Selectivity differences in arylene GC phases...pesticides and zebras.

Although not obvious even to a careful observer, no zebra has exactly the same stripe pattern. Fortunately for GCers, there isn’t that much variation in “5 type” columns, but users need to be aware that 5% pendant phenyl and 5% phenyl-as-silphenylene (or arylene) columns have slightly different selectivities. Recently we analyzed 31 pesticides on Rxi-5ms (pendant phenyl) and Rxi-5Sil MS (silphenylene). While the complete chromatograms looked very similar, close inspection revealed differences (see figure).

Remember that arylene phases have polymer backbone modifications to lower bleed. Restek makes it easy to remember which columns have this modification by using “Sil” in the name (e.g. Rxi-5Sil MS, Rxi-35Sil MS, and Rxi-624Sil MS). If you decide to change from your “standard” GC phase to an arylene phase, watch out for slight selectivity differences.