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Separation of monosaccharides by high-performance liquid chromatography: comparison of ultraviolet and refractive index detection

A novel water-holding adsorbent bonded with a zwitterionic polymer, diallylamine–maleic acid copolymer, was developed. With this adsorbent, hydrophilic solutes are partitioned by a hydration layer that forms on the zwitterions, as a main separating force. When the adsorbent was used to separate saccharides by normal-phase partition chromatography, the saccharides eluted in the order, mono-, di- and trisaccharide. The elution profile for mono- and di-saccharides was similar but not identical to that on anion exchange columns. This indicated that the adsorbent exhibited a complex retention behavior by the existence of both anion and cation exchange moieties in the functional polymer. Selecting Na⁺ as a counter-ion of the maleate moiety enhanced the retention of saccharide. When used in an high performance liquid chromatography (HPLC) system with gradient elution, the adsorbent enabled the simultaneous analysis of mono-, di- and oligosaccharides.

The correct labelling of dairy foods as “lactose-free” requires a suitably sensitive and valid analytical method for the quantification of lactose in complex food matrices. Thus, an ion-pair RP-HPLC method for the simultaneous determination of lactose, glucose and galactose in original skim milk was investigated. The samples derived from an enzymatic lactose hydrolysis approach (0.5 L) using the commercial β-galactosidase Godo-YNL2. After derivatisation with p-aminobenzoic acid and sodium cyanoborohydride, the samples were injected on a RP-C₁₈ column. Tetrabutylammonium hydrogen sulphate was used as the ion-pair reagent in the eluent system. The sugars were quantified using photometric- (UV; 303 nm) and fluorescence-detection (λ_ex 313 nm, λ_em 358 nm). The overall run time was 27 min. The limits of detection (LOD) were estimated at 2 mg L⁻¹ (UV detection) and at 0.13 mg L⁻¹ (fluorescence detection). The limits of quantification were 6 mg L⁻¹ (UV detection) and 0.45 mg L⁻¹ (fluorescence detection). Thus, this analytical method is suitable for sensitive lactose quantification in milk systems of less than 10 mg L⁻¹.

A photoelectrochemical detector (PECD) was developed for determination of organic compounds in flow injection analysis (FIA) and high performance liquid chromatography (HPLC) based on the extraordinary oxidation power of nanostructured TiO₂ photoanodes under UV illumination. The PECD is a simple, small, and compact photoelectrochemical cell consisting of low cost components such as a TiO₂ nanostructured photoanode and a UV-LED. Compared with conventional FIA and HPLC selective detectors, such as UV–Vis detector, electrochemical detector and fluorescent detector, the PECD has the advantage of being low cost, non-selective and sensitive. Using the FIA mode, the analytical principle of the PECD was demonstrated by detecting a large variety of organic compounds, such as sugars, amino acids, alcohol, straight chain carboxylic acids, and aromatic carboxylic acid. The PECD was subsequently coupled with a typical FIA and HPLC system for the determination of sugars. For the application in FIA, under the optimum experimental conditions, the linear ranges for glucose and sucrose were 25–600 μM and 25–500 μM, respectively, with the same detection limit of 10 μM. When the PECD was coupled with a HPLC system, the linear range for both glucose and sucrose was 7.5–200 mM with the same detection limit of 1 mM under the optimal experimental conditions.

This paper evaluates frontal analysis for routine sugar isotherm measurements at industrial conditions, that is concentrations up to 400 kg/m³ and a temperature of 60 °C. Sugar isotherms for a gel type cation-exchange resin loaded with metal ions were measured in a HPLC set-up equipped with a UV detector. It is shown experimentally that isotherms obtained with large concentration steps (step series method) underestimated the isotherm. The underestimation is larger for larger resin particle size. In contrast, isotherms obtained with small concentration steps (staircase method) yielded correct isotherms. The seldom-mentioned change of the sorbent volume during the course of an isotherm measurement is discussed. It is shown that shrinking of 4% cross-linked resin at high sugar concentration has a negligible effect on the isotherm. Furthermore, the isotherms obtained with staircase frontal analysis agreed very well with those obtained with the independent, though more laborious and time-consuming, adsorption–desorption method. Staircase frontal analysis is shown to be convenient and accurate and is therefore recommended for isotherm measurements covering large concentration ranges.

A high-performance anion-exchange chromatographic method that uses an alkaline mobile phase (20 mM NaOH) on an anion exchange column (RCX-30 Hamilton) at 30 °C coupled with pulsed amperometric detection was applied to the analysis of the glucose, galactose, xylose, arabinose, ribose, fucose, rhamnose and fructose in cider brandies. Data were compared with those obtained from aldoses- and uronic acids-p-aminobenzoic ethyl ester derivatives analysis by HPLC on a C₈ column at 45 °C with spectrophotometric detection. Both methods were validated and their advantages and drawbacks taken into account.

Gas chromatography and liquid chromatography have been used simultaneously to analyze sugars in honey. After statistical processing by principal components analysis, additions of exogenous sugars could be detected by the appropriate fingerprints of adulteration. Application to acacia, chestnut and lavender honeys enabled the detection of fraud resulting from 5 to 10% addition of sugar syrups. This method may be considered as a replacement of isotopic analysis, that has some limitations.