Multidimensional Parallel Column Gas Chromatography
P. M. Owens and D. W. Loehle
Center for Molecular Sciences
United States Military Academy
West Point, NY 10996
Figure 1. Multidimensional parallel column GC system
GC OVEN
Precolumn
ColumnsAnalytical
Polar SP
Semipolar SP
Nonpolar SP
SwitchDean's
DetectorAnalytical
DetectorMonitor
Injector
using nonpolar, semipolar and polar stationary phases (SP).
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
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
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
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
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)
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 ResultsHP20M HP17 HP1
• Sum of 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
Chromatography Relations
KD = k KD = Distribution constant
k = Partition ratio
= Phase ratio (Vg / Vs )
KD depends on three variables: 1) temperature, 2) solute, & 3) stationary phase
Retention & Thermodynamics
KD = k G = -RT ln KD
tr = tm + tm k G = H - T S
ln k + ln = -H / R T + S / R
ln k = - H / R (1 / T) + S / R - ln
-0.1
-0.05
0
0.05
0.1
RE
TE
NT
ION
TIM
E E
RR
OR
(M
IN)
C8 C10 C12 C14 C16COMPOUND
HP20M HP17 HP1
ERRORS IN PREDICTED RETENTION TIMEST PROG OF 12/MIN FROM 15/MIN & 8/MIN
-0.1
-0.05
0
0.05
0.1
RE
TE
NT
ION
TIM
E E
RR
OR
(M
IN)
C8 C10 C12 C14 C16COMPOUND
HP20M HP17 HP1
ERRORS IN PREDICTED RETENTION TIMEST PROG OF 20/MIN FROM 15/MIN & 8/MIN
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%
-0.2
0
0.2
RE
TE
NT
ION
TIM
E E
RR
OR
(M
IN)
C8 C7CL C8CL C9CLC10CLC11BR C16COMPOUND
HP20M HP17 HP1
ERRORS IN PREDICTED RETENTION TIMEST PROG OF 12/MIN FROM 15/MIN & 8/MIN
-0.2
0
0.2 R
ET
EN
TIO
N T
IME
ER
RO
R (
MIN
)
C8 C7AL C8AL C9AL C10AL C16COMPOUND
HP20MHP17HP1
ERRORS IN PREDICTED RETENTION TIMEST PROG OF 20/MIN FROM 15/MIN & 8/MIN
-0.1
0.1
Tr D
IFF
ER
EN
CE
(m
in)
6 8 10 12 14 16 18 20
HP20MHP17 HP1
Tr Variation on GC Stationary PhasesFOR GC RUNS 30 DAYS APART
900
1000
1100
1200
1300
1400
1500 T-P
RO
GR
AM
ME
D R
ET
IN
DE
X
C7CL C8CL C9CL C10CL C11BR
GC1-20M GC1-DB17 GC1-DB1
GC2-20M GC2-DB17 GC2-DB1
RETENTION INDICES FROM 2 INSTRUMENTSWITH .25mm & .53mm DB1/17/20M COLUMNS
LibraryCompounds
Predict Retention for Analyte
GC conditions
Predict AnalyteRetention under
Lib. GC Conditions
Single AnalyteChromatogramX
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