Bursting UV flow cells when ESI needle clogs

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

13 posts Page 1 of 1
Hi All

this has happened to us several times: Every once in a while our ESI needle clogs and then the UV flow cell bursts.

We can clean the needle but a new cell is over $1000!

Does anyone have a solution such as a "pressure fuse" between the ESI source and the UV detector to avoid this?
it varies with system! Shimadzu's Prominence PDA flow cell just leaks, it doesn't break. I've had this with fluorescence cells, and for this reason tend to operate fluorescence detectors parallel with a mass spec after teeing, rather than in series. If you have an adjustable back pressure regulator (I used to keep one for pump-testing, to insert in place of a column, instead of using a long bit of tubing, to create a bit of pressure) you can add a t-piece before the MS, with the back-pressure regulator on one limb, running to waste, and adjust it so that the pressure created by a healthy ESI needle doesn't cause any flow, but if it blocks, the regulator will create less back-pressure than would burst the flow-cell.
I'm retired, so going by memory. I thought that one could program in a maximum pressure into software like Agilent that would shut off the pump if that pressure was reached.

Maybe I'm incorrect.
Consumer Products Guy wrote:
I'm retired, so going by memory. I thought that one could program in a maximum pressure into software like Agilent that would shut off the pump if that pressure was reached.
Maybe I'm incorrect.


yes and no;
normally one can program such a shutdown, but that pressure is measured before the column; so you would limit your working pressure to this low setting.

Unless you have a pressure transducer after your column, you're stuck with passive components.

The "T" options as suggested by lmh seems the only option.

Maybe you can even split the flows, so that only a minor flow goes to the MS and the rest goes to the optical detectors? Depends on your sensitivity (maybe it could be even superior for the MS when feeding it with lower flow rates).
Then only a simple "T-piece" would be needed without any pressure regulators at all.
Hi All

thanks for the input. I wish ours just leaked!

The T-piece idea is pretty good.

The pressure option won't work for us.

We already have a T-piece set up for a 75:25 split for implementing runs of very high flow rate runs out of production labs and still being able to get mass spec. This avoids having to alter the existing method. I am concerned about getting variation in flow rate to the mass spec with this option and adding further complexity to our system.

I am looking for something like a "fuse", an analog to a rupture disc in the plant. I talked to a Dionex field engineer yesterday and she promised to get back to me. I'll update you here.
ok, here's the deal:

Agilent has this part: - Inline Pressure Relief Valve Kit (G4212-68001) $1,224.00

Thermo offers this part: - overpressure relief valve 60 bar (6083.9260) - $1,325.94

They appear equivalent to me and we'll get one of them to protect our cells.

The Thermo part comes in a 40 bar and a 60 bar flavor to protect the sensitive Vanquish flow cells. Our flow cell can take 120 bars. So there might be a premature rupture for us but 60 bar is still more than we probably want to have from our ESI source.
ah, nice information. maybe I will remember that expression if I need it somewhen.

have a look at the Idex HS website.
Maybe they do the same at a 1/5 of the price...

https://www.idex-hs.com/store/fluidics/ ... ators.html
Hi Hollow

thanks for the tip!

But is 100 psi (7 bar) enough pressure for an ESI source (Thermo HESI II) or will it trigger during normal operation? I guess I'll have to test that. The UV cell has a rated backpressure of 120 bar or 1700 psi.

I cannot find this type of valve with a higher relief pressure setting unfortunately.
100 psi may be too low, but there are also some with 1000psi (69 bar). Maybe you have to build your own tee by connecting the regulator with a small piece of tubing. It seemes the dedicated tees are only built with flat bottom connectors.
Yes, I just measured the post-UV cell backpressure on the system and it is around 8 bar at 0.5 mL/min with 50% aqueous mobile phase.

I also just thought about it a little more and I think I can just get a zero dead volume Tee and then connect a 1000 psi (70 bar) or something a little lower to the dead end of the tee. Should the pressure at the Tee rise above 1000 psi, the BPR would open, otherwise the Tee behaves as a straight tube.

Image
that's the set-up I'd envisaged. I used to have quite a nice little variable back pressure regulator, from Alltech who became Grace, but then Grace disappeared too, so I don't know where such things would come from now. It was also quite cheap, if I remember correctly.
If you look at the bottom of the page for Grace, it seems the small parts group was sold off to Optimize Technologies. Several of their items went to different companies according to that list.

https://grace.com/en-us/Pages/discovery-sciences.aspx
The past is there to guide us into the future, not to dwell in.
I successfully implemented the t-junction option with a 1000 psi bpr from IDEX. It works like a charm. It already triggered 3 or 4 times and saved the flow cell. Highly recommended.
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