Term
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Definition
| chemically inert gas such as He, CO2 or Ar that acts as the mobile phase in GC |
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Term
| Draw the Gas chromatography block diagram |
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Definition
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Term
| Draw the sample injection port |
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Definition
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Term
| What are the 2 types of injectors |
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Definition
1)Split junction
2)Splitless junction |
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Term
| Describe split junction injection |
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Definition
Ratio the amount of sample that goes to column vs waste
Provides better resolution then splitless |
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Term
| Describe splitless injection |
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Definition
everything injected goes straight on the column
Lower detection limits
Higher sensitivity |
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Term
| What are 2 types of columns |
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Definition
1)packed column
2)capilary column |
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Term
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Definition
1-5 meter long
2-4mm inside diameter
not widely used, need more sample |
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Term
| Describe capillary column |
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Definition
30m long
.25-.32 incid diameter
more theoretical plates |
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Term
| What are the characteristics of ideal column? |
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Definition
1)Inert
2)Thermally stable
3)Low volatility |
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Term
| Describe GC stationary phase in general |
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Definition
-Polyalkylated silanes are most common
-resolution must be great enough to separate similar things out
-Alternating R groups on silanes changes column characteristics |
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Term
| Draw general structure for polyalkylate silane |
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Definition
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Term
| Describe Chiral stationary phase |
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Definition
| Separates out stereoisomers |
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Term
| Draw the structure of a chiral stationary phase |
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Definition
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Term
| Describe Thermostate oven |
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Definition
| heats the column and sample either isocratically or by a gradient |
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Term
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Definition
| Oven stays on one temperature the entire time |
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Term
| Define gradient heating oven |
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Definition
Oven starts low and increases in temp over time
better resoluton
possibility for degradation |
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Term
| What are the 4 types of detector for GC and their relative sensitivities |
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Definition
1)Mass spec 10ppb
2)Flame ionization (FID) 0.1ppm
3)Thermal conductivity (TCD) 10ppm
4)Electron capture (ECD) 0.1ppb |
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Term
| Draw a flame ionization detector |
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Definition
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Term
| Describe flame ionization detector |
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Definition
-Hydrocarbons ionized in the flame
-measures current
-Insensitive to to non combustible gases
-Mass sensitive: responds to number of carbons entering per unit time |
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Term
| What are the characteristics of an ideal detector? |
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Definition
- adequate sensitivity
- good stability
- linear response over several orders of magnitude
- Thermostable Rt->400+
- Short response independant of flow rate
- high reliability and easy to use
- similar response to all solutes
- non destructive
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Term
| Draw a thermal conductivity detector |
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Definition
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Term
| Describe thermal conductivity detector |
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Definition
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 |
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Term
| Draw electron capture detector |
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Definition
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Term
| Describe electron capture detector |
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Definition
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 |
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Term
| Write out the b-emission process of an ECD. |
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Definition
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Term
| Describe the principle operation of the thermal conductivity detector |
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Definition
| based on the decrease in thermal conductivity of the helium or hydrogen carrier gas brought about by analyte molecules |
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Term
| Describe the principle operation of the flame ionization detector |
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Definition
| 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 |
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Term
| Describe the principle operation of the electron capture detector |
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Definition
| 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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