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2-D Gas Chromatography (or 3D with MS Detector). A powerful separations tool for complex volatile mixtures of heat-stable samples [information shamelessly taken from Wikipedia and other sources – see last slide]. History. Comprehensive 2-D gas chromatography (GC) (abbreviated GC X GC)

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2 d gas chromatography or 3d with ms detector

2-D Gas Chromatography (or 3D with MS Detector)

A powerful separations tool for complex

volatile mixtures of heat-stable samples

[information shamelessly taken from

Wikipedia

and

other sources – see last slide]

Wilkes University - CHM 341

history
History
  • Comprehensive 2-D gas chromatography (GC)
    • (abbreviated GC X GC)
    • a mature technique with commercial products on the market
    • technique has tremendous separation power
    • uses simple robust hardware
    • similar analysis times to temperature-programmed high-resolution capillary chromatography
  • Comprehensive 2-D LC (LC X LC)
    • still in its infancy
    • more complex to perform
    • driven by user needs, especially in proteomics
the concept
The Concept
  • additional physico-chemical criterion employed for the separation of the mixture of analytes (sample)
    • resolution and quality of chromatographic separation can be increased
    • higher specifity of the separation capability is obtained
    • separation of compounds indistinguishable by 1-D chromatography
  • Gas-Phase Chromatography, 2-D [an illustrative example]
    • coupling a second, short column to the first long column
    • shock-freeze eluents in order of elution from the 1st column
    • reheat them in order of elution for release into the 2nd column
    • transit time through the 2nd column needs to be shorter than the time until the next sample is reheated & released
  • Gas-Phase Chromatography, 2-D [an illustrative example]
    • one column is used to separate analytes
    • followed by Time-of-Flight Mass Spectrometer (TOFMS) detection as the second dimension
    • TOF-Mass Spectrometers used in gas chromatography can be very short

[ due to the limited range of m/z required]

the instrument requirements
The Instrument Requirements
  • two pieces of hardware are added to a conventional GC
    • a second column
    • an interface between the second column and the first (the modulator)
  • the time for analysis on the second column is very fast (short column)
  • the interface repetitively samples the effluent from the first column, and injects it onto the second
the instrument requirements6
The Instrument Requirements
  • Rt on the two columns may be thought of as lyingperpendicular to one another
  • 2nd column stationary phase different from the 1st
    • retention mechanism different from that of the 1st
    • retention mechanism are “uncorrelated”, “independent”, or “orthogonal”
    • molecules are separated on the basis of independent chemical properties in the 1st and 2nd columns
      • Ex. 1st column separates based on the basis of “molecular size” (volatility/b.p.)
      • 2nd column separates on the basis of polarity
        • the molecular property “polarity” is largely independent of the molecular property “size,” or volatility
        • Polar funct. groups can be attached to compounds of any size
the instrument requirements7
The Instrument Requirements
  • Modulator performs 3 tasks (in repetitive cycle):
    • accumulates sample eluting from 1st column
      • period of time equal to 1/3 to 1/5, of the duration of an individual peak from the first column
      • Ex. a first column peak is 9 seconds wide at the base: modulator will accumulate material every 2 (or 3) seconds, thereby “chopping” the peak eluting from the first column into “cuts”
    • focuses the material collected from each cut into a narrow “band”, “plug”, or “chemical pulse”.
      • by flash-freezing (with, for ex., a cold jet of CO2)
    • “launches” or injects the sharp chemical pulses sequentially onto the second column
      • a series of high speed gas chromatographic separations occur
      • one separation for each chemical pulse launched onto the second column
data interpretation
Data interpretation
  • each vertical column of the image may be integrated and plotted as a function of 1st column elution time
    • the conventional gas chromatogram, or “first-dimension chromatogram,” appears
  • scanning downward from each “peak” in the first dimension chromatogram, one can count the number of coeluents,
    • visible as discernable second-dimension peaks, of which the conventional one-dimensional peak actually consists
data interpretation10
Data interpretation
  • Most of the colored spots -- the chromatographic peaks -- in images such as Figure 4 (above) are believed to represent one, or a very few, of the chemical species present in the sample.
  • In the case of the diesel oil appearing in Figure 4, some 5,000 peaks are discernable.
  • Even with this very high peak count, co-elutions still occur at the higher carbon number region on the right hand side of the image. Nonetheless, valuable information is still available from rich and chemically significant peak patterns.
  • In the example of Figure 4, chemical classes are clearly visible.
  • Column bleed products eluting from the first column are also clearly distinguishable from the sample matrix.
  • Diagonal sub-bands appear throughout the chromatogram, corresponding to groups of isomers – the so-called “roof-tile” effect.
data interpretation the 3 rd d13
Data interpretation – the 3rd D
  • Liver – Drug induced damage
for more info
For more info . . .
  • Visit Zoex Corporation for info taken from their technical note http://www.zoex.com/technote_kt030505-1.html
  • LECO Corporation – product flyer PegasusHT

http://www.leco.com/products/sep_sci/pegasus_ht/pegasus_ht.htm

  • LECO Corporation – technical notes

http://www.leco.com/resources/application_note_subs/separation_science_application_notes.htm

  • Visit this site for info on comprehenisive LCxLC

http://www.chromatographyonline.com/lcgc/article/articleDetail.jsp?id=187969