The application of high throughput experimentation (HTE) in protein purification process development has created an analytical bottleneck. Recently, a new label-free and non-invasive methodology for analyzing multicomponent protein mixtures by means of spectral measurements was presented. Analytics based on the methodology was shown to increase analytical throughput for selective protein quantification significantly, however this was only demonstrated for one particular protein combination. In this work, the possibilities and limitations of the analytical method are investigated further. Principal component analysis (PCA) was performed on a broad range of absorption spectra to investigate their common characteristics and differences. The PCA was used both for cluster analysis and to define a measure for spectral similarity. For binary protein combinations, the calibration precision was shown to decrease exponentially with the defined spectral similarity factor. Knowledge of this correlation can be used to determine a priori whether a calibration will be successful or not. Calibration robustness was investigated by applying the analytics to liquid chromatography performed in HTE mode. Further it was shown, that a spectral difference of 0.6% was sufficient to sucessfully preform a spectral based calibration of two IgG1 monoclonals. Biotechnol. Bioeng. 2013; 110: 448460. (c) 2012 Wiley Periodicals, Inc.