S6. DETERMINATION OF RIBOFLAVIN BY UV-VIS SPECTROPHOTOMETRY
AIM
To determine the concentration of riboflavin in commercial tablets
INTRODUCTION
Riboflavin is also known as Vitamin B2, Vitamin G and the “yellow enzyme”. It was first
recognised in 1917 as important for growth and tissue in all animals
PROCEDURE Check the dilutions with your teacher as these will change depending
on the sample analysed.
Sample preparation
1. Weigh one riboflavin tablet on an analytical balance, record the mass
2. Grind the tablet using a clean, dry mortar and pestle
3. Accurately weigh about one fifth of the tablet and record the mass, in duplicate.
4. Quantitatively transfer the samples to 250 mL volumetric flasks.
5. Add 3 mL 1 M NaOH to the flasks and gently swirl to dissolve the sample.
6. Add 3 mL glacial ethanoic acid to the flasks and make up to the mark with water
7. Take a 5 mL aliquot from the 250 mL flasks and make up to 100 mL in volumetric flasks.
Standard preparation
1.Using the 100mg/L Riboflavin stock solution make 100 mL of the following working
solutions, diluting with 1% ethanoic acid, 2.5, 5.0, 7.5 and 10 mg/L.
2.Using the 1% ethanoic acid as the blank, scan the 5.0 mg/L standard and the sample
between 240 nm and 550nm.
3. Confirm the sample contains riboflavin by comparing the two spectra
4. Select the wavelength that gives the highest absorbance value for a clearly defined peak
5. Read all standards and the sample
Calculations

Plot the calibration graph and determine the concentration of riboflavin in the diluted
sample

Use the dilution factor to determine the mass of riboflavin in the original analytical
sample

Determine the percentage of riboflavin in the analytical sample

Compare the value obtained to the published value for the tablet, by calculating the
mass in the original tablet
RESULTS SHEET
Date of analysis:
Sample identity:
Mass of tablet
Mass of
analytical
sample 1
Mass of
analytical
sample 2
Wavelength for readings:
Standard
2.5 mg/L
5.0 mg/L
7.5 mg/L
10.0 mg/L
Sample 1
Sample 2
Absorbance
Have you?
Date
Completed the instrument log
Completed the sample register
Completed the standard register
Teachers signature
Signature