Figure 1.

Common situations where the nearest peak-based approach may fail to find the correct matching between the reference peaks (in solid contours) and test peaks (in dotted contours). The hypothetical reference peaks 1 and 2 are shifted to locations of the test peaks a and b, respectively, in the test spectrum as indicated by the solid arrows. (A) If the peak mapping starts from peak 2, the closest test peak a will be matched to it, and hence b will be matched to 1. This leads to an erroneous, sequence-dependent peak mapping shown as the dashed arrows. (B) If a noise peak c appears closer to peak 1 than to a, the noise will be matched to 1 and hence a to 2, leaving b unmatched.