As shown in figure 1, the curve progression representing the lower concentration range of these assays is predominantly linear, but it tends to flatten out with increasing amounts of protein. In order to cover as broad a concentration range as possible, a regression method should be selected that best represents the actual curve progression. The Eppendorf BioSpectrometer and Eppendorf BioPhotometer® D30, for example, allow a choice between 5 different modes of evaluation of the standard curve (linear, quadratic and cubic regression as well as linear and spline interpolation) in order to optimally fit the curve progression.
It is recommended to generate a new standard curve for each sample measurement in order to ensure that measurement conditions will always be identical between the samples and the standard curves.
The following table shows an overview of the relevant advantages and disadvantages of the colorimetric quantification method in comparison with the direct quantification method: