experiment is conducted on the principle
Background Information:
There have recently been allegations made
against Prime Eastern Pharmaceuticals that
their calcium tablets have been inaccurately
labeled. The accusations claim that there is
now less calcium in the tablet yet Prime
Eastern
Pharmaceuticals
has
failed
to
indicate this in their labeling. Therefore, it is
the objective of this experiment to either
confirm or deny these allegations.
With all things considered three experiments
that EDTA will form complexes with
Calcium ions according to the chelate effect.
The specific form of EDTA we used was
Na2H2Y
(disodium
EDTA).
Disodium
EDTA will remain protonated at its Amines
as the experiment was conducted in a
solution buffered with a pH 10. Therefore
the reaction that takes place between EDTA
and Calcium is:
Ca2+ + H4 Y → CaH2 Y + 2H +
have been specifically chosen to measure the
The progress of the titration was tracked by
conentration of calcium in the tablets
the addition of the indicators calmagite and
manufactured
Eastern
methyl red. The end of the titration is
Pharmaceuticals. The three methods are:
indicated when the solution turns from an
potentiometry using a calcium ion selective
initial red color to a final blue color. The
diode, titration of calcium solution made by
color of the final solution was compared to a
dissolving the tablet with EDTA, and flame
blank to insure accurate results.
by
Prime
atomic absorption. All experiments have
been selected so that the impurities included
with the calcium in the tablet (such as
cellulose
and
Vitamin
D)
will
have
negligible effects on the results of the
experiments.
The
first
After the EDTA titration experiment, flame
atomic absorption was used to determine the
relationship
between
absorbance
and
concentration (in ppm) of calcium ions in
solution. Using standard solutions, a linear
regression curve can be generated and used
experiment
undertaken
was
to interpolate the concentration of calcium
titration of the calcium solution with EDTA.
ion in an unknown solution. This is done
The objective of the experiment was to
using
achieve a volumetric result via titration
absorbance
which would lead to a quantitative calcium
concentration:
concentration through calculations. The
correlation
beer’s
law,
which
increases
states
linearly
that
with
𝐴 = 𝜀 ∗ 𝑙 ∗ 𝐶 establishes a
between
concentration
and
measured absorbance (𝐴) for calcium with
function can be created which can be used to
characteristic molar absorptivity (𝜀).
In
produce a calibration curve by measuring
flame atomic absorption, a flame is used to
voltage at several different dilutions of the
atomize the sample without ionizing any
calcium solution. Another important thing to
gaseous atoms.
note is that by adding KCl to the Calcium
It is then irradiated with
monochromatic photons of a characteristic
solutions
frequency, which is 422.7 n
conducted reduces the changes in Calcium
atoms.
for calcium
This value arises due to the
difference in energy levels between the
neutral and excited electron states in the
ion
before
the
experiment
was
from diffusing into the ion selective
diode.
Methodology
atom. This method takes advantage of the
absorption of photons by the sample at
EDTA Titration: The chemicals used in
different concentrations, and uses that
this experiment were Disodium Salt EDTA
relationship to provide an accurate method
Dihydrate, HCl, ammonium hydroxide,
for measuring the concentration of calcium
unknown Calcium tablet, pH 10 buffer
ions in a sample.
solution,
indicators.
The final experiment conducted employed
the use of calcium selective diodes to
fabricate a calibration curve which was then
used for interpolation to obtain a calcium
concentration. Calcium selective diodes
function by permitting ions through a
selective membrane which then interact with
an internal reference electrode. Eventually
an electrical gradient is created by the
calcium ions (via a redox reaction between
the calcium and silver atoms inside the
electrode). Hence, a current is created which
can be measured with a digital reference
meter. With the Nernst equation a linear
Calmagite
and
Glassware
methyl
used
in
red
the
experiment included a 250 mL volumetric
flask, three 250 mL Erlenmeyer flasks, a
500 mL beaker, a 150 mL beaker, a 1000
mL volumetric flask, bulb, pipet, and a
buret. The EDTA solution was prepared by
transferring 1.0 gram of EDTA salt into the
250 mL volumetric flask and diluting to 250
mL of warm water. The water was allowed
to cool, and topped off with roomtemperature DI water to allow the solution
to compress from its expanded volume at the
higher temperature. The unknown calcium
solution was formulated by measuring out
0.8 grams of the calcium powder into a 150
mL beaker, dissolving drop-by-drop with
concentration of calcium ions in parts per
6M HCl, adding 100 mL DI water, bringing
million.
