Methods of isolating and detecting metal ions from proteins
A method of detecting a metal ion in a protein-containing sample includes adding a protein degrading enzyme to the protein-containing sample to form an enzyme degradation product, adding an acid to the enzyme degradation product to provide a mixture, filtering the mixture to provide a supernatant, extracting the supernatant with an organic solvent to remove organic solvent soluble byproducts to provide a washed aqueous layer, and detecting the metal ion in the washed aqueous layer. The method is amenable to the detection of heavy metal ions in complex products such as milk. A kit includes reagents for performing the method.
1. A method of detecting a metal ion in a protein-containing sample comprising:
adding a proteinase K enzyme to the protein-containing sample to form an enzyme degradation product;
adding concentrated nitric acid to the enzyme degradation product to provide a mixture;
filtering the mixture to provide a supernatant;
extracting the supernatant with an organic solvent to remove organic solvent soluble byproducts to provide a washed aqueous layer; and
detecting the metal ion in the washed aqueous layer in a handheld GMR sensing device.
2. The method of claim 1 , wherein the protein-containing sample is liquid milk.
3. The method of claim 1 , wherein the protein-containing sample is powdered milk.
4. The method of claim 1 , wherein the protein-containing sample is a solution of a protein powder.
5. The method of claim 1 , further comprising a denaturing agent.
6. The method of claim 1 , wherein the denaturing agent is an anionic surfactant, a urea, a chelating agents, a sulfhydryl reagent, a serine protease, or combinations thereof.
7. The method of claim 1 , wherein the filtering step is performed with a 3 micron to 5 micron pore size filter.
8. A method of detecting a heavy metal ion in a milk sample comprising:
adding a proteinase K enzyme to the milk sample to form an enzyme degradation product;
adding nitric acid to the enzyme degradation product to provide a de-emulsified mixture;
filtering the de-emulsified mixture to provide a supernatant;
extracting the supernatant with chloroform to remove chloroform soluble byproducts to provide a washed aqueous layer; and
detecting the heavy metal ion in the washed aqueous layer in a handheld GMR sensing device.
9. The method of claim 8 , wherein the heavy metal ion is lead.
10. The method of claim 8 , wherein the heavy metal ion is uranium.