Development of a Solidification of Floating Organic Droplet-Based Liquid-Liquid Microextraction Method Utilizing a Schiff Base Ligand for the Determination of Nickel at Trace Levels in Saint John’s Wort Tea Infusions by Matrix Matching Calibration Assisted Slotted Quartz Tube-Flame Atomic Absorption Spectroscopy

A sensitive and economical analytical method involving the solidification of floating organic drop microextraction technique with a dispersive solvent is utilized for extraction and enrichment of nickel in St. John’s wort tea infusions. Bis-N,N′-(salicylidene)-1,3-propanediamine was used as the complexing agent. The analyses were done with a slotted quartz tube-flame atomic absorption spectrometer (FAAS). The experimental parameters for the preconcentration procedure were optimized. The developed method provided a 26.5-fold enhanced detection power compared to determination by conventional FAAS. The limits of detection and quantification were 24 and 79 µg/kg, respectively, within a linear range of 50–500 µg/kg. The applicability of the method was tested on infusions of two samples of St. John’s wort tea. Matrix matching was adopted to eliminate/minimize the interferences on the signal. Spiked experiments in which high recovery values in the range of 89.3–121.4% were obtained indicate the accuracy and validity of the method.