Ri-501 is the model corresponding to standard size analysis chromatography; ri-502 is the model corresponding to preparation chromatography; ri-504 is the model corresponding to semi micro type chromatography. These machines are state-of-the-art RI detectors that minimize peak broadening. According to the use of different sizes of chromatographic columns, different models can maximize the analytical capacity of chromatographic columns. Please choose according to your actual use.