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- Posts: 2
- Joined: Thu Oct 31, 2019 12:36 pm
For my internship i'm validating a GCMS method for the analysis of PAH and PCB in construction materials. The method in question is already being employed for soil samples.
Im using an Agilent 7890B in solvent vent mode with a 5190-2297 2mm splitless liner. The original method i'm supposed to validate uses an injection volume of 3 uL, the extraction solvent used is petroleum ether. According to solvent expansion calculations this volume would cause significant backflash. My question is: does the use of solvent vent mode allow for a larger expansion volume or does the liner volume set the limit for this? It's strange to me that they have 9 GCMS' running this method if the injection volume would surely cause backflash.
Now to continue my story, i accidentally used an injection volume of 6 uL for a control sample, i'm pretty sure this did in fact cause backflash. Ever since all my petroleum ether blanks show 3 peaks that are very constant in terms of retention time but vary in height and area. I have baked out the oven at 300 C several times and replaced the liner, septa and cleaned the inlet. This eliminated one peak which i believe to be naphtalene (m/z 128). two peaks remain with m/z values (257 & 285) that don't correspond to any of my analytes. Aside from these peaks the most abundant m/z values are 207 and 281, which are common for column bleed and septum contamination.
Since the retention times are so reproducable i think the contamination might be coming from the gas inlets due to backflash or the needle (which i don't think is likely with all the washing steps used). I'm hoping anyone has a clue as to what else could be the source of contamination. But mostly i would like to know how to go about cleaning the inlet and carrier gas lines in case of backflash.