Multidimensional%20Parallel%20Column%20Gas%20Chromatography

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Multidimensional Parallel Column Gas
Chromatography

• P. M. Owens and D. W. Loehle
• Center for Molecular Sciences
• United States Military Academy
• West Point, NY 10996

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Parallel Column GC Systems

• System 1 System 2
• Precolumns
• 5m, 0.53mm HP1 15m, 0.50mm UAC-1
• Analytical Columns
• 10m, 0.53mm HP1 15m, 0.25mm UAC-1
• 10m, 0.53mm HP17 15m, 0.25mm UAC-17
• 10m, 0.53mm HP20M 15m, 0.25mm UAC-CW

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Retention Time Equations

• tr tm tm k
• tm mobile phase hold-up time
• k partition ratio
• tr tr - tm
• tr adjusted retention time
• k (tr - tm) / tm tr / tm

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Parallel Column Retention EquationsSingle
analyte 3 columns w / diff. stationary phases
(SP)

• tr (SP1) tm tm k (SP1)
• tr (SP2) tm tm k (SP2)
• tr (SP3) tm tm k (SP3)
• The ks result from specific solute-stationary
  phase interactions and can therefore be used for
  solute identification

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Retention Time Calibration

• Day 1 tIS (1) tm1 tm1 kIS
• Day 1 tAN (1) tm1 tm1 kAN
• Day 2 tIS (2) tm2 F tm2 kIS
• Day 2 tAN (2) tm2 F tm2 kAN
• F corrects for changes in k

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Retention Time Adjustment

• tAN (2) / tIS (2) tAN (1) / tIS (1)
• ( t tr - tm )
• Accounts for variations in tms
• Accounts for linear variations in k (F factor)

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Relative Retention (a) Libraries

• a A, IS tA (2) / tIS(2) tA (1) /
  tIS (1)
• Generate GC library to tabulate as for each
  compound on all stationary phases
• Run int. std. with all analyte library runs
• Since as are T-dependent, run all samples with
  identical temperature programs

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Search Algorithms

• Sum of a differences
• Hit Metric S (aAN - aLIB )
• SP
• Euclidean distance
• Hit Metric 1- S (aN, AN aN, LIB )
• SP
• aN, AN and aN, LIB are normalized vectors from
  set of as for each compound

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Search Results

• HP20M HP17 HP1
• Sum of a differences
• Cyclooctane 1.85 1.77 1.46
• Cyclooctadiene 1.93 1.93 1.49
• 1-Heptanol 1.84 1.84 1.58
• Euclidean Search
• Cyclooctane 1.85 1.77 1.46
• Nonanoic Acid 3.05 2.87 2.46
• Octanoic Acid 2.71 2.57 2.19

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Chromatography Relations

• KD k b
• KD Distribution constant
• k Partition ratio
• b Phase ratio (Vg / Vs )
• KD depends on three variables 1) temperature,
  2) solute, 3) stationary phase

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Retention Thermodynamics

• KD k b DG -RT ln KD
• tr tm tm k DG DH - T DS
• ln k ln b -DH / R T DS / R
• ln k - DH / R (1 / T) DS / R - ln b

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Retention Prediction Errors (CV)Prediction Used
T-progs of 8oC/min 15oC/min

• Sample (C7-C11) 12 C/min 20 C/min
• Alkanes (C8-C16) 0.27 0.51
• Halogenated 0.38 0.87
• Ketones 0.56 0.59
• Aldehydes 0.61 0.62
• Alkanes (C9-C15) 0.33 0.45

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Library Compounds
Predict Retention for Analyte GC conditions
Predict Analyte Retention under Lib. GC
Conditions
Single Analyte Chromatogram
X
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Parallel Column Gas Chromatography

• Measures interaction on multiple stationary
  phases - a separate dimension of analyte
  information
• Requires the use of internal standards to
  characterize GC operating conditions
• Thermodynamic modeling allows adjustment of
  library retentions to current operating conditions

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Future Areas of Focus

• Interinstrument variability assessment
• Development of calibration procedures to minimize
  retention prediction errors
• Optimization of stationary phase selection
• Evaluation of an increased number of parallel
  columns
• Application for complex mixture analysis

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Acknowledgements

• Association of Graduates and Army Research Office
• Beverly S. Scott Rodney S. Gonzalez
• Tony Weaver
• Department of Chemistry, USMA