In the last decades, the extensive use of chromium in industrial activities has led to the discharge of different chromium species into the biosphere. The two stable chromium forms are Cr(III) and Cr(VI), which have dramatically different properties. While the first one is essential, the second is harmful and carcinogenic, even at very low concentration. Therefore, the appropriate analysis of chromium in environmental, biological, food and other kind of samples need a reliable separation and subsequent quantification of both Cr species. The present paper provides a critical review of chromium speciation methods in which solid phase extraction was employed as sample pretreatment using graphene and carbon nanotubes (and their diverse oxidized, functionalized and magnetic derivatives) as sorbents. The different published methods for the speciation of Cr(III), Cr(VI) or both species are described and classified on the basis of the separation strategy employed: (i) the selective retention of only one of the two species by the sorbent, (ii) the retention of a Cr-chelate formed by using a ligand selective for only one of the Cr-species, or (iii) the sorption of both Cr(III) and Cr(VI) species. In addition, the distinct applied SPE modes (on-column, dispersive or magnetic) and their automation possibilities, the analytical techniques utilized for measurement of the Cr-species after separation, as well as the analytical figures of merit of the methods developed up to date are evaluated. Finally, the expected future trends of solid phase extraction for Cr speciation based on carbon nanomaterials such as graphene, carbon nanotubes and their derivatives as sorbents are commented.

中文翻译：

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石墨烯和碳纳米管作为铬物种形成的固相萃取吸附剂：综述

在过去的几十年里，铬在工业活动中的广泛使用导致不同种类的铬排放到生物圈中。两种稳定的铬形式是 Cr(III) 和 Cr(VI)，它们具有截然不同的特性。虽然第一个是必不可少的，但第二个是有害和致癌的，即使在非常低的浓度下也是如此。因此，对环境、生物、食品和其他类型样品中的铬进行适当的分析需要对两种 Cr 物质进行可靠的分离和随后的量化。本论文对铬形态形成方法进行了批判性回顾，其中采用固相萃取作为样品预处理，使用石墨烯和碳纳米管（及其各种氧化、功能化和磁性衍生物）作为吸附剂。根据所采用的分离策略，描述和分类了 Cr(III)、Cr(VI) 或这两种物质的不同已发表方法：(i) 吸附剂仅选择性保留这两种物质中的一种， (ii) 通过使用仅对 Cr 物种之一具有选择性的配体形成的 Cr 螯合物的保留，或 (iii) Cr(III) 和 Cr(VI) 物种的吸附。此外，独特的应用 SPE 模式（柱上、分散或磁性）及其自动化可能性、用于测量分离后 Cr 物质的分析技术，以及开发的方法的分析品质因数日期进行评估。最后，基于石墨烯等碳纳米材料的 Cr 形态的固相萃取的预期未来趋势，