In a series of posts, we are going to talk about Mass Spectrometry.

1. Introduction-The dif­fer­ent con­fig­u­ra­tions and the Elec­tron Impact process
2. What types of mass ana­lyz­ers are there?
3. What type of detec­tors are there?
4. What types of analy­sis can be done?
5. How do you read the output?
6. How do they come to a qual­i­ta­tive mea­sure using software?
7. How do they quan­ti­tate the results?
8. Do you need chro­matog­ra­phy if you are using Mass Spectrometry?
9. Other top­ics of inter­est about GC-MS

Mass Spec­troscopy can be a very, very pow­er­ful tool if used prop­erly and if used in con­junc­tion with chro­matog­ra­phy (whether it is Gas Chro­matog­ra­phy or Liq­uid Chro­matog­ra­phy) can pro­vide struc­tural infor­ma­tion that can lead to foren­si­cally defen­si­ble con­fir­ma­tion of both qual­i­ta­tive (what is it) and quan­ti­ta­tive (how much is it) iden­ti­fi­ca­tion except for chi­ral compounds.

But just like we wrote before in the case of Gas Chro­matog­ra­phy with Flame Ion­iza­tion Detec­tor (Why say­ing the sam­ple was run on a gas chro­mato­graph is nearly mean­ing­less), sim­ply say­ing the analy­sis was per­formed by way of Gas (or Liq­uid) Chro­matog­ra­phy Mass Spec­trom­e­try is use­ful infor­ma­tion, but in no way is enough to deter­mine the sen­si­tiv­ity, selec­tiv­ity, resolv­ing power and the over­all use­ful­ness of the analysis.

In these series of posts, we will be focus­ing on Gas Chro­matog­ra­phy with Mass Spec­trom­e­try. In the future, we will look at Liq­uid Chro­matog­ra­phy with Mass Spectrometry.

One of the very first thing we have to learn is about the con­fig­u­ra­tion of the entire instrumentation.

• First, we need to know what col­umn was used in the GC as this will tell us about the the­o­ret­i­cal sep­a­rat­ing (resolv­ing) power of the chro­mato­graphic method.
• Sec­ond, we need to know about the means of trans­fer from the col­umn to the mass spec­trom­e­ter so we can tell about its dif­fu­sion. This we call the interface.
• Third, we need to know the Ion Source.
• Fourth, we need to know Mass Analyzer.
• Fifth, we need to know Detector.
• Finally, we need to know about the Ana­log to Dig­i­tal (ACD) sys­tem and soft­ware system.

Each of these six vari­ables can effect the out­put in terms of the qual­i­ta­tive and the quan­ti­ta­tive results.

After the basic chro­matog­ra­phy is per­formed in the GC, what­ever comes off the col­umn and is trans­ferred suc­cess­fully through the inter­face is then ion­ized. All that it means to ion­ize some­thing is to give it a charge. This is an elec­tri­cal process (as opposed to a chem­i­cal one which is what we mostly see in Liq­uid  Chro­matog­ra­phy). This process occurs in the “source.”

Source: http://www.chem.harvard.edu/mass/tutorials/eimovie.html

Tech­ni­cally, it is in area of the source where the elut­ing ana­lytes mol­e­cules com­ing off the col­umn are directly ion­ized through col­li­sion with a bom­bard­ing elec­tron stream emit­ting from a heated fil­a­ment (usu­ally made of rhe­nium or tung­sten) result­ing in the removal of an elec­tron to form a rad­i­cal cation species and us accel­er­ated through the source to the mass ana­lyzer as seen above. The result is that it is pos­i­tively charge. As it is an “elec­tron smash­ing” process, we get the name of the source from that action–Electron Impact Ion­iza­tion (EI).

How EI through the source works

In the next post in our series we will look at what types of mass ana­lyz­ers are there?