Street drugs can contain a wide range of compounds, including active ingredients like heroin and fentanyl along with various cutting agents. But many analytical techniques available to law enforcement officers are slow, require sophisticated equipment, or struggle to identify dilute compounds in mixtures. Researchers at Harvard University led by George Whitesides, in collaboration with the US Drug Enforcement Administration, have now demonstrated that magnetic levitation (maglev)—a technique that separates compounds on the basis of their density—can be used to analyze dilute compounds in powdered drug mixtures (Angew. Chem., Int. Ed. 2019, DOI: 10.1002/anie.201910177). A maglev device consists of two magnets flanking a vial of a weakly magnetic fluid. As the fluid is drawn toward the magnets, it pushes the particles of a foreign substance into clusters that hover at a level corresponding to their density. To analyze drug mixtures, the Harvard team designed a new magnetic solution that can separate very fine particles without dissolving them. Using gadolinium(III) chelate complexes dissolved in a mixture of hexane and tetrachloroethylene, the researchers were able to separate most powdered drug mixtures within 30 minutes. By visually inspecting the device, users can determine whether a sample contains a particular compound and roughly how much of the compound is present. If needed, the isolated compounds can be extracted and further analyzed. The researchers envision that with further development, the device could be made available to law enforcement officers for field use.