Low Response on ECD

[terryy]

I am attempting to convert our method for halogenated anesthetic gases (Desflurane, Sevoflurane, Isoflurane, etc.) from FID to ECD. Using the same column (RTX-Volatiles, 60 m, 0.32mm ID, 1.5 u) and conditions (280 C inj/det. 1 uL split injection 15:1), I get very little to no response from my early eluting compounds. I am doing this on two different instruments, the FID is on the Agilent 5890 w/ 7673 ALS and the ECD is on the Agilent 7890 w/ 7693 ALS. I even tried a concentrated sample of Vinyl Chloride and injected the same vial on the two instruments and I get a much larger response on the FID than I do on the ECD.

I've tried changing the injector parameters and even did a manual injection to eliminate the ALS as the source of the problem but I am stumped. Any ideas or suggestions would be greatly appreciated. Thanks.

[AICMM]

terryv,

I am not surprised by the lack of response for the VC by ECD since it has only one chlorine and does not have a very high electron affinity. This compound is better done by PID. I am a bit surprised by the lack of response for the anasthetics though, especially considering the degree of fluorination. I am further confounded by the fact that perfluoro compounds are used as a derivative to enhance the sensitivity of the ECD ...

Unfortunately, the only suggestion I can offer at this moment is to suggest that you lower the ECD temperature and try again. Sometime cooler is better with the ECD (depending on the capture mechanism) and this may be the case in this situation.

Best regards,

AICMM

[terryy]

Thanks for the suggestion about Vinyl Chloride. I tried a different Freon (Freon-114) and it eluted off the column where I was expecting (nearly un-retained) and it gave me very good response on the ECD. However when I run Desflurane or Sevoflurane, I get nothing but when I inject similar compounds like Enflurane or Isoflurane I get good peak responses. I've tried adjusting the injector and detector temperatures but still get the same results. I just have a hard time imaging what could be wrong with the system for peaks to not even show up. I've done just about everything imaginable with the injector (changed septa, liner, gold seal, syringe, injection speed). Any other suggestions would be appreciated. Thanks.

[AICMM]

terryv,

At first I thought maybe the poor responding components could have been eluting with air and this may suppress the response. However, unless the poor responders elute exactly between F-114 and the enflurane this track may not hold promise. If you think this might be the case, you might try a different column like the Fluorcol... but I am not holding my breath. The other big difference, and you already know this, is that the ones that do respond well have at least one chlorine to their fluorines.

I looked in my literature (briefly) at doped ECD with no success and looked at argon mode photoionization but the IP's are generally too high to be of much use. Potentially a good application for HID (which could replace the FID) but you have to have good separations for this mode to work because air will certainly interfere.

Sorry I could not be of more assistance.

Best regards,

AICMM