Method for the comparison of complex matrix assisted laser desorption ionization-time of flight mass spectra. Stability of therapeutical monoclonal antibodies

•Straightforward andeasy-to-implement method for comparing mass spectra by multivariate chemometrictechniques.•A home-made MATLABfunction called Protiago has been developed.•A new similarityindex named 'nearness index' which assess the spatial proximity of two vectorswas proposed.•The methodology wasapplied to the mass spectra of two therapeutical mAbs to state their chemicalstability over time.

This paper describes a straightforward and easy-to-implement method for comparing mass spectra using multivariate chemometric techniques in order to detect differences and obtain representative similarity metrics. For this purpose, we have programmed own MATLAB function called Protiago. Protiago successfully transforms complex vectors (i.e. intensities and m/z values from mass spectra) with different lengths in binary vectors with the same number of elements. In addition, Protiago is able to read and properly process a set of spectra vectors in order to carry out a proper similarity analysis using four similarity metrics (i.e. the coefficient of determination, the cosine of the angle, the Bray-Curtis index and the nearness index). The latter is a new similarity index proposed by the authors and applied for the first time in this study. It calculates a standardized Euclidean distance between two vectors in the space in order to obtain a numerical value, ranged between 0 and 1, of the proximity of both vectors. To supplement the similarity analysis information, two multivariate exploratory methods were applied, i.e. principal component analysis (PCA) and multivariate analysis of variance (MANOVA). As an example of the proposed method, the comparison of peptide mass fingerprints obtained using MALDI-TOF mass spectrometry from two therapeutical monoclonal antibodies, infliximab (INF) and rituximab (RTX), was carried out. By using this method it was possible detect changes in the primary structure of the two proteins in order to study their chemical stability for 7 days under two storage conditions (refrigerated at 4 °C, and frozen at −20 °C).

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