Comparing two metabolomic total ion chromatograms (TIC) from two different mouse phenotypes. An illustrative example of how normalization of metabolomics data based on total signal may generate bias in the data. Two mouse liver lipid profiles are drawn to scale, one from obese ob/ob mouse and one from lean wild type mouse. While the phospholipid profiles are similar in total amount, there is a large increase in triacylglycerols in obese mouse. Normalization based on total signal would wrongfully decrease the levels of phospholipids in obese mouse relative to the wild type to balance the increased amount of triacylglycerols.