Ghost peaks in reversed-phase gradient HPLC: a review and update.

New examples and sources of ghost peaks in reversed-phase gradient HPLC are described and related to previous publications to give a broad perspective of ghost peak problems. In one new example the ghost peak was found to be due to mixing problems caused by a period of non-delivery of the stronger "solvent B" in a stepped gradient system. In a second example the ghost peak was due to plasticizer contamination of the organic solvent. This paper includes tips and recommendations for the consistent running of ghost-peak-free reversed-phase gradient HPLC.