The present invention is thus directed to an automated system and method of varying the optical path length in a sample that a light from a spectrophotometer must travel through. Such arrangements allow a user to easily vary the optical path length while also providing the user with an easy way to clean and prepare a transmission cell for optical interrogation. Such path length control can be automatically controlled by a programmable control system to quickly collect and stores data from different path lengths as needed for different spectrographic analysis. Such a methodology and system, as presented herein, is able to return best-match spectra with far fewer computational steps and greater speed than if all possible combinations of reference spectra are considered.