Chromatography Forum

We would like to purchase a new LC system.
After we had tested the two systems in our lab we're pretty close to descision making.

But before, I would like to ask you about your recommendations or warning fingers.

What did/would you choose and why?
What are the "pros" and limitations of the two systems based on your experience?

The system should mainly be used in QC but also for developement/check methods of new products. The main focus for us is resolution and if it's also faster, we're not unhappy...

Thank you for your answers

If it is resolution you are after, why not try one of the 2.5um particle columns or one of the fused core columns as discussed in a previous thread. Have a look at http://www.sigmaaldrich.com/Area_of_Int ... press.html
This could save you a lot of money on a new system, and some of the problems that go with ultra high pressure LC. Also have a look at the thread "Are you Happy with your UPLC?"

If it is resolution you are after, why not try one of the 2.5um particle columns or one of the fused core columns as discussed in a previous thread. Have a look at http://www.sigmaaldrich.com/Area_of_Int ... press.html
This could save you a lot of money on a new system, and some of the problems that go with ultra high pressure LC. Also have a look at the thread "Are you Happy with your UPLC?"

Dear Developer

thank you for your reply. I have allready looked at the other threads.
But actually, I would like to hear your oppinions focused on the two systems.
In fact we need a new system for replacement of our about 20 years old systems. So we're going to buy one of the two mentioned.

Hollow,

You can get many opinions from those that post here. This question has come up before; search for posts on HPLC purchases. Here is one such discussion thread:

http://www.sepsci.com/chromforum/viewto ... highlight=

I would say that both are good systems. My recommendation would be to first evaluate the systems as you have already done. Then, base your recommendation, at least in part, on the follow up support that you expect to receive from each respective company. That follow up support is a big part of why people choose a system from a particular manufacturer. Note that the support received can vary from one region to another, although both of these companies generally have good global support.

Regards,
Dan

Hi Hollow,

You’ve already read this under the other topic, but I’ll remind you again. Think CDS! If you use Millennium/Empower you’ll find it easier to control Waters’ systems. The same goes for Chemstation/Cerity??? (I wonder what happened to Cerity). If you have it in the lab, then you’re better off with Agilent 1200.
Oh yes, I’m aware of the cooperation Waters and Agilent agreed on (supporting each others instruments and all that) but it doesn’t seem to give Waters stress – they are not in a hurry to implement Agilent 1200 support for instance. I wonder why

Best Regards

Hi Hollow

A few years ago I evaluated Waters UPLC and found it about ±5X faster than HPLC. If you are interested I could email you my report.

Thanks
Mike

I have worked with both Waters Aquiety and Agilent 1200, and there are benefits and drawbacks with both.

The Waters system is more a truly an UPLC due to the higher pressure, but it is also a more complex system than the 1200. If you need that last percent of increased efficiency/time saving, the Waters system is the most optimised. Since it is so optimised I feel that it is not so robust to work with. Our system has been down quite a lot, and it is still impossible to run acetate or formate buffers due to a terrible baseline. Waters has changed almost every part of the instrument without any change.

The 1200 is more a more robust system, and more similar to a standard LC. Any LC operator can work with this system.

If time is not your limiting factor, my experience is that you can just as well run the sub 2 µm columns on a standard LC. On a 2.1*150 mm column you get pressures under 400 bar at 0.4 ml/min at 50°C. There is no difference in plate count compared to running it on a UPLC. You just cannot do the separation as fast.

To run a long UPLC column on a standard HPLC instrument is not going to get you above the minimum of the van Deemter curve (for most realistic samples). Temperature is not a substitute for pressure.

One UPLC publication I read depicted Hmin for some small parabens at 2-3 mm/sec on 1.7 um media. This I think is in the region of 0.3-0.45 ml/min for the column listed previously. I really don't know if you can get these flow rates on a conventional HPLC.

With the influence of temperature on molecule diffusivity, does Hmin move one way or another on going from 25C to 50C?

JA: I just put my 5 cents on this subject into a paper to be published in J. Sep. Sci.

The pressure needed to reach the minimum of the plate height vs. velocity curve INCREASES with increasing temperature.

Consequence: increasing the temperature is NOT a substitute for increased pressure. Just the opposite....

JA> I have developed a tentative method that uses the parameters descrived above. When run on a standard Dionex LC I get the pressure of 340-350 bars which works fine.

Uwe> Ok, I thought the minimum was much lower in flow (with the 5 µm columns we were always working well above the minimum. Our Acquity is coupled with our MS, so the flow rates we use is typically 0.2 ml/min. That means that we are not fully using the potential of our 1.7 µm columns? Would it be better if we cooled the columns?

Thank you all for your replies

After the few tests we made on both systems I can "agree" with Mattias.

On the RRLC we had much less problems to run an adapted HPLC method.
On the UPLC, we get some more troubles. Unfortunately we couldn't figure out what was really the problem.

The problem was that we often get "split" or unsymmetrical peaks in the optimum flow rate range (400-600µl/min on a 2.1x50 mm C18 UPLC column).
Once it was caused by the sample solvent/injection volume, but even with a alkylphenone test mix it was there.

I've run a sequence with different flow rates, starting with 100ul/min up to finally 700ul/min of isocratic MeOH/H2O 40/60 (or was it 60/40? -> similar to Waters PQ test for UV-HPLC system).
As said, between 400 and 700ul/min the last two peaks (propio- and butyrophenon) gets split. Maximum split was at 500ul/min.
The phenomenon was reproducible, a 20x injection gets %RSDs of 0.1 in retention time and about 1.3 for (combined) area.
Interestingly the peak form gets better again with a flow rate of 700ul/min.

The same thing was about to be seen on a 2.1x100 mm column, but here I had to raise the temperature from 40 to 70°C to get a similar flow rate of 500ul/min. Higher rates than 570ul/min weren't possible cause of the pressure limit.

We told this to Waters CH, but they haven't got a solution yet (okay, it was just last week...)

@Uwe: Have you got any idea what it could had been? If you're interested in further details I can send them by mail.

Regards

Mattias:

at 50 degrees and 0.2 mL/min you are pretty definitely on the wrong side of the van-Deemter curve, unless you are running large molecules, like peptides.

Hollow:

There are several possibilities for split peaks. The first question is if you used the solvent preheater tube (nicknamed the Uwe tube) in this experiment. Second question: what was the wash solvent in the injector? Third question: I assume you used the standard mixer in the system, and did not remove the mixer for some reason.

JA:

Hmin may move with the retention factor. It is at somewhat higher flow rates for larger retention, and at somewhat lower flow for low retention. One usually does not want to go to too low a retention factor, and adjusts the solvent composition to stay in about the same range of retention factors when changing temperature.

I would not construct my separation by only looking at the van Deemter curve. You’re right when working at elevated temperatures the optimum shifts. The result is that you loose some plates. But I can demonstrate some applications where, despite you loose some plates, the resolution at elevated temperatures is increased caused by an improved selectivity factor.

My conclusion; it’s not about only about plate numbers