Final Project Report

The Determination of Calcium in Orange Juice via EDTA Titration
Christopher Myers
Chem 353 Quantitative Chemical Analysis
Chemistry Department
Augsburg College, MN 55454
***************************************************************************
Abstract The purpose of this experiment was to determine calcium content of orange juice and
compare between samples taken from the Augsburg College cafeteria and the University of St.
Thomas cafeteria. This experiment also compared methods used in calcium concentration
determination between EDTA titration and Atomic Absorption Spectoscopy. The results showed
that orange juice taken from the drink dispenser at Augsburg College had larger calcium
concentrations than that of orange juice taken from St. Thomas. It was also found that results
across both methods were congruent with one another. Future experiments will include more
trials for both EDTA titration and AAS to possibly obtain a statistical difference, as well as add
lanthanum to the solution preparation for EDTA titration.
******************************************************************************
Introduction
The purpose of this experiment was to determine calcium concentrations between two
different samples of orange juices: one taken from Augsburg’s cafeteria and another from St.
Thomas’s cafeteria. Another purpose of this experiment was to examine and compare methods
of calcium determination as both EDTA titration and Atomic Absorption Spectroscopy (AAS)
were used.
Calcium is the most abundant mineral in the body and is extremely important in bone and
tooth strength. Depending on ones age the daily calcium requirement varies from around 1000
mg to 1300mg. Since many foods and liquids such us, milk, yogurts, cheeses and juices are
common sources of calcium this analyte was chosen to be analyzed in a juice many people drink

quite often: orange juice1. This was taken a step further as a competition between Augsburg and
St. Thomas was established as orange juice from each cafeteria was used to determine which
concentration was higher.
EDTA titration2 and AAS3 are both common methods used to quantify calcium
concentration. In EDTA titration, EDTA acts as a ligand that is capable of forming covalent
bonds to most metal cations, in this case calcium. To determine concentration a color indicator
is used in order to establishe an endpoint. As the cation goes from free to the metal bound form
the color of the solution changes and concentration can be calculated based off of volume
titrated. Though relatively accurate this might not be as sensitive as AAS due to EDTA possibly
bonding to other cations other than the desired analyte (e.g Mg2+).
Experimental
Orange juice was taken from drink dispensers found in the cafeterias of Augsburg
College and the University of St. Thomas.
Solutions Preparation:
Solutions were prepared by first filtering the juices via centrifuge in order for the removal
of pulp. Each orange juice sample was then diluted by a 1:1 ratio of 0.1M HCl (50 mL) and
orange juice (50 mL). HCl was used in order for digestion.
An ammonia buffer with a pH of 10 was prepared next. This buffer was used in the
preparation of the 0.01M EDTA solution as 1.8615 g EDTA and 8 mL ammonia buffer were
added into a 500 mL volumetric flask. Deionized water was then added until the 500 mL line.
Orange juice solutions were finally prepared for titration by combining 10 mL of the
diluted solution and 5 ml of the buffer along with a few drops of calmagite indicator.
A 0.05 M CaCO3 solution was prepared for EDTA standardization by weighing out
0.4998 g CaCO3 and adding it to 100 mL of 0.1 M HCl. This was used to find the exact molarity
of the EDTA solution.
Analysis:
The fully prepped orange juice solutions were then titrated with the EDTA solution until
a color change from redish/purple to a blackish/blue was observed. The volume of the EDTA
was then measured of the burette. This was done in three different trials for both the Augsburg
sample and the St. Thomas sample.

In order to find the exact concentration of the analyte the exact molarity of the EDTA
solution needs to be known. This was done by titrating the EDTA solution into the 0.05 M
CaCO3 solution containing a few drops of indicator. The endpoint was determined when the
solution turned from redish/purple to blue. A trial of three was also used for this titration.
Results and Discussion
In this experiment no label information was obtained, as the dispensers did not display
literature value, therefore, no comparisons of determined calcium concentrations and actual
calcium concentrations could be made. What this experiment was set up to determine was, by
the use of the EDTA titration method, which school’s cafeteria has orange juice with a higher
calcium concentration; and do these results compare to the other method used (AAS).
As stated earlier, before any calculations could be made in order to determine the calcium
concentration the molarity of the EDTA first had to be determined based off of the volumes
titrated into the standardizing solution. What was found among the three trials was the average
volume EDTA titrated was 13.47 mL. This was used in accordance with the molarity of the
CaCO3 solution to find the number of moles EDTA in the given average of 13.47 mL EDTA.
This in turn was used to calculate EDTA molarity, ultimately giving a molarity of 0.011 M
(Table 1).
Table1.
EDTA Standardization
Trial 1
Start point 18 ml
End point 31.5 ml
Total 13.5 ml
Trial 2 Average Vol= 13.47
Start point 32 ml
End point 45.3 ml mol in 3ml CaCO3 0.00015
Total 13.3 ml Trial 1 M 0.011
Trial 3 Trial 2 M 0.011
Start point 10 ml Trial 3 M 0.011
End point 23.6 ml
Total 13.6 ml Average EDTA M= 0.011

