What’s in an Oil Drop?

Descrambled Data

After the voltage readings are amplified and digitized, an image signal, in waves, is produced that depicts the measurements of the packets over that second in time as they fell back to their original orbits. Looking like a tornado flipped sideways, this raw data is a composite signal of all of the cyclotron frequencies of all of the ions present, layered one on top of the other. Our crude oil sample came out looking like this:

Ion cyclotron resonance time domain signal.

Somewhere in all those lines Ion X is recorded. But you sure can’t tell from what we’re looking at. In order to make any sense out of this picture, we need to descramble the signals, convert them to frequency data and sort them out.

That magic is worked by a mathematical algorithm called a Fourier transform (finally we reach the FT part of our discussion!). A computer converts the raw data from an “amplitude over time” signal to a signal that separates out and depicts the spectrum of all the signals received. Our post-FT data looks like this:

Frequency domain spectrum of crude oil sample.

We’ll spare you the math behind it. For the purposes of understanding FT-ICR, you just need to know that Fourier transform shows you the amplitude of each of the different frequencies detected, which corresponds to the number of ions associated with that frequency.

At last, we come to the final step. The results of the Fourier transform are translated to produce a mass spectrum of our crude oil sample.

Enlarged region of the mass spectrum of a crude oil sample,
identifying individual hydrocarbons.
Click on image to enlarge.

This ought to look familiar – the detailed look of the crude oil sample we studied earlier. And there is Ion X, in the middle of the spectrum, in the neighborhood of 426.30 mass/charge ratio: C₂₈H₄₄N₁S₁. As it turns out, it's one of several hydrocarbons in the sample containing sulfur (S), and it's a good thing we found it. Sulfur is a strictly regulated pollutant in transportation fuels, and the regulations are getting more strict. So it's increasingly important to identify the molecules that have sulfur and measure how difficult it would be to remove it (a process called desulfurization). A crude oil sample with lots of sulfur molecules that resist desulfurization might not be worth drilling for.

This article has demonstrated just one way in which FT-ICR is used by scientists. Explore the links on the next page to learn more about this powerful and promising process.

Next Page Links and Resources

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Thanks to the Magnet Academy's scientific adviser on this article, Chris Hendrickson, Director of Instrumentation with the Magnet Lab's ICR Program.