Baseline noise at Less than 220nm

[roslin]

My baseline noise in hplc is very high at wavelength less than 220nm only . I am using mobile phase methanol/water 3:2
how do i resolve my problem?

[tom jupille]

How high is "very high" (what is your peak-to-peak noise measured in absorbance units)?
Are you pre-mixing your mobile phase or mixing in-line using the pump's proportioning system?
Is the noise periodic or random?

Possibilities include:
- dirty or contaminated methanol
- a dirty flow cell
- irregular pump flow
- dirty or contaminated water
- a dying lamp
- mixing problems

[skunked_once]

Pure methanol has a significant UV absorbance at 220 nm and the absorbance increases quickly below 220 which would result in a very high background signal.