Mass spectrometry is an analytical tool useful for measuring the mass-to-charge ratio (m/z) of one or more molecules present in a sample.  These measurements can often be used to calculate the exact molecular weight of the sample components as well. Typically, mass spectrometers can be used to identify unknown compounds via molecular weight determination, to quantify known compounds, and to determine structure and chemical properties of molecules. Very mass spectrometer consists of at least these three components Ionization Source, Mass Analyser, Ion Detection System.

IN Ionization Source Molecules are converted to gas-phase ions so that they can be moved about and manipulated by external electric and magnetic fields. In our laboratory we use a technique called Nano electrospray ionization, which is somewhat similar to how cars are industrially painted. This method allows for creating positively or negatively charged ions, depending on the experimental requirements.  Nano electrospray ionization can directly couple the outlet of a small-scale chromatography column directly to the inlet of a mass spectrometer.  The flow from the column is passed through a needle that is 10-15 um at its tip.

IN Mass Analyser Once ionized, the ions are sorted and separated according to mass-to-charge (m/z) ratios. There are numbers of mass analysers currently available, each of which has trade-offs relating to speed of operation, resolution of separation, and other operational requirements.  The specific types in use at the Broad Institute are discussed in the next section.  The mass analyser often works in concert with the ion detection system and in Ion Detection System the separated ions are then measured and sent to a data system where the m/z ratios are stored together along with their relative abundance.  A mass spectrum is simply the m/z ratios of the ions present in a sample plotted against their intensities.  Each peak in a mass spectrum shows a component of unique m/z in the sample, and heights of the peaks connote the relative abundance of the various components in the sample.

The evolution of mass spectrometry has been marked by an ever-increasing number of applications in science and technology. New applications and new developments have gone hand in hand to create a complex array of instruments, but all may be understood by tracing the ions through three basic elements: an ion source, a method of analysing the ion beams according to their mass-to-charge ratio, and detectors capable of measuring or recording the currents of the beams. These elements exist in many forms and are combined to produce spectrometers with specialized characteristics. The needs of users vary, as do the chemical form and the amount of sample available for analysis, which may be in sub microgram quantities. The result is a great variety of design. The separation of ions according to their mass is accomplished with static magnetic fields, time-varying electric fields, or methods that clock the speeds of ions having the same energies—the time-of-flight method. Static electric fields cannot separate ions by their mass but do separate them by their energy and so provide an important design element by functioning as an energy filter; they are described here along with magnetic fields.

Thanks & Regards,

Jessica Aaron

Associate Managing Editor