Qual and Quant MS: The Perfect Marriage

Let’s go back to the early 1990s when an important innovation was starting to cause a stir. Electrospray ionization (ESI) essentially allowed liquid chromatography (LC) and mass spectrometry (MS) to be combined much more easily as an analytical technique. By the mid-90s, it was clearly no longer a research-only tool – instrument companies had picked up on its power and successfully commercialized it. Mike Thurman was a GC-guy – which was the best technique for analyzing pesticides in water. But the revolution in LC-MS had turned his head. How could he convince his colleagues at the US Geological Survey (USGS) that it was the future?

After meeting Damia Barceló – an LC-MS aficionado – at an American Chemical Society meeting, Mike was invited over to the Department of Environmental Chemistry at the CID-CSIC in Barcelona on a short sabbatical to get to grips with the technology. Imma Ferrer was just finishing her PhD under Barceló and, luckily for Mike, Imma was given the task of training the new American guy...
Despite needing to clean the “ancient” instrument’s source after every five samples, together they discovered an important degradate of metolachlor in groundwater and published their first joint paper in Analytical Chemistry (1).

It was love at first analyte...

Fast-forward through nearly two decades of LC-MS innovation and Mike and Imma can still be found working hand-in-hand at the Center for Environmental Mass Spectrometry (CEMS) at the University of Colorado University in Boulder.

What happened after that first paper?

Mike Thurman: Well, the sabbatical was a success. We ended up buying an Agilent LC-MS (single quad) instrument in 1998. Imma came over to the US to do a postdoc in Denver. I was in Kansas City at the time, but we still got together to run samples. I retired from the USGS in 2003 (the LC-MS was still running samples when I left!) and Imma’s work visa had come to an end, so we both decided to move to the University of Almeria in Spain.

Imma Ferrer: At Almeria, we focused on pesticides in food – that region is known as the Garden of Europe. It has huge numbers of greenhouses, supplying much of Europe with fresh fruit and vegetables. It was also then that we started working on Agilent’s LC time-of-flight (TOF) MS system – the first one installed in Europe I think.

That’s when you both got hooked on MS?

MT: Yes. We got totally caught up in accurate mass analysis. It was as if mass spec was the key to unlock a door to another world – a world we’d never seen before. Measuring a concentration is one thing, but our interest really lies in the ability to elucidate the chemical structure of any compound that comes our way. We’re puzzle solvers in the mass spec world.

IF: Right. We even embarked on a project to measure the mass of an electron... And our interest in the capabilities – and possibilities – of the instrument has grown and grown. Instruments are now super sensitive (especially compared with 10 years ago) and virtually anyone with some skill can measure part per trillion levels. Identification of the unknown compounds in a sample  – and where they came from – is what we are really focused on now.

What excites you about your work?

MT: A great driving aspect of our work is when people ask for our help; can we find a certain compound in a plant or in an insect or in the water? Answering those questions is a thrill. We’ve spent many years trying to understand how chemical structure affects mass spectrometry. When we see a new chemical structure, we often know what we can achieve. And we’ve also grown adept at interpreting mass spectra, so we can identify compounds without shooting a standard. Once you start delving into how chemical structure affects activity, things get very interesting.

IF: Exactly – and because new compounds are being developed by pharmaceutical and chemical companies all the time, being able to detect emerging contaminants and degradates that no one has seen before is really exciting.

What’s hot right now?

IF: Hydraulic fracturing – “fracking” – to access new reserves of oil and gas. Millions of gallons of water with chemical additives are used in every well, so there are environmental considerations. We’ve been doing a lot of work on the analysis of these fracking fluids. In particular, we’re trying to identify the additives and their degradates with the purpose of tracking their transport through “fingerprinting.”

MT: Actually, we’ve got three new papers on this topic all looking at those compounds (2–4). Our skills of identification really paid off in this research because each company uses a proprietary recipe of additives and only publishes a list of generic chemical group names. Our job is to figure out exactly what was in the flowback samples without standards. And we’ve already identified about 25 percent.

Is it hard to remain neutral?