the solution to a pH of 6 with ammonium
prepared by measuring 0.1 grams of calcium
hydroxide, and diluting to 1000 mL. The
tablet into a 150 mL beaker, dissolving
titration was carried out by pipetting 50 mL
drop-by-drop with HCl, boiling in 100 mL
of the prepared calcium solution into three
DI water, and diluting to 500 mL. 20 mL
250 mL Erlenmeyer flasks with 15 mL
were then transferred into a 100 mL
buffer solution, 6 drops calmagite indicator,
volumetric flask, and diluted to the mark.
and 4 drops of methyl red indicator.
The standard solutions were used to plot a
Titration was carried out until clear. The
calibration curve with which to measure the
volume of EDTA used in each titration is
calcium ion concentration in ppm.
used to calculate the moles of calcium ion in
solution using a 1:1 stoichiometry for
Flame Atomic Absorption: The chemicals
used in this experiment included the
unknown calcium compound, pure calcium
carbonate, hydrochloric acid, and deionized
water. The glassware involved includes a
150 mL beaker, a 500 mL volumetric flask,
a pipet/bulb combination, and a 100 mL
volumetric flask. Two cuvettes were used
for measurement in the flame atomic
spectophotograph.
The
experiment was conducted by creating four
standard solutions, and then preparing an
unknown solution using the calcium sample
assigned.
Potentiometric Analysis:
The chemicals involved in this experiment
EDTA/metal ion complexes.
absorption
The unknown solution was
The standard solutions were
prepared by the TA with which to create a
linear regression model describing the
relationship between absorption and the
were pure calcium carbonate, the unknown
calcium tablet powder, deionized water, and
potassium chloride. The glassware used in
the
procedure
includes
six
100
mL
volumetric flasks, a two mL volumetric
pipette, and a measuring pipette.
To
measure the electric potential of each
sample, a calcium ion selective electrode
was used. To calculate the electric potential,
four standard solutions were prepared, in
addition to one unknown solution to be
tested.
The standard solutions were
formulated by dissolving 1.0 gram calcium
carbonate into a 100 mL volumetric flask
and diluting. 10 mL of that solution were
pipetted into a second 100 mL volumetric
flask and diluted again. From this solution,
volumes of 1, 2, 5, and 10 mL were
transferred
into
respective
100
mL
volumetric flasks and diluted. Once the four
standard
solutions
were
unknown
solution
was
prepared,
an
formulated
by
transferring 2 mL of unknown calcium
solution into its own 100 mL volumetric
approximate volume needed to reach
equivalence for each trial is shown in table 6.
The average volume required was found to be
31.70 mL of EDTA. Using the molar ratio of
EDTA to Calcium and also the fact that each trial
is one fifth of the total solution prepared, the
moles of Calcium can be calculated. Then from
the molarity of EDTA, moles of Calcium, and
molar mass of Calcium, the mass of Calcium in
the tablet can be determined for each of the
trials.
flask. Each solution was transferred to a
100 mL beaker and the potential measured
using the calcium ion electrode.
The
measured values for the four standard
The mass of Calcium was used to
calculate the percentage of Calcium in the
tablet. As shown in Table 1 the percentage was
solutions were used to create a calibration
Table 1
% Ca/tablet
mg Ca/tablet
curve with which to measure the calcium ion
found by multiplying by the proportion of the
concentration of the unknown solution.
tablet used in the experiment. The expected
Safety:
There was no significant safety
concern for these experiments.
In each
experiment, hydrochloric acid of a high
concentration was used. Hydrochloric acid
is corrosive, and should be handled with
Trial 1
Trial 2
Trial 3
Average
34.6141 34.3937
35.8268
34.9449
623.0544 619.0862
644.8821
629.0076
value of calcium of Calcium per tablet was
800mg, however the average calculated was
found to be 629.0076mg per tablet.
