Calcium Determination in Prime Eastern Pharmaceuticals, Natural Calcium 800 mg/ table with Vitamin D
Mike Gao and Alex Baker
____________________________________________________
ABSTRACT: To determine the actual amount of Calcium present in the Prime Eastern
Pharmaceuticals Natural Calcium 800 mg tablets there were three techniques used. The first was the EDTA titration, this technique forms a stable complex with the EDTA and the metal ion present in a 1:1 ratio. Which allows the determination of how much Calcium is present. The second technique was direct potentiometry, the particular experiment we used was ion-selective electrodes. The potential of ISE is related to the logarithm of the concentration of the measured ion by the Nernst equation. The final technique we used is AAS. T
Calcium is vital for our body health. It is necessary for our bones to keep healthy and for our teeth to keep strong over the years. It not only helps with strength but it is important for our muscles and nerves to function properly. Unfortunately in our society today, many people are calcium deficient. A glass of milk, ice cream and cheese are expected to keep our bones healthy but it is essential for our calcium intake to be boosted with calcium tablets.
When we take this extra step in consuming calcium tablets it is important to know that the amount of calcium that is being advertised is actually the amount we are consuming. In the following experiments we used a variety of techniques to see if the
Prime Easter Pharmaceuticals Calcium tablets really filled with the amount that is on the label. If the actual amount of calcium in the tablets were not the amount advertised it could not only be a hazard to the company’s reputation but the health of those relying on the calcium in it. When people do not get the daily amount of calcium they can eventually become calcium deficient or develop osteopenia and osteoporosis.
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It is important to investigate whether or not the
Natural Calcium tablets really have the amount advertised. The tablets supposedly have .8g of calcium in every ~1.7g tablet, meaning that there should be 47.0% calcium by weight.
The techniques used to determine the amount of calcium in the Natural Calcium tablets were EDTA titration, ion-selective electrode and Atomic Absorbance
Spectroscopy. These techniques allowed the calcium to be separated from other materials and allowed for an accurate reading of how much calcium was present. The EDTA titration established a 1:1 metal ion, while the ion-selective electrode was able to distinguish calcium from other elements with the ion-sensitive membrane that detected the change in ionic voltage particular for calcium. The atomic absorbance spectroscopy was able to compare the absorbance of standards compared to the calcium from the tablets.
This is done through a absorbance and concentration linear relationship.
The conclusions of these experiments will examine whether or not the calcium tablets had been modified without relabeling the product.
EXPERIMENTAL SECTION
Materials: All materials and chemicals were provided by Texas A&M Analytical
Chemistry department. The following are materials used for the analysis of calcium experiments; volumetric flasks, volumetric pipettes, beakers, mortar and pastel, calcium ion selective meter, AAS machine and

stirring rods. CaCO
3,
HCl, KCl, CaCl
2
and the calcium tablets provided by A&M were used for the determination of calcium in the
Prime Eastern Natural Calcium tablets.
EDTA Titration:
EDTA forms a stable 1:1 ratio metal-ion complex and can be used to determine concentrations of particular metals.
However, for this to occur three important criteria must be met; first stoichiometric, second, rapid reaction, and finally a stable product. This reaction requires a pH level of
10 for it to occur, this is important because the formation of the metal-EDTA complex is pH dependent. The EDTA was prepared to have a molarity of 0.01M. EDTA was measured to 1.1133 g. and was dissolved in
200 ml of heated deionized water. This mixture was cooled to room temperature, then diluted to 250 mL. The calcium tablets were prepared by weighing two tablets and crushing them into a fine powder with a mortar and pestle. We then transferred a small amount (0.2207 g) to a beaker and added HCl to allow the CaCO
3
to become soluble. Once the HCl has dissolved the powder heat the solution to boil to expel the
CO
2
. Allow again to reach room temperature. The 1M of ammonium is added drop wise until a pH of 6 is reached. Once the pH is reached transfer the mixture to a volumetric flask and dilute to the 250 mL mark with deionized water. 50 mL was then transferred quantitatively to 3 beakers. But before titration can proceed, there must be a blank made to allow for an example of the color that occurs when the reaction is complete. The blank contained 100 ml of deionized water with six drops caligmate and 4 drops methyl red.
