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.