Rules and Guidelines
1. New user MUST be trained by the captain or present users
1. Use a pipet to apply your liquid sample to the prism, being careful not to let the glass pipet tip touch the prism since this may scratch the prism glass. Add enough sample to achieve a thin film across the
whole prism, typically 10 μL is enough.
2. Close the prism assembly and turn on the lamp using the switch on the left side.
3. Adjust the lamp so the light shines on the prism and look through the eyepiece. If you are close to the index of refraction of your sample you should see that the view in the eyepiece shows a dark region on
the bottom and a lighter region on the top. If you do not see a light and a dark region, turn the handwheel on the right side of the instrument until you do.
4. Before making the final adjustment, it will usually be necessary to adjust the lamp position and to sharpen the borderline between the light and the dark regions using the compensator dial on the front of the
5. Once you have a crisp demarcation between the light and dark regions, turn the handwheel on the right hand side to place this borderline exactly on the center of the crosshairs.
6. To read the index of refraction, depress the switch on the left hand side of the refractometer until you see the scale through the eyepiece. The upper scale indicates the index of refraction. By carefully
interpolating you can read the value to 4 decimal place accuracy.
7. Record the refractive index.
8. After you are finished, clean the refractometer. First use a kim wipe with some water to dab away most of your sample. Then put some ethanol on a kim wipe and clean the prism.
9. After you have finished cleaning the prism, place a clean tissue in the assembly.
Before you leave make sure that the light has been turned off, and cover the refractometer.
- Jessica Metzger | December 2020