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The color change should be indicated when a light blue color appears with no purple tint at all. The samples were then titrated until the color change.
Ion- selective electrodes (ISE)
The ion-selective electrode experiment will use a Ca 2+ sensitive ISE and an Ag/AgCl reference electrode to measure the calcium voltage of the known and unknowns. In preparing the standards of .1 M CaCO3 we weighed 1.16 g of CaCO
3 and added the 6M of HCl to make CaCl
2
and diluted with deionized water. The preparation of 0.01M
CaCO
3
we used a 10-mL volumetric pipette to transfer 10 mL of the 0.1 M CaCO
3
into a
100-mL volumetric flask and diluted to the mark with deionized water. Next, four standard solutions must be prepared. The first will consist of 1 mL of 0.01 CaCO
3 with 10 mL of 1 M KCl, the second will consist of 2 mL of 0.01 CaCO
3
with 10 mL of KCl, the third will have 5 ml of 0.01
CaCO
3
with 10 mL of 1 M KCl and finally the fourth solution with have 10 mL of 0.01
CaCO
3
with 10 mL of 1 M KCl.
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Our unknown, which was the calcium tablet from Prime Eastern Pharmaceuticals, was prepared with the same procedure as the
EDTA titration. We used 0.2207 g of the powder and added HCl and 1 M of ammonium to reach a pH of 6 and the mixture was diluted with deionized water.
10mL of the calcium tablet solution was transferred to a 100mL volumetric flask. For the potentiometric analysis, transfer 60 mL of the calibration standards and the unknown into 100-mL beakers. Immerse the electrode into the solution so that it covers the junction but does not touch the sides or the bottom of the beaker. Measure standards from least concentrated to highest concentrated. Before each reading, rinse the electrode with deionized water and gently blot dry with Kim wipes. When taking the readings make sure to wait until the reading has stabilized to record. It is important not to rub the surface of the electrode since this may damage the membrane. Once all measurements have been made, plot the

calibration curve and check for Nernstian behavior.
Atomic Absorbance Spectroscopy
Using atomic absorption spectroscopy we can determine the amount of calcium in the
Natural Calcium tablet by creating a solution from the tablets given to us by the Prime
Eastern Pharmaceuticals and comparing it to the absorbance of standard calcium solutions. This can be done because it creates an absorbance and concentration linear relationship. The preparation of the unknown is done by measuring out 0.2207 g of the Natural Calcium tablet, dissolve it with 6M HCl and adjust the pH to level 6 with 1M ammonium then dilute with deionized water to the 100-mL mark. We used a pipette to put 2.5 -mL of the solution into a 100-mL volumetric flask and diluted it. 2 samples were then taken from that solution. Start the “Shimadzu AA-6200” program on the computer with the internet connected. Input “Ca” as the element and adjust the wavelength to “422.7”, 4
input the concentrations of the standards and begin to measure the absorbance starting with the least concentrated. Once the standards are measured, put the unknown calcium solutions in and measure the absorbance of the two unknowns and record the data.
Results and Discussion:
EDTA Titration
To determine how much calcium was contained in each of the 50 mL samples, the molarity of EDTA must first be determined.
The formula mass for EDTA is 340.2, and the experiment required approximately .01 molar of EDTA to be successful. We measured out 1.1133g of the pure EDTA, which is .003272 moles of EDTA. When dissolved in .250L of water, though, it gives us a .01309M EDTA solution. After preparing the unknown tablet samples, we titrated it with our EDTA solution and recorded the results. The first trial used 32.7 mL of EDTA, the second with 32.2 mL and the third 32.4 mL. The mean of the 3 results is 34.43 mL. Using the mean value, the calculated moles of EDTA used was 4.51E-
4. Because we know that calcium and EDTA have a 1:1 mole ratio, we can assume that the moles of EDTA used is the same as the moles of Ca that were present in the solution. Since 4.51E-4 moles of Ca were present in a 50 mL sample of our solution, then if we multiply that by 5, we can get the number of moles in the entire 250 mL solution, which turns out to be 2.25E-3 moles. If we multiply our number of moles of calcium by the molar mass of calcium
(40.08 g/mol), we get that there were .0903g of calcium originally in our 250mL solution.
With respect to the original .2207g of a calcium tablet in our solution originally, we get that the percent calcium by weight is
40.1%.
