Striking Oil: Separation Science in Marine Pollution Analysis
Chris Reddy from the Woods Hole Oceanographic Institution spoke to LCGC about the role of chromatography in the ongoing environmental analysis of the Deepwater Horizon oil spill, how comprehensive GCXGC works in practice, and why this oil spill led to the return of thin layer chromatography (TLC) to his laboratory.
Q: Tell us about your group’s involvement in the work at the Deepwater Horizon disaster site, which has attracted widespread attention in the media. What were the objectives?
It was an ongoing spill for 87 days with oil residues that we continue to find along the Gulf beaches as recently as November 2013. We have studied — and continue to study — a wide range of research questions from determining the flow rate, analyzing how nature breaks down or “weathers” the oil, and fingerprinting it to confirm that oiled samples we have found have come from the DWH disaster.
Our field work has led us to collecting samples using a robot right where the oil was coming out of the pipe that you may have seen on TV at the time. We have walked many miles of the Gulf of Mexico coastline and even 300 or 400 miles away from the explosion. So we have gone from analyzing oil samples a foot away from the source of the spill to hundreds of miles away
I expect to be working at the site for the next 10 years, alongside some other oil spills and projects .
Q: One of the main techniques you used was comprehensive two-dimensional gas chromatography (GCXGC). Why did you decide to use a comprehensive GCXGC method and what are the advantages of this technique compared to other methods?
Now, I want to be very clear here. A lot of people hear me say GCXGC can do more than GC–MS, and they immediately assume that GCXGC is a replacement to GC–MS, but it is not. It is just another tool in the laboratory that allows us to address some specific questions where a regular benchtop GC–MS cannot.
On the other hand, for polycyclic aromatic hydrocarbons (PAHs), I don’t think GCXGC can do any better than what a benchtop GC–MS can do and the GC–MS software is much, much more user-friendly. And so, in my lab, we don’t quantify PAHs by GCXGC. There’s no point. It’s easier and faster to do so with a GC–MS.
One of the main factors that makes GCXGC very powerful, that I think a lot of people miss out on, is that when you look at a chromatogram in two-dimensional GC space you are not only just able to identify and measure compounds (many, many more compounds than with traditional techniques), but also can convert retention times in the first and second dimension to vapor pressure and water solubility.
If you’re interested in the fate of oil there are two key questions you want to know: What is the vapor pressure of a compound (or what is the likelihood the compound will evaporate?); and what is the water solubility of the compound (what is the likelihood the compound will dissolve in water?)
Now if we use some newly developed algorithms, we can allocate how much of a compound evaporated versus how much dissolved in water. That is the real major leap in my mind: GCXGC allows us to discover where the compounds are going. It’s beyond just making your Excel spreadsheet bigger and identifying many more compounds. It allows us to say where is this compound going, or where has it gone.
Q: Can you describe an interesting example of the use of chromatography on the Deepwater Horizon project using GC?
Q: Are there any particular difficulties you have to overcome when developing GCXGC methods?
The cost of GCXGC with a flame ionization detector (FID) is comparable to a GC–MS, but it might take you months to achieve adequate and reproducible chromatograms sustainably.
Even then, the basic maintenance is a little tricky as you have a lot of potential for more leaks and so the learning curve is a lot steeper — what’s more there aren’t many manuals available on troubleshooting. This sounds negative, but I think it’s just that the technology hasn’t matured, and it’s probably where GC–MS was in the late 1960s.
To me, maturity will come from more users contributing to the field with manufacturers developing better and easier to use hardware and software. The more users out there, the more everybody learns the tricks, and the more that it will allow us to pollinate so that it can be more user-friendly.
Q: So, you see it evolving and being easier to use as time progresses? Do you think it could be used for routine analysis in the future?
For routine analysis, the one thing that needs to evolve is the software to interpret the data. It’s a case of “be careful what you wish for: You might get it!” You get a lot of resolved peaks and a lot of information, but the developments in hardware are way ahead of the software — data analysis is therefore not as easy as it is with a regular benchtop GC–MS to integrate peaks and such. The software exists but it needs to be refined and that’s what I also tell potential users — give it time and look for ways to improve it. I think there is a lot of low-hanging fruit and a lot of talented people can make this technology even better.
Q: Is there anything you would like to add about the use of GCXGC in your group?
Q: Any advice for chromatographers who are embarking on using GCXGC?
Q: Are there any actual other chromatographic techniques that you think are particularly interesting in the environmental analysis at the moment?
This approach has become useful for the DWH project because we believe there has been a lot of biology or photochemistry that has oxidized some of the oil samples that makes them difficult to be analyzed by any type of GC, but that can be easily separated and quantified on a TLC–FID. So I think there’s some irony that we have resurrected a piece of technology that was in my building and now there’s a queue of scientists waiting to use it. In fact, we’re thinking about buying another one. So there’s an interesting spin on using something that’s been around for a long time that we really think has a lot of power. It’s very easy and the curve is easy to get going. We have already published several papers using it. So it’s an interesting end of the spectrum from a chromatographic perspective.
Q: It seems simplicity sometimes has a lot to offer.
We found one in our building and we have a lot of chemists and biochemists, so naturally somebody had one on a shelf. And lo and behold, we brought some rods and some development tanks and we were in business.
Q: Interesting stuff! Your Institution does a lot of brilliant work. Is there anything you’d like to say about the role of separation science at your institute?
The analyses run the whole gamut from looking at methane to inspecting large molecular biopolymers that have much, much bigger molecular weights to any possible spectrum, potential usefulness, we have in our building. And it’s a lot of fun. We’ve had a lot of people come to our lab and say “I’ve never seen so many chromatographs.”
Q: So many professors in one laboratory!
We also only get a gas delivery on a Monday, Tuesday, and Friday. So if you are out of gas at four o’clock on a Friday afternoon and you’re trying to batch up samples over the weekend, you can’t run them.
That’s a huge problem for us. And so we’ve been working with our administration so that we can have a permanent plumbed gas source so we would remove all these tanks. Actually, it’s a lot cheaper and safer. And it will allow us to be more efficient. And so really in many respects, our two-biggest challenges in terms of day-to-day operations are good power and gas supply.
Q: How is this perceived from a cost perspective?
Chris Reddy is a senior scientist at Woods Hole Oceanographic Institution, Woods Hole, Massachusetts. He is currently studying the short and long-term fate of oil seeping off the coast of Santa Barbara, California, and the Gulf of Mexico, World War II wrecks in the South Pacific, and spills that have occurred in 1969, 1974, 1996, and 2003 in New England, two that occurred in 2007 in San Francisco Bay and South Korea, the Exxon Valdez, the 2002 Prestige spill along the Spanish coastline, and the Deepwater Horizon.
According to a 2010 survey by Thomson Reuters, he is one of the top cited and published scientists studying oil spill effects, remediation methods, and petroleum microbiology. He has extensive experience with the Deepwater Horizon, including being the academic liaison at the Unified Area Command where he interacted and provided guidance to state, Federal, and BP officials.
He had led or participated in two major research cruises on the DWH, many small boat operations, overflights, and sampled the beaches of the Gulf from Pensacola, Florida, to Port Fourchon, Louisiana, countless times.
He received his BS in chemistry from Rhode Island College, Providence, Rhode Island and his PhD in chemical oceanography from the Graduate School of Oceanography at the University of Rhode Island (Narragansett, Rhode Island).