Correction to: Development of a column-switching LC-MS/MS method of tramadol and its metabolites in hair and application to a pharmacogenetic study

In the original version of the article titled "Development of a column-switching LC-MS/MS method of tramadol and its metabolites in hair and application to a pharmacogenetic study", published in 41(5):554-563 (https://doi.org/10.1007/s12272-018-1013-7), unfortunately an important statement was missing in the Clinical study section by the author.