Thursday, August 6, 2015

Gentner Lab- Procedures & Steps to the Project

For our internship, Vanessa and I chose 4 main locations at which we collected air samples. As our source for anthropogenic (human-caused) emissions, we chose the I-91 off-ramp entering New Haven, as our biogenic (natural) source, East Rock Park, as our indoor emissions source, the Peabody Discovery Room, and as our “mixed emissions” source,  outside Yale Medical School.
The collection of the air samples for our lab involves first packing glass “TD” (thermal desorption tubes) with three main absorbent materials. These are quartz wool, glass beads, and tenax, in order from “least aggressive” in capturing compounds  as air is pumped through the tube, to “most aggressive”. The quartz wool captures the more dense compounds, the tenax the lighter compounds, and the glass beads, the ones with middle density.
Once every “sampling day”, we connect our pump (which is used to actually pull air through the TD tubes, which are attached to it) to a device called a “flowmeter”, which sets the pump to a constant air flow rate (.115 liters/minute). After equilibrating the pump’s flow rate, we  then proceed to one of our sampling sites, where we would then pump air through a “blank” tube (30-second sample, used for comparison) and 3 other tubes (one at a time) for half an hour each. Each day, we also take note of factors such as the temperature, humidity, wind pattern, and time of day we sampled, which are all factors that can affect the quality or even the contents of our samples.
Upon finishing sampling for the day, we then have to bring the samples back to the lab and put them in a freezer set to -30ยบ C, to prevent compounds from the air samples from diffusing. For the actual analyzing part of our project, we utilize a three-part system, called a TD (thermal desorber)-GC (gas chromatograph)-MS (mass spectrometer), into which we place the tubes, and the compounds caught in them are heated up and eventually ionized so that we can obtain a mass-to-charge ratio for each one, which we can later use to actually IDENTIFY the compounds.

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