Determination of volatile fatty acids (C ₂ —C ₅ ) and lactic acid in silage by gas chromatography

A gas chromatographic procedure using a graphitised carbon black packing coated with Carbowax 20M has been developed for the determination of volatile fatty acids and lactic acid in silage. This packing gave improved results compared with porous polymer column materials. The method was precise (relative standard deviation for each acid 0.5–5%) and gave a quantitative recovery of acids spiked into silage extracts (98–109%). The results for the determination of lactic acid in silage obtained by the GC procedure were in good agreement with results obtained by a classical distillation procedure; however, the GC method was more selective, more precise and less time consuming. The method has been shown to be of value in the determination of volatile fatty acids and lactic acid in connection with the assessment of silage quality.