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Cleaning | Reliable Density Measurement When Switching from Water to Oily Samples

Water residues in the DMA 35 measuring cell can cause challenges when switching from aqueous to oily samples. An intermediate rinse with isopropanol provides a simple and reliable transition while reducing rinsing time and sample consumption.

Portable density meters such as the Anton Paar DMA 35 enable fast and reliable density measurements directly at the sampling location. In routine use, however, switching between samples with very different properties can present a practical challenge. This is particularly relevant when changing from hydrophilic liquids, such as water, to hydrophobic liquids such as edible oils, lubricating oils, fuels, or other petroleum products.

A common example is a water check performed to verify the status of the instrument before starting a series of measurements. After the water check, small amounts of water may remain in the measuring cell. If an oily sample, such as sunflower oil, engine oil, or a petroleum product, is filled immediately afterwards, the remaining water cannot be easily removed by the sample because water and oil are immiscible. Water droplets may therefore remain in the measuring cell and affect the measured density. Removing these residues by repeatedly rinsing with the next sample is possible but can require considerable sample volume and additional time.

This application report presents a simple and effective solution: an intermediate rinsing step with isopropanol. Isopropanol is miscible with both water and many oily samples and can therefore act as a transition between the two. The intermediate rinse efficiently removes residual water from the measuring cell before the hydrophobic sample is introduced. This simple procedure reduces the amount of sample needed for rinsing, shortens the preparation time, and supports reliable density measurements when switching from aqueous to oily samples.

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