Mathematical alignment of wavelength-shifted optical spectra for qualitative and quantitative analysis

A multivariate method for aligning Raman spectra that suffer from spectral shifts resultant from diode laser mode-hopping is presented. This alignment method permits accurate alignment without necessitating a consistent reference peak while avoiding the uncertainties of estimating the maxima of broad or noisy peaks. This method differs from multivariate standardization methods in that the training set needs to be measured only once. The spectra are not compared to the spectra of a separate instrument. It is shown that the alignment enhances the performance of Raman spectroscopy for quantitative and qualitative applications. This evidence is supported by Monte Carlo simulations, quantitation of a mixture of aromatics by Raman spectroscopy, and imaging of a polymer surface by a Raman microscope.