Isolate and prepare the solution of interest. Using the polarimeter is straightforward but the process preceding measuring the polarimetry can be challenging. The polarimeter operates with extreme precision, so isolating the solution under study proves imperative. Before pouring your isolated solution into the polarimeter's sample tube, you may want to wash it with a polar, non-volatile cleaning agent such as ethanol. In order to ensure all debris and cleaning agents have been completely removed, wash out the sample tube again, but this time use small amounts of your solution.
Determine a solution's observed rotation via polarimetry by placing the sample tube into the polarimeter and closing the lid. The polarimeter will send a beam of plane-polarized light through the solution to an analyzer where it will determine how the light bends and then quantify this into what is called observed rotation. Observed rotation does not take into consideration the path length of the light beam nor the concentration of the solution; therefore, the researcher must calculate the specific rotation from the observed rotation.
Calculate the specific rotation using the equation [a] = a/lc. The specific rotation, [a], equals the observed rotation, a, divided by the product of the distance traveled by the light beam, l, and the solution's concentration, c, where the concentration units are in grams per milliliter. For example, if a solution's observed rotation is 20 degrees, the length of the polarimeter tube is one decimeter and the concentration of the solution was 1/5 gram per milliliter, then the specific rotation would be one hundred degrees. Chiral molecules with mirror images, called enantiomers, rotate light with the same magnitude but in opposite directions. Therefore, if the degree of rotation is positive, you can look up the isomers to determine which isomer is positive. From there you will know which isomer is dominant and to what extent.