RID problem

[qfiviera]

Hi everyone.

I´m having a problema with my RID detector. My system is an Agilent 1100. The problem is the baseline. Waves. Different mobile phases and columns. Purged the references several times, prepared and degassed the mobile phases more than once, the temperature is stable, room and in the detector. The first problem was, ACN:Water 1:1, flow 0.6 mL/min, detector and column T 50 °C, C18. Pumping with channel B. The last thing I tried was to change to channel A. Problem solved. Next problem. MeOH:Phosphate buffer (1:4), flow 1.2 mL/min, C18, T 35 °C in column and detector. Channel C. When changed to channel A, problem solved. But, before me, some peolpe had problems and they were using channel A.
I cannot realise if it is the RID or the pump, perhaps the mixing valve or some leak I´m not seeing. When I turn the pump to 0 mL/min, the baseline becomes stable, so I think it´s not a temperatur problem .

Any ideas?

[Consumer Products Guy]

Hi everyone.

I´m having a problema with my RID detector. My system is an Agilent 1100. When I turn the pump to 0 mL/min, the baseline becomes stable, so I think it´s not a temperature problem .

Any ideas?

Yep, sure sounds like a pump issue to me, you verified that when flow was set to zero. I'm going to assume that your system has an operational degasser. I'm also going to assume that you purged ALL four channels well, even though you may only be using some of them, important.

My question is: Since you pre-mixed the mobile phase (good !), have you tried bypassing the multi-channel mixing valve using the little adapter included with the system (Agilent Technologies #0100-1847) that routes from the degasser directly to the purge valve, makes it become an isocratic system. That's what we use with 1100 RID to get a stable baseline.

[qfiviera]

Quite good detective! Degasser yes. Purged all channels yes.
Bypassing the multigradient was going to be the next step, but I realise "hey, I don`t have the addapter...".
But, the thing is, we have been using without the addapter for fourteen years, and never had this problem.

Thank you for your answer.

[ATAlR]

I would try to check MCGV valve for quaternary pump. Just pump air bubble in all for channels, then switch between them and observe the movement of bubbles.
-If you have 100% composition on channel A, then the bubbles in other channels should not move.
-Also observe the movement of bubble, it should go straight down to pump, if it is moving up and down then there is probably defective check valve.
-If you don't have movement of bubble on selected channel, then there is probably a problem with clogged solvent filter.

[Consumer Products Guy]

Bypassing the multigradient was going to be the next step, but I realise "hey, I don`t have the addapter..."

Yeah, the adapter is "natural" color, looks very much like a 1/16 inch fingertight column nut. One was included with each new system, someone likely thought it was a column nut which didn't fit.

But, the thing is, we have been using without the addapter for fourteen years, and never had this problem.

"You never have a problem until you do" - Yogi Berra ....Look him up.

"It will either work, or it won't" - Yogi Berra

"If it ain’t broke, it will be" - Yogi Berra

"Good judgment comes from bad experience, and a lot of that comes from bad judgment" - Yogi Berra

When we need sensitivity (flatter baseline) using conductivity or RID, we bypass the MCGV here. Since that takes under 5 minutes, not worth not doing (I sound like Yogi there). In a "sandwich bag" I have the adapter, a plug for the MCGV so solvent doesn't leak out, and a union/plug for the line that was disconnected from the purge valve coming from the MCGV, so I can keep together as a kit

[qfiviera]

Thank you guys. As I had to do this analysis quickly or production guys were going to kill me, I put mobile phase on the 4 bottles, and "solved" the problem, so I suspect it is the MCGV. Now, I´m really going to solve it and find out what is really going on.

[Consumer Products Guy]

Thank you guys. I put mobile phase on the 4 bottles, and "solved" the problem, so I suspect it is the MCGV. Now, I´m really going to solve it and find out what is really going on.

So - in essence - you bypassed the MCGV doing that, as it didn't matter which reservoir it was actually drawing from. But you may not have a real issue, depends where your working range is. Using the Agilent fitting to bypass the MCGV is not a band-aid, it's a legitmate way to obtain zero cross-flow through the MCGV. All such MCGV have their tolerances, so 100% "A" cannot always be 100.0000% "A".

I had to do this analysis quickly or production guys were going to kill me.

Nah, never happens here........have to meet those arbitrary deadlines.....