In a mass spectrometer, the same thing is happening, except its atoms and molecules that are being deflected, and its electric or magnetic fields causing the deflection.
It consists of Inlet system Ion source Mass analyzer Detector
INLET SYSTEM Meant for; Sample introduction. Amount of Sample. Pressure Maintenance.
ION SOURCE Ionizes The Material Under Analysis. The Ions Are Then Transported By Magnetic Or Electric Fields To The Mass Analyzer.
ION SOURCERequirements For Ion Source: The sample must be in vapor phase prior to ionization. The sample should not undergo thermal decomposition during vaporization.
ION SOURCE The common technique used for the production of ions in mass spectrometer is by bombardment of electrons. These bombarding electrons are produced from an electrically heated tungsten filament. A few mgm of sample is produced as vapors in ion source at an operating pressure of 10-6mm. the vapors are allowed to pass into ion chamber. Here it is bombarded by electrons from filament. Due to bombardment the molecules generally lose one electron to form a parent ion radical.
ION SOURCE IONIZATION POTENTIAL : The minimum energy required to ionize an atom or molecule is called ionization potential. The energy required to remove one electron from neutral parent molecule is usually 10eV. With this much energy no ions are formed. But if energy of bombarding electron is around 70eV, then this results in the formation of fragment ions or daughter ions.
MASS ANALYZER The positively charged ions produced in the ion chamber are accelerated by applying an acceleration potential of 8 KV. These ions then enter the mass analyzer where there differentiate on basic of their mass to charge (mz) ratio.
MASS ANALYZER Positive ions travel in a circular path through 180o under a magnetic field H. suppose an ion having charge z is accelerated through a voltage V. Then the kinetic energy of ions is expressed as: 1/2mv2 = zV ……….. (a) v = Velocity of ions after acceleration V = Potential applied
MASS ANALYZER In a magnatic field H, any ion will experience force HzV. It produces an acceleration of v2/r in a circular path of radius r. hence from newton’s 2nd law of motion HzV = mv2 /r ……….. (b) Squaring both sides H2z2V2 = m2v4 /r2
MASS ANALYZER H2z2 = m2v2 /r2……….. (c) From equation (a) mv2 = 2 zV Putting in equation (c) H2z2 = m. 2 zV / r2 H2z = 2mV/ r2
MASS ANALYZER m/z = H2r2 / 2V From this equation this is clear that at a given magnetic field strength (H) and accelerating voltage, the ions of m/e value will follow a circular path of radius r. these ions reach the collector, amplified and recorded.
ION DETECTOR The detection and recording of ions can be done either by photographic plates or electrical method. PHOTOGRAPHIC PLATES ELECTRICAL METHOD
ION DETECTOR PHOTOGRAPHIC PLATES: In this method a photographic plate is kept at right angel to the path of ions so ions of successive m/e values form an image.
ION DETECTOR ELECTRICAL METHOD: in this method the detector is usually electron multiplier which produce electrical signal proportional to number of ions, sticking the detector. These signals are amplified by a series of dynodes. The result of these amplified signals is presented in the form of graph.
RECORDING OF SPECTRUM The amplified signals from electron multiplier is usually recorded by An oscilloscope A chart recorder A computer
RECORDING OF SPECTRUM An oscilloscope: Oscilloscope is useful for displaying peaks arising from a single ion in mass spectrum. It gives maximum sensitivity upon proper instrumentation.
RECORDING OF SPECTRUM A chart recorder: In cart recorded a photosensitive paper is used. This is used when ions are detected by photographic plate.
RECORDING OF SPECTRUM A computer: The use of an online computer for recording mass spectra now a day is most important method. The whole system is known as a data system which consists of a computer, a visual display unit (VDU) and a print plotter.
MASS SPECTRUM A mass spectrum is an intensity vs. m/z (mass-to- charge ratio) plot representing a chemical analysis. Hence, the mass spectrum of a sample is a pattern representing the distribution of ions by m/z ratio in a sample. It is a histogram usually acquired using an instrument called a mass spectrometer.
X-axis: m/z (mass-to-charge ratio) The x-axis of a mass spectrum represents a relationship between the mass of a given ion and the number of elementary charges that it carries. This is written as the IUPAC standard m/z. most of the ions formed in a mass spectrometer have a single charge, so m/z value is equivalent to mass it self. The IUPAC Gold Book gives an example: "for the ion C7H72+, m/z equals 45.5".
Y-axis:relative abundance(%) The y-axis of a mass spectrum represents of the ions. The most intense ion is assigned an abundance of 100, and it is referred to as the base peak.
ISOTOPE DATING AND TRACKING: Mass spectrometry is also used to determine the isotopic composition of elements within a sample. Differences in mass among isotopes of an element are very small, and the less abundant isotopes of an element are typically very rare, so a very sensitive instrument is required. These instruments sometimes referred to as isotope ratio mass spectrometers (IR-MS). Isotope ratios are important markers of a variety of processes. Some isotope ratios are used to determine the age of materials for example as in carbon dating. Labeling with stable isotopes is also used for protein quantification.
TRACE GAS ANALYSIS: Several techniques use ions created in a dedicated ion source injected into a flow tube or a drift tube: selected ion flow tube (SIFT-MS), and proton transfer reaction (PTR-MS), are variants of chemical ionization dedicated for trace gas analysis of air, breath or liquid headspace.
PHARMACOKINETICS: Pharmacokinetics is often studied using mass spectrometry because of the complex nature of the matrix (often blood or urine) and the need for high sensitivity to observe low dose and longtime point data. The most common instrumentation used in this application is LC-MS with a triple quadrupole mass
PROTEIN CHARACTERIZATION: Mass spectrometry is an important emerging method for the characterization and sequencing of proteins. The two primary methods for ionization of whole proteins are electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI).
GLYCAN ANALYSIS: Mass spectrometry provides a complementary method to HPLC for the analysis of glycans. Intact glycans may be detected directly as singly charged ions by matrix-assisted laser desorption/ionization mass spectrometry) or by fast atom bombardment mass spectrometry
SPACE EXPLORATION: As a standard method for analysis, mass spectrometers have reached other planets and moons. Mass spectrometers are also widely used in space missions to measure the composition of plasma.