Your experimental data should be in a tab-separated text file, with wavelength in the first column and signal values in all subsequent columns. Concentrations should be on first line, in list starting with the words "concs". The file should contain no other information.

How many components to retain in the analysis? (Default = 4)

Provide explicit basis spectra (highly recommended). Upload them here, as a tab-separated text file:
OR
choose to estimate basis spectra based on calculated spectral components:

For each basis spectrum you wish to use, enter coefficients for the corresponding spectral component.
For example, to construct a basis spectrum consist of the 1st component plus half of the 2nd, enter '1 0.5' (without the quotes). If you want a second basis spectrum to consist of the 2nd component minus twice the 4th, enter '0 1 0 -2' on a new line.
If you have no experimentally determined basis spectra, a good place to start is the sum and difference of the two most significant spectral components: enter '1 -1' and '1 1' on two separate lines.