|MadSci Network: Biochemistry|
I misread your question the first time and I had some help clearing up what you wanted to know. So sorry about the delay. :)
With a normal Spec. 20 like the ones you use in a General Chemistry Lab you should be able to go down to 1.0 mg/mL concentrations with no problems. If you need more sensitivity then there is the Lowry Assay (microgram range)
A book on biochemical methods would have a discussion on the limits of detection for the Biuret method. (Sorry I donít remember the title of mine) This webpage (http:// www.bio.mtu.edu/campbell/Protein2.htm) provides some general guidelines for limits of detection
Try the links in the MadSci Library for more information on Biochemistry.