Liquid-phase samples absorb very weakly in the near-infrared (NIR) region compared to the fundamental region. To detect weak vibrations in NIR region, one uses cells of relatively high pathlengths ranging from 0.1 cm to 5 cm. The selection of a particular pathlength depends upon the absorption strength of the vibration of interest.
M. Khalique Ahmed, "New Window Material for Near-Infrared Spectroscopy," Appl. Spectrosc. 47, 666-668 (1993)