All molecules exhibit unique molecular absorbance and transmittance spectra, and many also have unique fluorescence excitation and emission spectra that can be rendered as two-dimensional excitation-emission matrices (EEMs). For example, EM (emission) and EX (excitation) wavelengths can be plotted for dissolved organic matter in water, revealing spectral details of the mixture. Using a thermoelectrically cooled CCD fluorescence detector for rapid fluorescence-data acquisition and a double-grating excitation monochromator for stray-light rejection (<1%), the Horiba Scientific (Kyoto, Japan) A-TEEM hardware packaged with the Aqualog spectrometer system automatically corrects for inner filter effects (IFEs). These IFEs distort fluorescence spectra as sample concentrations increase because of the reabsorption of fluorescence in the region of spectral overlap with the absorption spectrum. Simultaneously measuring the absorption spectrum and EEM, A-TEEM corrects for absorbance of all the emission to reestablish the linear relationship between concentration and fluorescence intensity, thus reducing the need for dilution and allowing collection of precise spectral library components that are independent of concentration over a wide range.
A-TEEM fingerprints molecules with simultaneous absorbance, transmission, and IFE-corrected fluorescence at a rate of 6 million nm/minute, producing results in seconds. With excitation in the 200–800 nm region with photometric accuracy of ± 0.01 AU (absorbance units) and repeatability of ± 0.0002, A-TEEM identifies and quantifies single molecules and mixtures, protein conformation and aggregation changes, product adulteration, and the effects of aging, oxidation, and contamination. The instrument is suited to water-quality research and monitoring, wine-constituent analysis, protein purity, and vaccine quality-assurance applications. Reference: https://goo.gl/RjLsVH.