Our lab has recently been developing a method for the analysis of fluorocarbons on an Agilent 7890 GC-uECD, and we have hit a snag. I will preface by saying the instrument is used, and the detector is at least 8 years old. Our method is using a DB-5, 30m x 0.25um x 0.25mm column with Helium carrier gas at 1.2 mL/min. The oven ramps up to 325C. The detector temperature is stable at 325C across the run with 30 mL/min N2 makeup gas. The front inlet is an SSL, using a 2-uL pulsed splitless injection at 250C under 30 psi with a single-tapered, glass wool plugged liner (effective volume is 493 uL).
We are having trouble with sensitivity of the fluorine-based compounds. Agilent and other websites I have seen, list the relative response range for poly-F compounds (our primary analytes of interest) at 10^6 Hz. We are currently either seeing zero signal, or signal that we believe to be due to the other, weaker, electronegative functional groups (such as acrylates in a 10:2 FTAC and sulfonamides in N-methyl and N-ethyl FOSAs) on the molecule, based on cross reference GC-MS identification using the same method parameters. All mono, di, tri, and poly-brominated, chlorinated, and iodinated compounds we have run seem to show up with strong signal, near the response range listed by Agilent for their uECD, per electronegative, halide class.
We have tried changing multiple method parameters, such as replacing the type of column, carrier gas, multiple temperature changes in different locations (inlet, detector, oven), as well as replacing multiple consumables in the Inlet, Oven, and Detector that could be causing signal suppression of specific analyte groups, and replaced the lot of 99.9% purity gases. We have tried multiple different fluorine-based, volatile analytes with little to no improvement. Any ideas or thoughts would be appreciated as we attempt to navigate this crossroads.