Laboratory
Determination C118 of Iron in Total Cereal worksheet report
What do you consider when making choices for healthy food? Are you a label reader?
Nutrition Information for Total Cereal Serving size: ! cup or 30 g
Calories: 100 Total fat: 0.5 g Saturated Fat: 0g Trans Fat: 0 g Polyunsaturated Fat Cholesterol: 0 mg Sodium: 190 mg Potassium: 90 mg Total Carbohydrate: 23 g Dietary Fiber: 3 g Sugars: 5g Other carbs: 15 g Protein: 2g 100% of the RDA for following vitamins and minerals: Vitamin C, Calcium, Iron, Vitamin E, Thiamin, Riboflavin, Niacin, Vitamin B8, Folic Acid, Vitamin B12, Pantothenic Acid, Zinc Vitamin A: 10% Vitamin D: 10% Phosphorus: 8% Magnesium 5%
Potassium
Chemical/Physical properties of K (s) Soft, silvery metal Reacts explosively with water
What is the form of potassium in Total cereal?
Iron
Chemical/Physical Properties of Fe (s) Shiny, strong, ductile, magnetic easily oxidized (rust) What is the form of iron in Total cereal?
What is form of iron in vitamin tablets? Supplemental iron is available in two forms: ferrous (Fe2+) and ferric (Fe3+). Ferrous iron salts (ferrous fumarate, ferrous sulfate, and ferrous gluconate) are the best absorbed forms of iron supplements.
Recommended Dietary Allowances for Iron
Age
Males (mg/day)
Females (mg/day)
Pregnancy (mg/day)
Lactation (mg/day)
7-12 months 1-3 years 4-8 years 9-13 years 14-18 years 19-50 years 51+ years
11 7 10 8 11 8 8
11 7 10 8 15 18 8
NA NA NA NA 27 27 NA
NA NA NA NA 10 9 NA
Why is iron needed?
Integral part of enzymes and proteins Hemoglobin: Oxygen transport
Heme group is shown. There are 4 hemes in each hemoglobin molecule. Blue with no O2, red with O2 bound to Fe2+.
Dietary Sources of Iron
Heme (absorbed readily, 15-35%) Meat sources Chicken liver, cooked, 3" ounces Oysters, breaded and fried, 6 pieces Beef, chuck, lean only, braised, 3 ounces Clams, breaded, fried, ! cup Beef, tenderloin, roasted, 3 ounces Nonheme (difficult absorption, 2-20%) cereal, 100% iron fortified, ! cup Oatmeal, instant, fortified, Soybeans, mature, boiled, 1 cup Lentils, boiled, 1 cup Beans, kidney, mature, boiled, 1 cup Spinach, boiled, drained, " cup 18.00 10.060 8.850 6.635 3.420 3.220 mg Fe 12.87 4.525 3.220 3.015 3.015
Overview of Experimental Procedure 1) Remove iron from cereal with magnet 2) Dissolve Fe (s) in strong acid to produce Fe2+(aq) Safety precautions
Overview Experimental of Procedure
3) React Fe2+ in solution with color forming agent 4) Analyze using spectrophotometry What is missing?
Color Forming Agent
Unknown amount of Fe2+ in sample
+Fe2+
Intensity
Unknowns Intensity Level
+Fe2+
+2Fe2+
+3Fe2+
+4Fe2+
Amount of Fe2+
Preparation of Standards
Stock solution contains Fe2+ with concentration of 10 ppm.
What does ppm mean?
ppm = part per million
Preparation of Standards
Prepare 6 standards in the range 1-8 ppm from 10 ppm stock solution. Use a 10 mL graduated pipet and 10 mL volumetric flask. Example:
1 ppm is prepared by adding 1 mL of 10 ppm solution and diluting to a total volume of 10 mL with water 1 ppm = (1 mL * 10 ppm) / (10 mL) Or 3 ppm = (__ mL * 10 ppm) / (10 mL)
Color formation
Fe2+ Complex with 2,2-dipyridyl
2+
N N
Fe2+ + 3
N
N Fe N N
N N
Why does this bond to Fe2+ ? Why is it colored?
Color and Wavelength of Absorption The Fe2+ -dipyridyl complex is red. What color will be absorbed by the sample?
What wavelength range is this?
Electromagnetic spectrum
Color of light as it appears to the eye E.g., Red light appears red, if we mix all the colors together it appears white But, if we start with white light and remove cyan light by absorbing some, it appears red
Clicker Question
What wavelength will most strongly be absorbed by blue food dye? A. ~425 nm B. ~515 nm C. ~580 nm D. ~655 nm
Calibration Curve
Absrobance v s. Conce ntration
1.2 1 y = 0.1248x - 0.0054 R2 = 0.9994
Absrobance at 522 nm
0.8 0.6 0.4 0.2 0 0 2 4 6 8 10 Fe 2+ in ppm
Calculate the Fe2+ concentration in the unknown solution with absorbance = 0.46. Therefore, there is x = (y + 0.0054)/(0.1248) ppm = 3.73 ppm
Calculate the amount of iron in the original cereal sample. 1. Iron was extracted from 10.0 g of cereal. Does this collect all the iron from 10.0 g of cereal? 2. Iron was dissolved off stir bar in concentrated HCl. Does this dissolve all the iron from 10.0 g of cereal? 3. This solution was added to a 100 mL volumetric flask and diluted to the mark. Does this dilute all the iron from 10.0 g of cereal? 4. 2.0 mL of this solution was added with color forming reagents to 10 mL volumetric flask. Does this dye indicate all the iron from 10.0 g of cereal? 5. This was the solution analyzed in the previous slide, i.e., 3.73 ppm from the original sample of the cereal. Does this reflect all the iron from 10.0 g of cereal?