a) The liquid chromatography is to separate and detect the sample lactic acid of L isomer and D isomer by chiral chromatographic column and variable wavelength ultraviolet detector, available for the precise calculation of respective proportion of the two different isomers.

b) The specific rotation is to measure the optical rotation caused by the plane polarized light that passes through the optically active substance at a certain wavelength and temperature. The detection by specific rotation is not only related to the structure of detected substance, but also related to the solvent density, solution, length of the tube holding the solution, temperature and wavelength, etc.

c) The solution of lactic acid is easy to cause the etherification for its special molecular structure, and at a certain density, the monomeric lactic acid and polylactic acid will be present in the solution. In case of no treatment made on the sample and no fixation of analyzing conditions, the detection of optical rotation will be disturbed, and an inferior stability will be caused. Hence, the liquid chromatography is gradually used in the world, other than specific rotation.