Pressure variation in-syringe dispersive liquid-liquid microextraction associated with digital image colorimetry: Determination of cobalt in food samples

In the present work, preconcentration by pressure variation in-syringe dispersive liquid-liquid microextraction (PV-IS-DLLME) was used for the determination of cobalt by digital image colorimetry. The detection system, built in the laboratory, involved a portable multifunction microscope used for image acquisition. The extraction solvent was trichloroethylene, while 2,2'-(thiazolylazo)-p-cresol (TAC) was used as a complexing agent. The pH, volume of extraction solvent, sample volume, and time of extraction were evaluated using a fractional factorial design 2(4-1). All factors were significant, and their optimum values were established with a central composite design. The limits of detection and quantification presented by the method were 0.08 and 0.23 mg kg(-1), respectively, and the enrichment factor was 65. The procedure was applied to the analysis of real food samples (green banana flour, eggplant, Bahian seasoning, and Tribulus terrestris) and a certified reference material (NIST 1573a, tomato leaves). The PV-IS-DLLME technique presented itself as an efficient, simple, fast, and low-cost alternative for the preconcentration of substances at trace levels.