IF: I think scientists should stay neutral for the most part. Our job is to offer results and solutions. In terms of the effect on water quality, I’m not for or against fracking until I’ve seen all the data. That said, there are other factors at work, such as aesthetics, air quality, climate change, and so on...

MT: Funnily enough, the paper we recently wrote (2) changed my stance, especially as I was first author. Our university wrote a press release – “Major class of fracking chemicals no more toxic than common household substances” – and that caused a bit of a media frenzy. In fact, it went viral. People accused me of being paid off by oil and gas companies and so on. The backlash actually pushed me to the right. My feeling is that the oil and gas companies are being purposefully “green” with their chemical choices. We certainly haven’t found the endocrine-disrupting surfactants we’ve been looking for yet. But as Imma says, there are other considerations besides water quality.

Please give us a quick tour of your lab.

IF: In addition to our beloved sample preparation tool, we have three core LC-MS systems from Agilent Technologies. The workhorse of the lab is the LC-QTOF (Agilent 6500), which we use for accurate mass analysis and the detection of new contaminants. It allows us to perform huge screening methods to find everything in the sample. We use our triple quad instrument (Agilent 6460) in targeted methods when we want to analyze compounds that we suspect are present at very low concentrations. The combination of the two gives us the best of both worlds. The other instrument is an ion trap (Agilent XCT Trap), which is useful for deciphering fragmentation pathways of emerging contaminants.

How do you split the workload?

MT: Going against stereotypes, if something can be broken, I can break it – and so Imma takes on the role of mechanic. More seriously, I tend to focus on the qualitative screening side of the analysis. By using the QTOF and the databases that we’ve built – and our combined experience – we can identify leads for further investigation. Imma then begins quantitative work on the triple quad. Although I tend to take the credit for the screening and discovery side, I think Imma does much more than me. I probably do a little more talking... and a lot less fixing.

IF: I guess as an analytical chemist I am a specialist in quantitative analysis. Triple quad methods are great for low-level detection – and ours is one of the most sensitive. Over the years, we’ve developed several methods that we use routinely (for pesticide, pharmaceuticals, hormones, and so on); that’s the really smart and efficient way to do triple quad work. And yes – I am the plumber in the relationship.

What joint discovery stands out?

IF: A couple of years ago we were looking at uptake and metabolism of pesticides by plants. We discovered several new metabolites and of course published all of that work. It was unusual work and simply fascinating.

MT: Back in the early 2000s, we were really getting into ion chemistry and Imma told me that she had found a compound  that resulted in positive and negative ions of the same mass. “That’s impossible,” I said. We came up with a theory – that the accurate mass would differ by two electrons – but we didn’t have access to an instrument that could prove the point. Eventually, we got hold of an Agilent LC-TOF and made the measurement. But it was very difficult to get the paper published – the reviewer simply didn’t believe our data. Agilent were really excited about the work and offered to fly the reviewer over to see the live data. That was good enough for the editor and the paper was published (5). Very satisfying.

Why mass spectrometry?

IF: We have a saying in our lab: the instrument never lies. Sometimes it throws you an unusual result – but you have to figure it out. With mass spectrometry, you can spend hours and hours on a single sample – and I love puzzles. When the pieces fit together it’s very satisfying.

MT: What drives me is the joy of discovery. And mass spec is the best tool we have right now. Of course, not all of the work is exciting, but if you keep your head down and your eyes open, you just know something intriguing will come your way. Making the discoveries and then pursuing them further is a beautiful and wonderful thing.

References

1. I. Ferrer, E. M. Thurman and D. Barceló, Anal. Chem., 69 (22), 4547–4553 (1997).
2. E. M. Thurman et al., Anal. Chem., 86 (19), 9653–9661 (2014).
3. Y. Lester et al., Sci. Total Environ. 512-513, 637-644 (2015).
4. I. Ferrer and E. M. Thurman, “Chemical Constituents and Analytical Approaches for Hydraulic Fracturing Waters”, Trends Environ. Anal. Chem. (2015) In Press.
5. I. Ferrer and E.M. Thurman, Anal. Chem. 77 (10), 3394-3400 (2005).