UV/Vis determination of hexavalent chromium in polymer and metal samples

[myratidwell]

I am working on a method for hexavalent chromium determination in various metal and polymer samples and have come across a stumbling block when running a method recovery -- no unknown, just reagents spiked with a potassium dichromate standard.  When I run a 2ppm standard I get an 85% recovery but with a 25ppm standard (same prep process) I get a 30% recovery.

I am roughly following EPA 3060 and 7196, realizing that they were written for groundwater/wastewater/soils, etc, and not for polymers/metals.

Has anyone experienced this or have some idea of why this might occur?

I would appreciate any help I can get.

Thanks!

Myra

[skippymor1]

Hi Myra ... I have a lot of questions! Do you have an AAS available? Can you

give a more detailed report concerning what the matrix (metal and polymer) is,

how it was treated to dissolve the hex. chrome, etc. Also, you did not say

exactly how you treated the extracted sample - what was the final pH, etc. Did

you run a standard curve for hex. chrome? If so what was the maximum

concentration that can be used to give a straight line? Did you use UV or VIS

determination?

I recommend that you first make a 6 point standard hex. chrome curve (including

zero) utilizing the solution that was used for extraction initially. [e.g., 0,

2, 4, 8, 16,and 32 mg/l hex. chrome.] Note: The hex chrome 1000 mg/l standard

solution can be stabilized for a long time by adding NaOH solution to maintain

an alkaline pH of about 9.5 - 10 and keeping it in a polypropylene container.

I will get back to you soon.

John Morico