Modifying 5971 Transfer Line

[benhutcherson]

As I'm sure anyone who has ever used a 5971/5972 knows, the transfer line tip design is somewhat less than ideal for any purpose other than column installation. Basically, it has a solid end with 4 small holes in the side to allow transfer of analytes from the column to the source. This makes installing a column easy, as you just push it in until it stops and then pull back a bit, but lacks the "straight shot" to the source that most other GC-MSs have.

If you read contemporary literature, more than one person recognized this problem and suggested modifying the tip so as to feed directly into the source. It fundamentally seems like a good idea to me.

I'm wondering, though, if anyone here has actually done that. If so, how did you go about removing the material? I THINK the tip is gold plated-did you replate the now exposed metal after modification? Also, does this present any problems with heat transfer from the line to the analyzer?

If it weren't for the fact that transfer lines seem to bring as much on Ebay as complete MSs, I'd buy a spare transfer line to modify. Obviously, I'm a bit hesitant to just jump into it with the one I have now.

With that said, I'd appreciate any input from anyone who has tried or is otherwise familiar with this modification.

[LALman]

I've thought about it myself. Scientific Instrument Service sells the gold tip for the Agilent 5971 transfer line tip for $115. Agilent PN is 05971-20305 and SIS PN is HP99.

Downside is you would need to measure the exact length of the assembly with the bellows compressed to get it just right.

[benhutcherson]

Thanks! If I'm reading the SIS page correctly, it looks like it comes pre-modified...I might be ordering one today since that makes life a lot easier.

https://www.sisweb.com/ms/hp/transtip.htm

[LALman]

Thanks! If I'm reading the SIS page correctly, it looks like it comes pre-modified...I might be ordering one today since that makes life a lot easier.

https://www.sisweb.com/ms/hp/transtip.htm

Yes, that is my understanding, that it is a straight through. Let us know if it works well. I've been wondering.

[benhutcherson]

I didn't get it ordered today, but will try to do so tomorrow. The fiscal year is wrapping up, so this is a good time to do it and this isn't super expensive in the grand scheme of things.

I'm not sure whether or not I can make the case for a new electron multiplier(esp. since the current one tunes at ~1500V) but what type do you all like for the 5971?

The one I have now is an ETP that looks a lot like this but is probably better than 10 years old

https://www.sisweb.com/ms/etp/af516.htm

Is there one that gives better sensitivity in the 5971(might as well go all out)?

[James_Ball]

I didn't get it ordered today, but will try to do so tomorrow. The fiscal year is wrapping up, so this is a good time to do it and this isn't super expensive in the grand scheme of things.

I'm not sure whether or not I can make the case for a new electron multiplier(esp. since the current one tunes at ~1500V) but what type do you all like for the 5971?

The one I have now is an ETP that looks a lot like this but is probably better than 10 years old

https://www.sisweb.com/ms/etp/af516.htm

Is there one that gives better sensitivity in the 5971(might as well go all out)?

I have used both the tip and the ETP multiplier and prefer both. As for insertion depth, I installed the column before installing the transfer line to see that the column was just about 1mm past the end of the tip. The tip is connected to the opposite end of the transfer line where the column nut is, the bellows are independent of that piece, when they contract the just allow the tip to seat against the fitting that screws into the side of the radiator that goes into the source. That is the piece that determines the depth that the tip will enter the source chamber.

[LALman]

I didn't get it ordered today, but will try to do so tomorrow. The fiscal year is wrapping up, so this is a good time to do it and this isn't super expensive in the grand scheme of things.

I'm not sure whether or not I can make the case for a new electron multiplier(esp. since the current one tunes at ~1500V) but what type do you all like for the 5971?

The one I have now is an ETP that looks a lot like this but is probably better than 10 years old

https://www.sisweb.com/ms/etp/af516.htm

Is there one that gives better sensitivity in the 5971(might as well go all out)?

I have used both the tip and the ETP multiplier and prefer both. As for insertion depth, I installed the column before installing the transfer line to see that the column was just about 1mm past the end of the tip. The tip is connected to the opposite end of the transfer line where the column nut is, the bellows are independent of that piece, when they contract the just allow the tip to seat against the fitting that screws into the side of the radiator that goes into the source. That is the piece that determines the depth that the tip will enter the source chamber.

