Determination of Phenols,Inorganic Anions,and Carboxylic Acids in Kraft Black Liquors by Capillary Electrophoresis

Two methods are presented for the quantitative capillary electrophoretic (CE) determination of phenolic lignin degradation compounds as well as of inorganic anions and organic acids in Kraft black liquors. Important phenolic lignin degradation compounds can be rapidly separated by co-electroosmotic CE after acidification of the liquors and subsequent extraction of the compounds with chloroform. A capillary electrophoretic separation of phenolic compounds is performed by using a phosphate/borate electrolyte system and UV detection at 214 nm. In addition, a HPLC method using a gradient with water, methanol, and acetic acid is also developed. Inorganic ions which are of importance to the pulping process can be determined by simply diluting the black liquors after sampling and subsequent analysis with a chromate electrolyte system and indirect UV detection at 185 nm. In addition, the concentration of low molecular aliphatic carboxylic acids can be determined simultaneously within the same run. By method optimization it is possible to separate the anions within one minute and, at the same time, to increase the resolution of the solutes. The electrolyte systems for the CE separations were optimized by varying the pH value and by adding organic solvents. Short separation times are obtained by adding a polycationic EOF modifier (hexadimethrine bromide) to the electrolyte which reverses the electroosmotic flow. A migration of the anionic analytes in the same direction as the electroosmotic flow is thus established.