Measuring Concentration in Ternary Solutions

Aqueous solutions with more than two dissolved components can be difficult to measure and present different analytical challenges than a single component solution. For these solutions, density and sound velocity measurement offer a different approach to achieve results.


There are many techniques to measure a single component in an aqueous solution. A density meter or titration will work just fine in these situations.
It is far more difficult to accurately determine the concentration of two materials when they are both in the same solution due to both compounds having an influence on the density of the solution as a whole.

Overcoming this difficulty requires an analytical technique that can evaluate the two components based on a difference in chemical or physical properties. Chromatographic techniques can be very useful for this, but they can also be expensive in terms of equipment costs, training, labor, and materials. Titration is another possibility, but this requires twice the time, equipment, and chemicals to titrate both compounds individually. Additionally, not all compounds can be titrated individually without influencing the other component in solution.

A proven way to obtain accurate concentration determination for a binary solution is by density measurement. This requires a concentration table for your compound. Unfortunately, a second material in solution will cause changes to the density reading that will influence the concentration measurement. However, by adding a second parameter to density measurement it is possible to account for a second compound in solution. Sound velocity is a property that behaves independently of density and can be easily measured in liquids. A density and sound velocity analyzer can measure both properties simultaneously and use the combined data to determine the concentration of two components in an aqueous solution.

There has already been some research on a number of common ternary solutions. These liquids have established density and sound velocity data that allow for easy concentration measurement. Applications such as sugar inversion, which is the conversion of sucrose into fructose and glucose, can be monitored by means of density and sound velocity measurement. There are also other applications in chemical production processes. For example, density and sound velocity measurement can be used for quality control during sulfuric acid manufacturing, as well as during the production of formalin.

To measure samples for a new application, the concentration range of the two components in the aqueous solution has to be determined first.
Then, reference samples with exact concentrations of both components within their defined ranges can be prepared. By measuring these samples a concentration formula can be derived which later on uses the measured density and sound velocity of an unknown sample to calculate the concentrations of the two components. This makes it possible to get the concentration results of both components automatically in one go.

A density and sound velocity analyzer like the DSA 5000 M offers a solution to the challenges faced when analyzing a three-component mixture. The above-mentioned concentration formulae are automatically applied to the measured density and sound velocity to provide information about diverse three-component mixtures. Despite the strong application dependence of the measurement, it is worth investigating to see if this measurement technique – because of the relative ease of the measurement – is a viable option to traditional methods which can be time-consuming and expensive.

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