RESUMO
RP-HPLC using stepwise gradients of N,N-dimethylformamide (DMF) in a phosphate-buffered (pH 3.00) aqueous mobile phase and a wide-pore (30 nm) octadecylsilica column has been applied to the analysis of a variety of lignins--organocell lignin, dioxane lignin, Björkman lignin, and Klason lignins from both softwoods and hardwoods, respectively, in order to demonstrate the usefulness of the approach for their characterization. Tandem combination of spectrophotometric diode array detection and fluorimetric detection was used to acquire more detailed information about the chromatographic behavior of lignins. The results show that a ten-step gradient can reveal distinct features of lignins and humic substances. Combination of good solvating properties of DMF for lignins together with a wide-pore RP sorbent improves surface interactions of the analytes and suppresses the influence of size exclusion effects. Thus it provides reproducibility of characterization profiles and robustness of the method. The calculated repeatability of the retention time of selected peaks was +/- 0.46% RSD. The reproducibility of the data within one week (set of seven data) was +/- 1.1% RSD. These data are also representative of the other well-shaped peaks of analyzed substances.
