Fig. 1From: Mass recalibration for desorption electrospray ionization mass spectrometry imaging using endogenous reference ionsExample of the recalibration process for the Orbitrap dataset liver ES-. A FFT KDE is fitted from the matched masses for a candidate reference (303.2329 m/z). The points represent the difference in m/z between the observed and the theoretical values of the reference. The orange curve passing represents the spline fitted on the density local maxima. The GAM predictions are plotted in green. Points in white represent the inliers used to fit the GAM, while outliers are plotted in red. B The intensity corresponding to the matched points can be plotted to reveal their spatial distribution. This allows validating the consistency of the selected matches visually. C Finally, a regression model is fitted in each pixel using the only reference masses with similar errors in ppm (blue circles) within the residual intervals defined by the filter (Eqs. 6–7). In the case of TOF data, the degree of the polynomial corresponds to the smallest BIC value. The predicted values (black line, the grey bands represent 95% confidence intervals) are used to correct all observed masses in the pixel. In C, for clarity, the mass errors are plotted on the y-axis instead of the predicted observed massesBack to article page