This study aimed to develop a label-free, sensitive, selective, and environment-friendly fluorescent peptide probe His-His-Trp-His (HHWH) for determining the concentration of copper ion (Cu 2+ ) in aqueous solutions. The results demonstrated that the designed HHWH has a high selectivity and sensitivity for monitoring the concentration of free Cu 2+ via quenching of the probe fluorescence upon a binding of Cu 2+ . The fluorescence intensity of the HHWH had a linear relationship with the concentration of Cu 2+ between 10 nM and 10 μM, and the detection limit was 8 nM. Furthermore, HHWH could be regenerated with sulfide ions at least five times. The concentrations of Cu 2+ in three different real water samples were detected using this probe, and the results were consistent with the one detected using an atomic absorption spectrometer. Thus, HHWH can be used as an accurate and feasible fluorescent peptide probe for detecting Cu 2+ in aqueous solutions.

In combination with frozen pretreatment and carboxyl group derivatization, a novel workflow was developed for the determination of free fatty acids in milk powder. The workflow showed a significantly enhanced performance for comprehensive free fatty acid analysis owing to a highly efficient frozen extraction method. In addition, the advantages of the workflow also involved high sensitivity and great tolerance to a complex matrix. Characteristic fragment ions of derivatization reagents also provide clear evidence for the qualitative analysis of free fatty acids. Fourteen types of free fatty acids in a number of domestic and overseas infant milk powders have been successfully detected. The content of free fatty acids in the different samples was different, which probably indicates the diverse quality of infant milk powder. The workflow is expected to be a pragmatic tool for the analysis of free fatty acids in intricate matrices.