Real World: Determination of
Calcium in Milk
By Delaney Caudill, Ethan Nichols,
and Katie Vautier
Background
Methods Considered
• Ion Selective Electrode Method
• Trichloroacetic Acid Filtrate Method
– Use of this acid as a protein precipitator to
determine calcium content
• Complexometric Titrations
– A volumetric analysis in which a formation of a
colored complex is used to indicate the end point
of a titration
Purpose
• Determine and compare the calcium content
via a complexometric titration to listed values
of different types of milk
• Compare two different indicators
Procedure #1: Patton-Reeder
• Dry EDTA at 80°C overnight
• Make 750mL of 0.03408M EDTA
• Combine 10mL of sample, 40mL distilled
water, and 4mL of 8M sodium hydroxide
solution into an Erlenmeyer flask
• Add 0.1g of Patton-Reeder indicator
• Titrate w/ EDTA solution
Data
Whole Milk
Trial
mL EDTA added
Grams Ca2+
1
9.72
0.013276
2
9.47
0.012935
3
9.21
0.012580
4
9.39
0.012825
Avg.
----------
0.012904
% Difference
•
•
•
•
•
Fat free milk: 5.1%
1% milk: 2.5%
2% milk: 2.0%
Whole milk: 6.2%
Calcium Fortified: 9.0%
Before Titration
After Titration
Color Change?
Procedure #2: Eriochrome Black T
• Add 3mL of milk and 5mL ammonia buffer in a
250mL Erlenmeyer flask
• Calibrate a pH meter and measure pH of each
sample (needs to be 10)
• Add 0.03g of indicator
• Titrate with EDTA
Data
Whole Milk
Trial
mL EDTA added
Grams Ca2+
1
5.10
0.0069659
2
4.48
0.0061190
3
4.41
0.0060234
4
4.50
0.0061464
Avg.
----------
0.0063137
Results
• Whole milk: 54.1%
• Makes sense due to different indicator (EBT)
– pH of sample was 10
– pH had effect on sample?
Procedure #3: Eriochrome Black T
• Same as procedure #1 except used different
indicator: Eriochrome Black T
Data & Results
• No quantitative data
• No color change due to the solution having a
pH between 12 and 14
• Eriochrome Black T indicates a color change at
a pH of 10
No Color Change
Theoretical Grams of Ca per Serving
• Based on a 2,000 calorie diet, daily calcium
intake should be 1,100mg
• Each milk carton claims it contains 30% of
daily calcium intake
Example Calculations
• Grams Ca2+ in a serving of milk
•
Ex. Whole Milk
• Percent Difference
•
Ex. Whole Milk
Sources of Error
• INDICATORS!
– Subjective color change
• Different people titrated samples
• Reading the buret
• Wait for precipitate to come out of solution to
‘remove’ magnesium oxide
Future Work
• Investigate different indicators
• Change pH of samples to use Eriochrome
Black T indicator by changing molarity of
NaOH
• Try other calcium supplements such as
vitamins or orange juice
Conclusion
• Successful experiment
– Efficient method: complexometric titration
– Low percent differences
• Necessary to order Patton Reeder since
Eriochrome Black T yielded higher percent
difference
References
• Harris, Daniel C. Quantitative Chemical
Analysis, 8th ed.; W.H. Freeman and
Company: New York, 2010, page 240.
• http://www.chemteach.ac.nz/invesigations/d
ocuments/calcium.pdf
• http://www.jbc.org/content/90/3/747.full.pdf
Special Thanks
• Dr. Peterman
• Melissa, Kate, Pat, and Kiersten
• Professor Mowery