Baseline drift

[hossam kamal]

Hi everybody
I lately had a problem with an in house method for preservatives in herbal liquid extract ( potasum sorbate , sodium benzoate , methyl paraben sodium ) respect to their elution sequence , ion pair method , mobile phase consist of phosphate buffer pH 2.5 with 0.095% tetrabutyl ammonium hydrogen sulfate , acetonitrile and THF ( 90:5:5 %) respectively , because herbal extracts are very complex samples we have to increase K` for complete peak purity ( risk benefit concept ) and fortunately it fits for all types of herbs thyme , fennel , eucalyptus , guava , tilia we produce , we are using it for about 8 months now , we tried it on schimadzu system and two different waters systems with two different models it worked well but lately I had a drifting noise of the base line in all runs ( each run is about 50 minutes , back pressure is stable along runs ,column c18 250 x 4.6 mm flow rate 1.7 mL/min wavelength 235 nm and notice that this drifting appeared on two different systems with two newly maintained and calibrates dual wavelength detectors I hope you can help me

[tom jupille]

In an isocratic method with very strongly retained "junk", it's not unusual to see baselines drift up and down as 'CRUD" (Chromatographically Retained Undesirable Debris) gradually elutes. I suspect that what you are seiing is simply *very* strongly retained and hence *very* wide peaks.

If that's the case, then purging the column with a strongrr eluant should clean it up. You will have to spend the time to re-equilibrate the column afterward.

[HPLC chemist]

I agree with Tom. Reverse the column and clean with a strong reverse phase organic solvent like 95% IPA dissolved in water.

[hossam kamal]

Thanks alot for replying ,
It appears a part of my problem , the rest is that column got so old it makes higher back pressure than usual and lately base line shows drifting noise , firstly I thought it might be the detector or mobile phase impurities but then it is the column