MadSci Network: Chemistry

Re: instructions for testing for the presence of aluminum in foods

Date: Wed Dec 13 14:30:34 2000
Posted By: Phyllis Stumbo, Staff, Nutrition, University of Iowa
Area of science: Chemistry
ID: 974736432.Ch

Foods are generally complex materials that require digestion before they 
can be analyzed for minerals.  A chemist would use a spectrophotometer to 
analyze for aluminum.  The process involves heating to such a high 
temperature that the entire sample is vaporized and the vapors are measured 
in a spectrophotometer.  This machine will read the components of the vapor 
and print out an analytical "map".  This is a very specialized piece of 
equipment that may not be available to you.  

You might consider a qualitative method for detecting aluminum to determine 
whether or not your cooking method would leach aluminum from the cooking 
vessel into the food.  I did find a method for testing for aluminum on a 
chemistry website from Australia.  The website is:

Below is the method proposed for testing for aluminum: Group 3 Test for Al3+, Cr3+, Fe2+, Fe3+ 

   1.First test. 
        1.Add 8 drops of NH4Cl solution to 5 drops of the original 
        2.Test the solution with litmus paper. 
        3.Add enough drops of dilute NH3 solution to turn red litmus blue. 
             1.A green precipitate identifies Fe2+ or Cr3+. 
             2.A red brown identifies Fe3+. 
             3.A white glassy precipitate identifies Al3+. 
             4.If no precipitate forms, go to (Group 4 Test). 
   2.Second test. 
        1.Add to 5 drops of the original solution 6 drops of NaOH then 2 
drops of NaHClO solution boil then add 2 drops of lead(II) ethanoate 
(lead(II) acetate solution) 
        3.Use lead acetate test paper 
             1.A yellow precipitate indicates Cr3+. 
        4.(The following common test is too dangerous to be used in schools 
because potassium hexacyanoferrate(III) (potassium ferricyanide) reacts 
with strong mineral acids to release TOXIC potassium cyanide. 
        5.Add to 5 drops of the original solution 5 drops of K3Fe(CN)6 
             1.A deep blue precipitate identifies Fe2+. 
             2.A brown green precipitate identifies Fe3+.

Note that the experiments above assume you begin with a liquid.  Many food 
tests start by digesting the food with a strong acid so you have a clear 
liquid to work with.  Also this method does not indicate how much aluminum 
is present, just whether or not any aluminum is there.  I have not worked 
with this test so I cannot advise you of its practicality.  You have a very 
interesting project idea, good luck!

Phyllis Stumbo
University of Iowa

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