I am still working on finding the concentrations of Arsenic and Selenium. Here's what I am working with: AAnalyst400 atomic absorption spectrometer and MHS 15 hydride generating system.
My question is this: Does anyone know of a way to find get consistent results to find the concentration of As(up to 5ppm) and Se(up to 1pmm)? My samples are TCLP liquid extracts.
The problem I have with the hydride generating system is that it measures in concentrations for As up to 50ppb. I need to reach concentrations up to at least 5ppm. For Se, it measures up to 100ppb, I need to find up to 1ppm.
I thought that I could perhaps use flame AA with a nitrous oxide-acetylene flame. I am having trouble getting consistent results. The characteristic concentration/sensitivity check using is 25ppm for As. That concentration is given if I use the 10cm burner head with an air-acetylene flame (very poor results). That means the with the NOX flame, the absorbance would be half that, or 0.1. That said, the absorbance of a 5ppm solution sould be 1/5 that of the 25ppm solution, or 0.02. Additionally, using the 5cm burner head requires installing the spacer, which reduces sensitivity, but minimizes chemical interferences. The spacer reduces sensitivity by 2-3x. So that brings our absorbance down even lower. I am using the background corrector to improve the signal to noise ration, but I am still not getting consistent results.
Any suggestions? Is there another alternative? I don't think they'll jump at getting me an ICP-MS, so something relatively inexpensive as well... (I can't get a graphite furnace either...)