reference wavelength - how it is determined for a specific sample? (May/27/2010 )

in my old lab, we never measured our samples (BCA Assay...) at a reference wavelength!

why should this measurement normally should be done?
how can i determine the right wavelength to measure my reference??

i dont want to purchase more than one additional absorption filter (e.g. 600nm) for reference measurement of different applications!!

thx in advance

A reference measurement is done to correct for interference from different sources, examples are different absorbance by the cuvettes and particles in the solution.
If your samples and materials are well defined and the photometer and cuvettes well maintenanced it would not be necessary.
To find your reference wavelenght you have to get a spectrum and look for a wavelenght where the absorbance is low and stable at low and high values from your sample.