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9 Cards in this Set
- Front
- Back
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Interface between GC and MS |
GC: gas flow MS: high vacuum(10-5 10-8 Torr) Two stages of pump, mechanical (low) molecular (high) |
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Ionization methods GCMS |
Common is electron impact -gets to excited energy state, relaxation ruptures bond, more fragment , based on 70ev electron impact Second common is chemical ionization, little fragmentation, molecular ion peak and a few others |
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Ion sources |
Electrical impact and chemical ionization, range for both is 50-800mw, MS measure the mass to charge ratio of ions |
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Ms detector: quadruple mass analyzer |
voltage or electrodes are controlled to allow ions with limited range of m/z values to reach transducer, others strike the rods and become neutral |
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Time of flight mass analyzer |
Gives measurement of mass via flight time of ions having the same KE over a fixed distance 1) ions formed in same place and time, same energy by acceleration voltage 2) tof mass spec acts as racetrack for ions, low mass moving faster than high mass 3) determination of time of arrival of ions after start signal which gets masses |
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Ion trap mass analyzer |
Has two end caps and a ring electrode 1)Gas ions can be formed and confined by electric or magnetic field . 2)controlling voltage of electrode , ions are mass selectively ejected out to detector |
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Double focusing analyzer |
Electric and magnetic analyzer combined to focus velocity and direction of an ion beam(high resolving power) |
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Ion detectors GC/MS |
Electron multiplier : discrete dynode electron multiplier - Cu/Be surface: bursts of e are emitted when struck by energetic ions or electrons
Continuous dynode electron multiplier: made of glass and doped with lead
Provided high current gains and nanosecond response time |
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Two analysis modes GCMS |
1)scan mode(slow, qual): whole picture of analyte, MS scabs the masses repetitively during analysis , ion abundances can be plotted as function of time and gives total ion chromatogram , good for unknown ID
2) selected-ions monitoring (SIM) mode(fast) (more precision, qaunt): Only a few ions, only measure selected m/z value and monitor through entire process, used frequently |