Excellent point, I may have to just order that tip. I also prefer the ETP multiplier.

[benhutcherson]

Alright, ordered. I should hopefully have it by the end of the week-if all goes well I will install it on Friday and then let the instrument sit over the weekend(I've found that it can take the 5971 that long to stabilize out after venting).

Since I analyze caffeine at least somewhat often, I'm thinking that in the mean time I'm going to make up a set of caffeine standard both to determine LOD and linear range both on this and on the 5975. I know I can go to 5ppm all day on the 5975, but I've never tried lower as I've not had the need to. As I see it, that's both useful information to have for a common analyte, and also a like-for-like comparison with the original and modified tip.

[benhutcherson]

Alright, just jotting down some preliminary stuff that I can hopefully follow up on next week.

I made up a series of caffeine standards and went as low as .005 ppm. All were in DCM. I injected 1µL in splitless mode into a .18mmx 20m DB-5ms column. 225º inlet, temperature program 125-200º 40º/min, flow of 1.3mL/min He. RT for caffeine is about 5.5min. Every standard was injected in triplicate, and I ran a solvent blank between each standard. I installed a new liner and septum before starting this series of experiments. The column had maybe 20 "clean" injections on it before this series, and I'd fitted a new gold seal when it was installed.

I can detect it at .005 ppm, but reproducibility takes a big hit(rsds 70%+ under .1 ppm, 12% at 2.5ppm) and linearity also falls apart below ~5ppm(r^2=.7025). At 5ppm and higher, I'm seeing typical RSDs in the 2% range and it's nicely linear-r^2=.9997. I should add that .005ppm didn't require any special effort-it gave a noticeable peak above the baseline without

I'm venting and cooling now, so I'll get the straight-through tip installed today. I'm not necessarily sure it will do much for absolute LODs, especially given how low I was able to see it, but I'd be happy if it improves reproducibility and linearity at those ranges.

[James_Ball]

I think the biggest benefit to the open tip design is that after a dirty sample you won't have trouble cleaning inside the tip, since the column will actually be past the end about 1mm. With the closed tip design, once crud builds up inside the tip, it is nearly impossible to be sure you get it all out.

Did you try SIM and see what it does for the low end response and linearity?

[benhutcherson]

I wanted to do SIM but didn't get a chance to-basically my goal was to get it installed today so that I can do again next week. Caffeine is an easy one for SIM since the molecular ion(m/z 194) is also the main ion in the spectrum.

In any case, I do have another method where I do SIM looking for trace levels of clonazepam-a surprisingly tricky one that is doable on the 5975 but that I haven't been able to find on the 5971 reliably. I'll call it a complete success if I can even see it(much less quantitate it) with this fitted.

The sample carry-over is a good point, and it's something I can also easily monitor with the solvent blanks.

[benhutcherson]

I've been unbelievably busy so haven't had time to actually crunch some numbers, but as a few subjective observations:

At both low and high concetrations, my peak shape for caffeine seems a lot better. At low concentrations, it's definitely sharper. I was running into a problem at high concentrations of getting sort of broad area with 3 noticeable peaks(if this were NMR I'd call it a triplet)-I suspect that it may have been condensing inside the transfer line tip and then subliming to give the signal as that. I'm still getting a somewhat broad peak(relatively speaking) but it's now nice and gaussian.

Also, my blanks look a whole lot cleaner with almost no carry-over of this particular sample. That tells me-intuitively-that it should be more repeatable.

One other thing-SIS shows the tip as gold plated, but it's not. I suspect it doesn't actually matter since, with the column 1mm past the tip, no sample should come into contact with it.

[James_Ball]

Probably shouldn't need gold for it, and with the price of gold now the plating would be so thin it probably wouldn't last long. I am seeing that lately with gold inlet seals, they seem to tarnish quickly with even moderately dirty samples, the old ones 20 years ago you could just wipe off and keep going, the new ones it seems to eat through the gold plating.

If you do see any carryover or peak shape problems, you can just clean it with the alumina as you would the source, and if you want extra peace of mine hit it with a little SylonCT.