Types

• Refractometers come in different types such as the traditional and digital handheld models, as well as the Abbe and inline units. Abbe models are the most precise and are typically used in laboratory environments and resemble a microscope. Inline refractometers are most often used in industrial settings to take readings on fluids traveling though pipes. Handheld models are generally used by consumers, and the digital type is slightly more precise than a traditional unit. Handheld models are commonly used to measure a number of different solutions---including the salinity of water and the amount of sugar present in blood.
  
  

Calibration

• All refractometers will need to be calibrated before use to ensure an accurate reading. Place a drop of distilled water on the main prism and allow it to sit for 30 seconds to adjust to the temperature of the refractometer. Close the cover and adjust the calibration screw until the shadow lines up with the zero mark. Open the cover and dry the main prism using a soft cotton cloth.
  
  

Operation

• Place a drop of the sample you are attempting to measure onto the main prism and close the cover. Only a single drop is needed to obtain a reading but be certain that the drop is fresh. Readings must be performed hastily to avoid evaporation, which can distort the results. Look through the eye-piece and adjust the light so that the line between the light and dark area is in focus. Once this line is aligned with the scale, record the reading and make note of the temperature as well. Readings should be recorded to the nearest 0.1 percent. If you are using a digital refractometer there will be no eye-piece or manual adjustments required.
  
  If you are taking multiple measurements, dry the refractometer after each measurement with a soft cotton cloth. After every 10 to15 measurements, use an alcohol solvent to clean and dry the prism. Always store the refractometer in its original case when not in use.