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

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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

Parallel Column GC Systems System 1System 2 Precolumns 5m, 0.53mm HP115m, 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

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

Parallel Column Retention Equations Single analyte & 3 columns w / diff. stationary phases (SP) t r (SP1) = t m + t m k (SP1) t r (SP2) = t m + t m k (SP2) t r (SP3) = t m + t m k (SP3) The k’s result from specific solute- stationary phase interactions and can therefore be used for solute identification

Retention Time Calibration Day 1 t IS (1)= t m1 + t m1 k IS Day 1 t AN (1) = t m1 + t m1 k AN Day 2 t IS (2)= t m2 + F * t m2 k IS Day 2 t AN (2) = t m2 + F * t m2 k AN F corrects for changes in k

Retention Time Adjustment t’ AN (2) / t’ IS (2) = t’ AN (1) / t’ IS (1) ( t’ = t r - t m ) Accounts for variations in t m ’s Accounts for linear variations in k (F factor)

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

Search Algorithms Sum of  differences Hit Metric =  (    LIB ) SP Euclidean distance Hit Metric = [1-  (    N, LIB )] SP   and  N, LIB are normalized vectors from set of  ’s for each compound

Search Results HP20MHP17HP1 Sum of  differences Cyclooctane1.851.771.46 Cyclooctadiene1.931.931.49 1-Heptanol1.841.841.58 Euclidean Search Cyclooctane1.851.771.46 Nonanoic Acid3.052.872.46 Octanoic Acid2.712.572.19

Chromatography Relations K D = k  K D = Distribution constant k = Partition ratio  =Phase ratio (Vg / Vs ) K D depends on three variables: 1) temperature, 2) solute, & 3) stationary phase

Retention & Thermodynamics K D = k  G = -RT ln K D t r = t m + t m k  G =  H - T  S ln k + ln  = -  H / R T +  S / R ln k = -  H / R (1 / T) +  S / R - ln 

Retention Prediction Errors (CV) Prediction Used T-progs of 8 o C/min & 15 o C/min Sample (C7-C11)12 C/min 20 C/min Alkanes (C8-C16)0.27%0.51% Halogenated0.38%0.87% Ketones 0.56%0.59% Aldehydes0.61%0.62% Alkanes (C9-C15)0.33%0.45%

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

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

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

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

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