Mass Spectrometer

Mass spectrometry (MS) is a highly effective qualitative and quantitative analytical technique used to identify and quantify a wide range of clinically relevant analytes. Mass spectrometers expand analytical capabilities to various clinical applications when coupled with gas or liquid chromatography. In addition, mass spectrometry is an essential analytical tool in proteomics due to its ability to identify and quantify proteins. Most mass spectrometry data are presented in units of the mass-to-charge ratio (m/z), where m is the molecular weight of the ion (in daltons), and z is the number of charges present on the measured molecule. For small molecules (<1000 Da), there is typically only a single charge; therefore, the m/z value is the same as the mass of the molecular ion. However, when larger molecules such as proteins or peptides are measured, they typically carry multiple ionic charges, and, therefore, the z-value is an integer greater than 1. The m/z value is a fraction of the ion's mass in these cases. Sample preparation is crucial for successful mass spectrometry, particularly when analyzing complex matrices commonly encountered in clinical chemistry. This process typically involves one or more of the following steps—protein precipitation followed by centrifugation or filtration, solid-phase extraction, liquid-liquid extraction, affinity enrichment, or derivatization. Derivatization is the process of chemically modifying the target compounds to make them more suitable for analysis by mass spectrometry. This process typically involves the addition of some well-defined functional groups. The goals of derivatization vary depending on the application but typically include increased volatility, greater thermal stability, modified chromatographic properties, greater ionization efficiency, favorable fragmentation properties, or a combination of these. Mass spectrometers convert molecules into ions, which are then manipulated using electric and magnetic fields. This process requires 3 main components as follows: Ion source: A sample is placed into the mass spectrometer, which is then ionized by the apparatus. Mass analyzer: Ions are sorted in the device based on their mass-to-charge ratio (m/z). . Detector: Ions are measured and displayed on the mass spectrum chart. . Atoms and molecules must first be ionized before being accelerated through the mass spectrometer and detected. The sample molecule introduced into the mass spectrometer first gets a positive charge from an ionization source. This positive charge is achieved by removing a valence electron. Alternatively, protons can also be added to create a positive electrical charge. Once ionized, the molecule breaks apart into smaller fragments, then separated according to their mass-to-charge ratio in the mass analyzer. Of note, only the cationic fragments are separated. The neutral species in the mass spectrometer go undetected as they are either absorbed by the apparatus or removed by a vacuum. After the ions are separated, the detector quantifies the ions.  A chart is generated to analyze the mass spectrometer's results, with the mass-to-charge ratio (m/z) on the x-axis and the relative intensity on the y-axis.  For a given sample, the most abundant ion in the sample molecule is known as the base peak. This ion is set to 100% on the y-axis for its relative intensity, and all the remaining ion peaks are generated relative to this value. The molecular ion peak is known as the parent peak because it corresponds to the molecular weight of the sample. For example, if the specimen in the mass spectrometer is hexane, the m/z is 86, as the molecular weight of hexane is 86 g/mol. In addition, if there is a peak at m/z=87, this is classified as the m+1 peak because all atoms have various isotopes.