A novel method for determination and quantification of 4-methyloctanoic and 4-methylnonanoic acids in mutton by hollow fiber supported liquid membrane extraction coupled with gas chromatography

4-methyloctanoic acid (MOA) and 4-methylnonanoic acid (MNA) are the main compounds responsible for “sweaty” odor of mutton. A novel method for their determination has been developed and validated. Hollow fiber supported liquid membrane (HF-SLM) was applied to selectively extract MOA and MNA prior to gas chromatography (GC) analysis. For HF-SLM, the donor outside the fiber was the acidified supernatant (pH 4) from aqueous mutton slurry. Liquid membrane was 5% tri-n-octylphoshphine oxide in di-n-hexyl ether and 0.3 M NaOH aqueous solution filled in the lumen of the fiber was used as the acceptor. The extraction last for 4 h. After acidification with HCl, the acceptor was directly analyzed by GC. Importantly, HF-SLM provided high enrichment factors for MOA (133) and MNA (116). The method developed had low detection limits of 0.0007–0.0015 mg/kg, good linearity (R2 > 0.9956), reasonable recovery (88.54–122.13%), satisfactory intra-assay (7.83–9.73%) and inter-assay (15.68–16.14%) precision.