Determination of Sixteen Kinds of Free Amino Acids in Citrus by Liquid Liquid Microextraction/Solid Phase Microextraction Coupled with Gas Chromatography

Objective: To evaluate the quality of the citrus, a gas chromatography (GC) coupled with flame ion detector was established for the determination of sixteen kinds of free amino acids in citrus simultaneously. Methods: Firstly, the single factor tests werre used to optimize the derivatization conditions of isobutyl chloroformate. Subsequently, a method was developed by liquid-liquid microextraction (LLME)/solid phase microextraction (SPME) coupled with GC using a home-made sol-gel butylmethacrylate/divinylbenzene (BMA/DVB) fibers. Results: The results showed that the derivatization conditions were the best under one derivation with one min. The best SPME conditions can be obtained as follows: The extraction temperature of 40 ℃, the extraction time of 30 min and the 30% sodium sulfate at the extraction speed of 1000 r·min⁻¹. Under the optimized experimental parameters, there were good linear relationships for 16 analytes with correlation coefficients larger than 0.99. The limit of detection was 0.85~12.60 μg·kg⁻¹ and the standard recoveries of the spiked samples ranged from 82.51% to 121.75%, with relative standard deviations of 2.51%~12.80%. Conclusion: The method was convenient, accurate, and matrix resistant. It could be used as a new model for the determination of the free amino acids in citrus pulp samples and can also provide a valuable reference for the quality evaluation of cirtrus.