Differential refractometer

A liquid chromatograph having a flow line for feeding an eluent to a column by a feed pump, a sample injector provided in said flow line and a differential refractometer as a detector provided in another flow line connecting an outlet of said column with a drain, said differential refractometer comprising:

• a flow cell having two cells divided by a partition wall being inclined with respect to an optical axis of a measuring beam, so that a sample solution passes through one of said two cells and a reference solution passes through or is held in the other said cell;
• an optical system for transmitting said measuring beam passing through a slit through said flow cell, reflecting said transmitted measuring beam by a mirror for transmitting said measuring beam through said flow cell again and thereafter making said measuring beam from said flow cell form a slit image on a photodetector;
• said photodetector being divided into four portions by a first straight line being perpendicular to a direction of movement of said slit image and a second straight line being inclined with respect to said direction of movement of said slit image to intersect with said first straight line;
• and
• an operation part receiving output signals from respective said divided portions of said photodetector for calculating difference between outputs of said photodetector portions divided by said first straight line with said slit image being located across said first straight line for high-sensitivity detection, while calculating difference between outputs of said photodetector portions divided by said second straight line with said slit image being located across said second straight line for low-sensitivity detection.