Chromatography Forum

I also have a Waters 2695, in which my areas are 10X larger than they should be. I check the detector settings, and they are normal, the bulb is brand new. Mobile phase, samples and column, all work fine on another system.

I'm lost.

10X larger than they should be

How do you know what they should be? Comparing previous values on the same system? Comparing values on a different system (same or different model)?

Area counts are in arbitrary units (essentially mV-sec). Depending on full-scale-voltage setting and sampling rate, they can vary tremendously from one system to the next (that's why you run a calibration on each system). Those are the two settings to check first: what is the voltage range (mV per AU), and what is the sampling rate. If you're off by a factor of 10, it's probable that one of those is off.

I checked this against an identical setup.

My apologies. After all this, my peaks are actually extremely small compared to where they should be. I typically get an area of about 422 and as of today, I'm getting an area of 3.

I checked all the detector settings, and they are matched to the unit next to it. Any suggestions? Brand new lamp installed, and calibrated as well.

Crank up the sensitivity on both systems and look at the baseline noise values. If they differ by that same proportion, then it has to be a different setting. If the system with the smaller area also has significantly higher noise, then check to see if the flow cell windows are OK. I've seen them "solarize" with extended use.

Not really sure how to post an image here. But I have a screen capture of my baseline. It doesn't look normal. I'm having difficultly trying to figure out why it looks this way.

Let's see if this works......

Detector type & settings? Using Empower, or going through an external A/D?

If it's a digital UV signal for a wavelength between 200 and 300nm, that's a pretty noisy baseline...

Without knowing what the y-axis units are, it's hard to tell, but the stair-step nature suggests that you are simply getting a very weak analog signal which is at the limit of the A/D converter's resolution.

Check the lamp energy on the reference side. If that's out-of-spec low, you have your answer. If it's OK, take apart the flow cell, clean it, and replace the windows. If that doesn't solve the problem, check all the cables and circuit board edge connectors. If that doesn't work, it's time for a factory service tech.

I call this a ”blacked out” baseline. Either your mobile phase is polluted with something that absorbs light vastly at the wavelength you’ve chosen, or – as Tom suggests above – the flow-cell needs a thorough clean up and finally – worst case – replacement.

Best Regards

I'm going to try the cleaning process today. Thanks for all your help thus far!