A Tale of Two Columns (CLPesticides & CLPesticides2)—Part I: A Little History

Chlorinated pesticides are persistent environmental contaminants commonly analyzed using a variety of GC methods, including US EPA 8081, 608 and 508.  Due to similarities in chemical properties of these pesticides, selectivity must be carefully considered when choosing GC columns.  Historically, columns with phenyl methyl (5% phenyl, 35% phenyl, 50% phenyl columns) and cyanopropyl (1701 column) were recommended; unfortunately, the phenyl methyl stationary phases do not offer the best selectivity for the commonly analyzed pesticides and some coelutions are present.  While the Rtx-1701 offers better selectivity over the phenyl methyl phases, one drawback is a lower maximum programmable temperature.  This allows build-up of less volatile matrix components within the column, both affecting performance and reducing lifetime.  The 1701 columns also may degrade active components, such as DDT and methoxychlor, due to interactions with the stationary phase.

In the late 90’s, as an answer to the aforementioned woes facing analysts, Restek released a pair of proprietary columns known as the CLPesticides and CLPesticides2 columns.  These columns feature excellent selectivity of chlorinated pesticides and complement each other well for dual column analyses.  With the release of the CLPesticides and CLPesticides2 columns, baseline resolution of the standard 8081 method pesticides was now possible and the columns could be operated at higher oven temperatures to ensure “baking out” of contaminants from the dirty extracts typically found in environmental samples.

Upon the initial release of the column pair, one of the marketing claims was the ability to baseline resolve the common method 8081 pesticides in under 24 minutes (Figure 1 and 2), an impressive feat at a time when 50-minute runtimes were common. Since then, fast GC has become a major focal point for many laboratories and a 20+ minute run would no longer be considered acceptable.  After all, time is money!

Figures taken from original Restek marketing literature.

Fortunately, since that time, Restek has optimized methods on these columns to obtain considerably faster run-times.  In the upcoming Part II of this blog series, I will discuss some ways in which faster run times can be achieved.  Parts III and IV of this series will push the pedal even further using Restek’s recently developed GC Accelerator Kit with Agilent GC’s to achieve elution of all compounds in close to 5 minutes with complete instrument cycle times around 10 minutes.  Stay tuned for details...