Figure 2.

PCA scores plots obtained for USA-F (U) and Japan-F (J) nonspiked pooled urine samples (1), QC at low (2), and QC at medium (3) concentration level in three different validation series (freshly prepared, green; three freeze–thaw cycles, blue; long-term storage, red) in negative, R²X = 87.1%, Q²X = 75.6% (A), and positive, R²X = 85.7, Q²X = 76.0% (B) ion modes.