Quick determination of malodor-causing fatty acids in manure by capillary electrophoresis

The analysis of odor components in livestock waste has been extensively studied. Past research has identified volatile fatty acids, especially from C 3 to C 6, as indicators of malodor. Originally, the odorous components were analyzed by gas chromatography after a tedious absorption and troublesome extraction procedure or by a subjectively olfactory system or sense of smell. Thus, there is a need for the development of highly specific, quantitative analytical methods. In this research, a comprehensive liquid manure analysis approach—capillary electrophoresis (CE) with a systematic optimization procedure—was adopted to measure the concentration of propanoic acid (C 2H 5COOH, C 3), butyric acid (C 3H 7COOH, C 4), valeric acid (C 4H 9COOH, C 5) and caproic acid (C 5H 11COOH, C 6) in swine manure. Liquid samples after filtration were injected into CE directly. The following condition is finally proposed: fused-silica capillary, effective length 40 cm, 50 μm I.D.; buffer, 20 mM Tris and 10 mM p-anisate, pH 8.0; voltage 30 kV; temperature 25 °C. The results showed that CE provided a quantitative analysis of volatile fatty acids in liquid manure at the ppm level with minimum sample needed (nanoliter). Moreover, the use of CE is a timesaving technique; one measurement for the separation of those VFAs could be completed within 10 min.