There are instances when the presence of one species in a sample does not influence the
measurement of another species in the same sample; i.e., they do not interfere. In this
experiment two analytes are present and neither affects the light-absorbing properties of the
other. Thus, the absorption of light by the components of the sample solution is additive; that is,
the total absorption of light at any given wavelength is just the sum of the absorbances the two
substances would show if measured individually under the same conditions. You should be
aware that this is not always the case, and that strong interferences can preclude simple
simultaneous determinations of concentration. Indeed this experiment starts with you
demonstrating that the spectrum of the analyte mixture is the sum of the spectra of the two
components measured separately.