Update 7: The Importance of a Clean GC Needle

This week, I began by repeating the photochem experiment from late last week. I did this in order to gather more data points on turnover numbers since they were relatively inconsistent last week. However, these experiments varied catalyst concentrations by very small amounts. Therefore, I also began a new photochem experiment with the same catalyst, but decided to vary concentrations by factors of 10. Unfortunately, gas chromatography analysis proved difficult to interpret due to a large air peak. This peak overlapped with the hydrogen and methane peaks I need to integrate in order to calculate turnover numbers. While I was still able to calculate these, I was concerned about the quality of the data due to this interference.

Why was there so much air in my chromatograms? I had recently run out of 18-gauge needles which I used to vent my test tubes during degassing. Instead, I was using 20-gauge needles. These are smaller, so I used two for each test tube. Using two needles may have added complications. Luckily, a new shipment of 18-gauge needles arrived just after this experiment, so hopefully this improves my results.

I repeated this experiment, but began getting very strange looking chromatograms that had no peaks at all. They looked like squiggles. I repeated the experiment with the same procedure a couple times to see if I could fix this. To make a long story short, I spent the rest of my week collecting strange data until I realized the GC injection needle was clogged! Once this was replaced, my data looked normal again.

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