Sugar Analysis Using Hydrophilic Liquid Chromatography Combined with Raman Spectroscopy

The combination of chromatography and Raman spectroscopy is challenging because the eluate flows fast and limits the accumulation time of weak Raman signals. The total reflection of light in a liquid core waveguide (LCW) can enhance the Raman signal intensity and thus solve this problem. We used a vertical flow technique to form an LCW with a sample solution and combined Raman spectroscopy with hydrophilic liquid chromatography (HILIC). Additional techniques were used to eliminate the strong Raman signals attributed to the organic solvent used for HILIC. We report the HILIC-Raman analysis of five sugars (fructose, glucose, sucrose, maltose, and trehalose). These sugars were eluted over 11 min (fructose at 36.5 min and trehalose at 47.4 min) and identified by checking the Raman spectra. The limit of detection (LOD) was 60-80 μg mL^-1. The HILIC-Raman technique was also applied to analyze the sugar content of honey. The content of fructose, glucose, and sucrose in wt % was determined to be 39.9 ± 0.6, 26.5 ± 1.8, and 0.9 ± 0.5, respectively, and these values agreed with those determined using LC with the refractive index detector. The HILIC-Raman technique offers a novel approach of the quantitative analysis of solutes in the LC eluate.