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level: Level 3

Questions and Answers List

GAS CHROMATOGRAPHY

level questions: Level 3

QuestionAnswer
MOBILE PHASE: Always a gas Use for volatile materials Sample is vaporized and injected onto chromatographic columns and separated into many components GSC or GLCGAS CHROMATOGRAPHY
GAS CHROMATOGRAPHY Advantages: LIMITATIONSAdvantages: 1 Fast analysis 2 Efficient, high resolution 3 Sensitive, ppm or ppb 4 Non destructive 5 Highly accurate quantitative analysis 6 Required small samples, µL 7 Reliable and simple LIMITATIONS: 1 ONLY THERMALLY STABLE 2 SAMPLE REQUIRE DERIVATISATION 3 QUANTITATIVE SAMPLE IS DIFFICULT 4 AQ. SOLUTIONS AND SALTS CANT BE INJECTED
Mobile phase In steel tanks under high pressure Helium or Nitrogen and occasionally hydrogen, Argon or CO2 Helium – most prevalent carrier gasCarrier gas
most prevalent carrier gasHelium
Stationary phase: 1 In GSC (gas solid chromatography) – adsorbents used:__ 2 In GLC (gas liquid chromatography) – adsorbents used:__. 1 activated charcoal silica gel alumina glass beads 2 diatomaceous earth
Small chamber Sample is vaporize rapidly before entering Injection maybe manual or automatic injector Samples maybe pure liquid, solids dissolved in liquid solvents or gasesInjection Port
Tube Silica or stainless steel: Capillary Straight or coiled or U-shaped Designs: capillary and packed (glass)Column
IDENTIFY SOLUTES AS THEY EXIT the chromatographic column Solutes eluted from column → interact w/ detector → data system → chromatogram generated Flame ionization detector Fourier transform infrared- used for qualitative identificationDetector
Detector of FOURIER TRANSFORM FOR QUALITATIVE IDENTIFICATIONFourier transform infrared
also called Hot wire detector (HWD) or katharometerThermal Conductivity (TCD)
most frequently used detector in GC - highly sensitive - universal detectorFlame ionization (FID)
detector – extremely sensitive - respond to nanogram or even picogram - for HALOGENATED COMPOUNDS as pesticidesElectron Capture (ECD)
Probably the most sensitive and useful analysis can be made by combining __gas chromatography w/ MASS SPECTROPHOTOMETER (GC-MS)