NEME PCS

Mass error

This parameter represents the maximum allowed mass errors for individual isotopologues with respect to those of candidates from reference IPDB.

Profile Cosine Similarity

Profile Cosine Similarity is a mathematical measurement of two mass spectrometry profiles. PCS measurements can only take into account isotopologues from the reference IPDB.

$$ PCS = \sum_{i=1}^{NP} \frac{I_i^{lib}I_i^{exptl}}{{\sqrt {\sum_{i=1}^{NP} I_i^{lib}}}{\sqrt {\sum_{i=1}^{NP} I_i^{exptl}}}} $$

where $I_i$, $NP$, superscripts of $lib$ and $exptl$ values represent isotopologue intensities, number of isotopologues, and library and experimental isotopic patterns, respectively.

Normalized Euclidean Mass Error (NEME)

Normalized Euclidean mass error (NEME) is a new metric which is able to utilize resolution power of high-resolution mass spectrometry (HRMS) instruments to evaluate quality of isotopic matching.

$$ NEME = \sqrt {{\sum_{i = 1}^{NP}\left(M_i^{lib} - M_i^{exptl}\right)^2}/{NP}} $$

where $M_i$, $NP$, superscripts of $lib$ and $exptl$ values represent isotopologue masses, number of isotopologues, and library and experimental isotopic patterns, respectively.