1. MASS SPECTROSCOPY (with Gas Chromatography)

2. 5 Stages of the process – where do they happen? 1.Sample vaporised 2.Sample ionised 3.Ions accelerated 4.Ions deflected 5.Ions detected

4. +2 ion +1 ion Deflection Depends upon the mass/charge ratio (m/z) of each ion The lighter the mass & the greater the charge = greater deflection

5. Relative Atomic mass (A r ) 6 Li 7 Li 92.5%7.5% (92.5/100 x 7) + (7.5/100 x 6) = 6.475 + 0.45 = 6.925

6. butane CH 3 CH 2 CH 2 CH 3 Peak with greatest m/z value = MOLECULAR ION (M + ) C 4 H 10  [C 4 H 10 ] +. + e – m/z 58 Other peaks due to molecular ion breaking into fragments [C 4 H 10 ] +.  [CH 3 CH 2 CH 2 ] + +. CH 3 m/z 43 [C 4 H 10 ] +.  [CH 3 CH 2 ] + +. CH 2 CH 3 m/z 29 [C 4 H 10 ] +. [CH 3 CH 2 CH 2 ] + [CH 3 CH 2 ] + M + gives the M r of the compound

7. chloroethane CH 3 CH 2 Cl [CH 3 CH 2 37 Cl] +. [CH 3 CH 2 35 Cl] +. 35 Cl: 37 Cl = 3:1

8. bromomethane CH 3 Br [CH 3 81 Br] +. [CH 3 79 Br] +. 79 Br: 81 Br = 1:1

9. HIGH RESOLUTION MASS SPECTROSCOPY e.g.The following compounds all have M r = 60 at low resolution but at high resolution their M r ’s are different if they have a different molecular formula. Calculate each of the compounds M r CH 3 COOHmolecular formula = C 2 H 4 O 2 NH 2 CONH 2 molecular formula = CH 4 N 2 O CH 3 CH 2 CH 2 OHmolecular formula = C 3 H 8 O CH 3 CH(OH)CH 3 molecular formula = C 3 H 8 O 60.02112 60.03235 60.05751

10. Mass Spectrometry: Paired up Spectroscopy A powerful and widely used method is to couple Gas Chromatography with Mass Spectrometry (GC/MS). A mixture of compounds are firstly separated (GC step) and then analysed (MS step). Compound x Compound y

11. Uses of GC-MS?