Why is my baseline intermittently wavy when running an LC gradient separation at low UV wavelength in a mobile phase containing TFA? - WKB194719

ENVIRONMENT

• Wavy baseline
• Mobile phase
• Trifluoroacetic acid (TFA)

ANSWER

Improper mixing of the mobile phase is one potential reason.

ADDITIONAL INFORMATION

When using a low UV such as 210 nm, the organic solvent portion of your mobile phase may adsorb more. If mobile phase is not properly mixed during your gradient, then the concentration of organic may fluctuate a little as the gradient is mixed. As a result, you may see intermittent higher absorption (higher baseline) and lower absorption (lower baseline). The presence of TFA in your mobile phase may enhance this effect.  

It is also common for the baseline to rise as more organic is introduced when at low UV, because the organic (for example, acetonitrile) will absorb UV. The baseline returns back to normal when the amount of organic is back to the initial concentration.

Also see articles about other potential reasons for wavy baseline at low UV: 

Wavy baseline at low UV wavelengths

UV/VIS detector - wavy baseline