Food Dye Analysis by Spectrophotometry

Identifying artificial food colors by their absorption spectra

Colorimetry Intermediate (High School) 60 min ~$8.00

Objective

Determine the identity and concentration of artificial food dyes in commercial beverages by measuring their absorption spectra.

Background

Artificial food dyes have characteristic absorption spectra that serve as fingerprints for identification. FD&C Red No. 40 absorbs maximally at 504 nm, Blue No. 1 at 630 nm, and Yellow No. 5 at 428 nm. By scanning the absorption spectrum of a commercial beverage and comparing peak wavelengths with known dye spectra, students can identify which dyes are present and estimate their concentrations.

Safety Warnings

  • Food dyes can stain clothing
  • Do not drink any samples after use in the lab
  • Handle cuvettes by the frosted sides only

Required PPE

goggles lab_coat

Materials

  • Standard food dye solutions (50 mL each)
    Red 40, Blue 1, Yellow 5 (0.01%)
  • Commercial beverages (50 mL each)
    2–3 colored drinks
  • Distilled water (200 mL)
    For dilutions and blank

Equipment

UV-Vis spectrophotometer (or colorimeter with multiple filters) Cuvettes (quartz or plastic) Pipettes Volumetric flasks (25 mL, 4 total)

Procedure

1

If using a spectrophotometer, scan each standard dye solution from 400 to 700 nm to identify the λmax (wavelength of maximum absorbance).

10 min
2

Record the λmax for each standard: Red 40 (≈504 nm), Blue 1 (≈630 nm), Yellow 5 (≈428 nm).

5 min
3

Dilute commercial beverage samples if too concentrated (absorbance should be below 1.0). Record all dilution factors.

10 min
4

Scan each beverage sample from 400 to 700 nm. Record the absorption spectrum.

15 min
5

Compare the beverage absorption peaks with the standard dye λmax values to identify which dyes are present.

10 min
6

If a calibration curve was prepared for a specific dye, calculate the dye concentration in each beverage (accounting for dilution).

10 min

Expected Results

Each beverage should show absorption peaks matching one or more standard food dyes. Green drinks typically contain both Blue 1 and Yellow 5. Orange drinks often contain Red 40 and Yellow 5.

Cleanup

Pour dilute dye solutions down the drain with running water. Rinse cuvettes immediately to prevent staining.

Details

Category
Colorimetry
Difficulty
Intermediate (High School)
Duration
60 min
Est. Cost
$8.00
Steps
6
Materials
3

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Frequently Asked Questions

What is the objective of Food Dye Analysis by Spectrophotometry?
Determine the identity and concentration of artificial food dyes in commercial beverages by measuring their absorption spectra.
How difficult is Food Dye Analysis by Spectrophotometry?
This experiment is rated as Intermediate (High School). It takes approximately 60 minutes to complete.
What safety precautions are needed for Food Dye Analysis by Spectrophotometry?
Key safety precautions include: Food dyes can stain clothing; Do not drink any samples after use in the lab; Handle cuvettes by the frosted sides only.
What materials are needed for Food Dye Analysis by Spectrophotometry?
The main materials required are: Standard food dye solutions, Commercial beverages, Distilled water.
What results should I expect from Food Dye Analysis by Spectrophotometry?
Each beverage should show absorption peaks matching one or more standard food dyes. Green drinks typically contain both Blue 1 and Yellow 5. Orange drinks often contain Red 40 and Yellow 5.