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mately 250 compounds were measured on a squalane stationary phase at four
temperatures.1 From these data one can identify numerous reversals in elution
order of aliphatic and cyclic hydrocarbons. The solute interactions with a
squalane stationary phase, the most nonpolar stationary phase one can use,
are largely a result of dispersion interactions. The authors stated that the mag-
nitude of temperature variation is a function of the size of the molecule
expressed by the cross-sectional area of the molecules, which should also
prove my point in my next discussion over coffee with my former student.
Finally, coming back to our first example in Part 1, both components not only
show different functional groups, they also differ in their carbon skeleton
(Figure 3). Linalool is an aliphatic alcohol and camphor is a bi-cyclic ketone,
which means that not only the functional groups but also the difference in
molecular geometry will contribute to the cross-over phenomenon.
What can we learn from this discussion? Peak overlapping and cross-over in
peak elution order caused by variation of column temperature or temperature
programming rate can occur not only on polar stationary phases for com-
pounds with different functional groups but also on nonpolar or weak polar
stationary phases for compounds that differ in their carbon skeleton. The ana-
lyst should, therefore, carefully examine the structure of the compounds to be
separated if the information is available. Furthermore, it is recommended to
study analyte retention carefully at various temperatures for difficult separa-
tions as an important aspect of method optimization.
References:
1 Hively, R.A. and R.E. Hinton, J. Gas Chromatogr. 6 (1968) 203 – 217.
Retention Cross-over Phenomenon
inGas Chromatography—Can the
Mystery be Revealed? Part 2
Continued from page 2
Figure 2 Retention indices on squalane (IS) as a function of Tc for
isothermal GC at 27°C, 49°C, 67°C, and 86°C.1
TMP Trimethylpentane ECP Ethylcyclopentane
MCH Methylcyclohexane DMH Dimethylhexane
IS
Camphor (bp.: 209°C)
Figure 3 Functional groups influence elution order.
Linalool (bp.: 199°C)
Tradeshow Schedule
We’d be happy to talk with you at any of the
following meetings or shows. We’ll post our booth numbers
as they become available to us.
September, 2007
Date September 2-7
Show Dioxin 2007
Location Hotel Okura, Tokyo
Date September 13
Show New Jersey Mass Spectrometry Discussion
Group Annual Vendor Show
Location DoubleTree Hotel, Somerset, NJ
Date September 16-20
Show AOAC International 121st Annual Meeting &
Expo
Location Hyatt Regency Orange County, Anaheim, CA
Date September 25-28
Show Midwestern Association of Forensic Scientists
(MAFS)
Location Park Place Hotel, Traverse City, MI
Date September 26-28
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Location Providence, RI
October, 2007
Date October 2-4
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Date October 10-12
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Date October 13-20
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Location Chapel Hill, NC
Date October 16-17
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Galveston, TX
Date October 18-21
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Instrument Analysis
Location Beijing Exhibition Center,
Beijing, China, Booth #00
Date October 30-November 1
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Location Javits Convention Center,
New York, NY
Date October 30-November 2
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Location Las Vegas Convention Center,
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Date October 31-November 3
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November, 2007
Date November 1
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Location Burton Manor,
27777 Schoolcraft Road, Livonia, MI
Date November 7-9
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Recent Advances in Food Analysis
Location Diplomat Hotel–Conference Center,
Prague, Czech Republic
Date November 11-15
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Location Garden State Convention & Exhibit
Center, Somerset, NJ
Date November 11-15
Show 2007 AAPS Annual Meeting and Exposition
Location San Diego Convention Center, San Diego, CA
Date November 28-30
Show 31st Int'l Symposium on Capillary
Chromatography & Electrophoresis
Location Hotel Albuquerque, Albuquerque, NM
For latest updates, see our Tradeshow Calendar
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