Ion- Selective Electrodes
When using ion- selective electrodes, it is necessary to prepare standard solutions to compare an unknown to. 1.16g of pure
CaCO3 was used to prepare the standard.
Dividing it by formula mass of CaCO3
(100.08 g/mol) gives .0116 moles of
CaCO3. When put into a 100 mL solution, it makes the solution a .116M solution. 10 mL of that solution was then transferred to another 100mL volumetric flask and diluted completely, giving a .0116M solution. Then,
1mL, 2mL, 5mL, and 10mL of the standard solution were transferred to 4 100mL volumetric flasks. Those 4 flasks were

diluted to 100mL and then transferred to separate beakers. The molarities of these solutions were 1.16E-4, 2.32E-4, 5.80E-4, and 1.16E-3 respectively. The mV turned out to be 1.6, 8.7, 16.8, and 30.6 respectively. The mV of these solutions were then plotted vs the logarithm of [Ca].
Below is the resulting graph.
40 y = 27,818x + 110
30
Ряд1
20
10
Линейная
(Ряд1)
0
-6 -4 -2 0
The unknown solution was also measured and gave a mV of 23.5. Plot this value in the best fit line to get an X value of -3.1095.
This number is also the log[Ca] of the unknown solution. Solve for [Ca] and we get
7.77E-4. Since all the calcium came from the 10mL we transferred, the concentration of [Ca] in that 10mL is 7.77E-3M. With this information we can calculate that the number of moles in the entire 250mL solution is 1.94E-3. Multiply this by the molar mass of calcium to get .078g, giving the .2207g sample of the tablet 35.3% calcium by weight.
Atomic Absorbance Spectroscopy
The standards were tested and absorbances at 5ppm, 10ppm, 15ppm, and 20ppm, were
.0208, .0387, .0544, and .0709 respectively.
Plotting the relationship between absorbance and ppm, we get:
0,0800
0,0600 y = 0,0033x +
0,0047
Ряд1
0,0400
0,0200
Линейная
(Ряд1)
0,0000
0,00 10,00 20,00 30,00
Our unknown sample tested absorbances of
.0272 and .0241. The mean of these 2 samples is .02565. Plugging that value in the best fit line gives an x value of 6.348ppm.
6.346ppm means that there are 6.246 mg/L.
Since we only have 100mL, there is
.6246mg in each of the samples. This is the amount of Ca in 2.5mL of our original solution. Multiply the weight by 100 to find the original mass of the Ca from the .2207g sample. With this result we get .0625g of
Ca, which would give the sample of the tablet 28.8% calcium by weight.
Conclusion:
As we can tell from the experiments, the amount of Ca that is actually in the supplements is less than what is advertised on the bottle. The EDTA titration showed that the percent composition was 40.1%.
The ise- selective electrode gave us a percent composition of 35.3%, and the
Atomic Absorbance Spectroscopy showed
28.8% composition by weight. None of these experiments were able to show that the
% calcium in the tablets was what the bottle advertised. They all gave results that showed that the tablets weren’t pure calcium carbonate. It proves that Prime Eastern
Pharmaceuticals has changed their supplements without informing the public or changing the content on their labels. Not only is this a violation of FDA standards, but it calls into question: what is in the tablets that isn’t CaCO3? This is a possible health concern and should be addressed and tested as soon as possible.

References:
(1) "The Calcium Information
Resource." The Calcium
Information Resource . GlaxoSmith
Kline, 2011. Web. 25 Nov. 2011.
<http://www.calciuminfo.com>.
(2) Rowe, M.W., M. Hyman, A.E.
Miller, A.C. Javier, and E.
Binamira-Soriaga. "Determination of Mg by EDTA." Chemistry 318
Quantitative Analysis Laboratory
Manual (2011): 18-20. Print.
(3) Rowe, M.W., M. Hyman, A.E.
Miller, A.C. Javier, and E.
Binamira-Soriaga. "Determination of Fluoride." Chemistry 318
Quantitative Analysis Laboratory
Manual (2011): 26-29. Print.
(4) Shimadzu. Atomic Absorbtion
Spectrophotometer . Chiyoda-ku:
Shimadzu, 2010.
Shimadzu . Web. 1
Dec. 2011.