Basline problems

[Rganga]

I am running samples with gradient with the following method:
T(min) H2O Acetonitrile Methanol Flow
65.5 23.7 10.8 1
4 65.5 23.7 10.8 1
38 11.1 37.6 51.3 1
39.5 11.1 37.6 51.3 1
39.6 100 1
48 100 1
48.01 65.5 23.7 10.8 1

I have a lot of problem with my baseline and some strang peaks without injecting the sample. And the baseline is not linear, it is jumping exponentially. What could be the problem? The gradient, the detector.

Thanks

[tom jupille]

What stationary phase (column packing)?
What column dimensions?
What detector (if UV, what wavelength)?

Best guess is that your strange peaks are contamination in the "A" solvent reservoir. Your baseline problems may be normal, depending on your detector, wavelength, and column dimensions.

Try running through the HPLC Troubleshooting Wizard on the LC Resources web site:
http://www.lcresources.com/resources/resources.html
click on the link for the Troubleshooting Wizard.

[Rganga]

my column is c18 150 * 4.6 with 5 u package,
UV detection with 3 wavelenghts 234, 280 and 300 nm

Thanks

[tom jupille]

UV detection with 3 wavelenghts 234, 280 and 300 nm

And do you see the same strange peaks and baseline problems at all three wavelengths? And how much baseline drift do you actually have? Seeing a chromatogram would help (instructions for posting chromatogram are here).

If the baseline drift is worse at longer wavelength, then I would suspect refractive index effects. To some extent, this is normal (and unavoidable). If it is exessive, it can indicate that your flow cell is misaligned and that the detector requires service.