A method of determining components present in a sample from spectral data obtained from the sample including resolving each of a plurality of models of the spectral data, the plurality of models including models having a different number of component reference spectra selected from a set of predetermined component reference spectra; selecting a one of the plurality of models based upon a model selection criterion and determining one or more components present in the sample based upon the selected model. The model selection criterion includes a measure for each model, which balances improvements in fit quality of the model to the spectral data against a complexity penalty determined from the number of component reference spectrum used in the model.