Glycerin

The 2-Hydroxyethyl cellulose (Mn: ~90,000 g/mol) was purchased from Sigma Aldrich CO (St. Louis, MO, USA). Acetone, glycerin, and lactic acid were purchased from Daejung Chemical and Metals (Siheung, Republic of Korea). Polypropylene prefilter which pore sizes of 0.6 μm was purchased from Merck Millipore Ltd. (Darmstadt, Germany) All chemicals were used as received.

Tests were conducted using liquid samples of various known n_L (Dodecane (Sigma-Aldrich, anhydrous 99+%, n_L = 1.42), 40 M glycerin (Daejung, 99+%) solution (n_L = 1.44), 6 M CaCl₂ (Kanto, anhydrous 95%) solution (n_L = 1.44), and a mixture of 40 M glycerin and 6 M CaCl₂ (n_L = 1.46) to calibrate the measurement of n_L. Mixtures of sucrose (Junsei, guaranteed reagent) and DI water with concentrations varying from 0 to 60 wt%, of which n_L vary linearly from 1.33 to 1.44 were used to evaluate the versatility of the proposed measurement system. A commercial hand-held refractometer (ATAGO^®, R-5000) having a precision of 0.001 was used to check the accuracy of n_L measurement by the proposed system. To avoid the effect of temperature on n_L, all experiments were conducted at 25 ± 1 °C. A white light-emitting diode and a diffuser film were used to uniformly illuminate light. To avoid the dispersion effect and illuminate monochromatic light of wavelength 589 nm, we used an orange-colored filter in front of the light source. Images of GSP were captured using a digital single-lens reflex camera (Canon, 650D) and macro lens (Canon, MP-E 65 mm). The captured GSP images were processed using the Image Processing Toolbox™ of MATLAB^® R2012a to analyze the brightness profile in the GSP.