Two dimensional liquid chromatographic analysis of Bayer Humic substances

![CDATA[Humic substances play an important role in the Bayer process due to their adverse effect on the industrial scale production of alumina from bauxite. During the Bayer process the soluble organic species can accumulate in the process liquor because the caustic solution is recycled for the digestion of fresh bauxite after the precipitation of the aluminium hydroxide trihydrate. Organics in Bayer liquors are normally monitored by gas chromatography, but only small molecules (<1200 Da) can be analysed at the molecular level. High performance liquid chromatography (HPLC) in principle could be developed to analyse larger molecules. In this work a one-dimensional HPLC separation was developed to study the chemistry of higher (>1200 Da) molecular weight components of humic materials in the alumina refinery (Bayer Process). The optimum one-dimensional separation was achieved using a Nova-Pak C18 column at a flow rate of 0.5 mL/min. A step gradient was developed using tetrabutylammonium hydrogen sulfate (PIC® A) as the ion-pairing reagent and acetonitrile. To further improve on the one-dimensional separation a two-dimensional HPLC separation was developed for the analysis of a Bayer humic sample. The first separation incorporated a size-exclusion column, while the second separation was reversed-phase. The size-exclusion band in the first dimension was cut at 200 µL intervals, resulting in a total of 90 different sections. Each cut section showed a high degree of sample complexity and in many of these sections a number of bands were able to be isolated with a significant degree of resolution. Many of the isolated bands have been subjected to mass spectrometric analysis. Significantly more organic components of Bayer liquors may be analysed by this technique and we are now able to study equilibria in host guest complexes in these materials.]]