1. Chemistry Topic: Atomic theory Subtopic : Mass Spectrometer

2. What is mass spectrometer An instrument that measures the masses of individual molecules that have been converted into ions, i.e., molecules that have been electrically charged. An instrument which separates particles according to their masses & records relative proportions of these.

3. Basic principle Samples are analyzed by introducing them as gas into the analyzer tube where the constituent molecules are ionized by subjecting them to bombardment by a controlled beam of electrons originating from a hot-wire filament.

4. Simple diagram & Stages of Operation

5. VAPORIZATION

6. Stage 1- Vaporization If sample is solid or liquid, it must be heated to produce the vapor. This is connected to rest of the mass spectrometer by a fine tube or capillary so that the transfer of material into the body of instrument occurs very slowly (as MS must be kept at high vacuum).

7. Stage 2 Ionization The atom is ionized by knocking one or more electrons off to give a positive ion, by subjecting it to bombardment by a controlled beam of electrons originating from a hot-wire filament.

8. The electrically heated metal coil gives off electrons which collide with electrons in the sample. Some of the collisions are energetic enough to knock one or more electrons out of the sample particles to make positive ions Ionization

9. The need for a vacuum It's important that the ions produced in the ionization chamber have a free run through the machine without hitting air molecules.

10. Why +1 Most of the positive ions formed will carry a charge of +1 because it is much more difficult to remove further electrons from an already positive ion. These positive ions are persuaded out into the rest of the machine by the ion repeller which is another metal plate carrying a slight positive charge.

11. Stage 3 Acceleration The positive ions are accelerated by an electric field in electrostatic analyzer. The ions are accelerated so that they all have the same kinetic energy.

12. Stage 4-Deflection The ions are then deflected by a magnetic field by different amounts. The amount of deflection depends on: the mass of the ion- Lighter ions are deflected more than heavier ones. the charge on the ion- Ions with 2 (or more) positive charges are deflected more than ones with only 1 positive charge. These two factors are combined into the mass/charge ratio. Mass/charge ratio is given the symbol m/z (or sometimes m/e).

13. Deflection

14. In this diagram, ion stream A is most deflected - it will contain ions with the smallest mass/charge ratio. Ion stream C is the least deflected - it contains ions with the greatest mass/charge ratio. A & C ions collide with the walls where they will pick up electrons and be neutralized.

15. Stage 5 Detection Only ions of a certain mass (depending on the field strength) are detected by detector In the diagram, only ion stream B makes it right through the machine to the ion detector.

16. How might the other ions be detected - those in streams A and C which have been lost in the machine? Remember that stream A was most deflected - it has the smallest value of m/z (the lightest ions if the charge is 1+). Remember that stream C was least deflected - it has larger m/z value (the heavier ions if the charge is 1+).

17. Mass spectrum A mass spectrum is a graph of ion intensity as a function of mass-to- charge ratio. Mass spectra are often depicted as simple histograms

19. X-axis –Mass/Charge

20. Y-axis – Relative abundance

22. Base peak Each ion formed during ionization has a specific value of m/z therefore each ion will produce a signal whose intensity depends on its relative amount. The peak of highest intensity is called a base peak When 2 or more ions have same m/z, their peaks superimpose & peak intensity is due to combined abundance of all these ions.

23. Atomic masses & isotopes

25. Relative molecular masses

27. Applications Mass spectrometry is a powerful analytical technique that is used To identify unknown compounds, To quantify known compounds, and To elucidate the structure and chemical properties of molecules. Detection of compounds can be accomplished with very minute quantities. This means that compounds can be identified at very low concentrations (one part in 1012) in chemically complex mixtures. Mass spectrometry provides valuable information to a wide range of professionals: physicians, astronomers, and biologists, to name a few.

28. Mass spectrometry is used to... Detect and identify the use of steroids in athletes Monitor the breath of patients by anesthesiologists during surgery Determine the composition of molecular species found in space Determine whether honey is adulterated with corn syrup Locate oil deposits by measuring petroleum precursors in rock Monitor fermentation processes for the biotechnology industry Detect dioxins in contaminated fish Determine gene damage from environmental causes Establish the elemental composition of semiconductor materials