How to deal with a baseline drift?

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.



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