Baseline drift issue 2

[gys25016]

Dear all,

I encounter another case as well for baseline drift, this time the baseline go down rather than raising. The details are:

1. C18 column
2. Mobile phase A is 0.14% phosphoric acid, Mobile phase B is ACN
3. Wavelength is 241nm (VWD). Sampling rate >0.05min
4 gradient is 75% MPA and 25% MPB. After 12 minutes, MPB increases.

However, when the MPB change after 12 minutes, realize the baseline starts going down. This is just opposite compared with baseline drift issue -1.

Any advice?

Thank you!

[HPLCaddict]

When using gradient elution you'll almost always see a baseline drift. It might be positive or negative depending on the composition of mobile phase A and B. The causes are different UV absorptivities of mobile phase A and B due to the different composition and/or refractive index changes of the eluent. Absorptivity differences are usually more pronounced at low detection wavelengths whereas refractive index changes become more prominent at higher wavelengths.
So, a baseline drift with gradient elution is not a problem per se, it depends on how pronounced it is and if it interferes with the correct quantitation of your peaks. If you can tolerate the drift, just live with it. If it's too big, you may try other brands of solvents to see if the situation changes. If the problem is mainly due to absorption differences, you may try to match the absorbances of A and B by adding a tiny amount of a strong absorbant to the less absorptive mobile phase.