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Data Calculations and Graphs
Data Calculations and Graphs
Referring to the four graphs that keep temperature or time constant, it was clear for manganese that the concentration increases for increasing brewing time and temperature, but this was not the case for aluminum. Aluminum didn’t have a significant trend for either increasing temperature and increasing time nor did it have a clear relationship between plastic and cotton tea bags other than the fact that the concentration was higher with plastic tea bags.
However, if we project the shape of our Mn curves (green), we realize that the shape of the Al graphs (blue, red) are very different. The best explanation for this deviation is that the MP-AES Al detection limit of 2ng/mL was too high to accurately detect Al, but the Mn detection limit was low enough (.20ng/mL) to accurately detect Mn. Therefore, the Al time and temperature vs. concentration graphs are partially being shaped by the noise floor, as there is not enough signal in the Al wavelength to accurately detect it. The most important implication of this low S/N ratio is that the Mn data is more reliable than the Al data.
Conclusion
Conclusion
After completing numerous trials, it was clear that more metal was detected when tea was brewed with plastic tea bags compared to when it was brewed with cotton tea bags. The calculations of the control trials show that the sum of the concentrations of both (1) only tea leaves + only plastic tea bag + only water and (2) only tea leaves + only cotton tea bag + only water were very close to the experimental trial for 10 minutes and 70℃ with plastic tea bag, while they were much lower than the experimental trial for 10 minutes and 70℃ with cotton tea bag. Thus, it was reasonable to assume that the metal detected from the tea was mostly coming from the tea itself and not the tea bags.
Future Inquiry
Future Inquiry
In this experiment with MP-AES, we were able to determine which metals were present in our sample and in what quantities. With this information, we were able to show that the concentration of metals in {tea + plastic tea bag} is larger than {tea} + {plastic tea bag}. Unfortunately, we were not able to confirm our suspicion that this difference was due to microplastic adsorption. To address this uncertainty, we would like to learn more about metal::microplastic bonding using X-ray photoelectron spectroscopy (XPS). Unlike AES, XPS, a surface-sensitive technique, is able to shed light (literally) on the electronic structure of the microplastic surface and that of the metal, allowing us to make inferences about how the two might bond to one another.
During a future experiment, we would like to use high-performance liquid chromatography (HPLC) instead of MP-AES. Unlike MP-AES, HPLC is able to separate solutes from a solution by polarities, allowing us to more accurately determine the concentration of each metal. However, HPLC was not an option to use for this experiment because it would have taken too much time to elute the solutes, considering how many trials we had to do.
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