Calculation of lignin concentration

Calculation of Lignin Concentration from Refractive Index... 

Boutelje JB (1972) Calculation of lignin concentration and porosity of cell wall regions by interference microscopy Sven Papperstidn 75 683-686... 

In contrast to the approach utilized in the direct determination of lignin, indirect methods do not involve the isolation of a lignin residue. Instead, the lignin content may be calculated as the difference between 100% and the polysaccharide content of an extractive-free sample or, more commonly, by measuring some characteristic structural functionality, property, or chemical response and relating the result to concentration. 

To calculate lignin concentration from refractive index of the specimen, calibration values are required. For measurements in the secondary wall, value Na in Eq. (3) is the refractive index of the S2 region in a matched specimen of holocellulose. This value varies from specimen to specimen and must be measured each time a new specimen is examined (Donaldson 1985a). The only exception is for earlywood and latewood from the same growth ring. For measurements in the middle lamella, Na has a constant value of 1.516 which... 

The value of dn/dc and nG allows the calculation of the optical constant, K, from Eq. (4). A graph of Kc/AR(0) against the lignin concentration, c, gives the weight-average molecular weight from the intercept and the second virial coefficient from the slope. 

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