With the 0.011 M EDTA solution and averaged volumes needed to reach the endpoint for
each school’s orange juice solution, moles of calcium were determined. This was possible due to
the number of moles of calcium being equal to the number of moles EDTA used in the titration
(Table 2).
Table 2.
Augsburg Orange Juice St. Thomas Orange Juice
Trial 1 Vol 3.7 ml Trial 1 Vol 3.4 ml
Average Vol 3.67 ml Average Vol 3.47 ml
Trial 1 mol 0.000041 Trial 1 mol 0.000037
Average mol 0.000040 Average mol 0.000038
Calcium’s molecular weight was used in order to find the exact mg of calcium in the
number of moles found per 5 mL of orange juice. With this calculation made, all that was
needed was a few simple conversions of 5 mL to 8 fluid ounces to find how many mg of calcium
each orange juice had in a given serving. What was found was that Augsburg College orange
juice contained a calcium concentration of 76.49 mg/8 fl oz where St. Thomas orange juice
contatined 72.32 mg /8 fl oz (Table 3). Given that the recommended daily amount of calcium is
1000 mg a day for strong bones and teeth a person would need to drink roughly 13.1 servings of
Augsburg orange juice or 13.8 serving of St. Thomas orange juice.
Table 3.
Calcium (mg) 1.62 per 5 ml Calcium (mg) 1.53 per 5 ml
8 Fluid oz = 76.49 mg calcium 8 Fluid oz = 72.32 mg calcium
AAS determination of calcium concentration gave values of 82.42 mg/8 fl. oz for
Augsburg College and 79.95 mg/8fl oz for St. Thomas (Table 4). When looking at the methods
both agree with the determination that Augsburg orange juice has a higher calcium content. Also
the differences between Augsburg and St. Thomas values for each juice were also similar; 4.17
mg for EDTA titration and 2.47 mg for AAS. Since it was hypothesized that EDTA would also
form bonds with other cations in the solution it was surprising to find that the values were less
when compared to AAS. A possible explanation for this could be due to ending titration early as

an exact change in color to blue was hard to determine as the juice was yellow. Another possible
reason that AAS had a higher content was the fact that lanthanum was used to free calcium from
calcium phosphate. IT is possible that since EDTA titration did not use lanthanum not all of the
calcium was free and available for bond formation.
Table 4.
Conclusion
The results supported that Augsburg College orange juice had a higher calcium content
than St. Thomas Orange juice, though the difference was small. More trials should be run in
order to increase the degrees of freedom for EDTA titration in order to conclude that the
difference observed between the two schools is actually statistically significant. However, since
both methods seemed to be congruent with the findings, it can be concluded that Augsburg’s
orange juice does have a higher concentration, even if very little; Augsburg wins!
The results also indicated that both methods were sound in calcium concentration
determination. The values obtained and the differences between solutions were roughly the same
between both methods. What could be done in future experiments is to add lanthanum to the
EDTA titration as well.
Acknowledgement (optional)
Dave Bergstrand Determination of Calcium in Orange Juice via AAS
References
[1] Office of Dietary Supplements. Dietary Supplement Fact Sheet: Calcium.
http://ods.od.nih.gov/factsheets/CalciumHealthProfessional/ (accessed Apr 23, 2013).
[2] McCormick P. G. Titration of calcium and magnesium and milk with EDTA. J. Chem. Educ.,

1973, 50, 136.
[3] Strohl, A. N. The Flame Spectrometric Determination of Calcium in Fruit Juice by Standard
Addition. J. Chem. Educ. 1985, 62, 343.

Final Project Report

More Related Content

What's hot (20)

Viewers also liked (8)

Similar to Final Project Report (20)

Final Project Report