Accurate Detection of 8 Long-Chain Fatty Acid Ethyl Esters in Baijiu Based on Magnetic Solid Phase Extraction-Gas Chromatography-Mass Spectrometry Combined with Isotope Internal Standards

Long-chain fatty acid ethyl ester is one of the important factors causing the turbidity of Baijiu. In order to systematically analyze the effect of long-chain fatty acid ethyl ester content in Baijiu and improve the turbidity issue of Baijiu production, a method using magnetic solid phase extraction of aminated ferric oxide (Fe₃O₄-NH₂) coupled with gas chromatography-mass spectrometry (GC-MS) was established to simultaneously determine 8 long-chain fatty acid ethyl esters in Baijiu. Optimal extraction conditions were determined by evaluating factors such sample solution pH, ionic strength, adsorbent amount, adsorption time, desorption solvent type and pH, and desorption time. The results indicated that the linear relationship between the 8 long-chain fatty acid ethyl esters within their respective mass concentration ranges was strong, with correlation coefficients (R²) all above 0.99. Detection limits ranged from 9.1 μg/L to 42.9 μg/L, and quantitation limits from 5.2 μg/L to 200.0 μg/L. Recovery rates were between 79.6% and 99.3%, with a relative standard deviation of 8.0% to 10.7% (n=3). By applying the established method, along with the isotope internal standard approach, the accurate quantification of 8 long-chain fatty acid ethyl esters in 24 kinds of Baijiu samples with different flavor types and brands was carried out. Significant variations in types and concentration levels of long-chain fatty acid ethyl esters were observed, with the detection rate of long-chain fatty acid ethyl esters in sauce-flavored Baijiu reaching 100%. The method developed in this research was rapid and straightforward, requiring only a 10 min extraction time, yielding highly sensitive and precise outcomes. It effectively eliminated the background interference typically associated with conventional liquid-liquid extraction, and provided a new approach for the accurate detection of long-chain fatty acid ethyl esters in Baijiu.