Why don't the manufacturers do these? a place for ideas...

Off-topic conversations and chit-chat.

51 posts Page 4 of 4
Here's a software one, and it may well exist, but I haven't seen it in any of our systems.
Scenario: I'm developing a method with a methanol/water gradient. I can enter the percentages and flow rates as normal. I'd like the method to be fast, so I'm trying to use a high flow-rate, and it looks fine at the start, but the pressure hits a hideous maximum somewhere in the middle, the pump goes over-pressure, and it stops. So I have to go back and fiddle with the flow rates. The aim is to generate a method that reduces the flow-rate in the middle of the gradient, to balance the increased viscosity of MeOH/water mixtures, so that I run the whole gradient at the highest flow-rate I can get away with.

What I want: a system that will run my gradient at constant pressure, but remember the actual flow-rates, and will subsequently generate a method that runs at the measured flow-rate profile, whatever the pressure (because for stable retention times I want defined volumes of solvent passing through the column per unit time, even if the column starts to develop a bit of excess back-pressure).

I suppose Ideally I'd like to be able to choose whether to run my gradient during method development at known rate of change of percentage with time, or known rate of change of percentage with volume of solvent pumped.

This shouldn't be immensely complicated, but I haven't come across it. It'd be so practical: with a 400-bar column, you could set up your method with a target pressure of 330 bar or something, and have a happy safety margin for deterioration of the column, while keeping a good fast method.
I just had a re-read of this thread, and notice that our discussion of solvent quantities was ahead of its time. Shimadzu's current top-of-the-range LC system does indeed have weight-recording of its solvent bottles to assess how much solvent you've got in them. I haven't seen it in action, and I don't know how clever the associated software is, but maybe manufacturers are looking at this thread after all...
lmh wrote:
I just had a re-read of this thread, and notice that our discussion of solvent quantities was ahead of its time. Shimadzu's current top-of-the-range LC system does indeed have weight-recording of its solvent bottles to assess how much solvent you've got in them. I haven't seen it in action, and I don't know how clever the associated software is, but maybe manufacturers are looking at this thread after all...


Our new Shimadzu LCMSMS came with that option, but I still haven't figured out how to use it, and the one doing the training at install never mentioned it. I think it is so new they are not sure how it works :)

The Agilent method works as long as you remember to reset it when refilling the containers, it simply takes what you put in and subtracts the volume pumped out over time, and it will shut the instrument down when it is about to run out. But it still relies on the operator to keep it updated. The weight system from Shimadzu seems that it should work even better as long as the balance used is fairly accurate.
The past is there to guide us into the future, not to dwell in.
Oh yes, I remember! I am afraid I'm not as efficient as Agilent had hoped. The number of discussions I had with our old 1100 system (in a noisy lab, with few co-workers, it's easy to get into the habit of talking to the systems when you think no one is listening, and very embarrassing when it turns out someone is standing behind you, waiting to get a word in).
"Look, why did you stop? Can't you see, you've hardly taken anything out of that bottle at all! I gave you a whole fresh L of methanol yesterday. What on earth possessed you to stop on the third injection?"

I'll be interested how you get on with the Shimadzu system. In their previous system, they had tried to implement Agilent's method, but unfortunately they rather messed it up. The Nexera pumps come as standard with no solvent selection valve, but the engineer fits this (or a gradient proportioning valve if you want a low-pressure mixing system) on installation. Unfortunately the software deals with solvent selection in a very "oops, we forgot it, so we'd better add something" way. There's a box for selecting valve positions on the pump tab of the method, but the solvent monitor thing is blissfully unaware of solvent selection, and merely subtracts from a sum. So if you have two bottles, it doesn't track the contents of each. You could use it to avoid errors in a single run, but if you've got methanol and acetonitrile for example, multiple methods, and you don't replace the organics every time, then the system has no idea what's going on in the bottles. Maybe that was one of the things that prompted them to think of something better.
just curious:
how do they deal with the tara of the bottles?
If you need to enter this anywhere, you'll need to stuck with a certain type/volume of bottles or chances are, that it will run dry anyway (if tara is from small bottle but putting a big one on) or it may stop prematurely if you put a small bottle with the tara of a big one...

Personally, I'm quite happy with the Empower way of just showing me the estimated amount of solvent needed on each chanel for all sequences. Then I check the bottles if there is still enough in them.
Hollow wrote:
just curious:
how do they deal with the tara of the bottles?
If you need to enter this anywhere, you'll need to stuck with a certain type/volume of bottles or chances are, that it will run dry anyway (if tara is from small bottle but putting a big one on) or it may stop prematurely if you put a small bottle with the tara of a big one...

Personally, I'm quite happy with the Empower way of just showing me the estimated amount of solvent needed on each chanel for all sequences. Then I check the bottles if there is still enough in them.


I think you tare the bottle you will use when empty then fill it, but since I haven't tried it I am not completely sure. The brackets that hold the bottle above the balance pad are sized for 1L media bottles so maybe it knows the average weight of those plus the lines that are attached.
The past is there to guide us into the future, not to dwell in.
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