Use of poorly absorbing materials and low-contrast photometric reactions in thermal lens spectrometry

The capability of thermal lens spectroscopy as a highly sensitive method applicable to indicator reactions, the products of which appear poorly absorbing and/or insufficiently contrasting and, which there-fore cannot be utilized in traditional spectrophotometric analysis, are considered in a study of a number of model systems (phenanthrene, unsubstituted dibenzo-p-dioxin, polysaccharides, lyposaccharides, and other materials). It is shown that, in thermal lens spectrometry, the sensitivity of determination in such reactions can be increased by significantly increasing the sensitivity of thermo-optical measurements due to the formation of colloidal reaction products and the exploitation of the kinetic behavior of such reactions. Along with the increase in the sensitivity of absorbance measurements due to the thermo-optical effect itself, these factors also favor a gain in sensitivity in comparison to the spectrophotometry by 1–2 orders of magnitude.