Abstract: A method of determining a phase separation concentration of a sample substance in a solution, comprises the steps of measuring values of a physical quantity of the solution containing the sample substance with at least one sample substance concentration lower then the phase separation concentration, wherein the physical quantity characterizes an interaction of the solution with sound waves, determining a concentration function representing a dependency of the physical quantity on the sample substance concentration lower then the phase separation concentration, and determining the phase separation concentration as a concentration value at which the concentration function equals a predetermined critical value of the physical quantity of the solution containing the sample substance in a saturated condition. Furthermore, a concentration determining device is described.

Abstract: The invention provides a method for determining optimal concentrations of additives which are capable to protect sensitive biomacromolecules, e.g. proteins or nucleic acids, against denaturation and aggregation in a solution comprising at least one species of a biomacromolecule and at least one species of a protective additive comprising: a) treating said solution with ultrasonic waves; and b) recording the value of one or more ultrasonic parameters, such as the ultrasonic velocity in said solution and/or the ultrasonic absorption of said solution. The above method allows to detect critical changes of the ultrasonic parameter dependent from the concentration of the protective additive and indicative of interactions or changes of interactions between additive and biomacromolecules and/or between different biomacromolecules and/or changes of the conformation of the biomacromolecules.