Construction and transferability of a spectral library for the identification of common solvents by near-infrared transflectance spectroscopy

Abstract

A transflectance near-infrared spectroscopic method has been developed for the identification of 15 common solvents using correlation in wavelength space as the identification algorithm. Second-derivative absorbance spectra over the wavelength range 1136–2000 nm were found to give the optimum conditions for distinguishing between the solvents. The spectral library was tested on eight instrumental setups and found to be directly transferable between different instruments not only from the same manufacturer, but also between grating and Fourier transform systems. Identification was not affected by small changes in temperature or optical path length. The presence of water could easily be detected by visual insepection of the solvent spectra. However, small traces of water did not normally interfere with the identification process. Correlation coefficient values between a given solvent from different batches and/or between different instruments were generally >0.99. Values <0.99 invariably indicated the presence of impurities. Mixtures of similar solvents such as ethanol–methanol could not always be reliably differentiated from that of the pure solvent at the highest concentration.