Tips and Frequently Asked Questions for VEE GEE Refractometers

Posted by Kenneth Kreiman on


- The glass prism and daylight plate must be gently cleaned after each use. Any residue left on the prism will affect the way the light refracts on the next sample. If your sample is oily or sticky a mild detergent that is diluted can be used, along with a microfiber or non-abrasive lint-free cloth.

- Do not hold the refractometer under a stream of water from a faucet to rinse it off. The entire unit is not watertight, just the prism is sealed to the housing. This applies to our handheld and digital units.


- When calibrating a unit that includes Automatic Temperature Compensation (ATC), the calibration must be done in a room that is at or very near 68°F (20°C) so that the ATC works properly.


- Place a few drops of your sample on the prism and close the daylight plate. Make sure that the sample covers the entire daylight plate, with no bubbles or gaps. Re-apply if necessary to get full coverage. Gently pressing down on the daylight plate can help spread the sample to cover the prism.

 - Important point: when we talk about the temperature, we are talking about the temperature of the room/environment that the refractometer is in, not the solution temperature. The thin layer of solution that is used will quickly equilibrate to the temperature of the refractometer itself.

Frequently Asked Questions

“When I look through the eyepiece with no sample on the prism, all I see is blue.”

 With no sample, the scale will appear all blue. It is only when the light is refracted through a sample that there will be a blue section above a white section, the interface being where you would read.

“The interface line is fuzzy, no distinct line.”

There are a few things you can try with this. First, make sure that the sample completely covers the prism; reapply if it doesn’t. Second, ensure the prism doesn’t have any residue from previous samples and clean if necessary. Third, try using a stronger light source as this can clarify the interface line. Lastly, gently pushing down on the daylight plate with your finger while reading can clear the interface line.

If you are measuring the sap from a plant, there is a belief that the fuzzy line is an indication of calcium in the sap which is a good thing. A very distinct line, in this case, indicates a mineral deficiency.

“I put my solution on the prism and the scale is completely white in the eyepiece.”

Here’s an example of why this happens. I had a customer that had a 0-32% Brix refractometer. The sample was maple syrup, which tends to have a reading in the high 60’s. The scale showing as all white is an indication of the sample being over the range of the refractometer. We have a different model with a range of 60 to 92% Brix which would be the appropriate model for maple syrup.

“I’m measuring salinity for a shrimp farm. Which unit should I use, the SX-2 Sodium Chloride unit, or the STX-3 Salinity unit?”

Our STX-3 (item # 43036) would be the choice as it is calibrated for the salinity of seawater. Some salinity units on the market are calibrated just for sodium chloride, but seawater also includes some other salts such as magnesium and potassium salts. Our STX-3 is calibrated for the seawater salts; the SX-2 is calibrated only for sodium chloride.


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