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Multidimensional Parallel Column Gas Chromatography

Multidimensional Parallel Column Gas Chromatography. P. M. Owens and D. W. Loehle Center for Molecular Sciences United States Military Academy West Point, NY 10996. Parallel Column GC Systems. System 1 System 2 Precolumns 5m, 0.53mm HP1 15m, 0.50mm UAC-1 Analytical Columns

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Multidimensional Parallel Column Gas Chromatography

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  1. Multidimensional Parallel Column Gas Chromatography P. M. Owens and D. W. Loehle Center for Molecular Sciences United States Military Academy West Point, NY 10996

  2. 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

  3. Retention Time Equations tr = tm + tm k tm = mobile phase hold-up time k = partition ratio t’r = tr - tm t’r = adjusted retention time k = (tr - tm) / tm = t’r / tm

  4. 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 k’s result from specific solute-stationary phase interactions and can therefore be used for solute identification

  5. 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

  6. Retention Time Adjustment t’AN (2) / t’IS (2) = t’AN (1) / t’IS (1) ( t’ = tr - tm ) Accounts for variations in tm’s Accounts for linear variations in k (F factor)

  7. Relative Retention (a) Libraries aA, IS = t’A (2) / t’IS(2) = t’A (1) / t’IS (1) • Generate GC library to tabulate a’s for each compound on all stationary phases • Run int. std. with all analyte & library runs • Since a’s are T-dependent, run all samples with identical temperature programs

  8. 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 a’s for each compound

  9. 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

  10. 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

  11. 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

  12. 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%

  13. Library Compounds Predict Retention for Analyte GC conditions Single Analyte Chromatogram Predict Analyte Retention under Lib. GC Conditions X

  14. 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

  15. 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

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

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