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Lecture 32

CHEM 212 Lecture 32: Nov 25, 2016Premium

3 pages38 viewsFall 2016

Department
Chemistry
Course Code
CHEM 212
Professor
Hamilton M.Coreen
Lecture
32

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Chem 212!
Nov. 25/ 2016!
!
GC Detectors
-many types e.g. TCD, FID, ECD and MS!
-can combine GGC with Mass spec --> GC/MS or GC/MS/MS or LS/MS/MS!
"-separation technique plus characterization technique!
"-powerful quantitative and qualitative tools!
-ideally signal is proportional to amount go compound!
!
Thermal Conductivity, TCD!
-senses change sin conductivity of stationary phase when a compound is eluting!
-universal detector:r expounds to everything!
-Large linear range --> *********!
-Non-destructive---> doesn't break up your molecule like a mass spec!
-Not very sensitive: 10^-8 g solute/mL!
-Used for gas analysis and prep scale!
"-collecting a fraction!
!
Flame ionization, FID!
-Small H2/O2 flame pyrolyzes sample compounds creating ionic species!
-Ionic species are sensed via a current between 2 electrodes!
-Signal proportional to number of carbon atoms!
-Used for hydrocarbons!
-Large linear range !
-General purpose organics detector!
Destroys sample!
-Moderately sensitive 10^-13 g/mL!
!
Electron capture, ECD!
-Use of 63Ni source to cause movie phase to emit electrons!
-If sample components can capture these electrons, see a decrease in current = signal!
-Very selective response i.e. electronegative functional groups such as halogens, nitro and
phosphate groups!
-Non-destructive!
-Very sensitive 10^-15 g/mL!
-tends to be used for compounds with halogens or nitrogen containing compounds !
-came into the world in the 80s when the world realized how bad PCBs are!
!
Mass Sepctroscopy, GC/MSD!
-Each component eluted from the GC is sent to a mass spectrometer!
-Obtain MS spectrum of each compound separately!
-Powerful identification tool and also good for quantification!
-High resolution MS extremely sensitive 10^-18 g/mL!
"-very little noise because looks at very small area!
-cost about half a million dollars!
!
Application of GC - Both Qualitative and Quantitative
Qualitative!
-By retention time-!
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