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The Promise of True Peak Capacity Increase GCxGC Realized

  • Jack Cochran
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I mentioned in my last ChromaBLOGraphy post, Phthalate-Free Personal Care Products?, that we used GCxGC-TOFMS to determine phthalates in a Las Vegas Wash water sample.  While it doesn’t dive into specific compound identification, we recently published the first demonstration of a near theoretical maximum peak capacity gain for GCxGC (approximately 9x) in an open access Journal of Chromatography A article using that Las Vegas Wash sample extract.  You can download the paper for free (click on Download PDF after clicking on the link above).  An excerpt from our article is shown below to indicate the significance of the peak capacity increase.

“To put the potential peak capacity gain of GCxGC in perspective relative to 1D GC, consider the following. Peak capacity of an open tubular capillary column is proportional to L/dc where dc and L are the column internal diameter (i.d.) and length. A range of typical low and high efficiency columns in lab GCs might span from a 15 m × 0.32 mm to a 40 m × 0.10 mm capillary column.  The relative difference in peak capacities between these two columns is approximately 3.  Compare this entire range of 1D peak capacities with the fact that GCxGC has the potential to achieve a 10-fold or larger peak capacity gain in the same time frame.  For comparison, what would it take in terms of analysis time and resources to obtain a 10-fold peak capacity gain by simply increasing the length of a 40 m × 0.10 mm column in 1D GC analysis?  It would require a 100-times longer column (4 km instead of  40 m), 10-times higher inlet pressure (about 100 atm instead of about 10 atm for helium), and the analysis time would be 1000 times longer (1.5 months instead of 1 h or so for helium). Even an incremental 2-fold peak capacity increase would be beyond currently available 1D resources (requiring a 160 m long column, 20 atm inlet pressure, and unacceptable 8-h or longer analysis for helium).

The peak capacity of a 1D separation can also be increased by reducing the column diameter. However, this also comes with significant difficulties. Thus, doubling the peak capacity of GC–MS without changing the analysis time requires 8-fold narrower columns (12.5 µm i.d. instead of 100 µm i.d.), which leads to a 100-fold larger (worse) minimum detectable concentration (MDC) (minimum analyte concentration), a 16-fold higher pressure, etc.

These considerations highlight the significance of a 10-fold or larger peak capacity increase potentially available from GCxGC without the time increase and worsening MDC.”

JOCA Peak Capacity Article