Key concept: Tandem mass spectrometry. Many available instruments today have the ability to take 2 or more measurements of the mass-to-charge ratio for a single molecule. The consecutive measurements are referred to as being in tandem, and the application of these will be shown below.

Single, Tandem, and ms^n applications

In the context of mass spectrometry, experiments and their spectra are often referred to as being of the type single, tandem, or ms^n. These designations refer to the number of mass spectra measurements taken on a single population of molecules. Therefore a single mass spectrometry experiment involves a single measurement, a tandem involves two measurements, and an ms^n experiment involves n measurements (where n in an integer value generally greater than 2).Several instruments currently available use different types of mass detectors within one setup for tandem or ms^n applications - these are referred to as "hybrid mass spectrometers".

One obvious question to ask when confronted with the option of taking one or more mass spectral measurement in an experiment should be that of why one would want to measure the same molecule more than once. The answer is that generally, the same molecule is not measured multiple times. Rather, a population of molecules will be measured, then a sub-population will be selected. This sub-population (called the "parent ions") will then be broken into a population of smaller molecules (called the "daughter ions") that can be measured. This allows for further investigations of the molecular components of a large molecule. For some types of molecules (peptides in particular) it can be useful to continue breaking down the daughter ions into successively smaller pieces.