Both techniques will modify the lignin to some degree. Analysis Let's say we have separated out are components and wish to investigate structure. The most useful techniques rely on chromatographic and spectroscopic techniques. The pdf file below entitled Basics of HPLC provides an introduction to the technique and the file entitled Example Chromatograms describes its use in investigating lignin-tannin bonds in wood. For this technique to work, the sample has to be somewhat volatile.
Spectroscopy is also a useful technique.
This can be quantitated and the technique is often used to detect compounds eluting from an HPLC column. Bonds will stretch and vibrate at specific IR frequencies and this can be detected and quantitated in an IR instrument. Mass spectroscopy involves volatilizing a compound and essentially breaking it apart with a sledgehammer. The molecule will cleave in specific ways due to the functional groups it contains. These molecular pieces can be detected based solely on their molecular weight.