Abstract
A simple method for measuring water concentration from 1 to 10000 mg L−1 is described. The approach involves adding CaO powder to an oil sample and measuring the amount of Ca(OH)2 produced by the reaction of CaO with water. Collection of the powder occurs by passing a fixed volume of the oil through an infrared transparent membrane and the amount of water is determined from the intensity of the OH stretching mode of Ca(OH)2 at 3645 cm−1. The approach is demonstrated with transmission, vegetable, and extreme pressure oils. These oils represent classes of oils that are problematic for measurement by transmission infrared spectroscopy, using a fixed pathlength cell, as described in ASTM method E2412. Values for the water levels equivalent to those measured by Karl Fischer titration are obtained with a linearity R2 value of > 0.996 and %RSD of 6.7% over a wide detection range of 1 mg L−1 to 10000 mg L−1. No calibration is required, as the amount of water is determined using the extinction coefficient for the band at 3645 cm−1.
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