Introduction to Mass Spectrometer Fundamentals

Introduction to Mass Spectrometer Fundamentals

Sample Inlet

Gas, liquid and solid compounds can be introduced into the ion source through specially designed inlets with controlled flow. This can be done a number of ways depending on the state of the sample. Several of the common types of sample inlets are:
GC
LC
Direct Insertion Probe
Batch

Ion Source

Sample molecules are introduced into the ion source through the sample inlet. Before the mass spectrometer can analyze a sample, it is necessary that the sample molecule be ionized. One method used to ionize and fragment the sample is to bombard the molecules with electrons. This results in different fragmentation patterns which can be used to identify the sample compound.

 The filament is the source of electrons. A repeller is used to help direct ions through a series of lenses in the ion source. Without these components, sample molecules would not be ionized and they would not reach the mass filter.

 The fragmentation process which occurs in the ion source is important because the results are ultimately used to identify species. The other parts of the mass spectrometer, the mass filter and detector, are used to select and count ions.


Two common types of ionization are electron ionization and chemical ionization.

The ion source is used to:

Fragment and ionize sample molecules.
Direct ions through a series of lenses into the mass filter.

Mass Filter

Once ionized, the ions enter the mass filter. The mass analyzer moves selected ions from the ion source to the detector. The mass analyzer filters and separates ions based on their mass to charge ratio. Only an ion of one mass is passed through the mass filter at a given time.
Several common mechanisms or methods are used to select and filter these ions. Four common types of mass analyzers which separate ions by their mass to charge ratio are:
Magnetic Sector
Quadrupole
Ion Trap
Time-of-Flight (TOF)

The mass filter is used to:

Move ions from the ion source to the detector.
Filter ions according to their mass to charge ratio.


Detector


Once an ionized sample has been filtered by mass-to-charge ratio in the mass filter, the abundance must be detected and reported to the data system. A detector is used to collect and count ions. Only one ion is detected at a given time, whether the mass filter is a time-of-flight, separation by space, quadrupole filter or ion trap.



Once inside the detector, the ions generate a signal which can be displayed by the data system.


The detector is used to:

Count ions.
Generate an electrical signal.



Vacuum System


The ion source, mass filter and detector are in a vacuum. The vacuum system makes it possible for ions to move from the ion source to the detector without colliding with other ions, sample molecules, air and water.

A vacuum is created by removing all species from the mass spectrometer. Minimizing collisions with other ions ensures that more ions will be counted by the detector.



The vacuum system is used to:

Provide ions with a free path of travel from the ion source to the detector.
Remove all species from the instrument.


Data System

The data system has three purposes:
Controls the operational parameters of the ion source, mass filter and detector.
Graphically displays the results of the sample compound as a mass spectrum.
Manipulates data for identification and quantitation.

The data system is used to:

Control the mass spectrometer hardware.
Collect data and display it in a useful way.
Integrate data to produce reports.





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