Gas chromatography analysis of fatty acid esters and free fatty acids for the evaluation of lipase performance in textile treatment and washing

Fatty acid esters (FAE) can be found in textiles in many forms, both in manufacturing and as components of consumer products. Removal of FAEs and the resulting free fatty acids (FFA) poses a problem which can partially be solved by using enzymes. Lipases can potentially aid the removal of FAE-based spin-finishes and fatty stains from textile fibres. However, monitoring substrates and/or products of enzyme reactions is difficult, mainly because FAE and the resulting FFA are not sufficiently volatile for conventional analysis by gas chromatography (GC). Therefore, derivatisation is usually performed before analysis. Here, two methodologies for the analysis of FAE and FFA in textiles by GC (with mass spectrometer or flame ionisation detectors) were developed using methylation and silylation. While methylation allows for the analysis of total fatty acids (FAE + FFA), silylation allows the analysis of FFA/diacylglycerols/monoacylglycerols. Derivatisation of the sample by acid-catalysed methylation without prior extraction was found effective for total fatty acids analysis in both fat/oil soiled textiles and raw textiles containing spin-finishes. Silylation with N,O- bis(trimethylsilyl)trifluoroacetamide: trimethylchlorosilane allowed for the quantification of FFA in raw textiles, with a marked increase in concentration of FFA being observed after treatment with lipases. These derivatisation strategies allowed the evaluation of the performance of lipase-facilitated washing of textiles, by both (i) assessment of the efficiency of the overall washing process by the quantification of the FAE/FFA remaining on the textile, and (ii) determination of the activity of used lipases by quantification of the enzymatic hydrolysis products.