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

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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

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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

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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

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The Instrument - Background
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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

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The Instrument Requirements

• Rt on the two columns may be thought of as lying
  perpendicular 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

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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

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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

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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.

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Data interpretation the 3rd D
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Data interpretation the 3rd D
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Data interpretation the 3rd D

• Liver Drug induced damage

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Data interpretation the 3rd D
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Data interpretation the 3rd D
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For more info . . .

• Visit Zoex Corporation for info taken from their
  technical note http//www.zoex.com/technote_kt0305
  05-1.html
• LECO Corporation product flyer PegasusHT
• http//www.leco.com/products/sep_sci/pegasus_ht/pe
  gasus_ht.htm
• LECO Corporation technical notes
• http//www.leco.com/resources/application_note_sub
  s/separation_science_application_notes.htm
• Visit this site for info on comprehenisive LCxLC
• http//www.chromatographyonline.com/lcgc/article/a
  rticleDetail.jsp?id187969