Colorimetric Determination of Iron in Vitamin Tablets

Transcription

1 Colorimetric Determination of Iron in Vitamin Tablets

2 Big Picture Conceptual Approach

3 Vitamin Tablet How much Fe?

4 ph = 3.5

5 Vitamin Tablet How much Fe? Too difficult to eyeball so will have the colorimeter match the colors for us!! 0 mg Fe 100 mg Fe

6 % Transmission

7 Sample: Distilled Water

8 Sample: Distilled Water Sample: Orange Water % Transmission Not linear response

9 A = -log %T 100 % Transmission Absorbance

10 Best absorbing wavelength? 505 nm will give best linear response! How much Orange is in the water? What is the concentration of orange?

11 Read absorbance of unknown (at optimal wavelength). Computer will convert that absorbance to concentration (μg). Calculate the original mg of Fe in vitamin tablet will need to sort out the dilution factor!! A = abc A = absorbance a = molar absorptivity constant b = path length c = concentration Standards A = -log %T 100

12 Detailed Picture Procedural Details

13 1) Prepare Standard (Known) Iron Samples 2) Prepare (Vitamin) Sample 3) Read absorbance of standard samples Read absorbance of vitamin sample

14 (Vitamin) Standards (Known) (Vitamin) Standards and

15 1) Don t start timing 15 minutes until solution is boiling! 2) No boiling chips! 3) Cover beaker with watch glass! 4) Boil on hot plate in hood! 5) Cool a couple of minutes uncovered in hood SMELLS! Standards Standards and

16 While the vitamin sample is boiling, perform the following. See attached power point sheet. 1) Use 50 ml beaker 2) Use glass pasteur pipet for counting drops of sodium citrate!! Dispose in glass waste! 3) Check ph paper using glass stirring rod with ph paper on paper towel. Add about 20 drops sodium citrate check ph (match with chart Standards on hood) add a few drops at a time until ph is ) Steps 3 and 4 power point handout Standards and

17

18 Preparation of Standard Fe Solutions mg Fe/mL 10 ml 5 ml 1 ml Fe standard, ml Drops of sodium citrate ex o-phenanthroline, ml hydroquinone, ml dil to 100 dil to 100 dil to 100 Convert each standard to μg of Fe! 1) Mix and invert 17x. 2) Store standards in clean, labeled beakers or flasks at your station. 3) Do not prepare a blank. 4) Standards must sit about 10 minutes before reading absorbance.

19 Standards See attached power point sheet for steps 5,6. Standards and

20 Vitamin/ Preparation Step 1 Filter vitamin solution into 100 ml flask and dilute to 100 ml. Step 2 Place 5 ml of Solution A into a new 100 ml flask and dilute to 100 ml Step 3 Place 10 ml of Solution B into a beaker determine the # of drops of NaCitrate required to obtain ph 3.5 discard. Solution A 20X Solution B 10X Step 4 In a new 100 ml flask: a) Fresh 10 ml of solution B b) # drops of NaCitrate determined in step 3 c) 3 ml phenanathroline d) 2 ml hydroquinone e) Dilute to 100 ml Solution C f) Allow to sit 10 minutes g) Read absorbance of solution C

21 For vitamin sample, we will need to do several dilutions color will be too dark absorbance will saturate colorimeter is VERY sensitive.

22 Standards Reference instructions sheet for MicroLab Colorimeter. Standards and

23 Read absorbance of standards and unknown (at optimal wavelength) record optimal wavelength. Computer will convert absorbance of unknown to concentration (μg). Calculate the original mg of Fe in vitamin tablet will need to sort out the dilution factor!! Standards

24 Get from hood: 1) Fe standard little more than 40 ml in a 50 ml beaker 2) Sodium citrate fill large test tube about half way full (30 drops = 1.5 ml) 3) Hydroquinone fill large test tube about half way full 4) o-phenanthroline fill large test tube about 2/3 way full All waste down the drain today! Dispose of glass pasteur pipets in glass waste! When pipets need to be cleaned during experiment 1) rinse with dh 2 O 2) rinse with acetone at end of lab! When volumetric flasks need to be cleaned during experiment 1) rinse with dh 2 O Good idea to rinse all beakers/flasks with dh 2 O at end of lab (remove any traces of Fe)

25 Report: due Title: Purpose: Procedure: Data: Calculations: Conclusions: Before lab starts the week after Thanksgiving break As usual As usual As usual ID your vitamin 1) Reference graph (be specific!) 2) State R value from your absorbance/concentration graph and comment on the R value 3) State best absorbed wavelength and why you used this wavlength. 4) Record the micrograms of Fe in tablet given by MicroLab. 1) Reference and describe the use of the graph in this experiment (be specific!) 2) Calculate μg Fe in each of the four standards will need to do before graph can be made (one word, one number equation) 3) Calculate the mg Fe in the original vitamin tablet - be sure to account for the dilution factor! (word and number equation also describe how you determined the dilution factor) 4) Actual value for Gentlesorb vitamin is 18 mg calculate % error. Actual value for Western Familygreen iron supplement is 27 mg calculate % error 1) Restate mg Fe in vitamin tablet and percent error. ID your vitamin 2) Possible sources of error.

26 Please leave at your station: 3x 100 ml volumetric flasks with lids 1 ml volumetric pipet 2 ml volumetric pipet 3 ml volumetric pipet 5 ml volumetric pipet 10 ml volumetric pipet Pipet bulb or gun Colorimeter vial and lid Film canister Pasteur pipet bulb Small watch glass BEFORE YOU LEAVE: Rinse all pipets with acetone, rinse volumetric flasks with deionized water