Nutritional evaluation after copper cloud point extraction in spirulina (Arthrospira sp.) samples with determination...

This study presents the development of a procedure based on copper preconcentration at the cloud point of commercial spirulina dietary supplements, with determination by digital image colorimetry. A fractional factorial design 2^4-1 and Doehlert matrix were applied in the method optimization. The developed method presented 0.062 and 0.20 mg kg^-1 Cu as limits of detection and quantification, respectively. The main advantages of this procedure come from the pre-concentration and the speed resulting from its direct determination in the surfactant-rich phase, eliminating the stage of discarding the original bulky aqueous phase. The found precision values, expressed as repeatability, were 2.8 % (5.0 μg L^-1) and 2.2 % (20 μg L^-1). Trueness was assessed using spike test and analysis of certified reference materials (Apple leaves and Oyster tissue), demonstrating that the method presents adequate trueness. Copper concentrations in the analyzed samples ranged from 19.92 to 55.32 mg kg^-1, representing a low nutritional contribution of 0.66-1.54 %, considering this supplement's recommended intake of 3 g day^-1.