Danielle Miles's blog

During my last week as a summer undergraduate intern at CMOP, I managed to squeak in one more persulfate decay study. All of my solutions thus far have been fairly pure, filtered samples. For this study, I wanted to simulate (to an extreme) the effect of metal ballast tanks. I gathered three kinds of solid iron samples: Fluka filings, cast iron powder, and electrolytic grade iron powder. With 5 g iron in glass VOA vials with 40 mL of DI or Instant Ocean water in each, we aggitated them all weekend to simulate natural oxidation.

Here are some thoughts from/for my final paper. It gives some thorough discussion of my results. The data for additional sulfate/salinity/natural water studies are not included, but feel free to contact me if you have questions:

This week I made a vast number of dilute Instant Ocean and sulfate solutions. I conducted persulfate decay studies for each of these waters at 70° C with 5mM initial persulfate concentrations. Here, I show the normalized decay curves with observations and conclusions:

The Sulfate Study:

This week I compiled all of the persulfate decay curves I've collected across three temperatures and 4 solvents. Since my data is first order kinetics, I'm gathering k values from raw data and linearized plots (which gives an interesting comparison) to compile an arrhenius plot that should quantify the difference between persulfate decay in fresh and marine waters. From here on out my data will not be raw kinetics curves, but solely comparisons of k values. It's quite a change in perspective.

This week I embarked on another temperature study on the decay of persulfate. My previous data was taken at 70° C to provide strong comparisons with reference literature. That data was particularly clean and fit well to our hypothesis for first order kinetics decay model. The half life for persulfate decay was 8 hours in deionized water and 10-11 hours in saline samples. Unfortunately, my workday limited the possibility of taking measurements for sebsequent half lives. Therefore, at a lower temperature I could observe slower decay which extends over several days.

Now that the sun has come out it tends to be a little more difficult to stay in the lab for 8 hours a day, but I've been persevering and making the most of it! I have plenty of data to show for it too.

Recognizing certain discrepancies between my data on persulfate and that published by Liang et al. (2008), I've been returning to a couple initial diagnostic scans from the project. Below I've included key figures with additional comments.

Figures:

Calibration curves are an excellent asset to analytical chemistry; most often they are the key to calculations relating the absorbance of a solution to the concentration of colored reagents in solution. Since all subsequent calculations are based on the calibration curve, it's worth one's time to make sure each one is accurate.

Last week I moved from a desk covered in articles to a little bench clearing in the lab. I reveled in the opportunity to finally observe the chemistry I've been reading about. Already I've spent many days becoming well acquainted with the lab's spectophotometer, Lambda 20. I can tell already I will have a particularly special friendship with this instrument for the summer.

The ballast waters in ships are the primary culprit for distributing exotic (non-native) species between harbors, including both micro- and macro-organisms. Though regulations currently require offshore ballast water exchange and screen filters to mitigate the issue, longterm prevention requires some disinfection of the water carried between ports. Seeing this need is the direct inspiration for my project.