Hi Ifeffitters, I was trying to use the linear combination fitting function in Athena to quantifying Cr(VI) and Cr(III) species. I used two endmembers of Cr species as the two standards but the program fails and gives error message "The fit flagged a warning--probably that error bars could not be calculated. That is probably an indication that one or more of your standards are inappropriate for this fit." It appears I am either using the wrong settings or even wrong function to do the job, any suggestions. We have additional 3 spectra with variable combinations of Cr(VI) and Cr(III) as well. Cheers, Balwant Singh ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.