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- Posts: 4
- Joined: Mon Jan 14, 2019 7:45 pm
I am seeing very persistent carry over from my terpenes. No matter how many blanks I run or how many components we clean and replace, the carry over returns and stays. I have seen the carry over both using the Tekmar Headspace autosampler as well as just the GC. Here is my configuration and all of the maintenance performed to attempt to remove source of carry over:
Tekmar HT3 Headspace Autosampler
1 mL loop
Agilent 6890 GC with FID
Parameters:
h2 flow: 3.0 mL/min
split injection 25:1
GC oven hold at the end of ramp 5 min @ 310C
Our team performed thorough cleaning and maintenance this week to try to prevent the system from consistently experiencing buildup of the terpenes. I figured there must be a cold spot on the headspace side so I took my IR thermometer and looked for cold spots. I insulated the transfer line and ran at 300C. Upon confirmation using the thermometer the transfer line was staying sufficiently hot, as were all other components.
I flushed the transfer line with methanol, flushed the 8-port valve system on the Tekmar with hexanes, acetone, and methanol. I replaced the septum, gold seal, inlet liner, and column. I removed the split vent carbon filter and bypassed it ( we didn't have a new one in house). I cleaned the inlet thoroughly using methanol on a cotton swab.
I performed a manual injection directly into the injection port of the GC of a terpene standard and then ran a blank and saw no carry over. Then I ran a 25 ppm terpene standard on the Tekmar and the peaks were tailing and broad. I ran a second 25 ppm terpene standard on the Tekmar and the chromatogram appeared the same. I ran an instrument blank (no vial) on the Tekmar and saw carry over of the entire chromatogram. I also ran two blanks on the GC only and saw the same carry over.
I replaced the column and baked at 300C for one hour. I ran a blank on the GC only and saw the carry over on the brand new column. I ran a second blank on the GC only and see remnants of carry over. It is to note that the carry over is at the same retention time as the standards and if I change the method for a faster ramp or higher flow rate the carry over peaks do elute sooner.
Does anyone know of any solutions to attempt? I am not sure what else can be done at this point.
Thanks,
Taylor