I recall a gravimetric method in the AOAC decades ago.  You can adapt it.

For lignin, I would suggest the AcBr method. See Fukushima and Hatfield (2001), attached. They use a UV spectrophotometric assay.

I think Inductive coupled plasma mass spectrometer will be your best shot. also check literatures to see what other researchers have used and reported 

Infrared reflectance Spectroscopy is one of the reliable technique. The detailed procedure is on line available.

I am working currently with wheat straw. To get the compositional analysis of the material, I am using the procedures that can be found in this link:http://www.nrel.gov/bioenergy/biomass-compositional-analysis.html

I hope it helps you to solve your problem.