Hydrazone-based ligands for micro-solid phase extraction-high performance liquid chromatographic determination of biogenic amines in orange juice

Eight hydrazone-based ligands were synthesized, trapped in a silica sol–gel matrix, and were subsequently used in the micro-solid phase extraction (μ-SPE) of biogenic amines (BAs). The BAs investigated were tryptamine, phenylethylamine, putrescine, histamine, tyramine and spermidine. Prior to the extraction, dansyl chloride was added to the samples which were heated to 70 °C for 10 min. The samples were extracted with μ-SPE, after which analytes were desorbed using acetonitrile via ultrasonication. The extracts were analysed by high performance liquid chromatography (HPLC) with ultraviolet detection. Of the eight ligands investigated as sorbents, benzophenone 2,4-dinitrophenylhydrazone was found to be the most promising. The enhanced π–π interaction between the analytes and the ligand facilitated the adsorption process. Under the most suitable extraction conditions, the method demonstrated good linearity with correlation coefficient of more than 0.985 over a concentration range of 1–50 μg L−1. Satisfactory repeatability with relative standard deviations of 7.43–11.30% (n = 3) were obtained. Detection limits ranged from 3.8 to 31.3 ng L−1. The μ-SPE method exhibited lower recoveries (71.5–87.4%) when compared to the solid phase extraction technique (79.7–95.0%), but enrichment factors of 94–460 were obtained. The proposed μ-SPE-HPLC method was applied to the determination of BAs in orange juice purchased from local supermarkets, with satisfactory results. The orange juices were characterized by the presence of relatively high levels of putrescine (range, 550–2210 μg L−1) but tryptamine and phenylethylamine were not detected in any of the tested samples.