IA CH 27 GC

Define carrier gas
chemically inert gas such as He, CO2 or Ar that acts as the mobile phase in GC
Draw the Gas chromatography block diagram
Refer to book and notes
Draw the sample injection port
Refer to book and notes
What are the 2 types of injectors
1)Split junction
2)Splitless junction
Describe split junction injection

Ratio the amount of sample that goes to column vs waste

Provides better resolution then splitless

Describe splitless injection
everything injected goes straight on the column
Lower detection limits
Higher sensitivity
What are 2 types of columns
1)packed column
2)capilary column
Describe packed column
1-5 meter long
2-4mm inside diameter
not widely used, need more sample
Describe capillary column
30m long
.25-.32 incid diameter
more theoretical plates
What are the characteristics of ideal column?

1)Inert

2)Thermally stable

3)Low volatility

Describe GC stationary phase in general
-Polyalkylated silanes are most common
-resolution must be great enough to separate similar things out
-Alternating R groups on silanes changes column characteristics
Draw general structure for polyalkylate silane
Refer to book and notes
Describe Chiral stationary phase
Separates out stereoisomers
Draw the structure of a chiral stationary phase
Refer to book and notes
Describe Thermostate oven
heats the column and sample either isocratically or by a gradient
Define Isocratic heating
Oven stays on one temperature the entire time
Define gradient heating oven
Oven starts low and increases in temp over time
better resoluton
possibility for degradation
What are the 4 types of detector for GC and their relative sensitivities
1)Mass spec 10ppb
2)Flame ionization (FID) 0.1ppm
3)Thermal conductivity (TCD) 10ppm
4)Electron capture (ECD) 0.1ppb
Draw a flame ionization detector
Refer to book and notes
Describe flame ionization detector
-Hydrocarbons ionized in the flame
-measures current
-Insensitive to to non combustible gases
-Mass sensitive: responds to number of carbons entering per unit time
What are the characteristics of an ideal detector?

  1. adequate sensitivity
  2. good stability
  3. linear response over several orders of magnitude 
  4. Thermostable Rt->400+ 
  5. Short response independant of flow rate 
  6. high reliability and easy to use 
  7. similar response to all solutes
  8. non destructive

Draw a thermal conductivity detector
Refer to book and notes
Describe thermal conductivity detector
Made of set of resistor for the ref and the sample.
Measures difference in current
Non destructive
Low sensitivity, requires a lot of sample
Global use
Draw electron capture detector
Refer to book and notes
Describe electron capture detector

used for environmental samples (halogenated nitrogen, phosphorous, more electronegative makes for better e acceptor)

63Ni->63Cu+e (beta emitter) sample accepts electrons changing current in detector

excellent sensitivity 0.1ppb

Write out the b-emission process of an ECD.
63Ni->63Cu+e
Describe the principle operation of the thermal conductivity detector
based on the decrease in thermal conductivity of the helium or hydrogen carrier gas brought about by analyte molecules
Describe the principle operation of the flame ionization detector
based on the ionization of the analyte in a small air/hydrogen flame. the ions and electrons produced are collected by a pair of biased electrodes giving rise to current
Describe the principle operation of the electron capture detector
based on the attenuation by analyte molecules of a standing ion current generated in the effluent by ionization of mobile phase molecules with a beta-emitter. Electronegative functional groups are particularly effective at capturing electrons and reducing the ion current
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