Week Five: New Developments

Hi, and welcome to week five!

It was another busy week in the lab – the experiments I did this week were Dip Method Sensing with last Thursday’s PFOS Water MIP on Monday, PFOS Water MIP Fabrication and Time Trial Method Sensing on Tuesday and Wednesday, and another PFOS Water MIP Fabrication on Thursday. One of my coworkers will sense my Thursday PFOS Water MIP on Friday.

The Dip Method Sensing I performed on Monday was slightly different than what I’ve previously done as well. I still let the electrode soak in an aqueous sodium chloride solution over the weekend, but this time, instead of switching and letting the electrode soak in water before characterizing, I let it sit in the same sodium chloride solution for 20-minute intervals before characterizing or scanning for the current voltammograms.

I characterized the electrode after 20, 40, 60, 80, 100, and 120 minutes, for a total of six data points. Then, I inputted this data into RStudio to obtain the numerical peak current values. Additionally, instead of creating a box-and-whisker plot, I took the six current values from RStudio and plotted them against the time intervals on a scatterplot in Excel. The general trend I saw was stability in the first hour and a slight current decay in the second.

However, the 120-minute data point is most likely erroneous because I accidentally bumped into the fume hood cover after rinsing it and dropped it. At first, I panicked a little because I thought I’d lost it but turns out it was just behind the plastic glove box container right underneath (phew!). The MIP on the electrode surface is extremely sensitive, though, and because I dropped the electrode, the MIP must’ve dried and/or accumulated foreign particles like dust, affecting the current measured. It definitely wasn’t the greatest way to start the week, but I was still able to provide useful data.

Letting it sit in the same over weekend sodium chloride solution was an important factor because we were attempting to determine if switching between vials was having an adverse effect on the stability of the background (the soak solution). My experiment supports the fact that it does, as keeping the MIP in the same solution seemed to provide more stability. This is important because we want the PFAS to be the only cause of current decay as much as possible so that a decrease in current is indicative of PFAS detection.

For the PFOS Water MIP Fabrications, I increased the amount of 500 ppm PFOS in water (seen in the image below) from 5 mL to 15 mL this week. Basically, that’s a huge amount of PFOS in the water sample. What was more interesting is that I kept acquiring CVs that showed currents that were way lower than what was expected. The current was expected to be low with such a high concentration of PFOS, but the CVs I obtained were somewhat wonky, too. I don’t think I’m completing the procedure incorrectly, but I’m going to keep investigating why I’m getting such results.

(Fiona Xu)

As for the Time Trial Sensing on Wednesday, the procedure was the simplest I’ve done by far. After preparing the ferrocene methanol and characterizing the working reference electrode to make sure everything was working smoothly, all I needed to do was take my electrode out of the sodium chloride overnight soak and run 13 iterations of the characterization. Essentially, most of the time was spent waiting for the characterization to finish. After it was finished, I repeated the same data analysis process as the Dip Sensing and created a 13-data point scatterplot on Excel.

Other than lab work, I organized my literature review sources to the appropriate section of my paper and started identifying five specific sites of the Potomac River that will be the focus of my project. The Potomac surrounds four states – Maryland, Pennsylvania, Virginia, and West Virginia – in addition to Washington D.C., so I chose one site in each state and D.C. to research PFAS contamination and water quality characteristics on. Ideally, after I finalize the five sites, I’ll collect water samples from each to bring them into the lab, but I’ll see what time, resources, and conditions allow. I plan to collect the Virginia Potomac water sample very soon. I’ll have to be careful because I don’t unintentionally contaminate my water sample when I collect it, so that means not wearing or bringing any products that have PFAS in them such as waterproof clothing.

Until next week,

Fiona