Question

Depending on the sample of interest, different ion sources are used for mass spectrometry. What ion source would you use if you wanted to examine many different small molecules and compare your results to a large database? Why?

Answer 1

Mass spectrometry is a powerful analytical technique used to identify and quantify analytes using the mass-to-charge ratio (m/z) of ions generated from a sample. It is useful for the analysis of a wide range of clinically relevant analytes, including small molecules, proteins, and peptides. When mass spectrometry is coupled with either gas or liquid chromatographs, the resultant analyzers have expanded analytical capabilities with widespread clinical applications, including quantitation of analytes from myriad body tissues and fluids. In addition, because of its ability to identify and quantify proteins, mass spectrometry is widely used in the field of proteomics.

Techniques based on mass spectrometry require an ionization step wherein an ion is produced from neutral atoms or molecules. Electron impact and chemical ionization (CI) are often used in gas chromatography–mass spectrometry. In liquid chromatography–mass spectrometry, electrospray ionization (ESI) and atmospheric pressure CI are the most commonly used techniques. In microbiology, a desorption/ionization technique termed MALDI (matrix-assisted laser desorption ionization) is employed. Each of these ionization techniques is described in detail, and advantages of the techniques are highlighted. Once molecules are ionized, resultant ions are analyzed using either beam type analyzers (eg, quadrupole, or time-of-flight [TOF]) or trapping mass analyzers (eg, ion trap). Mass analyzers also can be combined to form tandem mass spectrometers, which allow further expending capabilities of the technique. Clinical applications of mass spectrometry are provided to illustrate the role of this technique in the analysis of clinically relevant analytes.