a.) Fluctuation of column temperature. (Even small changes cause cyclic baseline rise and fall. RI-, conductivity and UV detectors at high sensitivity are most often affected.)
Solution: Control temperature of column and mobile phase, use heat exchanger before detector.
b.) Mobile phase is inhomogeneous. (Drift usually to higher absorbance, rather than cyclic pattern from temperature fluctuation.)
Solution: Use HPLC grade solvents, high purity salts and additives. Degas mobile phase before use and apply a degasser or sparge solvents with helium during use.
c.) Contaminant or air buildup in detector cell.
Solution: Flush cell with methanol or other strong solvent. If necessary clean cell with 1 N HNO3 (never with HCl).
d.) Plugged outlet line after detector. (High pressure cracks cell window, producing noisy baseline.)
Solution: Unplug or replace line. Refer to detector manual to replace window.
e.) Mobile phase mixing problem or change in flow rate.
Solution: Correct composition/flow rate. Routinely monitor composition and flow rate to avoid problem.
f.) Slow column equilibration, especially when changing mobile phase.
Solution: Flush column with intermediate strength solvent, run 10-20 column volumes of new mobile phase through column before analysis.
g.) Mobile phase contaminated, deteriorated or prepared from low quality materials.
Solution: Check make-up of mobile phase.
h.) Strongly retained materials in sample (high k´) can elute as very broad peaks and appear to be a rising baseline. (Gradient analyses can aggravate problem.)
Solution: Use guard column. If necessary flush column with strong solvent between injections or periodically during analysis.
i.) Mobile phase recycled but detector not adjusted.
Solution: Reset baseline. Use new materials when dynamic range of detector is exceeded.
j.) Detector (UV) not set at absorbance maximum but at slope of curve.
Solution: Change wavelength to UV absorbance maximum.
k.) At higher lab temperatures (28°C) more baseline instabilities comparing to lower lab temperatures (22°C) when using ACN/Water or –buffer gradients and mixtures.
Solution: Higher temperatures can enhance the polymerization of ACN resulting in building of polymers. Filtration of ACN-eluent with Empore SDB-XC Polystyroldivinylbenzol filter.