Analysis of Calcium in Calcinate tablet from
Prime Eastern Pharmaceuticals
Raul Calzada, Steven Sullivan, Rose Thomas.
Abstract: Analysis on the quantity of Calcium in dietary supplement was performed using
complexiometric titration, potentiometry, and flame atomic absorption. Assuming an
average weight of 1.7 g per tablet; the calcium content was found to be in a range from 513
mg to 685 mg. Analysis of the variance using Statcrunch computer program and alternative
hypothesis testing at an α-level of .01 showed that the results are consistent and that they
deviate from the stated content of 800 mg per tablet.
It has been claimed that Prime Eastern
Pharmaceuticals has decreased the
content of calcium in its dietary
supplement pills without relabeling their
product. This is of interest because
people have then been paying the same
for a product that contains less calcium
than advertised and this would result in
an increase in the profits of Prime Eastern
Pharmaceuticals. To analyze the calcium
content in the pills we performed
complexiometric titration with EDTA in
a buffered solution at pH of 10,
Potentiometric analysis with Ionselective electrode for calcium ion, and
flame atomic absorption analysis. The
calcium in the pills is contained in the
form of calcium carbonate, and so it was
treated with hydrochloric acid to separate
the calcium and with ammonium to
neutralize the solution. Our goal was to
prove that Prime Eastern Pharmaceuticals
has decreased the content of calcium in
their pills from their claimed value of 800
mg per tablet.
Experimental Section.
Materials: A buffer of pH 10, Calmagite
and methyl red was used in the EDTA
titration, Potassium chloride was used in
the potentiometric analysis. Other
materials and chemicals used are listed in
the procedures.
Preparation of solutions: Two different
solutions were used in this project: A and
B. They were both prepared by
pulverizing the calcinate tablets and
treating them with hydrochloric acid and
ammonium. Solution A and solution B
contain 1.08 g and 1.0409 g of tablet
respectively. They were diluted to
different extents; A having an
approximate concentration of 0.05M and
B of 0.006M and has dilution factor of
0.128. Solution A was used for FAA and
for potentiometric analysis, while B was
used exclusively for EDTA titration.
Complexiometric titration: 4 aliquots of
50 mL from solution B were analyzed by
titration with EDTA. 15 mL of pH 10
buffer were added to get the solution to
an optimum pH level for the EDTA.
Methyl red and calmagite were used as
indicators. The 4 volumes of EDTA used
in this part were: 21.8 mL, 20.4 mL, 21.3
mL, and 20.3 mL.
Potentiometric analysis: Solution A was
diluted to 20/250 of its original
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concentration. A 2 mL aliquot of this new
diluted solution was mixed with 10 mL
of potassium chloride and analyzed with
an ion-selective-electrode. A standard
solution of known calcium concentration
(0.01M Ca) was made and measured with
the ISE to make a calibration curve. The
standard was prepared from calcium
carbonate, and was treated with
hydrochloric acid and boiled to expel
carbon dioxide. Ammonium was used to
neutralize the solution. The standard was
used to make four different solutions of
1/100 1/50, 1/20, and 1/10 of the original
concentration of .01M. Each of these
solutions contain 10 mL of potassium
chloride and the rest water in 100 mL
volumetric flasks. A calibration curve
was created and these functions obtained:
Trial 1: y= 19.03x + 82.75. Trial 2 : y=
19.13x + 81.5 were “x” is the logarithm
of the concentration of calcium and “y” is
the voltage. This is the Nernst equation.
FAA analysis: Solution A was diluted to
approximately 20 ppm by a dilution of
2.7/250. Standard absorption values were
provided for 5 ppm, 10 ppm, 15 ppm, and
20 ppm. A calibration curve was
constructed and this equation was
obtained: y = 0.003x + .001 were “x” is
concentration in ppm and “y” is
absorption. The analyte was then
compared to the values from the
calibration curve.
