A differential refractometer including a measurement section for measuring the diffractive index difference between a sample cell and a reference cell by radiating light on a measurement cell and detecting light which has sequentially passed through the sample cell and the reference cell includes a mobile phase supply section for delivering a mobile phase in a sample introduction channel that is connected to the sample cell. The mobile phase supply section includes a mobile phase container for containing the mobile phase. The inside of the mobile phase container is continuously stirred by a stirring mechanism, and the composition of the mobile phase inside the mobile phase container is made uniform.

The present disclosure describes a computer implemented method, a system, and a computer program product of determining intrinsic viscosity and Huggins constant of an unknown sample. In an embodiment, the method, system, and computer program product include, receiving specific viscosity values over time from a viscometer corresponding to a series of aliquots of an unknown sample injected into an instrument chain where the instrument chain includes the viscometer, calculating a total mass of each of the aliquots, calculating a first intermediate viscosity value of each of the aliquots, calculating a second intermediate viscosity value of each of the aliquots, and fitting the total mass, the first intermediate viscosity value, and the second intermediate viscosity value to a fitting, resulting in a calculated intrinsic viscosity of the unknown sample and a calculated Huggins constant of the unknown sample.