle of the membrane chip
The chip is placed inside the interface block, on top of which the EC-cell is coupled. In the cartoon, the equilibration of volatile analytes between electrolyte and sampling volume is shown..3
The membrane chip creates a direct coupling between the electrolyte and the high vacuum of a mass spectrometer (MS) without the use of differential pumping.
The membrane chip creates a well-defined liquid-gas-vacuum interface and controls the transfer of volatile molecules from the electrolyte to the mass spectrometer. Inside the chip, a buried sampling volume equilibrates to the outer environment without letting liquid in. The pressure in the sampling volume is precisely controlled by our embedded gas handling system. To pressurize the sampling volume, any type of make-up gas can be used. Owing to the small size of the sampling volume and of the electrolyte layer, equilibration between the gas and the liquid is nearly instantaneous. During equilibration, all volatile species in the liquid fill the sampling volume based on Henry’s law. The sampling volume is connected to the MS by a capillary which is designed to limit the flow of molecules to exactly 1015 molecules/sec. No differential pumping stage is thus necessary. Because the flow is known and all the molecules are collected by the MS, direct conversion of mass spectrometry signal to mol/sec is possible. This is what makes the Spectro Inlets the only existing truly quantitative EC-MS system. Finally, the pressurization of the sampling volume allows EC experiments at elevated pressures and temperatures.