Fourth derivative spectroscopy - a critical view

Three polynomial methods (Golay-Savitzky method, step-by-step filter approach and cubic spline differentiation) for obtaining fourth derivatives from absorption spectra linear to the wavelength are investigated. The comparison between them shows that the newly developed 'step-by-step filter' has some important advantages - lack of attenuation and substantial noise suppression especially in the long wavelength region. The appearance of so called 'computational noise' in the higher order derivatives is discussed.