Determination of bile acids by hollow fibre liquid-phase microextraction coupled with gas chromatography

• A method, using less hazardous solvents, was developed for analysis of bile acids.
• Hollow fibre liquid phase microextraction is efficient for enrichment of bile acids.
• HF-LPME permits analysis of limited caecum sample that can be obtained from a rat.
• Fermentable fibres reduce the formation of some secondary bile acids.
• Guar gum gave a more beneficial composition of bile acids than pectin.

A method based on hollow-fibre liquid phase microextraction combined with gas chromatography was developed for determination of specific bile acids in caecal materials of rats. Nine unconjugated bile acids, including the primary bile acids (cholic acid, chenodeoxycholic acid and α-muricholic acid) and the secondary bile acids (lithocholic acid, deoxycholic acid, ursodeoxycholic acid, hyodeoxycholic acid, β-muricholic acid and ω-muricholic acid) were quantified. Extraction conditions were evaluated, including: sample pH, type of organic solvent and amount of caecal material to be extracted. To compensate for sample matrix effects during extraction the method of standard addition was applied. The satisfactory linearity (r2 > 0.9840), high recovery (84.2–108.7%) and good intra-assay (6.3–10.6%) and inter-assay (6.9–11.1%) precision illustrated the good performance of the present method. The method is rapid, simple and capable of detecting and determining bile acids with limit of detection (LOD) ranged from 0.002 to 0.067 μg/mL and limits of quantification (LOQ) varied from 0.006 to 0.224 μg/mL. The results indicated that the concentration of some secondary bile acids, which usually are associated with health problems, were lower in rats fed with fermentable dietary fibre compared with a fibre free control diet, while the concentration of primary bile acids, usually connected with positive health effects, were higher in rats fed with diets containing dietary fibre. Of the dietary fibres, guar gum and to some extent the mixture of pectin + guar gum had the most positive effects. Thus, it was concluded that the composition of bile acids can be affected by the type of diet.