Chromatography Forum

Hi,

Recently we have observed negative dips in chromatography as seen below. This has been observed across multiple HPLC systems, multiple analysts, multiple products, multiple phases and multiple columns with no real common denominator. Has anyone observed this before and can give some information as to what may be causing this?

https://www.imghippo.com/i/ATROo1718887894.png

Not much to go on here...
Your photo did not come through (at least for me) - please find the suggestions for making that work among the forum's sticky posts.

Absent any specifics, I'd look at degassing techniques and whether these systems are in need of passivation. I'd also be curious about whether your water source is up to snuff and whether your in-line filters have been changed recently (or ever). These are likely common denominators for many labs.

Not much to go on here...
Your photo did not come through (at least for me) - please find the suggestions for making that work among the forum's sticky posts.

Absent any specifics, I'd look at degassing techniques and whether these systems are in need of passivation. I'd also be curious about whether your water source is up to snuff and whether your in-line filters have been changed recently (or ever). These are likely common denominators for many labs.

I've fixed the image issue now if this is more helpful

An air conditioner or another electric device working near your instruments might cause this.

Not enough information provided (you provided no methods or analysis info at all so probably are a new user). Based on the one image, here is a common reason large area of negative signal may appear during an analysis run that we see users without formal training in using the UV/VIS detectors make. Please review this article for more info.
"REFERENCE WAVELENGTHS (as used in HPLC UV/VIS); https://hplctips.blogspot.com/2011/03/r ... -hplc.html

PS. Your image does not show a "negative dip". It shows the entire signal move into the negative region as if the compound being measured has "negative" absorbance relative to the baseline reference signal used by the detector. If it were to occur quickly, at or near the injection (Tzero), then it would most likely be the result of using the wrong injection solvent (or dissolving your sample in the wrong solution). However, your signal drop long after the method is underway and retention has been established so it has to be related to the detector's signal settings (That you input for collection).

Did you compare previouse good result method with the one you posted. Maybr someone add some gradient lines to your time table
Regards,
PS