Spectroscopic apparatus and methods for determining components present in a sample

A method of determining components present in a sample, the method comprising:

• obtaining spectral data by carrying out Raman spectroscopy on the sample by:
• (i) exposing the sample to a laser beam;
• (ii) collecting light scattered from the sample;
• (iii) filtering the collected light to reject Rayliegh scattered light having a same frequency as the laser beam and allowing Raman scattered light to travel to a Raman analyser, the Raman analyser spectrally dispersing the Raman scattered light across a photodetector;
• and
• (iv) recording the spectral data with the photodetector;
• resolving each of a plurality of models of the spectral data, the plurality of models comprising models having different numbers of component reference spectra selected from a set of predetermined component reference spectra;
• selecting 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, wherein:
• the model selection criterion comprises a measure for each model of the plurality of models, the measure balancing 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;
• the resolving of each of the plurality of models comprises:
• resolving a current model of the plurality of models of the spectral data using a current set of component reference spectra;
• determining a current measure for the current model based upon the model selection criterion;
• resolving a plurality of further models of the plurality of models of the spectral data, each further model using a further set of the component reference spectra comprising the current set with a different one of the component reference spectra removed;
• and
• determining a further measure for each of the further models based upon the model selection criterion;
• and
• the selecting of one of the plurality of models comprises comparing the further measures to the current measure and selecting a best further model to be a new current model if the further measure for that best further model is better than the current measure.