Fibrous g-C3N4@Tio2 Nanocomposites-Based Dispersive Micro-Solid Phase Extraction for Chromium Speciation in Cow Milk by ICP-MS after Digestion Treatment with Artificial Gastric Juice.

Background: Chromium is an interesting element because its toxicity depends on its speciation. Thus, knowledge of Cr speciation in cow milk is essential to human health.

Objective: This study aims to achieve real bioaccessible species in cow milk, including Cr(III), Cr(VI), residual, digestible, and total Cr.

Methods: Samples were treated with artificial gastric juice, followed by dispersive micro-solid phase extraction (DMSPE) combined with ICP-MS for Cr speciation. Fibrous g-C3N4@TiO2 nanocomposites (FGCTNCs) were used as a novel adsorbent for DMSPE.

Results: The method detection limits were 110 pg/g (Cr(III)) and 260 pg/g (Cr(VI)) for milk powder (0.1 g), and 5.1 pg/g (Cr(III)) and 13 pg/g (Cr(VI)) for liquid cow milk (2 mL). The relative standard deviations (RSDs), obtained by analyzing the standard solutions containing 1.0 ng/mL of the analytes in sequence for nine times, were 4.3% and 5.1% for Cr(III) and Cr(VI), respectively. Linearity was observed over the range of 4 magnitude orders with correlation coefficients better than 0.9961. The enrichment factor of 100 was obtained. The majority of Cr in the samples was transferred into digestion solution. The content of Cr(III) is much higher than that of Cr(VI) in the digestion solution.

Conclusions: This method has the advantages of reduced solvent consumption, less adsorbent dosage, and high extraction efficiency. It may become a valuable strategy for elemental species in food samples.

Highlights: The samples were treated with artificial gastric juice to avoid the inter-conversion of species. FGCTNCs exhibit the merits of N-rich functional groups and selective adsorption for the analytes.