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

3. 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

4. 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

5. 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

6. 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

7. 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)

8. 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

9. 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

10. 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

11. 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

12. 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

15. 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%

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

21. 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

22. 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

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