Robust iterative peak matching with different references. (a) Sums of absolute values of all sample-vs.-reference peak discrepancies are normalized to the pre-alignment (iter = 0) value and plotted as a function of the number of iterations completed. Data are compared for four independent alignments, with different runs selected as the reference. Regardless of which run was used as the reference, most peak retentions were corrected in early iterations (in the Ref #8 case, all peaks were solved by iteration 5 and no 6th iteration was done). Comparing the same references, the number remaining unsolved after each iteration is shown in (b).