Hyphenation of ion exchange high-performance liquid chromatography with Fourier transform infrared detection for the determination of sugars in nonalcoholic beverages

Fourier transform infrared spectroscopy (FT-IR) is presented here as a molecular-specific detection system for high-performance liquid chromatography (HPLC) in an aqueous phase, focusing on the chromatographic separation of sugars in beverages. The separation was achieved with an isocratic HPLC setup using an ion exchange column (counterion, Ca2+). The FT-IR detection of the C-O bands in the mid-IR between 1000 and 1200 cm(-1) was performed in real time with a 25 mu m flow cell without elimination of the solvent. Characteristic FT-IR spectra of the common sugars sucrose, glucose, and fructose in concentrations of 1 mg/mL could be recorded during the separation. The calibration of these compounds in the 5-100 mg/mL range resulted in a linear correlation with a standard deviation of the method (s(x0)) of 0.11, 0.07, and 0.11 mg/mL for sucrose, glucose, and fructose, respectively. The method was, furthermore, applied to the analysis of nine soft drinks and fruit juices containing between 6 and 97 mg/mL of each carbohydrate, The accuracy of the method was confirmed by standard ion exchange HPLC with refractive index detection. The average deviation from the reference method was in the range of 0.5-0.9 mg/mL. Furthermore, the method was found to be suitable to identify and quantify also minor components in beverages, such as taurine (4 mg/mL) and ethanol (0.4 mg/mL).