Chromatography Forum

Although I already read in LCGC that the habit of increase flow rate in 0.1 to 0.1 ml/min steps for avoid damage to column is a legend, I heard this again from the Engineer that install the UPLC from Waters in Brazil.
I would like to hear the opinion from the manufacturers, at least the ones that frequent this forum: Dionex, Methron, Supelco and others. Any of you recommend this to your customers? Is this any kind of Urban Legend or really exist some true behind ??

Oh, I’m talking about silica based columns, of course.

Fabiano

I also would like to hear some comments on this one. And if Waters-people recommend a step up procedure, then why there isn’t a ramp up option in the UPLC- console? I’m aware of the “built inâ€

I do not increase flow step by step in fixed value like 0.1 to 0.1 ml/min, I increase it based on the pressure. The greater pressure needs smaller increasing step and vice versa.

Both the UPLC system and the Alliance system have automatic pressure ramps built in. In the Alliance system, they are addressable as well, since the system can be used with polymeric packings. For UPLC, soft packings are not suitable, and therefore the ramp per se can not be programmed. However, you can anyway program the flow rate any way you want, if you prefer a slower ramp.

All recent and current Dionex HPLC pumps have flow ramp built in. In fact, if you specify something too fast, you get a warning on the data system. It is true that modern silica based columns are more rugged (we do test for that), and for that reason 0.1mL/min/min is much slower than necessary. We currently recommend 0.4 to 4.8 mL/min/min. Clearly, a small diameter column would use a lower ramp rate than a larger one.

Flow ramps are definitely useful as pressure build-up is slower. Especially in case of a back pressure problem the high pressure limit is able to react better ( less overshooting).

Some of the old pump designs had a bad habit of racing on startup, or whenever they caught a bubble, or on a large change in flow rate. I have seen polymer-gel columns ruined in an instant by such bad behavior. The only way to tame them was the tedious procedure of manual, small flow steps. Modern pumps have smarter designs.

Ok, Thank you all.

So it's not a urban legend...

Suppose that I use a old manual control pump, what would be acceptable in term of time (faster) and safety for column?
set up my flow in 2 minutes using 0.2 steps? or let the pressure stabilize for a longer time?

If you are using a "conventional" silica-based column with pores in the 10 nm range, it probably doesn't matter a whole lot; just set the flow to 2 mL/min and don't worry. In my experience, such columns are quite robust. Furthermore, the system does not pressurize instantaneously in any case because there is always a "leak" (out through the column).

With resin based columns, as mentioned by Mark and Uwe, you need to be more careful. The same holds for very large pore columns used for protein work (the particles are fairly fragile). I'd say 0.5 mL/min increments until pressure stabilizes.

How about the pressure shocks due to injection valves, especially if one does it manually and is a bit slow?

How about the pressure shocks due to injection valves, especially if one does it manually and is a bit slow?

Columns with lower stability or lower packing quality may show problems in this case.
There are two ways to circumvent this:

1) do some work-out to speed up

2) use a pulse dampner