Step by step filter — an approach for noise reduction in the derivative UV-visible spectra

Methods for obtaining the more informative second derivative d2A(λ)dv2 from absorption spectra linear in λ are discussed. It is found that the noise level in the derivatives obtained is high, especially in the long-wavelength region. The efforts to reduce the noise level by use of classical smoothing procedures lead to irregular deformation of the derivative curves, which is stronger in the short-wavelength and weaker in the long-wavelength region. An alternative method for obtaining the more informative second derivative d2A(λ)dv2, as well as higher derivatives, called “general step by step” filter (GSBSF), is proposed. Its use considerably decreases the noise level in the derivative spectra without loss of spectral information in the short-wavelength region. This method could be used in UV-visible-near-infrared (UV-Vis-NIR) absorption spectroscopy, circular dichroism spectroscopy, UV-Vis densitometry, etc.