Agilent Multi channel gradient valve (MCGV)

[archie]

Hi all,

I have problem with my HPLC (Agilent 1200 with quarternary pump).There is 4 channel, that i used for :
A : water
B : metanol
C : acetonitrile
D : other solvent (like phosphoric acid 0.1%)
But now the B channel of my MCGV can't perfectly close, because of bubble there.
When I did the gradient test,the result was failed.
I want to know :
what factor cause this problem?
Is there any human error in this case?
Do you have any experience like this case?
How about other HPLC merk (Waters,Shimadzu,perkin elmer,etc)?

[Rolandas Plausinaitis]

If you primed system properly, problem probably is caused not by the buble but faulty valve. We had to change 2 or 3 valves in our 1100 instruments after something like 3-5 years usage. Just that we had problems on channel A used for water/buffers. Our Shimadzu HPLC also had this problem.

I'm afraid there is no other way just to exchange the valve.

[carls]

Are you sure the problem is with channel B? If not, purge each channel at 3mL/min with 20mL IPA followed by 20mL of water (A) or methanol (B). If the test still fails (how bad?) try the same thing with channels C and D. If C/D pass but A/B fail you may have a faulty MCGV.

[archie]

@all : thank you very much

@Carls : I'm sure that the problem is on B channel because we try to filled flow cell with water from A channel, there is contamination from organic phase from B Channel so the test was failed.But when we filled the flow cell with water from other LC, the test was passed.

@Rolandas : Is there any electrical problem in this case? Or the mobile phase as the factor cause this problem (for example : buffer, acid / base, THF in mobile phase)?Is there any contact between mobile phase and part of MCGV?

[Rolandas Plausinaitis]

In our case faulty channel tubing coming from the degasser had to be disconected and closed completely as it was "leaking" in all channels combinnations - i.e. C/D test should also fail in this case.

With the channel blinded we were able to use instrument untill repalacement valve arrived.

You can try to set pump to maximum flow rate trough one "good" channel (with open purge valve) and lift suspected channel intake tubing into air - usually you can see solvent moving and air entering the tubing - that would confirm the channel is faulty.

It is certainly not electrical fault, but I can't explain exact nature of mechanical problem - for some reason valve is not closed completely. It can not be dissasembled and there are no spare parts available, so it has to be excanged.

Regarding the primary cause I also can only speculate. Since on our instruments channel A failed - used in most cases for water/buffers - probably it is related to particles in the mobile pahase. Either due to the use of non-filtrated solutions or precipitation when solvent exchange procedures were not followed properly.

Even that You are using faulty channel for organics - is the bottle closed good? Is the solvent allways fresh in a new bottle or solvent just added in to the same bottle sitting on HPLC for months? Is the lab dusty?

[archie]

To Rolandas

I always changed the solvent bottle if the solvent was run out.
My lab is not really dusty..and I always use inlet filter (glass filter) in each bottle.
If it caused by dust..is it posibble that the glass filter cannot filter it?
For now, how do you maintain your MCGV?

thanks a lot

[Rolandas Plausinaitis]

Well, glas filter is for bigger particles and is more or less useless. We always have had discoloured PTFE frits in the purge valve. But our lab was in the area with high air polution from the cars, so it was coming from the air.

Now I work in different lab, using mainly Waters HPLC, but we did not take any extra measures regarding MCGV. Just exchanged it when needed. It was not more than once on each HPLC after several years of almost non-stop work.

We had about 8 analysts using 4 HPLCs for different tasks (mostly using the instrument which was free at the moment) so it is difficult to take proper care of the instruments.

[carls]

When I did the gradient test,the result was failed.

archie - was the gradient test you refer to above performed using ~0.1% acetone in water on the B channel? If not, could you provide more details on the test you're performing?

[archie]

@ carls : I used 0.5% acetone in water on the B channel.

[carls]

Did you try bypassing the degasser? As Rolandas stated that can be a contamination point. The micro degasser on the 1200's must be treated a little differently than those on the 1100 to avoid damage. For example, do not use a syringe to pull solvent thru it.

Is the pressure stable at 1mL/min and at least 100bar, i.e. what is maximum peak to valley pressure difference?

[archie]

@carls : Yes I did.Before Gradient test I always bypass the deggaser.
My HPLC 1200 have standard degasser,but in 1100 is Micro degasser.I never use syringe to pull solvent trough degasser.the different pessure +/- 1 bar

@ all : how long the frequent to replace PT FE frits?

[Multidimensional]

I see this is a VERY OLD post (2010), but for anyone who may find it trying to troubleshoot an HPLC quat pump, multichannel gradient valve (or "gradient" proportioning valve) problem, this free article may help you understand the problem AND how to solve it.

"HPLC Gradient Valve / Proportioning Valve / MCGV Leaks. How to Identify Them"; https://hplctips.blogspot.com/2021/08/h ... valve.html