SUMMARYMixtures of aldonic and aldaric acids are difficult to analyse. Aldonic acids can be separated in a satisfactory way on anion-exchange resins with a solution of sodium chloride as eluent. Under these circumstances, however, aldaric acids show unacceptably long elution times and peak broadening. The ability of aldaric acids to form non-adsorbable complexes with magnesium ions lowers their elution times, particularly of the low-molecular-weight acids, by up to 25 fold. This effect can be controlled by adjusting the magnesium ion concentration in the eluent. It is thus possible to achieve rapid, accurate analysis of mixtures of aldonic and aldaric acids by a proper choice of the magnesium and chloride ion concentrations in the eluent.

A method is described for the high-performance liquid chromatographic analysis of reaction mixtures from the heterogeneously catalysed oxidation of lactose to lactobionate and the homogeneous alkaline oxidative degradation of lactose to b-0-o-galactopyranosyl-(l-3)-r)-arabinonate.Two columns in series, a resin-based anion-exchanger in the acetate form and a resin-based cation exchanger in the H+ form with water as the eluent, allow the quantification of the sugars without interference from the oxidation and degradation products. Occasionally an RP-18 reversed-phase column was used for the determination of lactulose in the reaction samples. A resin-based anion-exchange column in the Cl-or SO:-form allows the determination of the anionic oxidation and degradation products without interference from the sugars present in the reaction samples. In the analyses of the anionic oxidation and degradation products a method was developed to determine some of these. products without their pure standards. The method is based on the regular behaviour in refractive index detection of members of a homologous series of aldonates.

High-performance liquid chromatography has been used for a qualitative and quantitative analysis of reaction mixtures of phenol or guaiacol and glyoxylic acid in aqueous alkaline solutions. The reactants and the a-hydroxyacetic acid derivatives of the starting aromatic compounds were analyzed using a strong cation-exchange resin (SCX) and an octadecylsilane modified silica (ODS) column, in combination with a refractive index detector or a fixed-wavelength UV detector. The application of a dilute aqueous solution of sulphuric acid as the eluent resulted in an almost identical elution pattern from the two columns. However, the selectivity for the aromatic compounds was found to be higher for the reversed-phase ODS column than for the ion-exchange SCX column. For both columns a separation mechanism based on hydrophobic interactions is suggested.