Analysis of Calcium in Vitamin Tablets
Keith Sager, John Marks, Sang Ho Han, Ahmed Omar (Group 4)
__________________________________________________________________
ABSTRACT: Three different experiments were performed in order to analyze the calcium
content in a mass-produced calcium supplement tablet. All of the methods involved creating a
solution containing a certain amount of the crushed tablets. In the first experiment, the tablet
solution was titrated with a solution of EDTA (with known concentration). The second
experiment involved using a flame atomic absorption apparatus to analyze the solution’s calcium
content. The last analytical method involved using an ion-selective electrode designed for
calcium ions. The various experiments all indicate that the actual average calcium content of a
single tablet is lower than the amount that is advertised on the bottle.
Calcium is an essential nutrient for
particularly useful for the determination
healthy bones and for critical bodily
of a mixture of different metal ions, such
functions such as controlling your blood
as calcium, in solution. An indicator,
pressure and maintaining your heart beat.
Calmagite and methyl red, capable of
The majority of the body’s calcium is
producing an unambiguous color change
stored in the bones and teeth. This
is usually used to detect the end-point of
calcium is taken from the bones as
the titration. Direct potenitometry with a
needed for use in critical bodily
calcium sensitive ion-selective electrode
functions. The calcium removed from the
allows us to measure the concentration of
bones is naturally replenished through
calcium in solution using the Nernst
dietary intake. If more calcium is taken
equation. Flame atomic absorption is a
than replenished then the bones become
very common technique for detecting
weak and break more easily. When the
metals by reducing the atoms to free,
calcium intake from diet is not adequate,
unexcited ground state atoms, which
dietary supplements are often used to
absorb light at characteristic wavelengths.
meet the recommended daily intake. One
Light of the appropriate wavelength is
such dietary supplement is Calcinate
supplied and the amount of light
produced
by
Prime
Eastern
absorbed can be measured against a
Pharmaceuticals. Recently, however,
standard curve.
claims have been made that the amount
of calcium in each tablet is not accurately
EXPERIMENTAL SECTION
reported on the product’s label. Our goal
To measure the amount of calcium in the
was to determine whether the amount of
form of calcium carbonate present in the
calcium in the tablets was accurately
tablets, we used three analytical
reported on the product’s label. This was
techniques: Volumetric Titration of Ca2+
accomplished using three techniques:
with EDTA, Potentiometric Analysis of
complexometric titrimetry, potentiometry
Calcium ions, and Flame Atomic
using an ion-selective electrode, and
Absorption. Each method determined the
flame atomic absorption analysis.
amount of calcium present using a
Complexiometric titrimetry is a form of
different property. Volumetric titration
Volumetric Analysis in which the
with EDTA measured the volume and
formation of a colored complex is used to
thus the molarity of Ca2+ ions with the
indicate the end point of a titration.
property that metal ions react completely
Complexometric
titrations
are
with EDTA. Potentiometric analysis
1
determined the concentration of Ca2+ ions
using its electric potential from a calcium
Ion-Selective-Electrode(ISE). Flame
Atomic Absorption measured the
concentration of calcium ions with the
fact that the free ions when vaporized
absorb wavelengths produced by a
calcium right bulb.
Volumetric Titration of Calcium
ions with EDTA required the calcium
carbonate present in the tablets to be
ionized into Ca2+ ions. These ions then
reacted with EDTA in a one to one ratio,
allowing us to determine the
concentration of Ca2+ with the known
concentration of EDTA and volume.
Potentiometric Analysis of
Calcium ions used the calcium selective
probe and measured the difference in
potential. With standard solutions of
known molarity we measured the
potential and then created a graph and
line of best fit to interpret the
concentration with electric potential.
Flame Atomic Absorption used a
flame to vaporize the solution of calcium
ions. A calcium bulb is then directed at
the vapor and the wavelengths are
compared with the control.
To prepare our sample for all of
the three methods, we ground the tables
with a pestle and mortar, dissolved it in
water and used HCl if it was not fully
dissolving, boiled the sample to remove
Carbon Dioxide that may have been
trapped in the deionized water, and
diluted accordingly. For the Volumetric
and Potentiometric analysis we had to
neutralize the sample using NH4OH.
The major solutions used were HCl,
EDTA, pure calcium carbonate standard,
KCl and NH4OH.
