5890/5971 resurrection

Basic questions from students; resources for projects and reports.

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Hi,

New poster here, with no experience of GC/MS other than some very limited undergrad chemistry over 25 years ago.

About 2 years ago I decided to embark on a completely crazy project to analyse vape eLiquids, due to my personal doubts as to the standards of manufacture.

I purchased a very well used 5890 GC with 5971 MSD in unknown condition pretty cheaply.

Initially, i had to perform a number of repairs to the GC:
1. Missing EPC pressure sensor. I had to obtain a spare to install.
2. EPC valve clogged. I cleaned it and built a test jig to balance the pressure control spring.
3. General clean-up of plumbing.
4. Fitment of an FID to replace the 5971.
5. Assemble a working 7673A robot from various partly defective spares.

The MSD didn't come with a foreline pump- but that was quite straightforward to replace with one i had been using for other vacuum experiments.

I was fairly certain i would never get the 5971 working again. The diffusion pump was incredibly dirty. The manifold had been contaminated with diff pump oil and the MSD had an old SmartCard 1 controller board that would only work with DOS or win31 Chemstation versions.

After cleaning the pump and manifold and having obtained a SmartCard II board at a surprisingly reasonable price I decided on an even crazier project.

After a long and winding course of action I now have the 5971 equipped with a Pfeiffer TPU062 turbo instead of the stock Edwards diff pump, as well as a working ionisation gauge.

Using the turbo pump requires a very minor modification to the 5971a power distribution board to fool the diff pump heater monitor into believing the heater is on whenever the pump controller provides a full RPM signal.

It is working with MSD Chemstation G1701BA under win7(!). Even though this version doesn't officially support the 5971a, the macros can be modified to recognise it. You also need to hand-edit the instrument configuration in win.ini for the 5971 not to be treated as a GCD1800.

Modern Keysight IO Libraries can be used with either an 82350B PCI or 82357A/B USB GPIB interface.

There are also an extremely bizarre config change needed in win7 (make C:\ root directory non-writeable by ordinary users) to make Chemstation load its macros correctly.

If anybody is interested in how to run G1701BA on win7 or any of the above modifications please let me know.

I've managed to perform some basic analyses of terpene mixtures from essential oils as well as a major component analysis of an eLiquid.

I can clearly identify d-limonene and citronellal in the terpenes and propylene glycol, glycerin and nicotine on the eLiquid.

I'd like to embark upon method development for trace component analysis of eLiquids.

I'm not happy with the quality of the chromatograms i am obtaining. Lots of wide and split peaks with the terpenes and trailing peaks on propylene glycol/glycerine with the eLiquid.

I can't justify spending money on new capillary columns until/unless i know the best possible one for my eLiquid method so I obtained a number of used columns.

At the moment, I'm using a CP-WAX 57CB 25m 0.25mm column which should give OK results for eLiquids (it's meant for alcohol analysis) but definitely doesn't work very well for terpenes (too polar I guess).

I'm using H2 as a carrier gas, 1.5ml/min flow, 150:1 split ratio and 5% solutions in methanol for major component analysis.

Do the trailing peaks suggest column overloading? Should i go to 1% solutions instead?

I've seen some suggested method write-ups from Agilent using completely different columns and would like some suggestions of suitable columns for eLiquid analysis.

I currently have an HP-5Ms, a DB-1701 or a HP-35 column available to try as a alternatives.

They're all used and of unknown quality, so i will need to condition them at the very least.

What solvents would you recommend for injecting dilute eLiquid mixtures? I'm currently using methanol but could easily switch to acetone, methylene chloride or ethyl acetate, or maybe n-hexane for the terpenes.

Apologies for the long post,

Dirk
Impressive endeavor! I'd say you're probably more experienced now than most of us who've been doing this for a long time.

Perhaps you should rebuild your inlet as well. That will be much easier than what you have done to get the MS working correctly. Tailing peaks usually means you have some active sites in the transfer of the sample to the column. Put a small amount (not packed tightly) of silanized glass wool in there to increase the surface area for vaporizing the solvent. Also, ensure that the column is installed correctly in the inlet. Agilent has literature that describes how to do all of these things. I know there's a youtube video on column installation.

The wax is an excellent choice for your analytes. I use it for analysis of these same analytes with good results. I don't analyze samples that have a lot of propylene glycol in them so I can't really comment on how that should behave. I've looked for more trace levels of PG (snooping out leaking heat exchangers in our process) but not high concentrations.

Good luck. That was a very good story! I enjoyed reading it.
Glycerin is tough for getting sharp peaks without derivatization, we always derivatized with BSTFA.

However for USP assay of incoming glycerin, we did use 624 columns and simply dissolved in methanol.
Good suggestion about rebuilding the inlet- The liner and gold seal are new but the inlet itself might need cleaning. It's also possible that the column is installed too far into the inlet- would that leave active sites exposed?

Liner is Agilent 5183-4711 which already has deactivated (silanized?) glass wool packing.
Also, because you mentioned using hydrogen as a carrier gas, hydrogen plus chlorinated solvents plus heat is a bad idea unless the inlet was made to handle it.
Just found this post, and really like reading it. Last year I spent several months corresponding with someone doing the same for a 5970, definitely takes time to bring these old ones back but they still have plenty of life left in them when you do.

You mentioned 5% and 1% standards. That is 50,000 and 10,000ppm, even at 150:1 split the 5% is 333ppm which is pushing upper limits for most 0.25mm columns, the 1% is 66ppm which is near the upper usable limit for most applications. Probably why you are getting tailing. If you can get enough sensitivity using hydrogen carrier I would try diluting standards and samples another 10x and the peak shapes should improve quite a bit.
The past is there to guide us into the future, not to dwell in.
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