Base line going negative

[mk12]

I am using PDA detector. My base line is always going negative so I am not able to see my peak..what is causing that? it is the flow cell or something else.

[mbicking]

What kind of PDA do you have? What wavelength are you measuring?

Is this an isocratic or gradient separation? What are the mobile phase components?

In some situations, a negative drifting baseline is normal. In other cases, it could mean that one solvent ("A" if this is a gradient) is contaminated.

[HW Mueller]

Why do your peaks disappear? Do you use a strip chart recorder for data collection?

[Rob Burgess]

MK - can you supply a example chrom?

See my earlier postings about strange baseline effects with a faulty flow cell on my UPLC system.

[mk12]

I am using Accela PDA(by thermofisher). My mobile phase is 70:30 Water:MeOH (isocratic).Flow rate is 0.2ml/min. Base line starts at 0 and then goes down to -2000-5000 and then I have normalise( auto intensity) to see the peaks.

[mk12]

wave lenght I am using 220 and 254.

[HW Mueller]

What I tried to ask is whether your data are lost when you don´t see the peaks while the chromatogra is running. I am just curious about what people hook up to a relatively modern machine like a PDA to do data analysis/workup.

[unmgvar]

-2000 to -5000 mAU is a lot.
accela models are pretty new so your instrument should be still under warranty logically.
first approach that i would take is use the vendors PQ test for drift.
if the test fails and the procedure uses water then there are 2 reasons for the failure.
the PDA itself or the water. make sure that you use good quality HPLC grade water for the test if it is required in the procedure.