A student placed a sample of a food coloring that contains a mixture of a blue dye and a red dye at the top of a chromatography column filled with a nonpolar stationary phase. When water is poured through the column, two bands of colors are seen in the column, as shown in the diagram above.

A student collects a sample of the blue dye from the column in a cuvette. Which of the following is least useful to determine the concentration of the sample using a spectrophotometer set at 640nm?

A. The volume of a sample
B. The path length of the cuvette
C. The absorbance of the dye at 640nm
D. The solar absorptivity of the dye at 640nm