ИСТИНА

Increasing difficulty of analytical tasks solved by ion chromatography (IC) requires the possibility of determining wide range of organic acids in the samples with complex matrices. One of the best stationary phases for solving that task via suppressed IC are hyperbranched anion exchangers, however, some organic acids aren’t resolved well in real samples even using the most selective stationary phases. Selectivity manipulation for hyperbranched anion exchangers is usually realized by incorporating various amines into the functional layer, but changing the temperature regime turned out to be more convenient alternative for already prepared stationary phases. The aim of the current work was to investigate the influence of temperature on selectivity and retention of mono- and divalent organic acids on the covalently bonded hyperbranched anion exchangers. For this purpose anion exchangers with different structure of internal and external part of the hyperbranched functional layers were synthesized. Hydrophilicity and charge of anion exchangers were varied by means of using different amino acids in the internal part of the layer and mono- and diamines of different hydrophilicity in the external part of the layer. The retention of organic acids on the obtained stationary phases was studied in isocratic mode of reagent-free IC in the temperature range from 30 to 50 oC. Van 't Hoff plots demonstrated the increase of organic acids retention with temperature growth for all obtained stationary phases. However, the retention increase for some organic acids was less significant than for others, which resulted in resolution improvement for some pairs of organic acids and even in the changes of elution order at certain temperatures. The revealed trends showed that temperature can be a useful tool for manipulating selectivity of hyperbranched anion exchangers toward organic acids.