Dear Sir, I face one quite confusing question. Hope to get your help about using Athena to do the fitting. What I am concerning is sulphur species in my char sample. However, I cannot get the good fitting results due to the standards i used. Please see the following figure. S1 in the figure means the dibenzothiophene standard, c26 is my char sample. I intend to fit the char sample by using the standards such as dibenzothiophene, dibenzyl disulfide, sulphate and so on, to get the sulphur species. However, because of the self-absorption, the pure standard spectra intensity is even lower than our char sample as shown in fig. 1. If I do like this, the fraction is higher than 1 in my sample, I cannot get the reasonable fitting data. So how to do the fitting? As I known, the spectra for standard diluted with BN and non-diluted are different. The peak of the non-diluted is low due to self-absorption, as shown in the figure below. S1 is non-diluted and s1_10 is diluted sulphur to about 3%. For dilution, the position of the peak is also changed. Therefore the non-diluted s1 spectra isnot the real spectra of dibenzothiophene. The question is what percentage should I dilute the standard to get the credible spectra for the standards?and how to explain the peak position change? Can I use Athena to counteract the self-absorption and get the credible spectra for sdandards? Waiting for your reply. Thank you very much. Best regards Juan Chen