Fig. 2

Assessment of data quality of the LC-MS/MS method. Overlapping total ion current chromatograms of QC samples indicated that the variations occurring during large-scale sample analysis were acceptable in negative ion (A) and positive ion (B) modes. Principle component analysis showed that all QC samples were clustered closely in negative ion (C) and positive ion (D) modes. The ratio between the number of compounds with < 3 0% coefficient of variation of the relative peak area in QC samples and all compounds detected was greater than 60% in both negative ion (E) and positive ion (F) modes