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 D2O 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-h6 in DMSO-d6 and CD3OH in CD3OH, CD2HOH, and CDH2OH at levels as low as 10-3% (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)