A novel instrument which is based on the use of the thermal lens effect to facilitate the sensitive measurements of the absorption in the near-infrared region has been developed. In this instrument, the near-IR excitation light was provided by a solid-state, spectra-tunable (from 860 to 1060 nm) titanium:sapphire laser. The heat generated as a consequence of the sample absorption of the excitation beam was monitored in the visible region by a He-Ne laser. The data obtained were analyzed by multivariate calibration methods for the nondestructive, noninvasive determinations of chemical and isotopic impurities in solvents. Water in D<sub>2</sub>O and in tetrahydrofuran can be detected at levels as low as 0.006 and 0.3% (v/v). The method can also be used for the simultaneous determination of water and DMSO-<i>h</i><sub>6</sub> in DMSO-<i>d</i><sub>6</sub> and CD<sub>3</sub>OH in CD<sub>3</sub>OH, CD<sub>2</sub>HOH, and CDH<sub>2</sub>OH at levels as low as 10<sup>-3</sup>% (w/w).
Chieu D. Tran, Victor I. Grishko, and Mauricio S. Baptista, "Nondestructive and Nonintrusive Determination of Chemical and Isotopic Purity of Solvents by Near-Infrared Thermal Lens Spectrometry," Appl. Spectrosc. 48, 833-842 (1994)