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Tandem mass spectrometry, or MS/MS, combines two mass analyzers in sequence, connected by a collision or interaction cell.

First, the samples are ionized to generate a mixture of ions, which enters the first mass analyzer.

This analyzer separates the ions and selects only a particular ion—the precursor ion—to move into the collision cell.

The collision cell contains inert gas molecules, which collide with precursor ions, fragmenting them into product ions.

These ions are run through the second mass analyzer, where they are separated and finally detected.

MS/MS generates various spectra.

Product-ion spectra are obtained when the first analyzer selects a precursor ion and the second analyzer scans all the masses.

Precursor-ion spectra are generated by scanning through precursor ions in the first analyzer and selecting a product-ion in the second analyzer.

To obtain neutral loss spectra, both mass analyzers are scanned together, with the second analyzer offset by the mass of a selected neutral fragment.

MS/MS is used for structural elucidation and complex mixture analysis.