Applications of novel nanomaterial-based solid phase extraction for complex samples

Accurate analyses of target analytes are of great importance in biomedicine, pharmaceuticals, environmental protection, and food safety. However, the diverse matrix, severe interference, wide dynamic distribution range, trace amount, and various components of inorganic and organic analytes make it extremely challenging to conduct direct sensitive detection and quantitative analysis. Detection sensitivity and signal strength of analytes can be improved by enriching the analytes or minimizing interference through simple and reproducible sample pretreatment. Nevertheless, traditional sample pretreatment methods suffer from complex operations, tedious and time-consuming steps, severe sample loss, low efficiency, and environmentally-unfriendly solvents. Thus, to overcome these disadvantages, solid phase extraction (SPE), which comprises conditioning, sample loading, washing, and elution, has been developed. SPE is an important and widely-used green sample pretreatment method for complicated samples. The extraction and purification functions are executed using the interaction between the analyte and adsorbent and the properties of the sample matrix and eluent. With respect to SPE absorbents, nanomaterials with small particle sizes (0.2-100 nm), large specific surface area, high surface energy, and high surface atomic fraction have shown excellent performance in sample pretreatment. In addition, they have considerably improved the effective separation and preconcentration efficiency of analytes. However, pretreatment methods often face difficulties, such as poor separation effect of compounds with similar properties in samples with complex composition, poor physical and chemical stability, low adsorption capacity, and limited reusability. In this regard, nanomaterials present unique optical, electrical, magnetic, and catalytic properties and have been widely used in structural materials, electronic information, chemical medicines, catalysis, energy, etc. In recent years, the study and application of nanomaterials in separation science have garnered considerable interest due to the rapid development of nanotechnology. Using a variety of nanomaterials as solid adsorbents can aid in the concentrated analysis of trace target substances and the low detection sensitivity of existing methods. Compared with traditional adsorbents, emerging nanomaterials exhibit better performance in the extraction and preconcentration of trace analytes, substantially improving the sensitivity, selectivity, and accuracy of detection. They also show promising practical applications via the maturity of the synthesis process and cost reduction. In this review, different types of nanomaterials, such as carbon-based nanomaterials, metal organic frameworks, covalent organic frameworks, and metal oxides, are comprehensively and systematically reviewed with respect to SPE performance improvement and applications. For example, the SPE selectivity and enrichment efficiency were improved using various strategies, such as modulating the interaction between nanomaterials and analytes, functionalizing moiety groups, or hybridizing with magnetic separation. In addition, the valuable applications of nanomaterials in fields such as biomedicine and environment and food safety are demonstrated and summarized. Further development and analytical applications of nanomaterials for the SPE-based sample pretreatment are also proposed.