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Analytical Chemistry

Density Analysis By Magnetic Levitation

Harvard chemists have devised a simple tool for analyzing food and water based on density

by Bethany Halford
May 24, 2010 | A version of this story appeared in Volume 88, Issue 21

Credit: J. Agric. Food Chem.
Droplets of whole (left) and skim (right) milk undergo MagLev analysis.
Credit: J. Agric. Food Chem.
Droplets of whole (left) and skim (right) milk undergo MagLev analysis.

Using the magic of magnetic levitation, Harvard University chemists have devised a simple, inexpensive, and portable tool for food and water analysis based on density (J. Agric. Food Chem., DOI: 10.1021/jf100377n). Magnetic levitation, or MagLev, uses magnetic fields to suspend objects. The phenomenon can be applied to measure density and estimate chemical composition on the basis of differences in density. Katherine A. Mirica, Scott T. Phillips, Charles R. Mace, and George M. Whitesides designed a MagLev device that consists of a vial containing a paramagnetic fluid—GdCl3, for example—between two NdFeB magnets. By suspending a diamagnetic object or droplet of sample fluid in the paramagnetic solution, the researchers were able to estimate the salinity of water; distinguish different plant oils according to their content of polyunsaturated and monounsaturated fats; determine fat content in milk, cheese, and peanut butter; and compare a variety of grains. “Potential applications of MagLev may include evaluating the suitability of water for drinking or irrigation, assessing the content of fat in foods and beverages, or monitoring processing of grains,” the researchers note.


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