# Recent Advances in Sample Preparation for Cosmetics and Personal Care Products Analysis
## 1 Introduction  
The use of cosmetics and personal care products is increasing worldwide, and Europe is a key market for the cosmetics industry. In fact, the European cosmetic market generated more than EUR 120,000 billion in 2019 [1]. Regulation 1223/ 2009 [2] includes the definition of cosmetics and establishes rules to be compiled with by any cosmetic product made placed on the market, to 'ensure the functioning of the internal market and a high level of protection of human health'. For this purpose, it provides a 'List of substances prohibited in cosmetic products' (Annex II) which currently includes more than 1400 chemical compounds. On the other hand, Annex III lists the substances allowed for use as cosmetic ingredients, although most of them present restrictions in terms of maximum permitted concentration depending on the use of the final product or the product type. In addition, different positive lists of substances for several ingredient families, such as colorants, preservatives, and UV filters (Annexes IV, V and VI, respectively) are included [2, 3]. It is important to note that although Regulation 1223/2009 came into force in 2013, it is continuously revised and updated (with more than 60 amendments since it came into effect). From the point of view of their composition, cosmetics are very complex, with variable matrices formed by a high number of substances from highly lipophilic to moderately polar, or exhibiting basic, acidic, or neutral properties. In addition, it is quite frequent that technical mixtures containing impurities or unknown or banned/unexpected compounds that can be formed by the reaction of compounds become present in the formulation under particular exposition conditions [4,5]. Taking into account that cosmetic products marketed on the European Union must comply with the Regulation [2], and that this compliance must be analytically verifiable, the analysis of cosmetics and personal care products is a challenge. A previous sample pre-treatment before analytical determination is usually required. Sample pre-treatment has two objectives: to ensure the pre-concentration of the target analytes as well as to minimize analysis matrix effects. In recent years, several reviews covering this topic have been published [3, 5, 6, 7, 8, 9, 10, 11], most of them focused on specific types of cosmetics ingredients such as fragrances, preservatives or dyes since they are the most common compounds present in the formulations [3,9,10]. Regarding the reported sample preparation methodology for cosmetics analysis, traditional liquid-liquid extraction (LLE) and solid-liquid extraction (SLE) are still employed, although the use of advanced techniques such as ultrasound-assisted extraction (UAE), solid phase extraction (SPE), matrix solid-phase dispersion (MSPD) or pressurized liquid extraction (PLE) [3,4,6,7,12] is growing. In recent years, green analytical chemistry (GAC) principles have been increasingly implemented for cosmetics analysis through the miniaturization of classical extraction procedures, as well as the substitution of hazardous chemicals and solvents by environmentally friendly alternatives, as the main objective is to improve their environmental friendliness without compromising method performance [13, 14, 15]. The separation and determination of the target analytes in the cosmetics matrices are mainly performed by gas chromatography (GC) and liquid chromatography (LC). The choice between them depends on the chemical nature of the target analytes. In general, LC is the preferred option for the most polar compounds such as preservatives or UV filters, especially for hydroxyl preservatives or benzophenone-UV filters derivatives. On the other hand, GC is the preferred chromatographic technique for the separation of volatile or semi-volatile compounds such as fragrances, although non-polar compounds (UV filters, preservatives, etc.) are also successfully analysed by GC.