However, the following values were
found from the various methods:
Method
Titration with EDTA
Flame Atomic
Absorption
Potentiometry with
Ion-Selective
Electrode
Calcium Content
(mg Ca/tablet)
653
584
531
The average value being 589 mg
Ca/tablet.
Flame atomic absorption was the
most reliable method in that it was the
simplest procedure with the least number
of solutions and sources of error
compared to the other two methods. This
coincides with the value from this
experiment being very close to the
average value found.
The largest error we encountered
in this lab was the unknown solutions
remaining cloudy despite adding
substantial amounts of acid. The standard
solutions were clear because they did not
contain any impurities. The unclear
solution or impurities could have been
caused by the tough other shell of the
tablet. When grinding the tablet, before
we could access the CaCO3, we had to
crack the tough outer shell. Some of this
powdered outer shell could have been
insoluble, which would account for the
fine white power or tint. These impurities
however were so fine that they could not
be removed by filtration. When
preforming the analysis with EDTA, the
unknown sample was clear, which is why
we believe that these results are far more
accurate than the other methods or
analysis despite the procedure for Flame
Atomic Absorption being the most
reliable.
RESULTS AND DISCUSSION
The vitamin tablets are advertised to
contain 800 mg of Calcium per tablet.
2
In order to obtain a clear sample
for Potentiometric Analysis, we had to
first dilute the sample to 15/100 of the
original concentration. This change in
glassware could leave residual amounts
of the sample solution on glassware
which would lower the calcium
concentration in respect to the theoretical
value. After the dilution, we added excess
amounts of HCl until it became clear and
then neutralize the solution with NH4OH.
The large amount of NH4Cl could have
affected the electric potential of the
solution which would result in a faulty
potential and concentration.
The results of this lab validate the
complaints of the people which states
there is actually less calcium in the
vitamin tablet than is advertised. This
means that individuals who use this
product are being cheated by not getting
as much calcium as they believe they are.
If deprived of enough calcium, those
individuals could face adverse health
conditions.
Figure 1: Concentration vs
Absorbance
0.0800
0.0700
y = 0.0033x + 0.0047
Absorbance
0.0600
0.0500
0.0400
0.0300
0.0200
0.0100
0.0000
0.00
5.00
10.00
15.00
Concentration (ppm)
20.00
25.00
Figure 1: Flame Atomic Absorption
This is the plot of the concentration vs. absorbance of the standard solutions. The
absorbance was the measurable quantity in this procedure With the best fit line as the
calibration curve, the concentration of the unknown sample can be determined
mathematically.
3
Figure 2: Voltage vs Log[Ca] for
Standard Solutions
45
40
35
Voltage (mV)
30
y = 28.759x + 114.76
25
20
15
10
5
0
-3.0500 -3.0000 -2.9500 -2.9000 -2.8500 -2.8000 -2.7500 -2.7000 -2.6500 -2.6000 -2.5500
Log[Ca]
Figure 2: Potentiometry with Ion-Selective Electrode:
This is the plot of log(concentration) vs. voltage of the standard solutions. (The
relationship is linear because the horizontal axis is on a logarithmic scale). The voltage
was the measurable quantity in this procedure. With the best fit line as the calibration
curve, the concentration of the unknown sample can be determined mathematically.
4
Without receiving the daily
recommended intake of calcium, the
customers will not be able to replenish
the calcium lost in their bones, which will
lead to weaker bones and other possible
health risks.
CONCLUSIONS
Our results from each technique
used verified that the amount of calcium
in a tablet of Calcinate produced by
Prime Eastern Pharmaceuticals does not
match the labeled value of 800 mg. Using
an average of the three techniques
performed, we determined that there was
589 mg of calcium in a tablet of
Calcinate. Based on these calculations,
the actual amount of calcium per tablet is
approximately 26% less than the reported
value. This is a significant difference that
adversely affects the consumers of this
product. By falsely reporting values for
the amount of calcium in their product,
Prime Eastern Pharmaceuticals is directly
affecting the health of its customers.
REFERENCES
(1) Journal of Chemical Education
(2) The Chemical educator
(3) Analytical Chemistry
(4) Harris, Daniel C.; Quantitative
Analysis
(5) Rowe, M.W.; Hyman, M.; Miller,
A.E.; Javier, A.C.; Binamira-Soriaga, E.
Quantitative
Analysis
Laboratory
Manual
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