Nanofibers comprising polystyrene and zinc acetate for extraction of salivary histidine prior to its determination by HPLC–DAD

A novel nanofiber-based solid phase extraction (NFSPE) coupled with HPLC–DAD was developed for the determination of salivary histidine, a new potential index of physiological events. The treatment of the sample was based on a coupling reaction of histidine with the diazotization products of sulfanilic acid and sodium nitrite in a slightly alkaline medium, followed by NFSPE. Nanofibers comprising polystyrene and zinc acetate were used as a novel solid-phase sorbent to extract derived histidine via the chelation of Zn 2+  with the imidazole group in the analyte. The eluted target compound was analyzed by HPLC–DAD. Good linearity was achieved with the concentrations of histidine ranging from 0.645 to 64.5 µM; the detection limit was 0.193 µM. The intra-day and inter-day coefficients of variation were less than 8.0%. The method was successfully applied to the determination of salivary histidine in the subjects exposed to a public speaking stress. Graphical abstract