Absorbance assay at 280 nm.  This method is just as convenient as for absorbance at 280 nm.  It may be preferred if there is excessive contamination by nucleic acids, since nucleic acids absorb very little radiation at 205 nm.  Setting the wavelength is a bit tricky since 205 nm is right on the shoulder of the protein peak.

Protocol: Absorbance Assay 205 nm