GC Analysis of Monomeric Products

The GC internal standard is usually hexacosane (C26) and/or tetracosane (C24) For complex samples, such as those represented by lignocellulose residues, it is advisable to add both of these internal standards The amount of each internal standard (C26 and/or C24) to be added is 0 5 mg/20 mg of extractive-free wood, 0 25mg/20mg of extractive-free straw, and lmg/5mg of milled wood lignin (Note 6) 

Silylation the final CH2C12 solution of the thioacidolysis sample is again carefully dried over Na2S04, 5-10/d of this dried organic solution is trimethylsilylated (TMS) at room temperature with 50/i of N,0 bis (trimethylsilyl) trifluoroacetamide (BSTFA) and 5 1 of GC-grade pyridine in a 200-/d reaction vial fitted with a Teflon-lined screwcap For soluble lignin samples, the silylation is complete within a few minutes, for lignocellulose residues, silylation is complete within 2 to 4h In both cases and with well-dried samples, silylations performed in the aforementioned vials are stable for several days (at least 48 h) 

Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analyses GC analyses are performed on a WCOT (wall-coated open tubular) polydimethylsiloxane fused silica capillary column (1 fim film thickness, 50m x 0 32mm ID ) Shorter columns for example 25m, or columns with thinner films, for example 0 2/im, may also be used successfully Injection of the silylated sample (2/d) is performed with a moving needle-type injector, other types of capillary GC injection systems may be used after optimization of the concentration and amount of sample to be injected With a 50-m capillary 

The main syringyl (S) and guaiacyl (G) monomeric products from the thioacidolysis of lignins are isolated by preparative-scale experiments (Lapierre et al. 1986a,b). The only difference between these and the previously described analytical procedure is that the reaction mixture (500 ml of reagent and 3-6g of lignin sample) is refluxed. The product yields are identical for both analytical and preparative procedures. 

The response factors of the main syringyl, guaiacyl, and p-hydroxyphenyl (H) trithioethyl C6C, diastereoisomers, defined as the ratio of relative concentration (underivatized compound) to relative area, are identical and equal to 1 50 using either tetracosane or hexacosane as an internal standard For minor products, which are not isolated in preparative experiments, use of the same response factor is justified on the grounds that their structures are similar to those of the main products 

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