The
experimentally determined value of Calcium per
tablet was about 200mg lower than the stated
value.
care to avoid contact with the skin and eyes.
Ammonium hydroxide is caustic; similar
Two trials were prepared by flame
Avoid contact
atomic absorption from different tablet masses
with skin and eyes with calmagite and
to be viable comparison. Four standards were
methyl red indicators, as both are associated
prepared by a teaching assistant and used to
with a pH, thus potentially irritant to the
make the two calibration curves in Figure 1
eyes and skin.
using Beer’s law.
care should be practiced.
Results/Discussion:
Three separate trials were used to
titrate EDTA into calcium. The concentration of
the EDTA was determined to be 0.01109M. The
Absorbance vs
Concentration
Figure 1
0.3000
Absorbance(nm)
0.2500
0.2000
0.1500
0.1000
y = 0.0143x - 0.0386
R² = 0.9679
0.0500
0.0000
0.00
10.00
20.00
30.00
Concentration(ppm Ca)
Table 3 [CaCO3] Trial 1 [CaCO3] Trial 2 log[] Trial1 log[] Trial 2 Trial 1 (mv) Trial 2 (mv)
1 1.02E-04 1.02E-04 -3.99097426 -3.99097426 -4.5
-4
2 2.04E-04 2.04E-04 -3.68994426 -3.68994426 3.7
3.6
3 5.11E-04 5.11E-04 -3.29200425 -3.29200425 15.2 13.7
4 1.02E-03 1.02E-03 -2.99097426 -2.99097426 23.4 22.3
5 0.000352136 0.000362076 -3.45329 -3.4412 10.5 10.2
For more precise data comparison, two trials
were performed. Equations from Figure 2 and
Figure 3 were calculated from the plots from
Table
3.
The equation in Figure 2 was used to determine
the ppm each sample which was used to find
the mass fraction of Calcium. This was then
used to find the percent weight of Calcium and
the mg of Calcium per tablet. As stated in Table
2, the average value was 582.80004 mg per
tablet which is also smaller than the expected
800mg.
Table 2
Trial 1
Trial 2
Average
Actual mass(g)
0.1016
0.1113
0.1065
% Ca/tablet
33.6860
31.0696
32.3778
mg Ca/tablet
606.3480
559.2528
582.8004
Absorbance(nm)
0.1571
0.1592
0.1582
ppm
13.6853
13.8322
13.7588
The
Calcium
Carbonate
dilutions
prepared for the direct potentiometric analysis
were done the same way to prepare the
Calcium tablet to ensure accurate dilutions.
The measured values were plugged into these
equations and then corrected for dilution to
solve for an initial concentration.
From the
concentration the molecular weight of Calcium
was used to find the percent Calcium per tablet
and mg per tablet. The average mg Calcium per
tablet in Table 4 was found to be 640.25 mg of
Table 5
EDTA
Flame Atomic
Potentiometric
Standard Deviation(%)
0.7717
0.0185
0.0070
Calcium per tablet, which is once again less than
the expected value.
The Potentiometric method also resulted in the
largest amount of mg of Calcium per tablet.
Table 4
Trial 1
Trial 2
Average
%Ca/tablet
0.35073
0.36064 0.355685
mg Ca/tablet
631.3
649.2
640.25
All three methods resulted in different
values for the amount of Calcium in the tablet.
However none of the methods produced a
value that was close to the stated value of each
Calcium tablet.
The Potentiometric method
proved to be the most consistent throughout
Conclusion/Statistics:
As shown in Table 7, nearly 200mg are
missing from each tablet. The expected value
for calcium was 800mg.
Table 7
EDTA
Flame Atomic
Potentiometric
Average Calcium Content(mg)
629.0076
582.8004
640.2500
the three trials. It was found, as shown in Table
5, Potentiometric had the lowest standard
deviation between the three methods, which
makes it the most accurate.
These Proves consumer complaints are justified
and nearly one fourth of the product is missing.