# Proposal for a New Differential High-Sensitivity Refractometer for the Simultaneous Measurement of Two Refractive Indices and Their Differences

## TL;DR

This paper proposes a new refractometer that can measure refractive index differences with high sensitivity, useful for detecting nanoparticles and environmental pollution.

## Contribution

A novel differential refractometer design that enables highly sensitive and simultaneous measurement of refractive index differences.

## Key findings

- The refractometer achieves high sensitivity with refractive index measurement accuracy below 7×10−6.
- The device can detect nanoparticles in solution and assess environmental nano-pollution in water samples.
- The design reduces laser intensity fluctuations by measuring both solution and solvent simultaneously with one laser pulse.

## Abstract

The refractive index of a liquid serves as a fundamental parameter reflecting its composition, thereby enabling the determination of component concentrations in various fields such as chemical research, the food industry, and environmental monitoring. Traditional methods for refractive index (RI) measurement rely on light deflection angles at interfaces between the liquid and a material with a known refractive index. In this paper, the authors present a new differential refractometer for the highly sensitive measurement of RI differences between two liquid samples. Using a configuration with two cells equipped with flat parallel plates as measuring elements, the instrument facilitates accurate analysis. Namely, the sensor signals from both the solution and the solvent cuvette are generated simultaneously with one laser pulse, reducing the possible fluctuations in the laser radiation intensity. Our evaluation shows the high sensitivity of RI measurements <7×10−6), so this differential refractometer can be proposed not only as a high-sensitivity sensing tool that can be used for mobile detection of nanoparticles in solution samples but also to determine the level of environmental nano-pollution using water (including rain, snow) samples from various natural as well as industrial sources, thus helping to solve some important environmental problems.