The document describes an experiment to determine the amount of blue food coloring, patent blue V, contained in a single Smurf candy. Students prepare a solution by dissolving one candy in water. They then create calibration solutions of known patent blue V concentrations and measure their absorbances using a spectrophotometer. From the calibration curve, students determine the concentration of patent blue V in the Smurf solution is 6.6 mg/L. Given the volume of the Smurf solution, they calculate the mass of patent blue V in one candy is 0.33 mg. Finally, using the acceptable daily intake value set by the EU, students calculate one could safely eat around 450 Smurf candies in a day.

1. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the
views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.
Teaching Innovative Practices in STEM (TIPS)
2015-1-ES01-KA219-015719_1
TIPS GUIDE
Chemistry
C. Laugel, M-L. Frey
Lycée Marguerite Yourcenar (Erstein), FRANCE
0. Introduction
TIPS stands for Teaching Innovative Practices in
STEM, an Erasmus+ KA219 funded project where
four European schools from Belgium, France, Italy
and Spain, have worked together for two years
(2015-2017), sharing their best practices in STEM
(Science, Technology, Engineering and Maths)
subjects. More info on the project can be found
on the project web: http://bit.ly/2rRCpEI.
1. Abstract
Smurf candies, like many other candies, contain
food colouring such as patent blue V which is
responsible for the blue colour [1]. For each
colouring, the European Union sets the
Acceptable Daily Intake, that is an estimate of the
amount of a substance in food or drinking water
that can be consumed over a lifetime without
presenting an appreciable risk to health. The
experiment described in this guide aims at finding
out the number of candies that one can eat in one
day without exceeding the acceptable daily intake
for patent blue V. To do so, we have to determine
the mass of patent blue in one candy: the method
uses spectrophotometry. The final result is many
hundreds of candies per day, far away from the
quantity one can eat!
2. Materials and methods [2]
For each group of pupils:
 scissors
 one smurf candy
 a 100 mL Pyrex beaker
 distilled water
 a stirring rod
 a hot plate
 a 500 mL volumetric flask and its stopper
 a plastic pipet
 a 50 mL beaker
 a test tube and its stopper
On the teacher’s laboratory table:
 A graduated buret containing a stock solution
of patent blue V (E 131 food colouring), mass
concentration c = 5.6 mg/L (solution 1)
 A graduated buret containing distilled water
 A spectrophotometer (in this article :
Biochrom Libra S 6)
 Transparent cuvettes and plastic pipets
 Optional: 10 mL of a 11.2 mg/L solution of
patent blue V (solution 2) and 10 mL of a
16.8 mg/L solution of patent blue V.
Preparation of solution 1:
 If you have patent blue V sodium salt
(M = 582 g/mol): dissolve 5.82 mg of salt for
one litre of solution.
 If you have patent blue V calcium salt
(M = 1160 g/mol): dissolve 11.6 mg of salt for
one litre of solution.

2. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the
views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.
Teaching Innovative Practices in STEM (TIPS)
2015-1-ES01-KA219-015719_1
Preparing the smurf solution[3]
 Cut off the cap of a smurf candy (Figure 1)
using scissors, to keep only the blue part of
the body. Take care not to remove blue parts
or you would underestimate the mass of the
colouring. Be also careful not to leave any
coloured cap, especially if it is red, otherwise
you would overestimate the concentration in
blue. Indeed, the anthocyanins responsible
for the red colour absorb at the maximum at
about 520 nm, so they still absorb at around
640 nm which is the wavelength chosen on
the spectrophotometer (maximum of
absorption for blue patent). There is no
problem with the yellow colouring (lutein),
which does not absorb at this wavelength.
Figure 1. Smurf candies (Haribo)
 Put the smurf into a 100 mL Pyrex beaker.
 Add distilled water (20 to 30 mL maximum).
 Heat the beaker on the hot plate and keep on
stirring the solution until the candy is
completely dissolved.
 If needed, let the solution cool down until it
becomes warm.
 Transfer it into a 50 mL volumetric flask.
 Rinse the beaker with a small amount of
distilled water and add the rinses into the
volumetric flask. Be careful not to use too
much water: you must not exceed the
calibration mark.
 Add distilled water up to the calibration mark
using a plastic pipet.
 Plug and shake to get a homogeneous
solution.
 Transfer the solution into a 50 mL beaker:
the solution is ready for analysis.
The prepared solution, called smurf solution, is
blue and contains the quantity of patent blue V
contained in ONE smurf candy.
When performing this experiment with the
Erasmus+ group, each of the 7 groups of pupils
prepared his own smurf solution.
Preparation of the dilute solutions of patent
blue V
You have to prepare dilute solutions of patent
blue V using stock solution 1. Two graduated
burets are provided for the pupils on the teacher’s
table. One of them contains solution 1, the other
one distilled water. Each group receives a number
related to the dilute solution they have to
prepare. Depending on the pupils’ knowledge and
on the time you have, you can:
 either ask the pupils to find the volumes
of solution 1 and distilled water needed
for the dilution, knowing the mass
concentration or the dilution factor.
 or give them the complete experimental
protocol.
A volume of 10 mL of each dilute solution is
enough for the measure using the
spectrophotometer. In a test tube, each group
pours V1 of solution 1 and Vw of distilled water
according to the data of their group number. The
test tube is then plugged and shaken to get a
homogeneous solution.
The sampling of the solutions can also be made
using graduated pipets.
An example of dilutions, done by the Erasmus+
group, is shown in table 1.

3. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the
views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.
Teaching Innovative Practices in STEM (TIPS)
2015-1-ES01-KA219-015719_1
Cuvette containing the
coloured solution to analyse
Table 1. Preparation of dilute solutions of patent blue V:
mass concentrations of patent blue V and volumes of
stock solution of patent blue V (solution 1) and of
distilled water to sample
Group number 1 2 3 4 5 6 7
Mass concentration
c in mg/L
5.04 4.48 3.92 3.36 2.80 2.24 1.68
V1 in mL 9.0 8.0 7.0 6.0 5.0 4.0 3.0
Vw in mL 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Absorbance measurements
Each group measures the absorbance A of the
dilute solution they have prepared. To do so:
 Adjust the wavelength of the
spectrophotometer on the maximum of
absorption of patent blue V that is 640 nm.
 Blank the spectrophotometer on distilled
water.
 Measure the absorbance of the prepared
dilute solution (Figure 2).
Figure 2. Spectrophotometer cuvette containing the
solution to analyse
We also measure the absorbance of solution 1,
and, if required, of solutions 2 and 3.
All these measurements will help plot the
calibration curve (see Results and evaluation).
Then each group measures also the absorbance AS
of their smurf solution.
3. Results and evaluation
Spectrophotometry and calibration line
Our eye is very efficient to detect colours, yet it
cannot make measurements! A spectrophotometer
is a device that measures the intensity of the light
getting through a coloured solution: more precisely,
it measures the intensity of the light before and
after having gone through the solution (Figure 3)
and calculates a quantity called absorbance A (no
unit).
Figure 3. Beams of light before and after the crossing
through the cuvette containing the coloured solution to
analyse
Absorbance depends on several parameters, such
as the chemical that gives the solution its colour,
the concentration of this chemical, the width of
the cuvette containing the solution and the
wavelength of the light that goes through the
solution. In our work, we can use Beer’s law,
which states that absorbance and concentration
are proportional:
A = k c (k being a constant)
Plotting A versus c leads to a line and gives us the
link between the absorbance of patent blue V and
its concentration in solution. This line is called
calibration line.
This line can then be used to find out the
concentration of the smurf solution, reading its
value directly on the graph or calculating it using
the equation of the line.

4. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the
views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.
Teaching Innovative Practices in STEM (TIPS)
2015-1-ES01-KA219-015719_1
Results
 Absorbance of solutions 1, 2 et 3
Solution 1: A1 = 1.06
Solution 2: A2 = 1.47
Solution 3: A3 = 2.27
 Absorbance of the dilute solutions
The results of the Erasmus+ group are given in
table 2.
Table 2. Absorbance of the dilute solutions according to
their mass concentration of patent blue V
Group number 1 2 3 4 5 6 7
Mass concentration
c in mg/L
5.04 4.48 3.92 3.36 2.80 2.24 1.68
Absorbance 0.73 0.67 0.59 0.52 0.42 0.27 0.32
 Calibration line
The 10 measures allow to plot the calibration line
A = f(c) (Figure 4).
 Finding out the concentration of patent
blue V of the smurf solution
Each group of pupils has measured the
absorbance AS of their smurf solution and they
can use it to determine the concentration of
patent blue V. All the measures can also be
pooled so that the average is calculated.
The results for the Erasmus+ group are shown in
table 3.
Table 3. Absorbance of the smurf solutions (Erasmus+
group)
Group number 1 2 3 4 5 6 7
Absorbance of the
smurf solution© 0.89 0.78 0.99 0.98 0.92 0.94 0.99
Average : AS = 0.93
Figure 4. Example of calibration line for patent blue V (Erasmus+ group)
0
0,5
1
1,5
2
2,5
0 2 4 6 8 10 12 14 16 18
AbsorbanceA
Mass concentrationc (mg/L)
AS = 0.93
Equationof the line
A = 0.14 c
cS = 6.6 mg/L

5. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the
views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.
Teaching Innovative Practices in STEM (TIPS)
2015-1-ES01-KA219-015719_1
We can find out the concentration of patent
blue V of the smurf solution:
 Reading directly on the graph:
We copy the value of the absorbance AS on the y-
axis, we put the dot on the line whose ordinate is
AS and we look for its abscissa (Figure 4).
Erasmus+ group (using the average): cS = 6.6 mg/L
 Using the equation of the line :
AS = k × cS so cS = AS / k
Erasmus+ group: cS = 0.93 / 0.14 = 6.6 mg/L
 Finding out the mass of patent blue V
contained in one candy
To find out the mass of patent blue V in one
candy, we must remember that the smurf solution
has been prepared using just one candy. So the
mass of patent blue V in the 50 mL solution
matches the mass of patent blue V in one candy:
mS = cS × V = cS × 0.050
Erasmus+ group: mS = 6.6 × 0.050 = 0.33 mg
The mass of patent blue in one smurf candy was
0.33 mg.
 Number of candies that can be eaten safely
Firstly we need to take into account the
acceptable daily intake (ADI) for patent blue V: its
value is 2.5 mg per kg of bodyweight per day. As a
result, for a person who weighs 60 kg, the ADI is:
ADI = 2.5 × 60 = 150 mg.
This person can eat 150 mg of patent blue V in
one day without any risk for their health.
The number of candies they can eat is:
ADI / mS = 150 / mS
Erasmus+ group:
150 / mS = 150 / 0.33 = 450 candies.
One pack of candies contains about 40 candies, so
450 candies would stand for about 11 packs.
We can find food colouring in a lot of food,
especially in sweet, and their use often runs
debates. This protocol allows to understand what
the limits (ADI) ordered by the European Union
means practically speaking. The method,
spectrophotometry, is one of the analysis
methods used by fraud control government units
to check the conformity of food.
4. Acknowledgements
The authors would like to thank the Erasmus+
programme of the European Union for funding
the TIPS project under grant 2015-1-ES01-KA219-
015719_2.
5. References
(1) N. Coppens et al., Physique-chimie Terminale S
spécifique, collection Sirius (Nathan, 2012)
(2) Académie de Versailles, Le bleu des bonbons
Schtroumphs©
:
http://www.phychim.ac-
versailles.fr/IMG/pdf/schtroumpfs_profs.pdf ou
http://www.phychim.ac-
versailles.fr/spip.php?article755
(3) M. Meyniel, spectroscopie UV-visible : bonbons
Schtroumph©
http://sciences-physiques-vesinet.e-
monsite.com/medias/files/tp-8-spectroscopie-uv-
visble-schtroumpf-bis.pdf