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Collecting Water Samples, Astoria Adventures, and Success in the Lab!

I can't believe I completed my 7th week at CMOP already!  Time is certainly flying by.  This week the interns were treated with a visit to the CMOP outpost in Astoria.  We were taken on a tour of the facility and were given talks on the equipment they use to measure various metrics in the ocean and on the Columbia as well as a brief overview of some of their current research projects.  I was fascinated by the gliders that they use to collect data.  The engineering that goes into the gliders certainly piqued my interest.  It was just a subtle reminder of the overlapping scientific and engineering disciplines that can be found here at CMOP. 

While in Astoria I was able to collect some water samples.  We used the samples for running tests on the FlowCAM and micro flow cytometer as well as with DLS.  It turned out that the water samples were incredibly useful since we came up with the idea of testing the effects of sea water mixing and possible aggregation of particles.  By adding various concentrations of laboratory-prepared sea water to the water samples from Astoria we were able to simulate the gradual mixing of the Columbia River freshwater with the Pacific Ocean sea water.  So far I have not been able to reach a conclusion in regards to the sea water's effects on particle aggregation but I will be sure to provide an update next week.

Recently I discovered that while the DLS is regarded as useful for characterizing particles in the 4 - 6000 nm size range, it was ineffective at reporting the particle sizes on 5 micrometer standardized latex beads.  At first I thought it may have been due to the concentration of beads being too low.  However, after running a sample through the FlowCAM I knew this was not the case.  It turns out that the beads were sinking to the bottom of the cuvette before accurate measurements could be made.  In order to theoretically confirm this hypothesis I calculated the terminal velocity of the beads using the Stokes equation for terminal velocity.  This equation relates the buoyancy forces (and hence viscosity of the fluid) with the gravitational force exerted on the beads to the terminal velocity of the beads.  I made a few simplifying assumptions, such as the modified viscosity of the bead solution and the density of the latex beads.  I also took into account that the beads weren't all starting to fall from the top of the cuvette.  I assumed that there was a fairly even distribution of beads throughout the vertical column of the solution.  The result, although merely an approximation, confirmed my theory that the beads were in fact sinking, and hence the concentration of beads was rapidly decreasing.  

In order for the bead diameters to be measured by dynamic light scattering I tried increasing the viscosity of the solution that the beads were in.  This was done by adding a polymer, Xanthan, to the bead solution.  The polymer was added in hopes of stabilizing the system.  I crossed my fingers and hoped it would work.  Voila! It did!  Adding just a small amount of the polymer slightly increased the viscosity of the solution and allowed a proper measurement to be made.  This week I will be focusing on stabilizing water samples in a similar manner and finding a way to systematically identify particle sizes that are attributed to the Xanthan and not particles in the water samples themselves.