Results and Discussion: It should be
noted that to find the mass per tablet, an
average weight of 1.7 g per tablet was
assumed in all experiments to keep the
results consistent. EDTA forms a 1:1
complex with calcium ions and so we
were able to find the quantity of calcium
in the unknown from the volume of the
titration. For trials 1-4, the results of
mass of calcium per tablet are: 551 mg,
516 mg, 538 mg and 513 mg, with an
overall average of 529 mg. The EDTA
titration had the most consistent results
and the smallest variance across all
experiments (but its also had the largest
sample). The problem with EDTA
titration though, is that color indicators
are not as reliable and carry a lot of the
error; this could be a reason why the
results obtained from the EDTA titration
are slightly lower than the other
procedures. In the potentiometric analysis
we obtained values of 3.4 mV and -0.3
mV for the unknown, which translate into
concentrations of 0.042M and 0.033M
after correction for dilution (dilution
factor = 1/625). From the concentrations
we found the quantity of calcium per
tablet with the results being 667 mg for
trial 1 and 522 mg for trial 2 with an
overall average of 595 mg. Both trials
produced very close results, but the
measurement of the unknown carries
some error because it fell outside the
range of the curve and so the values
calculated are extrapolated from the func
Unknown
potential (mV)
3.4
-0.3
Concentration
6.77E-05
5.30E-05
correction for DF
0.042
0.033
Moles of Ca
0.011
0.008
424
332
39.3%
30.7%
mg/tablet
667
522
average
595
Mass (mg)
% composition
Table of results of potentiometric
analysis.
tions.
2
The FAA analysis provides the best
results because the values fall in the
range of the calibration curve. Correcting
for a dilution factor of 2.7/250 and
knowing the volume of the original
solution we found the mass per tablet to
be 576 mg for trial 1, 685 mg for trial 2,
and an overall average of 630 mg.
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Statistical analysis: Its easy to see from
one look that the average weight per
tablet is lower than advertised, but we are
also concerned with how the results vary
with each other. Using Statcrunch, we
performed an analysis of the variance of
the data.
Assuming that the samples came from
normal populations and with similar
variances, this ANOVA shows that the
samples have the same mean. This is by
comparing the F value obtained from the
test with an F test table with 2 and 5
degrees of freedom (F.05 value at df 2,5 =
5.79. 5.79 > 2.0705) The F value is
obtained by comparing 2 approximations
of the variance, which are SS/(n-1) (sum
of squares) and MS/(n-k) (mean square).
Now that it is established that the
samples have the same parent mean, we
can test the hypothesis that Prime Eastern
Pharmaceuticals has not changed the
content in its dietary pills. For this we
compare the average of all measurements
with the claimed value of 800 mg.
Overall mean: 571, standard deviation:
68.1, t.01 with 7 df: -2.9979. n:8
t obtained from test: ( 800571)/68.1/sqrt(8) = -9.51
Since we are interested with our mean
being smaller that the claimed mean the
fact that the t obtained is smaller than the
t.01 confirms, with 99% confidence, that
Prime Eastern Pharmaceuticals has
changed the contents of its tablets.
Although the statistical analysis can show
mathematically that the results deviate
from the claimed value, the ANOVA is a
very robust analysis and big assumptions
had to be made to make it work (like
assuming all samples came from normal
populations and had similar variances).
Still, just comparing the average of 571
mg per tablet with 800 mg per tablet
raises doubts on Prime Eastern
Pharmaceuticals claim.
Conclusion: Results obtained from the
three methods are consistent with each
other and show that Prime Eastern
Pharmaceuticals has indeed changed the
contents of its supplementary diet
calcium tablet. The values of milligrams
of calcium per tablet vary among the
three experiments from 513 mg to 685
mg, and have an overall average of 571
mg, a change of 28% from 800 mg per
tablet. This means that Prime Eastern
Pharmaceuticals is theoretically saving
28% on the making of the tablet, while
the costumers are uninformed of the
changes. For better results, more samples
could have been made, especially for
FAA and potentiometric analysis since
only two trials were performed in each.
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Reference:
1) Harris, Daniel C. 1999, Quantitative Chemcial Analysis, W.H. Freeman and
Company New York city, 19,77 p.
2) Johnson, Richard A. 2000, Probability and Statistics for Engineers, Prentice Hall,
Upper Saddle River, NJ, 245-246, 392-397 p.
3) Fall 2011 CHEM 318 syllabus.
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