Mass Spectrometry: How to Weigh an Atom

Mix and Match

This is where Humayun’s innovation comes into play – and how it achieves its incredible efficiency.

The aerosol produced by the laser is split into two separate samples, which are funneled into two separate mass spectrometers. The machine, in essence, bifurcates.

About 10 percent of the sample is diverted into the first of the two mass spectrometers, featuring a magnet designed especially for fast scanning. Because there are always more of the lighter elements floating around than trace elements, the machine requires just that small portion of the sample to figure out how relatively abundant they are. Attached to this analyzer is the same type of ion detector described in the NASCAR example.

Meanwhile, the remaining 90 percent of the sample takes the road more traveled, into a separate analyzer whose more powerful magnet is calibrated to usher the rarer trace elements into a special set of detectors designed for them. In fact, these few-and-far-between heavyweight elements are serviced by eight detectors; it’s called a multi-ion detector.

The whole machine owes its efficiency to its ability to analyze the same sample in different ways simultaneously (as opposed to sequentially, as in other models). Every little bit counts: While some 400 kilograms of moon rocks have been brought to Earth, Stardust’s total booty amounted to less than one dash of the salt shaker. Nothing should go to waste.

Humayun’s machine promises many applications, and is likely to be used by chemical oceanographers and other scientists. But first in line are the comet grains.

If these grains could talk, they’d speak volumes. With machines like Humayun’s, scientists now have ways of making them talk. They may tell us about the history of matter in the interstellar medium, an area of gas and dust between stars. They will tell us what kind of minerals and metals they contain, and perhaps about a star they might have come from. They may tell us they contain water only in its frozen form (comets are, after all, largely ice), or also in the form of hydrated silicates. If the later is the case, it could suggest that comets are actually fragments of bigger bodies.

Most scientists don’t think that’s likely. Then again, much of what we presently think about comets is, as Humayun says, “educated guess work – which may be wildly off.” From Christopher Columbus to Lewis and Clark to Apollo 13, explorers have always encountered the unexpected. And appropriately so: Why dole out hundreds of millions of dollars for a space mission if all that comes of it is a smug “I told you so” from scientists?

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Thanks to the Magnet Academy's scientific adviser on this article, Dr. Munir Humayun, Associate Professor of Geochemistry at Florida State University and Magnet Lab research associate.