Chromatography Forum

Hi all,

This is my first post to the forum.

We are currently looking for a good method for tracking pressure increases over time in order to monitor column lifespan. While this can be done with a chromatogram of the pressure reading, interpreting it is somewhat subjective. It would be nice to have a single number to use for trending.

We are using a Waters 2695 with Empower 2 software. It is an RP-HPLC method with a gradient elution.

My initial thought was to apply a mean smoothing to the pressure chromatogram, and then integrate the entire pressure trace (to account for the changing pressure during the gradient) as a single peak with a baseline of 0 psi. I have figured out how to force the integration as a single peak using the "Force Peak" event, but can't find a way to force a baseline of 0 psi.

If this is not possible, is there a way to extract a pressure value from a fixed time point (or even better, over a time range) and report this as a number?

Does this make sense? Any ideas? What do other folks do to track pressure increases between runs?

Thanks!

edit: I do have one semi-kludgy solution, which is to end the gradient with a short period of 0 flow rate, which should cause the pressure to drop to 0, and then force the baseline backward from that point. I'd prefer something a little cleaner though . . .

What is a pressure chromatogram? Normally one would attempt to clean a column when the pressure gets to an unacceptable level.

Although there are exceptions, we have found that logging pressure at the start of each run for a given column allows us to notice when back pressure has increased appreciably over time (to the extent that a particular column is used for a particular method).

You can collect a system pressure channel from you 2695 into Empower.

With that data you have a couple of choices.

1. The hard way. Manually look at each pressure trace and write down the system pressure at a constant time point (usually at the very beginning or very end of the run). Plot the data in a spreadsheet.

2. The easy way. Write a custom calculation within empower to do "the hard way" for you. Use a control chart report within empower to display the data.

Thanks for the replies!

You can collect a system pressure channel from you 2695 into Empower.

With that data you have a couple of choices.

1. The hard way. Manually look at each pressure trace and write down the system pressure at a constant time point (usually at the very beginning or very end of the run). Plot the data in a spreadsheet.

That's what I'm doing now. Manual examination of the pressure trace.

2. The easy way. Write a custom calculation within empower to do "the hard way" for you. Use a control chart report within empower to display the data.

This is more in-line with what I want to be doing. I'll look into the custom calculations and see what I can figure out (I'm pretty new to this software, hence my questions). Thanks for pointing me in the right direction.