Selective protein quantification on continuous chromatography equipment with limited absorbance sensing: A partial least squares and statistical wavelength selection solution

Abstract Real‐time selective protein quantification is an integral component of operating continuous chromatography processes. Partial least squares models fit with spectroscopic UV‐Vis absorbance data have demonstrated the ability to selectively quantify proteins. With standard continuous chromatography equipment that is only capable of measuring absorbance at a few user‐defined wavelengths, the problem of selecting appropriate wavelengths that maximize the measurement capability of the instrument remains unaddressed. Therefore, we propose a method for selecting wavelengths for continuous chromatography equipment. We illustrate our method using sets of protein mixtures composed of bovine serum albumin and lysozyme. The first step is to refine the raw wavelength set with a statistical t ‐test and an absorbance magnitude test. Then, the wavelengths within the refined spectroscopic range are ranked. Three existing techniques are evaluated – sequential forward search, variable importance to projection scores, and the least absolute shrinkage and selection operator. The best technique (in this case, sequential forward search) determines a subset of three wavelengths for further evaluation on the BioSMB PD. We use an exhaustive approach to determine the final wavelength set. We show that soft sensor models trained from the method's wavelength selections can quantify the two proteins more accurately than from the wavelength set of 230, 260 and 280 nm, by a factor of four. The method is shown to determine appropriate wavelengths for different path lengths and protein concentration ranges. Overall, we provide a tool that alleviates the analytical bottleneck for practitioners seeking to develop advanced monitoring and control methods on standard equipment. Application of a wavelength selection method that consists of a spectroscopic wavelength refinement step, followed by a wavelength ranking step and then a final wavelength verification step using in‐line absorbance data. The soft sensor partial least square models trained from the method's wavelength selections can selectively quantify proteins more accurately than from a set of 230, 260, and 280 nm wavelengths. The proposed method is shown to generate appropriate wavelengths for data sets of different path length and concentration ranges.