Tips & Tricks on Correct Usage of Refractometers

As a service to its chemical industry laboratory partners, METTLER TOLEDO is pleased to announce some simple yet effective tips and tricks to ensure accurate refractive index determination.

The refractive index is normally determined as a part of the characterization of liquid samples. It helps to identify or confirm the identity of samples, to determine the concentration of a solute in a solution and to assess the purity of a sample. While the principle is straightforward, measurement can sometimes be tricky, especially if the operator is not experienced. However, there are quite a few tips and tricks that can greatly help to improve results and simplify the process, including:

• Use Enough Sample
  The prism has to be covered with the sample, as otherwise light scattered by air may hit the Charge-Coupled Device (CCD) sensor and influence the result.
• Organic Solvents
  The surface tension of organic solvents or samples containing organic solvents such as ethanol or acetone is low compared to water. Such samples act as wetting agents and form a concave meniscus. Thus, add more sample to achieve sufficient filling height of the prism.
• Removal of Sample and Rinsing Solvents
  To remove sample or rinsing solvents from the refractometer, it is suggested to use a syringe without needle to suck in the liquid. This syringe can be used multiple times, but we suggest to mark it, for instance with black tape. Using a syringe saves a lot of soft tissue cleaning wipes and reduces waste. Instead of utilizing cheap two-component syringes, it is suggested to use three-component syringes (with rubber O-ring), which allow for smooth sucking up of waste.
• Sample Temperature
  Differences in the temperature of the prism and the sample will influence your results. Always allow for sufficient time for temperatures of sample and prism to adjust. Digital meters with built-in thermostat automatically wait for temperature equilibration before taking the result.

About METTLER TOLEDO
METTLER TOLEDO specializes in the area of precision instruments for professional use. METTLER TOLEDO laboratory instruments are used in research, scientific, drug discovery, and quality control labs, amongst many others in the pharmaceutical, chemical, food and cosmetics industries. METTLER TOLEDO comprehensive industrial solutions cover the various steps in a host of manufacturing processes at many of the same customers that laboratory serves. Solutions range from receiving raw materials through various manufacturing processes, in-line process control and end-of-line packaging control, to logistics and shipping. Increasingly, these solutions are fully integrated into the customer's IT environment, helping automate their workflows. In food retail, our offering for fresh food management ranges from receiving and pre-packaging, to in-store solutions for self-service departments, deli counters, and checkout terminals.

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