Spectrophotometric Determination of Iron in Vitamin Tablets

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  • Topic: Laboratory glassware, Tablet, Sodium citrate
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Lab 2: Spectrophotometric Determination of Iron In Vitamin Tablets

-To determine the amount of iron in a generic vitamin tablet on a per tablet (in grams) basis. -To prepare standards using a pre-made iron solution to help determine the iron content in our generic vitamin tablets -Determine absorbances of our vitamin tablets and standards using the spectrophotometer

1.Mass three vitamin tablets that contain iron
2.Place each vitamin in a 125-mL Erlenmeyer flask with 25 mL of 6M HCl 3.Do the same as above with no vitamin (This will be the reagent blank) 4.In the hood, simmer until the vitamin completely dissolves plus an additional 3 minutes. 5.After vitamin dissolves, allow to cool and then filter to a 100-mL volumetric flask. 6.Be sure to wash original beaker with water to allow for a quantitative transfer 7.Dilute to the mark on the beaker and mix well

8.Use citrate solution to determine how many drops are needed to make 0.5 mL of the vitamin extract to pH ~ 3.5, using the pH paper. (Count the drops; Only need to do this once) 9.Using a micropipette take 0.5 mL of originally diluted solution (vitamin extract) and place into a new 100 mL volumetric flask. 10.Add number of drops determined before of citrate solution 11.Add 2 mL of hydroquinone solution

12.Add 3 mL of o-phenanthroline solution
13.Dilute to the mark again and mix well.
14.Let color develop for 20 minutes

1.Use a pipet to place 10 mL of 0.04 mg/mL iron solution into a beaker. 2.Measure the pH and add citrate solution until pH ~ 3.5 is reached (Count the drops) 3.Use a pipet to place a fresh 10 mL of the 0.04 mg/mL iron solution into a 100 mL volumetric flask 4.Add number of drops determine previously of citrate solution 5.Add 2 mL of hydroquinone

6.Add 3 mL of o-phenanthroline solution
7.Dilute to the mark using water and mix well
8.Do the same to make standard solutions using 5, 2 and 1 mL of the 0.04 mg/mL Fe Solution. 9.Add proportional amount of sodium citrate solution to volume of the Iron solution 10.Let color develop for at least 20 minutes

Measuring the Absorbances:
1.Measure the absorbances above and below 510 nm.
2.Use wavelength with the strongest absorbance (Should be around 510) 3.Zero the absorbance using distilled water in the cuvet
4.Measure absorbances of the vitamin extract diluted solutions in addition to the standards we prepared 5.Measure absorbance of a DI blank and one calibration standard at the start, end and every 10 absorbance measures

Data / Calculations / Results:

See attached sheets for data tables, standard curve and observations…

Vitamins used:
-CVS Daily Multiple + Iron
-Color: Orange

Hot Plate:
-Manufacturer =
-Setting ~ 3
-While heating simmering the tablet on the hotplate, there was water vapor condensing on the sides of the flask

-Set spectrophotometer to 510 nm

**Did not record time phenanthroline was added to the vitamin extract solution**


In this lab, we were able to achieve our main objective to determine the amount of iron in a generic vitamin tablet on a per tablet (in grams basic). We achieved this through preparing different standards using a pre-made iron solution and recording the absorbances for each. After plotting the results from the standards on a curve, we were able to come up with the slope of the curve to able to determine the concentration at a given absorbance. The equation I resulted with was, y = 195.4x -0.0040. Using this equation, the concentration of mg iron per mL in the vitamin extract solution for the three tablets was determined. From there, it was easy to determine the amount of iron in each vitamin and also the amount of iron per gram of a tablet. The slope of the standard we achieved seemed rather excellent when looking at the r^2 value. Our r^2 value was 1, which proves that our data resulted in linear line. As stated on the dosage...
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