Weird NMR Samples: They Analyzed WHAT?

Nuclear Magnetic Resonance (NMR) is an incredibly useful characterization technique. Assuming certain properties are met, the nucleus of an atom interacts with a magnetic field. The exact nature of that interaction is highly dependent on the environment around the atom. So you can get a ton of information about the structure of a molecule by NMR. Sometimes NMR is silly based on how we fix the equipment. Or our acronyms. And sometimes it’s a bit strange because you see some weird NMR samples.

I’ve personally done NMR on both shingles and gravestones. But those were industrial projects, so I can’t go into the details and there’s no publication to go with them. And of course, Glenn Facey’s blog has some really interesting sample choices for explaining various NMR phenomena. But today, we’re looking at things that can be found in the peer reviewed literature that prompt “They did NMR on WHAT?”

Cheese

This was my first encounter with weird NMR samples. I was looking for something else entirely when I got sidetracked by the fact that cheese was mentioned in the title. That’s like the test students pull to see if their TA is actually reading their lab report!

There’s actually some really interesting science at work with “Distribution and mobility of phosphates and sodium ions in cheese by solid-state ³¹P and double-quantum filtered ²³Na NMR spectroscopy” though. Gobet et al were looking at the sodium spectra in order to determine how much it’s moving and what structural role it was playing. The overall goal was a simple health concern: Could they reduce the sodium content of the cheese without compromising the texture. Flavour is a qualitative question, but NMR can give hard numbers when it comes to what the salt does to the physical structure.

I still never expected to see “Preparation of Cheese” in the experimental section of a chemistry paper. Though really, the kitchen is where most people run into chemistry the most.

Wine and Whiskey

Really, where else could we go after cheese? We need some wine with it! There’s some interesting pulse sequence work going with this one, because the biggest signals are going to be water and ethanol no matter what. So they had to use a sequence that would suppress those signals. In this case, it did not have a particularly amusing acronym.

And good news wine snobs! They did find some differences in the smaller components of the wine. They could almost always correctly identify the kind of grape involved. And nearly as often they could pinpoint the region that the wine was from. So there’s potential application to identifying counterfeit/mislabelled wine. Wine, after all, is serious business.

Solvent suppression to study alcoholic beverages is a decently common investigation. There’s a very recent paper looking at Scotch. A lot of studies of what makes Scotch different from other kinds of whiskey have used mass spectrometery. And while you can get a lot of information on that, the analysis conditions can be overly fussy. With a good enough solvent suppression method, NMR lets you actually have a robot do most of the work. The paper did not draw any conclusions on what it is that makes Scotch special.

Olive Oil

Another case of “Where is your food coming from?”. In the case of olive oil the spectrum looks pretty simple as a glance. While wine experiments focus on suppressing the main signals and examining other tiny components, olive oil is characterized by the complexity of the individual lines.

Certain regions of Italy are particularly known for their olive oil to the point where there are laws about branding oil from olives grown elsewhere as being from the region. So this is another case of counterfeit protection. The other interesting thing this particular paper looked at was determining where exactly geography starts to play into the oil. Which is a really good question when previous designations were in the end rather arbitrary.

Paintings and Violins

Unusual samples do go far beyond food science. Though I did have to take a break from writing this post to have lunch.

Recently, portable NMR based techniques have been developed. The portable devices can’t get the complex molecular information that a stationary spectrometer gives, but they can still produce useful data. NMR is a non-destructive technique in that it doesn’t damage the sample over the course of the experiment. But you still need to actually get the sample into the magnet, and that could potentially involve damage.

The handheld instrument can determine the moisture content of fresco walls. Once the conservationists know how much moisture is actually under the surface, they have a better idea of how to proceed to make sure the fresco stays intact. And that’s how you avoid disastrous touch-ups.

The same techniques can give insight into what exactly it is that sets famed historical violins apart from their modern counterparts. While no one is about to scrape some of the varnish off to analyze its chemical composition, scientists have learned a lot about the physical properties of the wood itself. With better resolution, we’ll be able to see things like how many layers of varnish were used.

Really, the takeaway here is that arts and science interact in all sorts of interesting ways.