Real World: Determination of Calcium in Milk

By Delaney Caudill, Ethan Nichols, and Katie Vautier

BackgroundMethods 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

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

Whole Milk

% 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

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

Whole Milk

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/documents/calcium.pdf

• http://www.jbc.org/content/90/3/747.full.pdf

Special Thanks

• Dr. Peterman• Melissa, Kate, Pat, and Kiersten• Professor Mowery

Questions?