Chromatography Forum

Made the swich from Helium to generated H2 on an Agilent 6890N/5973N and have lost almost all sensitivity.

Here's what I've looked at:

- Changed column from 30m DB-1 w/ 250um diameter, 0.25um film thickness
to 20m DB-1 w/ 180um diameter, 0.18um film thickness.
- Have good moisture, O2, N2 filtration
- Tunes to PFTBA are equivalent to or better than with Helium
- Cleaned source, repeller, and lenses
- Changed column and carrier gas type in ChemStation
- Right now it's set at 1 mL/min initial flow, 69 cm/sec average velocity, and 15 psi initial pressure, but I have tried running
at 0.5-0.7 mL/min flows that bumped the velocity down around 40-45 cm/sec. It lowered the baseline, but no improvement
in sensitivity.

We run some known mixtures monthly and after service to evaluate the performance of the instrument. On this particular instrument the abundances of the mixtures come out around 4-4.5 million. After the conversion, I get a broad bump for one of the peaks in the mixture and it's only 5k above the baseline, ~15-20k abundance total. I don't even see the other peaks in the TIC.

I'm not sure where to go from here. From some searching I've seen people suggest a different drawout plate in the source. Any recommendations or more info needed?

Thanks!
Dan

Agilent has recommended hardware configuration changes on their newer 7890/5975 systems that include the larger drawout. Not sure what the verdict is on a 5973.

What kind of split are you using and what kind of compounds are you looking at?

1 ml / minute of hydrogen may be more than the turbopump can handle. Does it have an inert source?
Agilent has some information available about what they have done to make the 5975 work with hydrogen on their website. There is also a Webinar from Thermo on the conversion as well as an Agilent Webinar hosted on the C&EN website.

I have been testing Hydrogen carrier on one of my 5973/6890 systems with purge and trap. So far the only problem I have had is hitting the BFB tuning criteria for m/z 95 and m/z 96 ratios where the limit is 5-9% and I can not get m/z 96 below 18% of m/z 95. Other than that it works pretty well.

From the Thermo webinar the suggestion is to not use any copper tubing if possible, though I did plumb mine with copper, but if you use copper always use new tubing, never recycle what was used with Helium. It seems Hydrogen cleans the copper and will slowly draw out any gasses and contaminates that were adsorbed on the copper, that could be causing some of your problems. Hydrogen will also clean your whole system and I found you need to let it go several days before all the background comes down and your signal to noise will improve.

I believe the 73 and 75 EI sources are the same so get the larger opening drawout plate for H2. Agilent also has a seminar available on their website on demand. They also recommend a conditioning protocol which consists I believe of leaving the filament on all night.

Yep I am in the process of switching my H2 line (for the FID and FPD) to steel. The copper lines it was running for years look dull and brittle.

I have gotten the 96/95 ratio to pass, but it was under different conditions than what I run my normal samples at. I can still get it to pass under those circumstances, but it is definitely hit or miss (mostly miss) when using hydrogen and hovers around 10%.

I have gotten the 96/95 ratio to pass, but it was under different conditions than what I run my normal samples at. I can still get it to pass under those circumstances, but it is definitely hit or miss (mostly miss) when using hydrogen and hovers around 10%.

Did you alter source temps possibly? I have been adjusting it lower but haven't hit the sweet spot yet to get the BFB to pass.

I have sent an email to EST to see what they are doing concerning this since they do some custom work on Agilent sources. I asked them if anyone has tried making extra vents in the ion chamber to help remove the excess hydrogen. Also spoke with one of Agilent's service engineers and we discussed using the CI valves to inject a small amount of He or N2 into the source to see if that helped but I can't seem to get any time that our one instrument with the CI setup is free to experiment with.

We are using the volatiles package (higher temps, 6mm drawout, etc.). I have been able to get it to pass without messing with the tune at all, just the GC and MS parameters.

We are using the volatiles package (higher temps, 6mm drawout, etc.). I have been able to get it to pass without messing with the tune at all, just the GC and MS parameters.

I went with the larger drawout, but was lowering my source temps, maybe I should increase it. We normally run 230C with He, never went much higher as I lost sensitivity and had more noise. I will give it a try though once I can switch back to H2.

Sorry, I dropped off the face of the Earth for a while. We had strep throat and Flu run though everyone in the house over the past week and a half. I'll try to hit all the questions in order.

- Running splitless and we analyze controlled substances, i.e. cocaine, heroin, pharmaceuticals.
- 1 mL/min probably is too much as I don't have a turbo pump, this unit has a diffusion pump.
- According to Agilent all the 5973 models have inert sources, that was only an issue with the 5975.
- I did use copper lines, but I used new "cleaned" copper tubing. Fortunately the tuning criteria for our work is pretty relaxed as we're only concerned with a qualitative identification of the substance.


I also spoke with Agilent and they emailed the power point of the 5973/5975 Conversion that a lot of you have mentioned. The body of the email wasn't very comforting. It basically said do everything in this power point and if you can't get a good tune we recommend you switch back to Helium. Uh, thanks I guess?

I went ahead an ordered the 6mm drawout plate and I guess I'll see where that puts me. Thanks for your help and I'll let you know if the drawout plate gives me improvement.

I will be presenting a poster on this subject at Pittcon this year, which is why I am a little hesitent on providing too many details until then. We have shown plausibility, but something will need to change as the methods themselves don't even allow for hydrogen carrier gas at this point, although I know it is on EPA's radar.

Nathan,
Should this be on EPA - OSWER radar? SW-846 is undergoing an update cycle and this is a question that has come up. In your opinion is there enough information out there to put some language in 8260 and 8270 about hydrogen as a carrier gas?

I've heard that it will be looked at in the next set of method updates for the ones you bring up. Our goal was to be proactive as there are other implications on our instrumentation that we need to examine as well that aren't necessarily addressed in the methods themselves.

It is being looked at but so far I haven't seen anything specific to include that won't be outdated within a year or two.