Decreased detector response

[ivana nj]

Hi,
I am running ion-pairing chromatography (DAD detector) with a mobile phase consisting of 80% phosphate buffer (1 mM octanesulfonic acid) and 20% acetonitrile. A few days ago, I noticed a significant decrease in response. All peaks are still present at similar retention times, and the pressure is stable, but the overall response (including both standards and blanks) has dropped by almost 10-fold. I’ve checked the mobile phase and performed a system check (which passed), but the issue persists. Does anyone have any suggestions on what could be causing this?
Thanks in advance.

[DR]

dirt or bubble in flow cell, lamp deterioration...

what wavelength are you monitoring?
have you changed the scan rate or bandwidth?
do you filter your OSA solution?

[vmu]

What do you mean by "response"? Do you mean peak areas? What kind of "system check" did you do? Did you check that all the method parameters (injection volume, wavelength, etc) were not changed (maybe unintentionally)?

[ivana nj]

I did not change any of parameters. The wavelenght Im monitoring at it 257 nm. I do filter OSA. I also came to idea it could be dirt or air bubbles in flow cell or maybe in syrige. But than again, peak area of my analyte is repeatable, only much lower than before.

[JI2002]

What’s the injection volume? The blank is supposed to be free of the target, why does the response of the blank drop 10x?