What is it? Why is it Important?

I designed and built a low-cost portable gas chromatograph using off-the-shelf components, which is capable of identifying individual compounds from a mixture of two VOCs. As an initial proof of concept, this is a significant benchmark, because it shows that a GC can be miniaturized for less than $200.

What is a Gas Chromatograph? How does it Work?

A gas chromatograph is used to identify the individual chemical compounds present in an air sample. This is done by introducing the sample into a flow of some moving known gas (called the mobile phase), which passes through a tube (called the column) that is packed with a solid chemical compound (called the stationary phase). The mobile phase has no specific interaction with the stationary phase; however, the different compounds present in the sample may have different affinities to the stationary phase (some compounds may "stick" to the solid more than others), resulting in those compounds taking differing amounts of time to completely pass through the column. I like to think of it as similar to washing a stain (the sample) off a piece of clothing. Some foods stick to your clothes (the stationary phase) and require more water (the mobile phase) effort to scrub off than others! Chromatography works the same way. The amount of time it takes for each individual compound to completely pass through the column is called the elution time. This property is then used to identify the compound.

What Makes My Design Special?

As stated above, one of the greatest benefits to my design is the low cost and small size. The reduced weight and volume lead to its ability to be applied as a drone payload, floating sensor, or even an in-line clinical monitoring tool — something unheard of in current systems. These applications are actively being explored with the device.

Another challenge faced by portable and non-portable GCs alike is the use of the mobile phase (remember, that is the nonreactive gas used to drive a sample through the system). Mobile phases are usually purified noble gases such as argon or helium, which are difficult to generate and whose storage adds to the size taken up by the system. My design uses clean air as the mobile phase, which is beneficial in that it can be generated as needed from the immediate surroundings, and thus, requires no storage, while prolonging the runtime of the system. This also means that the waste products can be immediately released into the environment, as no chemicals are added to the sample for analysis. This has the potential to significantly reduce the environmental impact of analyses.

Lastly, and perhaps the most significant feature, is that the system uses active listening to determine when to begin analysis. The system begins by directly allowing environmental air to pass over the VOC detector. When a sufficient concentration of VOCs is detected, then it will switch to analysis mode, where the components of the sample are separated for analysis. Afterward, it continues "listening", waiting to trigger analysis once again. Because an analysis of a sample by a GC can take a few minutes, it is imperative that this is initiated at the appropriate time, to ensure that an ideal sample is not missed due to the analysis of a less relevant one. This also means that the system is much more autonomous, allowing it to be deployed over long periods of time unlike traditional GCs, which must be activated manually. An overview of this system is

The culmination of these factors makes this a novel system, with the potential to provide more widespread access to analysis tools. I sincerely hope that my work will inspire others to develop similar instruments in their own work.