Influence of extraction methods on the distribution pattern and concentration of fatty acids and hydroxy fatty acids in soil samples: Acid digestion versus saponification

Abstract

Fatty acids (FAs) and hydroxy fatty acids (OH-FAs) are universal in sediments and widely used in paleoclimate reconstruction. In environmental samples, they linked to macromolecules via different bonds including amide bonds and ester bonds. The influence of different methods on the distribution of the extracted FAs and OH-FAs, however, is often neglected. In this study, FAs and OH-FAs were extracted from soil samples through two different hydrolysis procedures, acid digestion and saponification. Abundant iso, anteiso and normal 3-hydroxy fatty acids (3-OH-FAs) were obtained by both methods, but the yields are much higher in acid digestion than in saponification. In contrast, more long-chain 2-hydroxy fatty acids (2-OH-FAs) and FAs were obtained by saponification. This discrimination suggests that in soil samples, acid digestion is more suitable to extract 3-OH-FAs, while saponification shows higher efficiency in extracting 2-OH-FAs and FAs.