In order to propose the shelf life of a drug substance, its stability must be assessed by means of a forced degradation study. In the example here, different antibody-derived molecules were subjected to a range of stress conditions.
Baseline-corrected spectra for a total of 60 measurements (10 samples, n = 6) display a high signal-to-noise ratio—crucial for the detection of minor differences.
Simultaneously obtained absorbance data can be used for normalization of CD spectra to eliminate effects of slightly different sample concentrations.
After normalization, CD spectra appear to overlap virtually perfectly. But do they really? Without automated CD instruments that ensure high reproducibility, there has been no alternative to visual assessment of spectral data until recently. Would you conclude that these spectra are similar, just by looking at them? Fortunately, such user bias is now a thing of the past.
Statistical analysis enables objective evaluation of spectral results. Some degradation conditions (oxidation, high light stress, and extreme pH), actually affected the antibody's Higher Order Structure. Does this result agree with your visual assessment?
Unlike classic secondary structure decomposition analysis, HOS comparison analysis is not limited to far-UV data. Detect changes in tertiary structure with near-UV data, too!
In this example, low light stress affected the tertiary structure of IgG1 but not its secondary structure.