Differential refractive index detector

A purging method, suitable for purging a flow cell of a differential refractive index detector, wherein the differential refractive index detector comprises:

• a light receiving element, receiving a measuring light to generate a slit image, wherein the measuring light is made to pass through a slit to reach the flow cell for being transmitted as a transmitted light, and then, by means of being reflected by a reflecting mirror, the transmitted light is made to re-transmit through the flow cell, and in the flow cell, a sample solution passes through one cell of two cells spaced apart by a spacer inclined with respect to an optical axis of the measuring light, and a reference solution passes through the other cell;
• a zero glass, making the slit image parallelly move on the light receiving element;
• and a zero glass driving unit, making the zero glass rotate;
• the purging method comprising:
• storing a rotating angle of the zero glass in a storing portion when the same solution fills up the two cells;
• and
• comparing a current rotating angle of the zero glass with the rotating angle of the zero glass stored in the storing portion during a purging operation of replacing the reference solution of the flow cell, wherein when the difference between the two angles falls into a specified range, the purging operation is finished.