A new approach for measuring water concentration in oil using copper sulfate powder and infrared spectroscopy.

An approach for measuring water concentration in oil, based on the use of CuSO4 particles and infrared spectroscopy, is described. The particles interact with both dissolved water and water droplets to form the monohydrate, CuSO4·H2O. These particles are collected on an infrared transparent membrane and then an infrared spectrum in transmission mode is recorded. Strong interaction of the water with the CuSO4 shifts and intensifies the water bending mode to produce a unique band at 1743 cm-1. The method provided values which are equivalent to those measured by Karl Fischer titration over the range of 10 to 3500 mg L-1 with a linearity R2 value of > 0.99 and an average %RSD for all measurements was 6%. No matrix specific calibrations are required.

Measurement of water concentration in oils using CaO powder and infrared spectroscopy.

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.

A reagentless and rapid method to measure water content in oils.

A simple method for measuring water levels from 1 mg L-1 to 5000 mg L-1 in oils that uses no chemical reagents or matrix specific calibrations is described. The approach involves capturing the water from the oil on an infrared transparent membrane and then recording an IR spectrum in transmission mode through the membrane. A classic spectrum of liquid water is obtained for all oil types, as both dissolved water and emulsion-based water are extracted to form an adsorbed layer of water on the membrane surface. The method was tested with three types of oils that are identified as difficult in the ASTM method E2412, as these oils, exhibit distortions in the water bands due to interactions of the water with the oil, or have significant levels of scattering due to the presence of water droplets. In comparing water concentrations measured by Karl Fischer titration, a high level of linearity (R2 > 0.995) is obtained over the range of 1 mg L-1 to 5000 mg L-1 with slope values of 0.99 for power steering fluid, 0.98 for vegetable oils, and 0.95 for extreme pressure fluid. This shows that water concentration obtained by the membrane method were comparable to those obtained by Karl Fischer. No matrix calibrations were needed as the concentration of water in oil was determined using literature values for the extinction coefficients of water. The wide detection range is obtained by varying the volume of oil (30 µL-30 mL) passed through the membrane and by choosing the water band for quantification.