Mass Spectrometry: How to Weigh an Atom

Old Idea, Fresh Take

When considering how to analyze comet dust, Humayun knew that of all existing types of mass spectrometers, the LA-ICP-MS was the best starting point. He knew that the “LA” part – the laser ablation – would allow him to better pinpoint the tiny solid particles he wished to examine, while the “ICP” part – the inductively coupled plasma – would offer both high accuracy and the ability to detect a wide range of metals and trace elements (we’ll explain that momentarily).

It’s an impressive machine. But Humayun needed more. He would, after all, have very little dust to work with: He had to use it as efficiently as possible. With this in mind, he conceived of a way to customize the LA-ICP-MS design for his specific purpose. The adaptation, he says, promises dramatic results, measuring 40 times more information in about the same amount of sample.

Let’s take a closer look at this unique hybrid.

First, the laser will let researchers analyze sample sizes even smaller than those measurable by other machines. In fact, the laser Humayun will use will be able to target areas measuring as little as 4 microns across: You’d have to take one of your hairs and slice it into 20 or more equal-sized pieces – lengthwise – to get something so small. This will allow Humayun to examine comet dust in numerous locations across a single grain. Each of those analyses could reveal a different makeup. This approach yields far more information than if one were to sample the grain as a whole. In other words, data-wise, the sum of the grain’s parts is much greater than its whole.

Second, this machine ionizes samples not by bombarding them with electrons, as in the example described earlier, but by injecting them into an extremely hot plasma created from argon gas. (By plasma we mean a highly ionized gas, not blood). The plasma’s intense heat (in the neighborhood of 7000 kelvin, hotter than the surface of our sun) succeeds in ionizing most of the naturally occurring elements in the periodic table, even the ones that resist ionization. By comparison, another type of machine scientists are using on comet particles, called a Secondary Ion Mass Spectrometer, can only ionize and measure one third of the elements.

Next Page Mix and Match

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