EPH and PAH testing on GCXGC-FID/MS

Hello Kurram! The Agilent reverse flow modulator does not have limitations on sample volatility and can modulate your molecules of interest. Successfully eluting up to nC44 and 6-ring PAH will require using high temperature columns in both dimensions. I suggest a combination of DB-1ht or DB-5ht for your non-polar dimension, and a DB-17ht for your polar dimension.

The DB-17ht has a maximum programmable temperature of 365 C and will be the limiting factor for your application. You may need to exceed this oven temperature to successfully elute 6-ring PAH and nC44 (depending on your required resolution and runtime). Doing so will slowly decompose the DB-17ht stationary phase and, over time, you will experience increasing retention loss and increased column bleed. The rate of degradation will depend on the cleanliness of your carrier gas and the amount of time the oven spends above 365 C. Based on this, I have three recommendations:

• Use carrier gas filters and be diligent about changing them when they are spent. Oxygen in the carrier gas will greatly accelerate degradation of the stationary phase at elevated temperatures. The 8890 GC has built-in Early Maintenance Feedback (EMF) counters that track the amount of time and/or the number of injections each consumable part of your system has experienced since the last time it was changed. The EMF counters for the gas filters are stored in the “System” section of the “Maintenance” menu on the front panel. You can use this EMF counter to track when the filter was last changed, and the Gas Clean Purification filters also have a visual indicator for the filter health. We also manufacture a sensor that can alert you when the filter is spent (part number CP179885).
• If you must exceed the maximum rated temperature of the DB-17ht, do not hold the oven above that temperature and do not go any further above that temperature than necessary. “Time” and “temperature” are both major contributors toward column lifetime.
• Use a “normal column set” for your GCxGC method where your polar column (DB-17ht) is the second dimension. This will prevent excessive column bleed from entering the modulator, and instead drive it toward the FID. The FID jet is easy to clean or replace if fouled and is inexpensive compared to the modulator.

For Extractable Petroleum Hydrocarbons by GCxGC-FID/MS, the limiting factor will be the mass spectrometer transfer line and the source temperature. You may have short-term success with such a setup, but the temperature limitations of the MS may prevent long-term stability from being achieved for samples with a high final boiling point. Regardless, the above recommendations still apply.

-Scott