Currently, I am using a static setup, which consists of a large glass jar with an electric fan at the bottom (for air circulation) and liquid volatile samples are injected through a septum in the jar lid. I'm detecting small organics, such as amines, alcohols, and benzene analogs. I am concerned about sample loss due to adsorption to the glass walls of the jar, so I'd like to move to a dynamic flow-chamber type of setup. My question is, what is the ideal setup, in terms of push vs. pull (pressure-driven carrier flow or vacuum) and chamber size/type (glass or Teflon, dimensions) and flow rate (~100 mL/min?). I need to get an apparatus going quickly and cost is a major factor.
Hello Andrew,
I have used a stainless steel reaction chamber during my phd studies for gas-sensing experiments (see attached papers).
The setup has contained of a steel reaction chamber with a low volume, a ZnSe-window for temperature control by means of a pyrometer beam, the sensor material on an IDE chip with integrated backside heater and a precise gas control and mixing system (up to four certified test gases controlled by mass flow controllers).
An advanced setup was build for simultaneous DRIFT spectroscopy (again see attached papers).
One of my colleges had used the same setup for sensing of different organics.
The advantages of this kind of setup are the possibility of a high flow rate, so you have static concentrations (after a short equilibration time). But your system is dynamic enough to test different concentrations or gases.
It is quite easy to build with a standard university workshop, but mass flow controllers and test gases are quite expansive stuff.
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Hello Andrew,
the type of setup proposed by Thomas works quite well; we're using similar setups at our group (see e.g. figure 1 of doi: 10.1016/S0040-6090(01)00980-4). The costs for (calibrated) gas mixtures are quite high, but since you're measuring vapours (in contrast to permanent gases) you could you vaporizers/bubblers to dose your analyte instead of test gas mixtures. By mixing a carrier gas (N2 or air) and carrier gas saturated with analyte (e.g. ethanol) by a bubbler, you can control the concentration. Since the saturation vapour pressure depends on the temperature you could additionally control the concentration range by cooling the bubbler (to obtain lower test gas concentrations).
Best,
David
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