Expert: Henry Boyter - 11/10/2006

Question
Which method should be chosen for filtration of soil solution contaminated with heavy metal ions, Pb2+, Cd2+ and Cu2+? Here, soil solution means 25 mL of above heavy metal solutions with various concentrations(about 1 to 10 ppm) and adding with 0.2 g of soil to each solution and leavind for 2 minutes.
After filtration, the concentration of metal ions in the solution will be determined by using atomic absorption spectrophotometer, AA-680.PLEASE KINDLY ANSWER TO MY QUESTION. PLEASE!

Answer
You need to define what you are trying to measure since what you describe is called "extractable metals" and there are various ways to fo it.  A common method would follow the soluble metals procedure found in EPA Method 3005A which just calls for the use of "Dissolved metals - All samples must be filtered through a 0.45-ìm filter".

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/3005a.pdf

For the digestion step, EPA Method 3050B calls for Filter paper - Whatman No. 41 or equivalent for the digestion step.

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/3050b.pdf


If you are trying to speciate the metals by type of complex, compound, orphysical state, the filtrations can be much more complicated and you will need to define the problem in more detail.  The above is for the measurement of total metals and total dissolved metals.