# Recent Advances in Sample Preparation for Cosmetics and Personal Care Products Analysis
## 2 Sample Preparation Strategies for Cosmetics Analysis
### New Sorbent Materials for SPE
These are synthetic 2-dimensional nano-structured inorganic materials with general formula: M\({}^{2+}\)\({}_{1-\mathrm{x}}\)M\({}^{3+}\)\({}_{\times}\) (OH)\({}_{2}\)]\({}^{\mathrm{x}}\)+ [A\({}^{\mathrm{n-}}\)\({}_{\mathrm{x/n}}\)-m\({}_{\mathrm{H}}\)O]\({}^{\mathrm{x-}}\), where M\({}^{2+}\) is a divalent metal ion (Zn, Mg, Cu, Co or Ni), M\({}^{3+}\) is a trivalent metal (Al, Fe or Cr), x is the ratio of M\({}^{3+}\)/(M\({}^{2+}\) + M\({}^{3+}\)) and \(A^{n-}\) is a \(n\)-valent anion. A large variety of materials can be obtaining by varying the proportion of the divalent and trivalent cations [84]. The use of a nickel-zinc-aluminium layered double hydroxide (Ni-Zn-Al LDH) was assessed to extract the UV filter p-aminobenzzoic acid (PABA) from sunscreens [50]. Results showed quantitative recovery values, a high repeatability and matrix independence even at the low concentration levels showing the suitability of this nano-structured composite. SPE on-column is the most employed mode [42; 43; 44; 45; 46; 47; 48; 49; 50], although the on-batch mode has also been reportedly employed. Dispersive (d)-SPE is an alternative approach to conventional SPE. In d-SPE, the sorbent is dispersed into the sample. The close contact between the sorbent particles and the analytes greatly favours the sorption, increasing the efficiency of the whole procedure. Finally, the extracted analytes are eluted from the sorbent [85]. The use of MWCNTs in dispersive (d)-SPE has been proposed to determine volatile-N-nitrosamines in skin care cosmetics [52]. After extraction, the MWCNTs were removed before LC-MS/MS analysis. Analytical performance showed good recoveries and precision, although LODs were quite high compared to those obtained for nitrosamines employing \(\mu\)-MSPD-GC-MS/MS analysis [74]. The use of nanocomposites as well as metal-organic frameworks (MOFs) is increasing as SPE sorbents in d-SPE applications. MOFs have emerged as new crystalline porous materials with promising applications. They are hybrid inorganic-organic microporous crystalline materials self-assembled straightforwardly from metal ions with organic linkers via coordination bonds. MOFs present interesting characteristics such as a high surface area, uniform structure cavities and a permanent nanoscale porosity, among others. Moreover, the availability of various building blocks of metal ions and organic linkers makes it possible to prepare an infinite number of new MOFs with myriad structures and great potential for diverse applications [86; 87]. The efficiency of different MOFs: HKUST-1, MOF-5 and MIL-53(Al) has been assessed to extract parabens from cosmetics [53]. After a deep optimization of the experimental conditions, HKUST-1 proved to be the most suitable sorbent. The whole d-SPE(MOF)-HPLC-DAD showed very low LODs (<0.1 \(\mu\)g L\({}^{-1}\)), and only 0.05 g of cosmetic sample were required. A SBA-15/polyaniline _para_-toluenesulfonic acid nanocomposite supporting d-SPE was developed for the extraction of parabens from cosmetic products. The experimental parameters were optimized by a central composite design. Under the optimal conditions which involve the use of only 10 mg of sorbent, the d-SPE (SBA-15/PANI-\(p\)-TSA-NCs)-HPLC-UV method was satisfactory validated, showing LODs lower than 0.4 ng mL\({}^{-1}\)[54].