L9 - Announcement Lab reports for October 7 lab session...

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Announcement Lab reports for October 7 lab session will be due Tuesday October 18 in class
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Lecture 9 GC Detectors
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Overview Flame Ionization Detector (FID) Electron Capture Detector (ECD) Compare and contrast FID and ECD Environmental Applications of ECD Introduction to GC-MS
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Flame ionization detector (FID) Electron capture detector (ECD)
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GC Detectors A good GC detector … Works in the gas phase Gives a linear response to analytes Does not give a response to the mobile phase Detects analytes at low amounts (picograms!) Is selective for only certain compounds (???)
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Ever seen a picogram? 1000 pg in 1 ng… 1000 ng in 1 μg… 1000 μg in 1 mg… 1000 mg in 1 g! GC detectors can be VERY sensitive!!
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Flame Ionization Detector (FID) Almost-universal detector for organic compounds Overall premise based on combustion in a flame Ions created during combustion by the analytes are detected to give a signal Robust, inexpensive, simple to operate Large linear dynamic range for calibration
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0 20 40 60 80 100 120 140 160 180 200 220 Sample FID Chromatogram - Lab 0 Trifluralin Heptachlor Malathion
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Flame Ionization Detector (FID) Basic operating principle: A hydrogen/air flame is ignited inside the detector Combustible organics from the GC column burn in the flame and produce ions, mainly CHO + and H 3 O + Ions travel to a collector and are detected, giving rise to a signal in the chromatogram
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Flame Ionization Detector (FID) Most sensitive to C-H, C-C groups Relatively insensitive to C=O groups and halogenation (already highly oxidized carbon) Requires extra gases: fuel and oxidizer for the flame During combustion with oxygen, CHO + ions are produced from hydrocarbons CHO + reacts with water to produce H 3 O + H 3 O + migrates to the collector where a signal is detected and amplified
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We have ignition! The FID flame is often a HYDROGEN/AIR flame Fuel hydrogen and oxidizer air must be plumbed in separately from the carrier gas Ignition is done automatically or manually by a spark Typical H 2 flow = 45 ml/min Typical air flow = 450 ml/min c.f. Typical carrier gas flow = 1 ml/min Flow rates through the detector are FAST Absolutely no negative effects on peak shape possible with FID
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