{"id":76447,"date":"2014-12-07T00:00:00","date_gmt":"2014-12-07T00:00:00","guid":{"rendered":"https:\/\/discover.restek.com\/?p=76447"},"modified":"2025-12-26T19:50:54","modified_gmt":"2025-12-26T19:50:54","slug":"peak-capacity-in-capillary-gc","status":"publish","type":"post","link":"https:\/\/discover.restek.com\/ja\/blogs\/gnbl5524\/peak-capacity-in-capillary-gc","title":{"rendered":"Peak Capacity in Capillary GC"},"content":{"rendered":"\n

Peak Capacity<\/em> in capillary gas chromatography is different than sample loading capacity<\/em>, which is something I\u2019ve posted on multiple times recently in ChromaBLOGraphy.  Peak capacity is simply the number of theoretical peaks that can \u201cfit\u201d inside a chromatogram under some definition of how much they should be separated (e.g. baseline resolved or some other criterion).  While peak capacity is something we like to maximize in GC, it always comes at the cost of speed of analysis.<\/p>\n\n\n\n

I did some experiments to define peak capacities on a 30m x 0.25mm x 0.25\u00b5m Rxi-5ms using hydrogen carrier gas under efficiency-optimized flow (EOF), speed-optimized flow (SOF), and optimal heating rate conditions, and then filled in spaces between and outside-of those starting points.  I analyzed SV Calibration Mix #5, a polycyclic aromatic hydrocarbon (PAH) standard, with split injection \u2013 GC-FID.  This standard includes 16 PAHs across a wide volatility\/elution range from naphthalene to benzo[ghi]perylene.  Split injection via a Precision split liner with wool minimizes injection band widths, which is critical to estimating peak capacity based on the column<\/em> conditions.<\/p>\n\n\n\n

As you can see from the graph below, peak capacity plateaus in the range of 1.3 to 2.5 mL\/min hydrogen carrier gas under the imposed criterion of using an optimal heating rate (OHR) of 10\u00b0C divided by the holdup time in min.   Importantly, using SOF with an OHR drops the analysis time substantially without a huge loss in peak capacity.<\/p>\n\n\n\n

The Performance Measurements<\/em> table shows that resolution between PAH isomers benzo[b]fluoranthene and benzo[k]fluoranthene holds up well for EOF and SOF conditions.  Not surprisingly, as faster column flow and heating conditions are used, signal-to-noise is better for analyzed components.<\/p>\n\n\n\n

In summary, if you are looking to maximize the number of peaks you can put in a chromatogram, while simultaneously paying attention to speed of analysis and detectability, give EOF and SOF and OHR a try.  These are great concepts as method development starting points.  Use the EZ<\/em>GC Method Translator and Flow Calculator to help with holdup time and other considerations.<\/p>\n\n\n\n

Finally, don\u2019t forget stationary phase selectivity, which is the most important parameter for separating specific<\/em> components.  But we\u2019ll get back to that in a later post\u2026<\/p>\n\n\n\n

Theory of Fast Capillary Gas Chromatography \u2013 Part 3: Column Performance vs. Gas Flow Rate Leonid M. Blumberg Journal of High Resolution Chromatography  \u2013 1999, 22, (7) 403-413<\/p>\n\n\n\n

Optimal Heating Rate in Gas Chromatography L.M. Blumberg and M.S. Klee Journal of Microcolumn Separations \u2013 2000, 12 (9), 508-514<\/p>\n\n\n\n

Plate Height Formula Widely Accepted in GC is Not Correct Leonid M. Blumberg Journal of Chromatography A \u2013 2011, 1218, 8722-8723<\/p>\n\n\n\n

Temperature-Programmed Gas Chromatography Leonid M. Blumberg Wiley-VCH Verlag & Co. – 2010<\/p>\n\n\n