|So it would be nice to have an alternative method, cleaner than both the Klason and Morison method.
Such an alternative may be the following: if you extract plant material with chloroform/methanol,
you remove all kind of soluble and lipophylic material such as sugars and lipids, etcetera.
(See here for the overall extraction scheme). At the same time, a number of proteins will precipitate.
The residue of this extraction (R2 in the extraction scheme) can be treated with 3% HCl. This will
remove non-structural carbohydrates, such as starch and fructans that resisted the first extraction.
The residue that is left (R3) is a mixture of cellulose, hemicellulose, cell wall protein, precipitated other
proteins, and possibly some minerals like silica etcetera. If you ash part of this material,
you know the mineral fraction, which is usually rather small, but extremely important to know.
Deduct that from the total weight of R3 that is measuredOn the other part of R3 you can do a CN-analysis.
Assuming that the N comes from protein, with an overall composition of 16% N and 53% C, you can estimate
the amount of protein in the residue, and deduct that as well. What is left after the deduction is a mixture
of cellulose/hemicelluloses on the one hand and lignin on the other. Knowing the mineral content and
the [C] of protein, you can calculate what the [C] is of this mixture. Cellulose and hemi-cellulose have
a very different C-concentration (circa 43%) than lignin (circa 71%). So, if you have calculated what the
C-concentration of the mixture was, you can also determine its relative proportion (hemi-)cellulose and lignin,
and in the end you can calculate back what the concentration must have been in the plant material you started with.
|This method, described in Poorter & Villar (1997), except for the mineral correction that can be found in Aerts (????)
relies on a number of assumption, and no doubt will not only specifically measure lignin, but probably also
some other secondary compounds of 'nasty' nature, like the Klason method. It also cannot be calibrated,
like any of the other methods. But contrary to the Klason and Morison method, it is clean, and more friendly
for the environment and personal health.