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 mg 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.

中文翻译：

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螺旋藻 （Arthrospira sp.） 样品中铜浊点提取后的营养评价，用数字图像比色法测定


本研究介绍了一种基于商业螺旋藻膳食补充剂浊点铜预浓缩的程序的开发，并通过数字图像比色法测定。在方法优化中应用了部分因子设计 2^4-1 和 Doehlert 矩阵。开发的方法分别以 0.062 和 0.20 mg ^kg-1 Cu 作为检测和定量限。该程序的主要优点在于预浓缩和在富含表面活性剂的固定相中直接测定所带来的速度，消除了丢弃原始大体积水相的阶段。发现的精密度值（以重复性表示）为 2.8 % （5 mg ^L-1） 和 2.2 % （20 μg ^L-1）。使用加标检验和认证参考物质（苹果叶和牡蛎组织）的分析来评估正确度，证明该方法具有足够的正确度。分析样品中的铜浓度范围为 19.92 至 55.32 毫克公斤^-1，考虑到该补充剂的推荐摄入量为 0.66-1.54 克-¹，营养贡献较低。