Spectrophotometric Analysis of Mixtures:
Simultaneous Determination of Two Dyes in Solution
Seoiyoung Ahn
SID: 23768027
Abstract
The objective of the experiment was to figure out the concentrations of Yellow 5 and Red
40 solutions in the food dye and beverage by using spectrophotometry, a common form of
analysis used to determine concentrations of certain solutes in solutions, based on the Beer-
Lambert Law. After the absorption spectra of ten solutions of varying concentrations were
measured by using Vernier SpectroVis Plus Spectrophotometer, the wavelength at which
absorbance was at its maximum was recorded for both Red 40 and Yellow 5 solution. Applying
absorbance of food dye and beverage at wavelengths chosen to Beer-Lambert law determined the
concentrations of Red 5 and Yellow 40 solutions in food dye and beverage. However, in the
calculation of concentrations of both dyes, uncertainty were generated and analyzed.
Introduction
Spectrophotometry is widely used to determine the concentrations of solutes in solutions.
In this lab, colored solutions in cuvets are placed in spectrometer, consisted of a spectrograph
and a photograph. A spectrograph shoots a light of a certain wavelength, and is calibrated to
indicate the color of the light it produces in terms of wavelength, usually expressed in
nanometers. The photometer then measures the intensity of the light beam at a given wavelength.
The fraction of incident electromagnetic radiation absorbed by several diluted and
colored solutions Yellow 5 and Red 40 (25mg/L, 12.5mg/L, 6.25mg/L, 3.125mg/L, 1.5625mg/L).
For they were colored solutions, they all have peak wavelengths. After the specific wavelengths
of interest were chosen (500.80nm and 423.1nm), the absorbance of unknown solutions were
measured when wavelength equal 500.80nm and 423.1nm. Then using the equation that

=423.1nm
=500.8nm
The concentration of red dye and yellow dye were obtained after solving these equations.
Therefore, separate absorbance of different two solutions lead us to find out the concentration of
unknown solutions (the mixture of Red 5 and Yellow 40 with certain ratio.
Method
Yellow 5 and Red 40 of known concentration (50mg/L) were diluted into several
different concentrations—25mg/L, 12.5mg/L, 12.25mg/L, 6.125mg/L, 3.1625mg/L. Then, the
absorbance spectra for these several yellow 5 and red 40 solutions of different concentrations
were measured by using the Vernier SpectroVis Plus Spectrophotometer. Furthermore, two of
wavelengths, which are 500.8 nm and 423.1 nm, at which the absorbance was maximized, were
chosen as well. The absorbance spectra of Yellow 5 and Red 40 at chosen wavelengths (500.80