Troubleshooting Problems with Ghost Peaks

Possible Cause	Prevention/Solution
Ghost Peaks
Contamination in column or injector	Use only HPLC grade solvents Flush column to remove impurities Flush injector between analyses
Late eluting peak from the previous injection	Extend run time A flush column with the strong mobile phase at end of each run For gradient runs, end at a higher concentration
Contaminated water in RP HPLC	Use HPLC-grade water
Unknown interferences in the sample	Use sample clean-up (e.g. SPE)
Negative Peaks
Refractive index of solute lower than that of mobile phase (RI detector)	Use mobile phase with a lower refractive index Reverse detector polarity to obtain positive peaks
Absorption of solute lower than absorption of mobile phase (UV detector)	Change UV wavelength Use mobile phase with lower UV absorption
Sample solvent and mobile phase differ in composition	Change sample solvent and dissolve sample in mobile phase if possible
Spikes
Air bubbles in the mobile phase	Degas mobile phase Install back pressure restrictor at detector outlet Ensure all fittings are tight
Column stored without endcaps	Store columns with endcaps Flush RP column with degassed methanol

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