circular dichroism cd spectroscopy https://www.creative-proteomics.com/pronalyse/circular-dichroism-spectroscopy-far-uv.html Creative Proteomics is an expert in CD spectroscopy. The purity of samples for CD spectroscopy must be at least 95% (HPLC, MS or SDS-PAGE). The buffer should not have a high absorbance in region 190-250 nm of the spectrum. For example, high concentrations of DTT, histidine, or imidazole, cannot be used in the far-UV region. For many formulated protein samples, the absorbance of the excipients prevents collecting spectra below 200 nm. If this does happen, the calculated percentage of different kinds of secondary structure will not be reliable.