# Recent Advances in Sample Preparation for Cosmetics and Personal Care Products Analysis
## 2 Sample Preparation Strategies for Cosmetics Analysis
### New Sorbent Materials for SPE  
In recent years, new trends in SPE are closely related to the improvement of sorbents that can be more effective to obtain higher analyte enrichment efficiency. These new materials include carbon nanotubes (CNTs), graphene-sponge (GS) and graphene-oxide (GO)-based materials, layered double hydroxides (LDHs) and metal organic frameworks (MOFs)--among others. Their applications as SPE sorbents for cosmetics analysis are presented below. Carbon nanotubes (CNTs) were introduced by [PERSON] in 1991 [81]. CNTs are cylindrical nanostructures composed of single or multiple rolled graphene sheets. The hollow fibres have a diameter of 1-50 nm with length in the range of microns. They can be classified into single walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs), depending on the number of graphene sheets [82]. MWCNTs have attracted great attention for their specific characteristics to increase sensitivity, improving enrichment and extract clean-up [80]. The combination of SPE with MWCNTs has been proposed to extract parabens from cosmetics prior to corona-charged aerosol detection (C-CAD) [45]. Another advantage of using MWCNTs is the fact that their surface can be functionalized, thus enhancing their sorption performance and selectivity. In this way, the functionalization of MWCNTs with a molecularly imprinted polymer (MIP) is an option that has been employed for the determination of the corticosteroid prednisone in cosmetics [46]. This combination allowed a reduction in the extraction time, and the sorbent material could be reused up to four times without losing extraction efficiency, representing a suitable option for specific analyte extractions in complex matrices. The use of MIPs has also been reported to extract bisphenol A from leave-on and rinse-off cosmetics [47]. The analytical performance was compared with those obtained employing classical C18 sorbents, showing that the use of imprinted silica nanoparticles allowed higher specific extraction, with less interference. Another recently developed nanomaterials employed as SPE sorbent for cosmetics analysis is graphene sponge (GS). This material presents special characteristics such as negligible weight, open-hole structure, high surface area and variable surface chemistry [83]. It has been employed to extract benzotriazole UV filters from water and cosmetics [48]. The sorbent efficiency was compared with the use of MWCNTs and C18. Results revealed that GS showed the best extraction efficiency for the target compounds, which is attributed to hydrogen bonding, \(\pi\)-\(\pi\) stacking and hydrophobic interactions between GS and the benzotriazoles. In addition, the large surface area and pore size of GS probably enhance the extraction capability. Another graphene-based sorbent that exhibits a large surface area, chemical stability and durability is graphene oxide (GO). Its adsorption capacity can be attributed to the delocalized \(\pi\)-electron system, and its properties can be improved by chemicals modifications such as the carboxylation of hydroxyl and epoxy groups on the GO surface, greatly improving its extraction selectivity. In this way, the use of carboxylated GO with polyvinyl chloride (CGO/PVC) was proposed to determine different sulphonamides as contaminants in cosmetics' products followed by IC-UV analysis [49]. A novel monolithic capillary column with embedded graphene was developed and used for polymer monolith microextraction (PMME). The monolith capillary contained poly butyl methyl acrylate-ethylene dimethylacrylate-graphene (BMA-EDMA-GN) and it was successfully applied for the extraction of nine glucocorticoids from cosmetics. High enrichment capacity was observed in the case of a GN-entrapped monolith showing satisfactory reusability and stability during extraction [51]. Other nano-structured materials gaining special attention in recent years for their special physicochemical properties include layered double hydroxides (LDHs).