New low-index liquid refractive index standard: SRM 1922

Area of Science:

• Metrology
• Optical Physics

Background:

• Accurate calibration of refractometers is crucial for various industries.
• Existing standards may lack comprehensive characterization for specific temperature ranges.

Purpose of the Study:

• To introduce a new Standard Reference Material (SRM 1922) for refractometer calibration.
• To characterize the temperature dependence of the refractive index for SRM 1922.

Main Methods:

• Refractive indices were measured at five visible wavelengths using the minimum deviation method.
• The change in refractive index with temperature (dn/dT) was determined.
• A two-term Cauchy function was fitted to wavelength-dependent refractive index data.

Main Results:

• SRM 1922, a mineral oil, has a refractive index (nD) of 1.46945 at 20°C.
• The refractive index and its temperature coefficient (dn/dT) were characterized between 15°C and 35°C.
• Measurement uncertainty was ±(2-3) x 10⁻⁵ at 20°C, with overall nD uncertainty of ±6 x 10⁻⁵.

Conclusions:

• SRM 1922 provides a reliable standard for refractometer calibration within the Brix scale range.
• The detailed characterization allows for accurate calibrations across a defined temperature range.
• This new standard enhances measurement accuracy in applications relying on refractometry.