Hi, firstly u need to determine the suitable supporting electrolyte mixing with milk powder ( play around with the concentration) to reduce background signal. Then, followed by heavy metal study. Many parameters that u can explore eg pH electrolyte, types of supporting electrolyte, scan rates, optimize electrode fabricate, milk concentration, heavy metal concentration, and so on. Just my cents

Thanks.

Thanks Mr Jahwarhar for your answer.. i should go with supporting electrolyte to reduce background signal.. thats why i got weird graph..

You will most likely have to destroy the organic matter in the milk powder using a digestion procedure.   You can use a nitric/sulfuric acid mix or possibly hydrochloric acid with hydrogen peroxide.  You should be able to find procedures in the literature.

If you try to analyze the milk powder directly by diluting in a supporting electrolyte, you will probably get very poor results due to the protein present in the sample adsorbing on the electrode surface.   

Before the analyses, You have to use a digester such as ( BUCHI UNITE) to digest the milk solution - removing the organic materials by heating the milk up to ( 150 - 180)  centigrade,  adding  mixture of (2 : 3 ml ) sulfuric to nitric acid until removing all organic material and you have clear solution . make the PH  between 4 and 6 then run your samples good luck  .

Thank you very much Dr. Noori Kh Fayad.. Im really appreciate it.. :-)

Digesting the organics before you start measuring will indeed be important. You might also use UV-digestion. You can make it yourself, see article below.

Design and development of a low cost, high performance UV digester prototype: Application to the determination of trace elements by stripping voltammetry

Thanks Dr. Francis Amore for your suggestion. Basically, the procedures likely the same to detect heavy metal using ICP-OES and AAS right?

Thankfulness to Dr. David Deruytter. By the way, if I using Acid Microwave Digester, that will meet the same purpose is it?