Trace elements at sea’s skin (by Alina)

Most of the people when studying ocean are sampling into the water column. However before entering into the oceans a skin have to be crossed. The few micrometers separating the water column and atmosphere is called microlayer and many interesting process occur. Alina explain us how to sample the microlayer and analyze trace metals (metals elements with very low concentration).

Sampling the Microlayer:

Microlayer sampling system during an experiment in 2011.

Microlayer sampling system during an experiment in 2011.

I have devised a new sampling method to get microlayer samples for trace metals.  The sampler is a quartz tube that is dipped vertically into the water; then slowly raised out of the water vertically. The water that drips off the tube is, in theory, the microlayer and is collected into a funnel that is connected to a receiving bottle.  Normally sampling the microlayer is done on calm days with little to no wind and waves.On Friday March 1 however, we had a treat and it was windy! It is good to get days where we think there is no microlayer (or it is well mixed) to compare to the calm days. The surface team had a fun roaster coaster ride on the cubi and earned the title of only team to sample that day!

Microlayer team sampling on the cubis during a very windy day (we had to cancel the other sampling)

Microlayer team sampling on the cubis during a very windy day (we had to cancel the other sampling)

After Collection Analysis:

The real fun begins for me after I leave this campaign…well, not really, but the bulk of sample analysis for me will be done in the labs on Florida State University’s campus and also at the National High Magnetic Field Lab, located down the street from campus.  So for those of you that are jealous of my afternoons off, don’t be because once I go home I will have 12 hour days for a few weeks.  Ever wonder how to analyze trace elements in nMolar concentration in seawater? Well, you have come to the right person! I have spent the better part (or worse depending on my mood that day) of the last 3 years learning techniques to determine the concentrations of trace elements in the dissolved and particulate phases of the water column.

Seawater extraction column

Seawater extraction column

The dissolved phase, for me, is what passes through a 0.4 μm pore sized filter.  I look at 10 elements, iron (Fe) being the most important as it is a major minor nutrient for marine critters.  The concentrations typically found in the dissolved phase are nMolar to pMolar in oligotrophic environments for Fe and the other elements I study (I have them all listed on my information page).  My research group uses an inductively-coupled plasma-mass spectrometer (ICP-MS) to determine the concentrations.  Now, anyone who has worked around an ICP-MS knows that sending straight seawater through it is a very bad idea. All the salts in seawater cause many issues and your data would not be reliable, if you manage to get any before your front end clogs up.  In order to get around the problem, my research group uses extraction columns which remove the metals from the seawater (Milne et al., 2010).  The column has resin inside that acts as a binding site for the metals.  The metals will adhere to the resin while the rest of the salts will pass through into waste when you get the pH of the sample right (something that takes a lot of practice).  Nitric acid (1.0 Molar) is then sent over the column that elutes the metals and sends them to a small collection vial.  The extraction process also concentrates the metals about 10 times, which makes it easier to analyze them on the ICP-MS.  This process (I left out a couple of steps for simplicity sake) takes 9 minutes per sample.  40 samples per day are about my limit as I must sit with the system the entire time.  The whole process is done in a Class-100 clean lab and I wear my little pastry chef outfit (hairnet, lab coat, gloves, clean lab shoes) to keep things as clean as possible.  The extracted samples are then ready to analyze on the ICP-MS.  Sounds like fun, right?

Me in my clean lab back in Florida

Me in my clean lab back in Florida

The particulate phase is a quicker and an easier process.  I save all my filters that my samples went through.  The filters are simply digested in order to get the total metal concentrations on the particles.  The digestion potion is a lovely combination of concentrated nitric, hydrochloric, and hydrofluoric acids (yum!) that dissolves the particle minerals.  They are then dried down, re-suspended in 0.34 Molar (2%) HNO3 and analyzed on the ICP-MS.  So, if I don’t die from digesting ~200 filters, I will be able to share the metal particulate concentrations.

Lots to do when I get home and not a lot of time to do it as I’m working on writing my Master’s thesis for an October 2013 defense and a publication on my microlayer sampler!  Good thing we didn’t sample today or tomorrow, maybe I can be productive?

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One thought on “Trace elements at sea’s skin (by Alina)

  1. Pingback: Nice square meter, three boxes, one sampler and one boat hook… | MedSeA Villefranche 2013

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