Figure 5

Errors in peak alignment. A portion of the hypothetical alignment table with two types of errors that occur in within-state peak alignment highlighted. The rows of the table represent metabolites and column represent individual experiments. The numbers shown are peak retention times in minutes. Panel (a) shows the type A error (peak mixing) where one or more peaks are shifted to an incorrect metabolite row. Panel (b) shows the type B error (metabolite splitting) where the metabolite row is split to create an artificial metabolite in the alignment table. The condition of minimum peaks is often imposed in practice (see Methods), in which case this type of error results in the deletion of the artificial metabolite (nevertheless the original metabolite is affected as it contains one or more missing peaks). If in the example shown on panel (b) it is assumed that the minimum peak cut-off is three peaks, and therefore both metabolite1 and metabolite2 will be deleted from the alignment table as the net result of the splitting error and the removal of spurious metabolite rows.