Determination of sucrose by flow injection analysis with fourier transform infrared detection

Glucose and Fructose Hydrates in Aqueous Solution by IR Spectroscopy

In the mid-infrared attenuated total reflectance (MIR-ATR) spectra of aqueous d-glucose and d-fructose solutions, two hydrates were found by factor analysis (FA) for each sugar, d-glucose penta- and dihydrates and d-fructose penta- and monohydrates. We obtained the spectra and abundances for these hydrates as a function of carbohydrate concentrations. The biggest difference in these spectra lies in the CO stretch region. From the distribution of the species, the equilibrium between d-glucose pentahydrate and dihydrate is 3(H2O)2+2(C6H12O(6).2H2O) right arrow over left arrow 2(C6H12O(6).5H2O), with the equilibrium constant KG=(3.2+/-0.6)x10(-5) L3 mol-3. For d-fructose, the equilibrium is between pentahydrate and monohydrate, 2(H2O)2+C6H12O6.H2O right arrow over left arrow C6H12O(6).5H2O, with the equilibrium constant KF=(7.1+/-1.2)x10(-3) L2 mol-2. The four hydrates are present only in aqueous solutions and cannot be obtained in the solid state.

Liquid chromatography-Fourier-transform infrared spectrometry

Over the past years the coupling of liquid chromatography (LC) and Fourier-transform infrared spectrometry (FT-IR) has been pursued primarily to achieve specific detection and/or identification of sample constituents. Two approaches can be discerned in the combination of LC and FT-IR. The first and simpler approach is to use a flow cell through which the effluent from the LC column is passed while the IR spectra are continuously recorded. The second approach involves elimination of the LC solvent prior to IR detection using an interface which evaporates the eluent and deposits the analytes onto a substrate. This paper provides a general overview of flow-cell based IR detection and briefly discusses early solvent-elimination interfaces for LC-FT-IR. A more comprehensive description is given of interface systems which use spraying to induce rapid eluent evaporation, and which basically represent the state-of-the-art in LC-FT-IR. Finally, the interface systems suitable for reversed-phase LC are summarized and the perspectives of LC-FT-IR are discussed. The overview indicates that flow-cell LC-FT-IR has rather poor detection limits but can be useful for the specific and quantitative detection of major constituents of mixtures. Solvent-elimination techniques, on the other hand, provide much better sensitivity and enhanced spectral quality which is essential when unambiguous identification of low-level constituents is required.