Convenient method for checking detector response of spectrophotometers at three wavelengths

We describe the use of a water-soluble dye, available as green food coloring, to check the linearity of detector response of spectrometers and spectrophotometers at three wavelengths. The dye has absorbance maxima at 257 nm, 410 nm, and 630 nm. The advantages of using this solution for this important instrument function check are: one solution with absorption maxima in the opposite ends of the visible spectrum as well as in the ultraviolet region; safe; inexpensive; readily available; easy to use; absorbance not dependent on pH from 2.5 to 10.0 or on temperature from 4 to 56 degrees C.