6. Quantification of key excipients
In addition to protein structure and glycosylation, other compounds can be quantified using FTIR spectroscopy. This quantification can be realized for any compounds which has specific adsorption bands and with a concentration above 0.01 mg/mL. The quantification limit cannot be determined in general as it depends on the matrix (buffer, salt,…) present in the sample.
In order to provide such quantification, a predictive model need to be calibrated. Standard samples for which the concentration of the compounds of interest is known, have to be prepared. FTIR spectra of these standard samples are recorded and used with statistical tools such as Partial Least Square Regression (PLSR) for the calibration of the predictive model.
This quantification is particularly relevant for key excipients such as Tween or polysorbate in monoclonal antibodies formulations or lipids in membrane proteins or in virus like particles (VLP’s).