Spectrum acquisition.

After you have optimized the protein sample concentration, you are ready to acquire a real spectrum.
To do so, I suggest you use the following parameters:

Wavelength range : 180-260 nm (at least 185-260 nm)
Scan speed: 5 nm/min
Response: 16sec
Accumulation: 3
Spectral width: 1nm
Resolution: 1nm

Note the lower scan speed and the increased number of accumulations to keep a lower noise level in the spectrum.
This time, the measurement will require about 1h, so please ensure you have enough nitrogen in the nitrogen reservoir and then have a coffee break.

After the data collection is finished, save the data (Jasco users: you have to go in the Standard Analysis component and save the spectrum there EVEN AFTER PRESSING "OK" IN THE MESSAGE BOX WHICH APPEARS AT THE END OF DATA COLLECTION!!!!).

Now clean up the cuvette properly (3 times with bidistilled water) then fill it with the sample buffer.
Collect a spectrum of the buffer under the same conditions you used for the protein. Please note that this is not an optional step, because you have to subtract the buffer background contributions from your spectrum before the data analysis. Save the spectrum of the buffer and then eventually go to the data analysis section of this tutorial.