Silyl-8 GC Column Conditioner?

[jonjon]

Wondering if anyone knows if this is still available? Pierce use to sell it, talked with ThermoFisher, no luck and/or they have no idea. I have seen a couple references about direct injection of BSA. Thoughts on options or alternatives.

Basically we have a couple of bad actors in our separation. We have gone to the newer "better" inert columns, these work but still degraded separtion over time(days). Wondering if silanizing agent would help stablize the process.


Thoughts
Thanks
Jon

[Peter Apps]

In my experience, many years ago, these column conditioners do no good at all on capillary columns - they were developed in the days when all columns were packed and sample loads were in micrograms. You might see a temporary improvement in adsorptive activity but you pay for that will huge levels of baseline drift from bleed, and by the time you have conditioned the bleed away the activity is back.

Deteriorating separations are many many times more likely to be due to the inlet than the column (unless you have dirty carrier gas and are taking the column to its maximum temperature for long periods).

Peter

[GOM]

Hi Jon

I used to use Silyl-8 (silylate) from Pierce but for packed columns

For others, this is just silylating (neutralising) any active sites in the injection port or a non-polar column

BSA or Trisil-BSA would perform a similar function

https://www.sigmaaldrich.com/content/da ... a_tmcs.pdf

My concern is that you have problems with " newer "better" inert columns, these work but still degraded separtion over time(days)." sic

Would you give some more details of your analysis?

Regards

Ralph

[Yama001]

My recollection of this stuff is similar to Peter's. The problems with packed columns that is was aimed at were mostly addressed by moving to capillary columns.

Supelco (Sigma?) might still sell it.

[jonjon]

Ralph,

Condensing down what I have learned/tried. We have a "reactive" gas valve manifold on a GC/MS system (actually MS/MS), with a second independent PID channel (the manifold was purchased installed). All valves are He purged, all He is gettered. The PID channel looks good against background air and the MS tunes with air/water showing less than % level for all air/water. So the system seems tight. The MS channel uses a "DB-1" type column and has given me the most problems. My current challenge is our tetrafluorosilane standard at 100ppm. Roughly the GC starts at -40C, holds for a few minutes then ramps to 200C, this is being modified now. The original column recommended was a 5um PDMS, (Ive tried a few other options as well along the way and seems like the big issue is the column, I realize there are other pieces along the way). At -40C I never saw the solute, but at 150C the peak was sharp (inbetween temperatures was more of a square wave tailing). Fast forward to last week. I installed a new "inert" column (1um df, 1-ms), and at -40C got a very good reproducible sharp peak, excited. Set the oven to 75C for the weekend, came in Monday and reran the tetrafluoro at -40C, I got a sharp peak, but now showed a small but obvious tailing hump, similar to the adsorption of previous columns.

So I am wondering if periodic injections of BSA, for example, would help?
I know this is a older approach for deactivation and have seen it for packed column

I ran across a paper by Varaprath and Lehmann for dimethylsilanediol where they injection 1uL of BSA.

So trying to think what I am missing.

Thanks for any advice.

Jon

[Peter Apps]

Hi Jon

From the point of view purely of adsorptive activity tetrafluorosilane is actually quite tractable, so if you are seeing tailing it is not the kind that can be fixed by deactivating siloxane or silanol groups - which is what Silyl 8 etc do.

I am a bit uncertain what you are doing with your column temperature, normal practice would be to start cold and programme the temperature up at about 5 C/min for a 30m column, but I get the impression that you are holding the temperature until your peak comes out and then heating very rapidly. Also why start at -40C ?, TFS's MW is about the same as heptane's, which will come out as a nice peak at 40C, are there impurities you are looking for that need the very low temperature to get sensible retention ?

Presuming that your valves and connectors are warm/hot to stop adsorption you might have an uneven and poorly repeatable transition from the hot connectors to the cold column, which could be enough to give a slight tail on a peak.

Peter

[KM-USA]

We just injected a few microliters of BSTFA a few times.

[jonjon]

Peter,
Thanks for your insight. The TFS has been a solute like I havent encountered before in its apparent behavior. Its MW maybe close to heptane, but its BP is -65C. All lines and valves are heated (90C nominally) on the valve manifold and line running into the GC/MS is plumbed into the injection port (SR 10:1), this column is attached to injection port (225C). The starting temperature of -40C is primarily for a permanent gas channel (with a PPQC) column. The oven ramp is -40C for 5, ramp at 5 to 10C, hold, ramp at 20C to 150 hold, ramp at 20C to 200, hold.

I wasnt expecting TFS to behave like it is either. But the few bits of information that I have gathered and learned suggest otherwise. I havent been able to find much in the literature on trace TFS separations. I found one by Bruno, Capezzuto, Crammarossa, dealing with SF6 with TFS and an impurity and they mentioned the non linear behavior at low concentrations and the need to "passivate" the system with 100% TFS, but this was using a PPQS packed. I actually tried a micropack PPQS for this application. It worked ok at higher temperature (~0C, I saw peak, but tailing some), but was a struggle to a adequate separation at -40C, due to the need of the other perman gas column, to many compromises. We had some collaborates who had a similar setup (using a PDMS column), and they also mentioned the need to "passivate", but they were using a 2% standard TFS.

When I installed the new "inert" column, this was the first time I was able to sharp peak to elute at -40C. The odd thing is regardless of the starting temperature (-40C, 0C, 50C,...) TFS still elutes very near the dead volume, or staying differently, compared the to other impurities the oven starting temperature seems to have minimal effect on retention for TFS.

So I am wondering if injecting a silylating agent would help or maybe more importantly will not hurt. Thinking isothermal at 175C then ramp up to burn anything else off?

Thanks everyone.

Jon