The Use of Carbon Fiber Restricted Access Material for Cadmium Determination in Milk Whey

Milk is a widely consumed drink in the world given its numerous beneficial nutritional properties to human health. It might contain toxic elements due to its sources, such as the area where livestock are kept, as well as their food and water. In addition, it can become contaminated during and after milking, in its industrialization process and during transport and packaging. Furthermore, it might contain some metallic elements in proteins linked to amino acids or in ionic whey which is often discarded during milk manufacturing processes. However, there are some useful applications of whey as by-product which are quite advantageous due to waste reduction thereof, thus making it an environmentally friendly process. Ergo, this work proposes an FIA-FAAS system using activated carbon fibers (ACF) modified with albumin to generate a restricted access material (ACF-RAM) with the aim of using it as adsorbent in SPE to find cadmium in whey. The acronym adopted for this method was FIA-SPE-ACF-RAM-FAAS. The RAM allows a direct introduction of whey samples into the system with no prior treatment, since only ions can be adsorbed in ACF. Larger molecules, e.g., proteins, are discarded as waste during the process. Thus, the FIA system has been optimized using chemometric tools such as the factorial design and Doehlert matrix. Limit of detection was 0.24 µg L⁻¹, and limit of quantification was 0.81 µg L⁻¹. The method was employed using a whey sample, and its precision was assessed through relative standard deviation, which was ever less than 5.0%. Its accuracy has been verified through a spiked sample, and its recovery ranged between 95 and 105%.