Honey is well-known as a food product that is rich in active ingredients and is very popular among consumers. Free amino acids (FAAs) are one of the important nutritional components of honey, which can be used not only as a nutritional indicator of honey but also as an indicator of plant source identification. In this study, the contents of 20 FAAs in seven types of honey from 11 provinces in China were examined for the first time. The 20 FAAs were analyzed by ultra-performance liquid chromatography-mass spectrometry/mass spectrometry (UPLC-MS/MS). By analyzing 93 honey samples from seven types of honey, the FAAs were found to range from 394.4 mg/kg (linden honey) to 1771.7 mg/kg (chaste honey). Proline ranged from 274.55 to 572.48 mg/kg, and methionine was only present in some of the linden honey, chaste honey, acacia honey, and rape honey. Evaluated by amino acid principal component analysis, multifloral grassland honey had the highest overall evaluation score, acacia and jujube honey were the most similar, while chaste honey was the least similar to the other types of honey. In addition, DNA was extracted from 174 Xinjiang grassland honey samples and different plant leaves for PCR and sequencing to identify the species of nectar plants. As a result, 12 families and 25 species of honey plants were identified. The results confirmed the diversity of FAAs in dissimilar types and sources of honey. This study provides a reference for expanding honey quality standards and verifying the authenticity of honey.

A robust method for the determination of six organotin compounds (OTs), monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), monophenyltin (MPhT), diphenyltin (DPhT) and triphenyltin (TPhT), in sea products was developed using gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS). The target compounds were extracted by hexane containing 0.01% tropolone, derivatizated by Grignard reagent n-PrMgBr, purified on a serial connection of silica and florisil solid-phase extraction (SPE) columns, and finally analyzed by GC-MS/MS. Improved sensitivity and selectivity were achieved using tandem MS/MS rather than single MS, especially in reducing complex interferences in biotic matrices. The limits of detection (LODs) for the six OTs were all below 0.1 μg Sn per kg in the case of wet samples, and were no higher than 0.5 μg Sn per kg for dry samples. The linearity coefficients (r²) for the six OTs were all above 0.999 within the linear range from 0.4 to 200 μg Sn per kg. The accuracy of the method was thoroughly validated using the certified reference material Mytilus edulis (ERM-CE477) and a spiked recovery test in four different biotic matrices, including tonguefishes, sea snails (Neverita didyma), scallops (Patinopecten yessoensis) and the Asian moon scallop. The butyltin concentrations determined for CE477 agreed well with the certified values, and the relative standard deviations (RSDs) for the six OTs were all below 12.1%. The spiked recoveries in four biotic matrices were within the range 70.5–105.3% for MBT, DBT, TBT, DPhT and TPhT, and 82.2–133.5% for MPhT, and the RSDs ranged from 0.5% to 12.5%. The proposed methodology was applied to the determination of butyltin and phenyltin compounds in nine different sea products sampled from the Bohai coast, China, with total OTs ranging from 1.36 to 20.54 μg Sn per kg wet weight.