It is well known that polar substances can cause problems in GC analysis, such as tailing peaks and degradation. In many cases it requires a derivatization step prior to introducing it to the column. If polar products are formed in the pyrolysis the same applies to them.

This problem may be overcome by a method called direct alkylation: An alkylation agent is added to the sample. Polar pyrolysis products such as carboxylic acids and alcohols are then methylated by hydrolysis and heat when the sample is pyrolyzed, and thus become non-polar. The method is called thermally assisted hydrolysis and methylation (THM) and has successfully been used with Pyrola pyrolyzers in the analysis of e.g. paints.