Fourier Transform Infrared Spectroscopy (FTIR) can be used to rapidly characterize and quantify cellulose-hemicellulose-lignin composition prior to and after application of various methods of pre-processing and pre-treatment of biomass (Adapa et al., 2009). The quantitative analysis of FTIR absorption spectrometry is based on the Bouguer-Beer — Lambert law (Sherman Hsu, 1997). According to this law, the intensities of absorption bands are linearly proportional to the concentration of each component in a homogenous mixture or solution.

Regression equations to predict the lignocellulosic content of agricultural biomass can be developed using pure cellulose, hemicelluloses and lignin as reference samples, and
subsequently mixing them in different proportions to determine the change in absorption intensity at characteristic peak height (Adapa et al., 2011b). An overview of the experimental procedure to characterize the lignocellulosic composition is provided in Figure 3.

Pure cellulose has five distinct characteristic/ prominent peaks at wavenumbers of 1431, 1373, 1338, 1319 and 1203 cm-1. Similarly, hemicellulose (xylan) has prominent peaks at wavenumbers of 1606, 1461, 1251, 1213, 1166 and 1050 cm-1. The lignin spectrum has characteristic peaks at wavenumber of 1599, 1511, 1467, 1429, 1157 and 1054 cm-1. The intensity of absorption at characteristic peak heights of cellulose, hemicellulose and lignin were used to develop regression equations to predict lignocellulosic composition of any agricultural biomass (Table 1) (Adapa et al., 2011b).

FOURIER TRANSFORMED INFRARED (FTIR) SPECTROSCOPY USING PHOTOACOUSTIC CELL

Obtain FTIR spectra of samples at the Mid-Infrared Beamline, Canadian Light Source (Synchrotron Radiation); average of 32 interferograms collected from wavenumbers of 2000 to 400 cm’1 at a resolution of 4 cm ■*

NORMALIZE FTIR DATA

Carbon Black Data: Eliminate wavenumber-dependent instrumental effects
Mass of Sample: Eliminate effect of bulk density of samples
Normalize from 0 to 1: Standardize the methodology

PEAK HEIGHT METHOD

Characteristic peak heights and corresponding wavenumbers of 100% cellulose, hemicellulose and
lignin were determined. Subsequently, characteristic wavenumbers were used to determine the pea
heights of lignocellulose in reference sample mixture

A comparision between results from lab
experiments and predicted values was
performed to validate the regression
models

Fig. 3. Experimental procedure followed to characterize lignocellulosic composition of agricultural straw (Adapa et al., 2011b).

%Cellulose = -135.10 + 781.35 (РЯ_1319) — 795.57(РЯ_1431) — 135.26(РЯ_1203) + 436.11 (РЯ_1338) — 94.24(РЯ_1373)

VoHemicellulose = 1638.72 — 2581.71(РЯ_1251 X РЯ_1461) — 1260.90(РЯ_1213)

— 2518.05(РЯ_1166) + 1573.69(РЯ_1213 X РЯ_1251)

+ 118.74(РЯ_1050) + 3128.51(РЯ_1166 X 1251)

+ 2179.65(РЯ_1461) + 92.36(РЯ_1606) — 2294.15(РЯ_1251)

— 59.29(РЯ_1461 X РЯ_1606)

%Lignin = 7110.87 + 388.32(РЯ_1511 X РЯ_1599) — 16440.93(РЯ_1467)

+ 447.36(РЯ_1599)2 + 19572.82(РЯ_1157 X РЯ_1467)

+ 18374.36(РЯ_1157) + 15659.98(РЯ_1054 X РЯ_1429)

— 4952.80(РЯ_1157 X РЯ_1599) + 800.20(РЯ_1511)

— 3032.75 (РЯ_1429)2 — 11269.16(РЯ_1429)

— 948.04(РЯ_1511)2 + 3444.69(РЯ_1599)

________________ — 12344.90(РЯ_1054) — 16689.44(РЯ_1157)2_____________

Note: PH — Characteristic Peak Height (Photoacoustic Units)

Table 1. Regression equations to predict the lignocellulosic composition of agricultural biomass (Adapa et al., 2011b).