GC-FID Analysis of Ileal Digesta SCFA Profiles

Short chain fatty acid profiles of the ileal digesta were determined by Alimetrics Diagnostics (Espoo, Finland) using gas chromatography (GC; Agilent Technologies, Santa Clara, CA, USA) with pivalic acid (Sigma-Aldrich, St. Louis, MO, USA) used as an internal standard. The chromatography procedure used a glass column packed with 80/120 Carbopack B-DA/4% Carbowax stationary phase, helium as a carrier gas, and a flame ionization detector (FID) and has been described previously by Apajalahti et al.^{86 (link)}. Lactic acid and the VFA (acetic acid, propionic acid, isobutyric acid, butyric acid, 2-methylbutyric acid, isovaleric acid and valeric acid) were derivatised to the respective phenyl esters using phenyl chloroformate reagent. The resulting esters were analysed by Agilent GC-FID (Agilent Technologies). Matrix-matched internal standard calibration with butyric-d7- and acetic-d3 acids was used in quantitation.