MASS SPECTROSCOPY PDF
Mass spectroscopy pdf. 1. CONTENTS: 2. INTRODUCTION Mass spectrometry ( MS) is an analytical technique that measures the. Mass Spectroscopy is a technique causing the formation of the gaseous ions with or without fragmentation; the gas phase ions are then characterized by their. Mass Spectrometry. Principles and Applications. Third Edition. Edmond de Hoffmann. Université Catholique de Louvain, Belgium & Ludwig.
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In mass spectrometry, one generates ions from a sample to be analyzed. Mass- spectrometry has evolved from the experiments and studies early in the 20th. Lecture Note on Mass Spectroscopy - Free download as PDF File .pdf), Text File .txt) or read online for free. Mass spectrometers use the difference in mass-to-charge ratio (m/z) of ionized Therefore, mass spectroscopy allows quantitation of atoms or molecules and.
In chemical ionization sources, the analyte is ionized by chemical ion-molecule reactions during collisions in the source. Karas and F. Hillenkamp . Hard ionization and soft ionization[ edit ] Quadrupole mass spectrometer and electrospray ion source used for Fenn's early work In mass spectrometry, ionization refers to the production of gas phase ions suitable for resolution in the mass analyser or mass filter. Ionization occurs in the ion source.
There are several ion sources available; each has advantages and disadvantages for particular applications. LC-MS , since at atmospheric pressure, the filaments used to generate electrons burn out rapidly.
Thus EI is coupled predominantly with GC , i. GC-MS , where the entire system is under high vacuum. Hard ionization techniques are processes which impart high quantities of residual energy in the subject molecule invoking large degrees of fragmentation i. The most common example of hard ionization is electron ionization EI. Soft ionization refers to the processes which impart little residual energy onto the subject molecule and as such result in little fragmentation. Inductively coupled plasma[ edit ] Inductively coupled plasma ion source Inductively coupled plasma ICP sources are used primarily for cation analysis of a wide array of sample types.
In this source, a plasma that is electrically neutral overall, but that has had a substantial fraction of its atoms ionized by high temperature, is used to atomize introduced sample molecules and to further strip the outer electrons from those atoms. The plasma is usually generated from argon gas, since the first ionization energy of argon atoms is higher than the first of any other elements except He, O, F and Ne, but lower than the second ionization energy of all except the most electropositive metals.
The heating is achieved by a radio-frequency current passed through a coil surrounding the plasma. Photoionization mass spectrometry[ edit ] Photoionization can be used in experiments which seek to use mass spectrometry as a means of resolving chemical kinetics mechanisms and isomeric product branching.
Other ionization techniques[ edit ] Mass selection[ edit ] Mass analyzers separate the ions according to their mass-to-charge ratio. This technique is used for large biological molecules that are difficult to get into the gas phase.
The atomic beam is produced by accelerating ions from an ion source through a charge-exchange cell. The ions pick up an electron in collision with neutral atoms to form a beam of high energy atoms. Mass analyzer designs The purpose of the mass analyzer is to separate the ions produced in the ion source according to their different mass-to-charge ratio.
The most common analyzer designs include the quadruple, magnetic sector and time-of-flight mass analyzers. Quadruple A quadruple field is formed by four electrically conducting parallel rods. The applied voltages affect the trajectory of ions travelling down the flight path centred between the four rods.
For given voltages, only ions of a certain mass-to-charge ratio are allowed to pass through the quadruple filter, while others are carried away as uncharged molecules. By varying the electrical signals to a quadruple it is possible to vary the range of the mass-to-charge ratio transmitted. This makes spectral scanning possible.
Magnetic sector analyzer The magnetic sector analyzer employs a magnetic field that causes ions to travel in a circular path of , 90 or 60 degrees. Initially ions are accelerated through slit B into the metal analyzer tube.
Ions of different mass can be scanned across the exit slit by varying the field strength of the magnet or the accelerating potential between slit A and B. The ions passing through the exit slit fall on a collector electrode, resulting in an ion current that is amplified and recorded. Time-of-flight analyzer A time-of-flight mass spectrometer uses the differences in transit time through a drift region to separate ions of different masses.
The ions from the ion source are accelerated by an electric field pulse. The accelerated particles then pass into a field-free drift tube that is about a meter in length.
Separation of ions: Mass spectrum: The heaviest peak is the molecular ion peak and its mass will give the mass of the molecule.
Isotope peak: Isotopes present in the molecule may generate additional peak. The relative abundances of these isotopic peaks are proportional to the 13 abundance of the isotope in nature e. For an ion containing n number of carbon atoms, the abundance of isotope peak is nX1.
It will. The relative abundances of this isotopic can be used to determine molecular formula. Ionization method: Ionization of volatile materials b. Ionization of nonvolatile materials.
Electron impact ionization IE 2. Chemical ionization CI. Electron impact ionization: The product is cation radical. Chemical ionization CI: Field desorption: In this way molecules are thrown into the gas phase as a positive molecular ion without thermal decomposition. Desorption ionization by particles or radiation: Laser desorption LD II.
Californium plasma desorption IV. Secondary ion mass spectrometry SIMS.
To overcome this problem, a matrix is used and the technique is known as matrix assisted laser desorption ionization technique MALDI. In MALDI, a low concentration of the sample is embedded either in a liquid or a solid matrix molar ratio 1: In this way, the energy is transferred indirectly to the sample, and in a controlled manner which avoids sample decomposition. The sample is dissolved in a matrix of low volatility.
Probe sample ion Mass analyzer Sample in matrix. Diglycerol 1: These ions are then accelerated out of the source into the analyzer system.
Different technique for analyzing ions in a mass spectrometer: Magnetic sector b. Time of flight c. Quadrupole d. Ion cyclotron resonance e.
Ion trap. Time of flight mass analyzer: The technique requires that all the ions produced in the ion source should leave at the same time. Since all the singly charged ions will acquire the same kinetic energy, the largest mass will have the lowest velocity and the longest time of flight over a given distance.
Quadrupole analyzer is a relatively compact instrument and inexpensive. Low-resolution mass spectrometer LRMS: LRMS employs a single stage analyzer.
As all have the same integral mass High-resolution mass spectrometer HRMS:Thus separation, molecular weight, and chirality can all be determined in one experiment. Show More. Sometimes it is necessary to heat the emitter with an electric current. There are several ion sources available; each has advantages and disadvantages for particular applications.
By measuring, simultaneously, velocity and charge of individual ions, together with measuring the acceleration voltage, one can compute the mass of the ion. A photographic plate can give a higher resolution than an electrical detector. This chamber contains a high energy reagent gas like helium He or argon Ar with which the ions collide.